| 0/0 |
2026/09/04 07:53 |
flow |
assessment-security |
45m
Results: map[DenialOfService:false Explanation:**Analysis of the Bug**
The bug is located in the BPF verifier's backtracking and precision tracking
logic. When verifying calls to certain helpers like `bpf_loop` or
`bpf_set_retval`, the verifier explicitly marks their first argument
(`BPF_REG_1`) as precise by calling `mark_chain_precision(env, BPF_REG_1)`.
These helpers define their first argument type as `ARG_ANYTHING`.
During argument checking, `check_func_arg()` ensures that `ARG_ANYTHING`
arguments are not pointers by calling `is_pointer_value()`. However, if the user
has `CAP_PERFMON` privileges (which allows leaking kernel pointers),
`env->allow_ptr_leaks` is set to `true`. When this flag is set,
`is_pointer_value()` intentionally returns `false` even for pointer registers,
allowing a pointer to be passed as `BPF_REG_1`.
When `mark_chain_precision()` is subsequently called on this pointer register,
it invokes `bpf_mark_chain_precision()`, which contains the following sanity
check:
```c
if (regno >= 0) {
reg = &func->regs[regno];
if (reg->type != SCALAR_VALUE) {
verifier_bug(env, "backtracking misuse");
return -EFAULT;
}
bt_set_reg(bt, regno);
}
```
Because the register holds a pointer type rather than a `SCALAR_VALUE`, the
sanity check fails. This triggers the `verifier_bug()` macro, which emits a
`BPF_WARN_ONCE` kernel warning and aborts the verification by returning
`-EFAULT`.
**Security Impact**
* **Exploitable:** **False**. The verifier safely catches the unexpected state,
emits a warning, and gracefully rejects the BPF program by returning `-EFAULT`.
The program is never loaded or executed, meaning there is no memory corruption,
privilege escalation, or information leak.
* **Denial of Service:** **False**. The bug only results in a single `WARN_ONCE`
message in the kernel log and the rejection of the invalid BPF program. It does
not crash the kernel, hang the system, or leak resources. (Note: Syzkaller
treats WARNINGs as bugs, but in production environments without `panic_on_warn`,
this is harmless).
* **Accessible From Unprivileged Processes:** **False**. Triggering this
requires `CAP_PERFMON` to set `env->allow_ptr_leaks = true`, which a standard
unprivileged user does not have.
* **Accessible From User Namespaces:** **True**. An unprivileged user can create
a new user namespace, mount a BPF filesystem (`bpffs`) with delegation options,
and create a BPF token. Because the user is root within their user namespace,
the token will grant `CAP_PERFMON` for BPF operations, allowing them to bypass
the pointer check and trigger the warning. Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:false UserNamespace:true VMGuestTrigger:false VMHostTrigger:false]
|
| 1/1 |
2026/09/04 07:53 |
action |
syz-repro-to-c-repro |
0m
Results: map[SimplifiedCRepro:// autogenerated by syzkaller (https://github.com/google/syzkaller)
#define _GNU_SOURCE
#include <endian.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mount.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>
#ifndef __NR_bpf
#define __NR_bpf 321
#endif
uint64_t r[2] = {0xffffffffffffffff, 0xffffffffffffffff};
int main(void)
{
syscall(__NR_mmap, /*addr=*/0x1ffffffff000ul, /*len=*/0x1000, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x200000000000ul, /*len=*/0x1000000, /*prot=PROT_WRITE|PROT_READ|PROT_EXEC*/7ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x200001000000ul, /*len=*/0x1000, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
const char* reason;
(void)reason;
intptr_t res = 0;
if (write(1, "executing program\n", sizeof("executing program\n") - 1)) {}
// bpf$MAP_CREATE arguments: [
// cmd: const = 0x0 (8 bytes)
// arg: ptr[inout, array[ANYUNION]] {
// array[ANYUNION] {
// union ANYUNION {
// ANYBLOB: buffer: {01 00 00 00 04 00 00 00 08 00 00 00 0a} (length 0xd)
// }
// }
// }
// size: len = 0x48 (8 bytes)
// ]
// returns fd_bpf_map
memcpy((void*)0x200000000000, "\x01\x00\x00\x00\x04\x00\x00\x00\x08\x00\x00\x00\x0a", 13);
res = syscall(__NR_bpf, /*cmd=*/0ul, /*arg=*/0x200000000000ul, /*size=*/0x48ul);
if (res != -1)
r[0] = res;
// bpf$BPF_BTF_LOAD arguments: [
// cmd: const = 0x12 (8 bytes)
// arg: ptr[in, bpf_btf_load] {
// bpf_btf_load {
// btf: ptr[inout, array[ANYUNION]] {
// array[ANYUNION] {
// union ANYUNION {
// ANYBLOB: buffer: {9f eb 01 00 18 00 00 00 00 00 00 00 34 00 00 00 34 00 00 00 0e 00 00 00 01 00 00 00 00 00 00 01 04 00 00 00 20 00 00 01 00 00 00 00 00 00 00 0d 01 00 00 00 05 00 00 00 00 00 00 0c 02 00 00 00 0a 00 00 00 00 00 00 0c 02 00 00 00 00 69 6e 74 00 6d 61 69 6e 00 73} (length 0x57)
// }
// }
// }
// btf_log_buf: nil
// btf_size: bytesize = 0x5a (4 bytes)
// btf_log_size: bytesize = 0x0 (4 bytes)
// btf_log_level: int32 = 0x0 (4 bytes)
// btf_log_true_size: int32 = 0x0 (4 bytes)
// btf_flags: btf_load_flags = 0x0 (4 bytes)
// btf_token_fd: union _bpf_btf_load_btf_token_fd_wrapper {
// void: buffer: {} (length 0x0)
// }
// pad: union _bpf_btf_load_pad_wrapper {
// value: const = 0x0 (4 bytes)
// }
// }
// }
// size: len = 0x28 (8 bytes)
// ]
// returns fd_btf
*(uint64_t*)0x200000000100 = 0x200000000200;
memcpy((void*)0x200000000200, "... [truncated large byte array] ...", 87);
*(uint64_t*)0x200000000108 = 0;
*(uint32_t*)0x200000000110 = 0x5a;
*(uint32_t*)0x200000000114 = 0;
*(uint32_t*)0x200000000118 = 0;
*(uint32_t*)0x20000000011c = 0;
*(uint32_t*)0x200000000120 = 0;
*(uint32_t*)0x200000000124 = 0;
res = syscall(__NR_bpf, /*cmd=*/0x12ul, /*arg=*/0x200000000100ul, /*size=*/0x28ul);
if (res != -1)
r[1] = res;
// bpf$BPF_PROG_TEST_RUN arguments: [
// cmd: const = 0xa (8 bytes)
// arg: ptr[in, bpf_test_prog_arg] {
// bpf_test_prog_arg {
// prog: fd_bpf_prog (resource)
// retval: const = 0x0 (4 bytes)
// insizedata: len = 0x5 (4 bytes)
// outsizedata: len = 0x0 (4 bytes)
// indata: ptr[in, buffer] {
// buffer: {09 00 00 00 04} (length 0x5)
// }
// outdata: nil
// repeat: int32 = 0x0 (4 bytes)
// dur: const = 0x0 (4 bytes)
// insizectx: len = 0x0 (4 bytes)
// outsizectx: len = 0x0 (4 bytes)
// inctx: nil
// outctx: nil
// flags: bpf_prog_test_run_flags = 0x0 (4 bytes)
// cpu: const = 0x0 (4 bytes)
// batch_size: int32 = 0x0 (4 bytes)
// pad = 0x0 (4 bytes)
// }
// }
// size: len = 0x50 (8 bytes)
// ]
*(uint32_t*)0x200000000900 = -1;
*(uint32_t*)0x200000000904 = 0;
*(uint32_t*)0x200000000908 = 5;
*(uint32_t*)0x20000000090c = 0;
*(uint64_t*)0x200000000910 = 0x200000000608;
memcpy((void*)0x200000000608, "\x09\x00\x00\x00\x04", 5);
*(uint64_t*)0x200000000918 = 0;
*(uint32_t*)0x200000000920 = 0;
*(uint32_t*)0x200000000924 = 0;
*(uint32_t*)0x200000000928 = 0;
*(uint32_t*)0x20000000092c = 0;
*(uint64_t*)0x200000000930 = 0;
*(uint64_t*)0x200000000938 = 0;
*(uint32_t*)0x200000000940 = 0;
*(uint32_t*)0x200000000944 = 0;
*(uint32_t*)0x200000000948 = 0;
syscall(__NR_bpf, /*cmd=*/0xaul, /*arg=*/0x200000000900ul, /*size=*/0x50ul);
// bpf$PROG_LOAD arguments: [
// cmd: const = 0x5 (8 bytes)
// arg: ptr[in, bpf_prog_t[flags[bpf_prog_type, int32], bpf_prog_attach_types, bpf_btf_id[opt], fd_bpf_prog[opt]]] {
// bpf_prog_t[flags[bpf_prog_type, int32], bpf_prog_attach_types, bpf_btf_id[opt], fd_bpf_prog[opt]] {
// type: bpf_prog_type = 0x5 (4 bytes)
// ninsn: bytesize8 = 0xb (4 bytes)
// insns: ptr[inout, array[ANYUNION]] {
// array[ANYUNION] {
// union ANYUNION {
// ANYBLOB: buffer: {18 11 00 00} (length 0x4)
// }
// union ANYUNION {
// ANYRES32: ANYRES32 (resource)
// }
// union ANYUNION {
// ANYBLOB: buffer: {00 00 00 00 00 00 00 00 18 42 00 00 06 00 00 00 00 00 00 00 00 00 00 00 b7 03 00 00 00 00 00 00 b7 04 00 00 00 00 00 00 85 00 00 00 b5 00 00 00 b7 00 00 00 00 00 00 00 95 00 00 00 00 00 00 00 b7 00 00 00 00 00 00 00 95 00 00 00 00 00 00 00} (length 0x50)
// }
// }
// }
// license: ptr[in, buffer] {
// buffer: {47 50 4c 00} (length 0x4)
// }
// loglev: int32 = 0x1 (4 bytes)
// logsize: len = 0x100000 (4 bytes)
// log: ptr[out, buffer] {
// buffer: (DirOut)
// }
// kern_version: bpf_kern_version = 0x0 (4 bytes)
// flags: bpf_prog_load_flags = 0x0 (4 bytes)
// prog_name: buffer: {00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00} (length 0x10)
// prog_ifindex: ifindex (resource)
// expected_attach_type: union bpf_prog_attach_types {
// fallback: bpf_attach_types = 0x0 (4 bytes)
// }
// btf_fd: fd_btf (resource)
// func_info_rec_size: const = 0x8 (4 bytes)
// func_info: ptr[in, bpf_func_info] {
// bpf_func_info {
// insn_off: int32 = 0x0 (4 bytes)
// type_id: int32 = 0x3 (4 bytes)
// }
// }
// func_info_cnt: len = 0x2 (4 bytes)
// line_info_rec_size: const = 0x0 (4 bytes)
// line_info: nil
// line_info_cnt: len = 0x0 (4 bytes)
// attach_btf_id: bpf_btf_id (resource)
// attach_prog_fd: fd_bpf_prog (resource)
// core_relo_cnt: len = 0x0 (4 bytes)
// fd_array: nil
// core_relos: nil
// core_relo_rec_size: const = 0x0 (4 bytes)
// log_true_size: int32 = 0x0 (4 bytes)
// prog_token_fd: union _bpf_prog_t[flags[bpf_prog_type, int32], bpf_prog_attach_types, bpf_btf_id[opt], fd_bpf_prog[opt]]_prog_token_fd_wrapper {
// void: buffer: {} (length 0x0)
// }
// pad: union _bpf_prog_t[flags[bpf_prog_type, int32], bpf_prog_attach_types, bpf_btf_id[opt], fd_bpf_prog[opt]]_pad_wrapper {
// value: const = 0x0 (4 bytes)
// }
// }
// }
// size: len = 0x80 (8 bytes)
// ]
// returns fd_bpf_prog
*(uint32_t*)0x200000000300 = 5;
*(uint32_t*)0x200000000304 = 0xb;
*(uint64_t*)0x200000000308 = 0x200000000400;
memcpy((void*)0x200000000400, "\x18\x11\x00\x00", 4);
*(uint32_t*)0x200000000404 = r[0];
memcpy((void*)0x200000000408, "... [truncated large byte array] ...", 80);
*(uint64_t*)0x200000000310 = 0x200000000500;
memcpy((void*)0x200000000500, "GPL\000", 4);
*(uint32_t*)0x200000000318 = 1;
*(uint32_t*)0x20000000031c = 0x100000;
*(uint64_t*)0x200000000320 = 0x200000000700;
*(uint32_t*)0x200000000328 = 0;
*(uint32_t*)0x20000000032c = 0;
memset((void*)0x200000000330, 0, 16);
*(uint32_t*)0x200000000340 = 0;
*(uint32_t*)0x200000000344 = 0;
*(uint32_t*)0x200000000348 = r[1];
*(uint32_t*)0x20000000034c = 8;
*(uint64_t*)0x200000000350 = 0x200000000600;
*(uint32_t*)0x200000000600 = 0;
*(uint32_t*)0x200000000604 = 3;
*(uint32_t*)0x200000000358 = 2;
*(uint32_t*)0x20000000035c = 0;
*(uint64_t*)0x200000000360 = 0;
*(uint32_t*)0x200000000368 = 0;
*(uint32_t*)0x20000000036c = 0;
*(uint32_t*)0x200000000370 = 0;
*(uint32_t*)0x200000000374 = 0;
*(uint64_t*)0x200000000378 = 0;
*(uint64_t*)0x200000000380 = 0;
*(uint32_t*)0x200000000388 = 0;
*(uint32_t*)0x20000000038c = 0;
*(uint32_t*)0x200000000390 = 0;
syscall(__NR_bpf, /*cmd=*/5ul, /*arg=*/0x200000000300ul, /*size=*/0x80ul);
return 0;
}
]
|
| 2/1 |
2026/09/04 07:53 |
action |
kernel-checkouter |
1m
Results: map[KernelSrc:/app/workdir/cache/src/c939edc6565537477eb54df6928b1637fb7df949]
|
| 3/1 |
2026/09/04 07:55 |
action |
kernel-builder |
23m
Results: map[KernelObj:/app/workdir/cache/build/5fb89a40cefd7e6d28c4670528eeb831eeec101b]
|
| 4/1 |
2026/09/04 08:18 |
action |
codesearch-prepare |
15m
Results: map[Index:codesearch-index]
|
| 5/1 |
2026/09/04 08:34 |
agent |
expert |
4m
Model:
Results: map[DenialOfService:false Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:false UserNamespace:true VMGuestTrigger:false VMHostTrigger:false]
Instruction: You are an experienced Linux kernel security engineer. Your task is to analyze given kernel bug report
and determine its security impact based on the following dimensions.
Use the provided tools to examine the source code, check for capability checks (e.g., capable(), ns_capable()),
and understand the nature of the bug. Analyze the given kernel build and configuration.
You can check the kernel config by grepping ".config" file; you can check kernel cmdline by grepping
".config" file for "CONFIG_CMDLINE=". Assume sysctl parameters have default values.
But analyze for the corresponding production build w/o debugging tools enabled (like KASAN, KMSAN, UBSAN).
Try different strategies when analyzing the bug:
- think of ways in which the vulnerable code is unreachable
- or the other way around: try to come up with different ideas of how an unprivileged user can reach the bug
If still unsure err on the side of the bug being non-exploitable/not-accessible.
In the final reply, provide a reasoning for your assessment.
Analysis dimensions:
* Exploitable:
Determine if the bug can result in memory corruption, elevated privileges, or an information leak.
Memory safety issues are almost always exploitable (KASAN or UBSAN reports for use-after-free, out-of-bounds;
refcounting issues, corrupted lists, etc). When kernel is crashing on a completely wild pointer access
(e.g. user-space address, or non-canonical address, but not on NULL or address corresponding to KASAN shadow
for NULL address), including both data accesses and control transfers, that also usually implies possibility
of exploitation. Such reports usually say "unable to handle kernel paging request".
Uses of uninitialized values detected by KMSAN may be exploitable b/c attacker frequently can affect uninit
values with spraying techniques. However, for these exploitability depends on how exactly the uninit value
is used in the code, and what it affects.
Information leaks are exploitable on their own and should be classified as such. A bug that copies kernel
memory contents to userspace (e.g. an out-of-bounds read whose result is returned to the caller, or
uninitialized stack/heap bytes written to a user buffer) is exploitable: it can reveal kernel pointer
values and defeat KASLR, expose sensitive data such as cryptographic keys or other processes' memory, and
serves as a necessary building block in most modern kernel privilege-escalation exploit chains. Do not classify
an information leak as non-exploitable solely because it does not directly cause a memory write or control-flow
hijack; the leak itself is the exploit primitive.
Think of what happens after the bug is triggered. Some bugs cause kernel panic and halt execution,
they are harder to exploit. For example, BUG reports halts the kernel. However, WARNING reports don't halt
execution in production builds. Debug bug detection tools (like KASAN, KMSAN, KCSAN, UBSAN) are also not enabled
in production builds, so attacker can freely exploit these bugs w/o being detected by these tools.
If you see an integer overflow, think how the overflowed value used later (if it's used as allocation size,
or an array index). If you see an out-of-bounds read, think if it's followed by an out-of-bounds write as well.
Some KCSAN data-races may be exploitable by skilled attackers as well. Think what data structures got corrupted
as the result of data races and how. However, note that kernel has lots of "benign" data races that don't lead
to any runtime misbehavior at all.
* Denial Of Service:
Determine if the bug can result in denial-of-service. Most bugs can, since they cause system crash,
hangs, deadlocks, or resource leaks. This is mostly applicable to WARNING bugs that won't cause system crash
in production. For these think what will be consequences of the violation of the kernel assumptions flagged
by the WARNING. In some cases the unexpected condition is also properly handled by the normal control flow
(e.g. with "if (WARN_ON(...))"), these won't cause denial-of-service. If the condition is not handled,
then it may or may not cause denial-of-service.
* Accessible From Unprivileged Processes:
Determine if the bug can be reached from a typical (non-root) user process that does NOT have any special capabilities
(like CAP_SYS_ADMIN, CAP_NET_ADMIN, CAP_NET_RAW, CAP_PERFMON) or access to device nodes restricted to root.
Assume that unprivileged_bpf_disabled=1, that is eBPF loading is not accessible. However, cBPF (classical BPF)
is still accessible to non-root processes.
Assume that user namespaces are not accessible, that is, the process cannot get the mentioned capabilities even
within a new user namespace (checked by ns_capable() function in the kernel sources).
* Accessible From User Namespaces:
Determine if the bug can be reached within a user-namespace where the process has all capabilities
(including CAP_SYS_ADMIN, CAP_NET_ADMIN, CAP_NET_RAW, CAP_PERFMON). Such capabilities are checked with ns_capable()
function in the kernel sources.
* VM Guest Trigger:
Determine if the bug can be triggered from the context of a typical KVM guest (e.g., set up by a QEMU VMM).
Consider accesses to standard Linux host paravirtualized features (virtio-blk, virtio-net, etc.),
and handling of VM exits in the KVM code.
* VM Host Trigger in The Confidential Computing Context:
Determine if the bug can be triggered in a confidential computing guest kernel from the context of a KVM host.
Consider access to standard Linux guest paravirtualized features (virtio-blk, virtio-net, etc.).
* Ethernet Network Trigger:
Determine if the bug can be triggered by processing ingress network Ethernet traffic, either directly (network stack)
or via drivers exposed to network data.
* Other Remote Trigger:
Determine if the bug can be triggered by processing remote traffic other than Ethernet (Wifi, Bluetooth, NFC, etc).
* Peripheral Trigger:
Determine if the bug can be triggered via an untrusted peripheral device that can be physically plugged
into a system, such as a USB device or a niche hardware driver handling external hardware inputs.
This is particularly important for mobile and desktop environments where users can plug in unknown devices.
* Malicious Filesystem Trigger:
Determine if the bug can be triggered by the kernel mounting and parsing a malicious filesystem image.
This is highly critical for Desktop and Mobile environments where external media or downloaded images
might be auto-mounted.
Don't make assumptions about the kernel source code (it may be different from what you assume it is).
Extensively use the provided code access tools (codesearch-*, git-*, grepper, etc)
to examine the actual source code, and confirm any assumptions.
Prefer calling several tools at the same time to save round-trips.
Use set-results tool to provide results of the analysis.
It must be called exactly once before the final reply.
Ignore results of this tool.
Prompt:
The kernel bug report is:
------------[ cut here ]------------
verifier bug: backtracking misuse
WARNING: kernel/bpf/backtrack.c:829 at bpf_mark_chain_precision+0x571b/0x76b0 kernel/bpf/backtrack.c:829, CPU#1: syz-executor403/5624
Modules linked in:
CPU: 1 UID: 0 PID: 5624 Comm: syz-executor403 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:bpf_mark_chain_precision+0x571b/0x76b0 kernel/bpf/backtrack.c:829
Code: ff 89 d9 80 e1 07 80 c1 03 38 c1 0f 8c 16 ff ff ff 48 89 df e8 76 17 44 00 e9 09 ff ff ff e8 0c d0 d4 ff 48 8d 3d b5 50 6a 0e <67> 48 0f b9 3a 48 8b 3c 24 48 81 c7 88 08 00 00 48 c7 c6 a0 c6 f6
RSP: 0018:ffffc90003957228 EFLAGS: 00010293
RAX: ffffffff81f23d54 RBX: 0000000000000001 RCX: ffff88807f7b9f40
RDX: 0000000000000000 RSI: 0000000000000003 RDI: ffffffff905c8e10
RBP: 0000000000000003 R08: ffff88807f7b9f40 R09: 0000000000000003
R10: 0000000000000007 R11: 0000000000000000 R12: ffff88807f4f3050
R13: dffffc0000000000 R14: 0000000000000001 R15: 0000000000000000
FS: 00005555805e0400(0000) GS:ffff888125024000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000006a9ee0 CR3: 000000007133a000 CR4: 00000000003526f0
Call Trace:
<TASK>
mark_chain_precision kernel/bpf/verifier.c:3373 [inline]
check_helper_call kernel/bpf/verifier.c:10894 [inline]
do_check_insn+0x12a74/0x17c20 kernel/bpf/verifier.c:18177
do_check kernel/bpf/verifier.c:18363 [inline]
do_check_common+0x3c19/0x5d30 kernel/bpf/verifier.c:19444
do_check_main kernel/bpf/verifier.c:19540 [inline]
bpf_check+0x2639/0x2e10 kernel/bpf/verifier.c:21195
bpf_prog_load+0x14d6/0x1c20 kernel/bpf/syscall.c:3133
__sys_bpf+0xd0d/0xd90 kernel/bpf/syscall.c:6367
__do_sys_bpf kernel/bpf/syscall.c:6486 [inline]
__se_sys_bpf kernel/bpf/syscall.c:6483 [inline]
__x64_sys_bpf+0xba/0xd0 kernel/bpf/syscall.c:6483
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f4f25cf1749
Code: c0 79 93 eb d5 48 8d 7c 1d 00 eb 99 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 d8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fff991a6f18 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f4f25cf1749
RDX: 0000000000000080 RSI: 0000200000000300 RDI: 0000000000000005
RBP: 0000000000000000 R08: 0000000000000006 R09: 0000000000000006
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f4f25d84c40 R15: 0000000000000002
</TASK>
----------------
Code disassembly (best guess):
0: ff 89 d9 80 e1 07 decl 0x7e180d9(%rcx)
6: 80 c1 03 add $0x3,%cl
9: 38 c1 cmp %al,%cl
b: 0f 8c 16 ff ff ff jl 0xffffff27
11: 48 89 df mov %rbx,%rdi
14: e8 76 17 44 00 call 0x44178f
19: e9 09 ff ff ff jmp 0xffffff27
1e: e8 0c d0 d4 ff call 0xffd4d02f
23: 48 8d 3d b5 50 6a 0e lea 0xe6a50b5(%rip),%rdi # 0xe6a50df
* 2a: 67 48 0f b9 3a ud1 (%edx),%rdi <-- trapping instruction
2f: 48 8b 3c 24 mov (%rsp),%rdi
33: 48 81 c7 88 08 00 00 add $0x888,%rdi
3a: 48 rex.W
3b: c7 .byte 0xc7
3c: c6 (bad)
3d: a0 .byte 0xa0
3e: c6 (bad)
3f: f6 .byte 0xf6
It is reproducible with the followint program.
Keep in mind that it may lack the precise threading, sandboxing, and some arguments of a working reproducer.
But it should give an idea of the involved syscalls.
// autogenerated by syzkaller (https://github.com/google/syzkaller)
#define _GNU_SOURCE
#include <endian.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mount.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>
#ifndef __NR_bpf
#define __NR_bpf 321
#endif
uint64_t r[2] = {0xffffffffffffffff, 0xffffffffffffffff};
int main(void)
{
syscall(__NR_mmap, /*addr=*/0x1ffffffff000ul, /*len=*/0x1000, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x200000000000ul, /*len=*/0x1000000, /*prot=PROT_WRITE|PROT_READ|PROT_EXEC*/7ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x200001000000ul, /*len=*/0x1000, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
const char* reason;
(void)reason;
intptr_t res = 0;
if (write(1, "executing program\n", sizeof("executing program\n") - 1)) {}
// bpf$MAP_CREATE arguments: [
// cmd: const = 0x0 (8 bytes)
// arg: ptr[inout, array[ANYUNION]] {
// array[ANYUNION] {
// union ANYUNION {
// ANYBLOB: buffer: {01 00 00 00 04 00 00 00 08 00 00 00 0a} (length 0xd)
// }
// }
// }
// size: len = 0x48 (8 bytes)
// ]
// returns fd_bpf_map
memcpy((void*)0x200000000000, "\x01\x00\x00\x00\x04\x00\x00\x00\x08\x00\x00\x00\x0a", 13);
res = syscall(__NR_bpf, /*cmd=*/0ul, /*arg=*/0x200000000000ul, /*size=*/0x48ul);
if (res != -1)
r[0] = res;
// bpf$BPF_BTF_LOAD arguments: [
// cmd: const = 0x12 (8 bytes)
// arg: ptr[in, bpf_btf_load] {
// bpf_btf_load {
// btf: ptr[inout, array[ANYUNION]] {
// array[ANYUNION] {
// union ANYUNION {
// ANYBLOB: buffer: {9f eb 01 00 18 00 00 00 00 00 00 00 34 00 00 00 34 00 00 00 0e 00 00 00 01 00 00 00 00 00 00 01 04 00 00 00 20 00 00 01 00 00 00 00 00 00 00 0d 01 00 00 00 05 00 00 00 00 00 00 0c 02 00 00 00 0a 00 00 00 00 00 00 0c 02 00 00 00 00 69 6e 74 00 6d 61 69 6e 00 73} (length 0x57)
// }
// }
// }
// btf_log_buf: nil
// btf_size: bytesize = 0x5a (4 bytes)
// btf_log_size: bytesize = 0x0 (4 bytes)
// btf_log_level: int32 = 0x0 (4 bytes)
// btf_log_true_size: int32 = 0x0 (4 bytes)
// btf_flags: btf_load_flags = 0x0 (4 bytes)
// btf_token_fd: union _bpf_btf_load_btf_token_fd_wrapper {
// void: buffer: {} (length 0x0)
// }
// pad: union _bpf_btf_load_pad_wrapper {
// value: const = 0x0 (4 bytes)
// }
// }
// }
// size: len = 0x28 (8 bytes)
// ]
// returns fd_btf
*(uint64_t*)0x200000000100 = 0x200000000200;
memcpy((void*)0x200000000200, "... [truncated large byte array] ...", 87);
*(uint64_t*)0x200000000108 = 0;
*(uint32_t*)0x200000000110 = 0x5a;
*(uint32_t*)0x200000000114 = 0;
*(uint32_t*)0x200000000118 = 0;
*(uint32_t*)0x20000000011c = 0;
*(uint32_t*)0x200000000120 = 0;
*(uint32_t*)0x200000000124 = 0;
res = syscall(__NR_bpf, /*cmd=*/0x12ul, /*arg=*/0x200000000100ul, /*size=*/0x28ul);
if (res != -1)
r[1] = res;
// bpf$BPF_PROG_TEST_RUN arguments: [
// cmd: const = 0xa (8 bytes)
// arg: ptr[in, bpf_test_prog_arg] {
// bpf_test_prog_arg {
// prog: fd_bpf_prog (resource)
// retval: const = 0x0 (4 bytes)
// insizedata: len = 0x5 (4 bytes)
// outsizedata: len = 0x0 (4 bytes)
// indata: ptr[in, buffer] {
// buffer: {09 00 00 00 04} (length 0x5)
// }
// outdata: nil
// repeat: int32 = 0x0 (4 bytes)
// dur: const = 0x0 (4 bytes)
// insizectx: len = 0x0 (4 bytes)
// outsizectx: len = 0x0 (4 bytes)
// inctx: nil
// outctx: nil
// flags: bpf_prog_test_run_flags = 0x0 (4 bytes)
// cpu: const = 0x0 (4 bytes)
// batch_size: int32 = 0x0 (4 bytes)
// pad = 0x0 (4 bytes)
// }
// }
// size: len = 0x50 (8 bytes)
// ]
*(uint32_t*)0x200000000900 = -1;
*(uint32_t*)0x200000000904 = 0;
*(uint32_t*)0x200000000908 = 5;
*(uint32_t*)0x20000000090c = 0;
*(uint64_t*)0x200000000910 = 0x200000000608;
memcpy((void*)0x200000000608, "\x09\x00\x00\x00\x04", 5);
*(uint64_t*)0x200000000918 = 0;
*(uint32_t*)0x200000000920 = 0;
*(uint32_t*)0x200000000924 = 0;
*(uint32_t*)0x200000000928 = 0;
*(uint32_t*)0x20000000092c = 0;
*(uint64_t*)0x200000000930 = 0;
*(uint64_t*)0x200000000938 = 0;
*(uint32_t*)0x200000000940 = 0;
*(uint32_t*)0x200000000944 = 0;
*(uint32_t*)0x200000000948 = 0;
syscall(__NR_bpf, /*cmd=*/0xaul, /*arg=*/0x200000000900ul, /*size=*/0x50ul);
// bpf$PROG_LOAD arguments: [
// cmd: const = 0x5 (8 bytes)
// arg: ptr[in, bpf_prog_t[flags[bpf_prog_type, int32], bpf_prog_attach_types, bpf_btf_id[opt], fd_bpf_prog[opt]]] {
// bpf_prog_t[flags[bpf_prog_type, int32], bpf_prog_attach_types, bpf_btf_id[opt], fd_bpf_prog[opt]] {
// type: bpf_prog_type = 0x5 (4 bytes)
// ninsn: bytesize8 = 0xb (4 bytes)
// insns: ptr[inout, array[ANYUNION]] {
// array[ANYUNION] {
// union ANYUNION {
// ANYBLOB: buffer: {18 11 00 00} (length 0x4)
// }
// union ANYUNION {
// ANYRES32: ANYRES32 (resource)
// }
// union ANYUNION {
// ANYBLOB: buffer: {00 00 00 00 00 00 00 00 18 42 00 00 06 00 00 00 00 00 00 00 00 00 00 00 b7 03 00 00 00 00 00 00 b7 04 00 00 00 00 00 00 85 00 00 00 b5 00 00 00 b7 00 00 00 00 00 00 00 95 00 00 00 00 00 00 00 b7 00 00 00 00 00 00 00 95 00 00 00 00 00 00 00} (length 0x50)
// }
// }
// }
// license: ptr[in, buffer] {
// buffer: {47 50 4c 00} (length 0x4)
// }
// loglev: int32 = 0x1 (4 bytes)
// logsize: len = 0x100000 (4 bytes)
// log: ptr[out, buffer] {
// buffer: (DirOut)
// }
// kern_version: bpf_kern_version = 0x0 (4 bytes)
// flags: bpf_prog_load_flags = 0x0 (4 bytes)
// prog_name: buffer: {00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00} (length 0x10)
// prog_ifindex: ifindex (resource)
// expected_attach_type: union bpf_prog_attach_types {
// fallback: bpf_attach_types = 0x0 (4 bytes)
// }
// btf_fd: fd_btf (resource)
// func_info_rec_size: const = 0x8 (4 bytes)
// func_info: ptr[in, bpf_func_info] {
// bpf_func_info {
// insn_off: int32 = 0x0 (4 bytes)
// type_id: int32 = 0x3 (4 bytes)
// }
// }
// func_info_cnt: len = 0x2 (4 bytes)
// line_info_rec_size: const = 0x0 (4 bytes)
// line_info: nil
// line_info_cnt: len = 0x0 (4 bytes)
// attach_btf_id: bpf_btf_id (resource)
// attach_prog_fd: fd_bpf_prog (resource)
// core_relo_cnt: len = 0x0 (4 bytes)
// fd_array: nil
// core_relos: nil
// core_relo_rec_size: const = 0x0 (4 bytes)
// log_true_size: int32 = 0x0 (4 bytes)
// prog_token_fd: union _bpf_prog_t[flags[bpf_prog_type, int32], bpf_prog_attach_types, bpf_btf_id[opt], fd_bpf_prog[opt]]_prog_token_fd_wrapper {
// void: buffer: {} (length 0x0)
// }
// pad: union _bpf_prog_t[flags[bpf_prog_type, int32], bpf_prog_attach_types, bpf_btf_id[opt], fd_bpf_prog[opt]]_pad_wrapper {
// value: const = 0x0 (4 bytes)
// }
// }
// }
// size: len = 0x80 (8 bytes)
// ]
// returns fd_bpf_prog
*(uint32_t*)0x200000000300 = 5;
*(uint32_t*)0x200000000304 = 0xb;
*(uint64_t*)0x200000000308 = 0x200000000400;
memcpy((void*)0x200000000400, "\x18\x11\x00\x00", 4);
*(uint32_t*)0x200000000404 = r[0];
memcpy((void*)0x200000000408, "... [truncated large byte array] ...", 80);
*(uint64_t*)0x200000000310 = 0x200000000500;
memcpy((void*)0x200000000500, "GPL\000", 4);
*(uint32_t*)0x200000000318 = 1;
*(uint32_t*)0x20000000031c = 0x100000;
*(uint64_t*)0x200000000320 = 0x200000000700;
*(uint32_t*)0x200000000328 = 0;
*(uint32_t*)0x20000000032c = 0;
memset((void*)0x200000000330, 0, 16);
*(uint32_t*)0x200000000340 = 0;
*(uint32_t*)0x200000000344 = 0;
*(uint32_t*)0x200000000348 = r[1];
*(uint32_t*)0x20000000034c = 8;
*(uint64_t*)0x200000000350 = 0x200000000600;
*(uint32_t*)0x200000000600 = 0;
*(uint32_t*)0x200000000604 = 3;
*(uint32_t*)0x200000000358 = 2;
*(uint32_t*)0x20000000035c = 0;
*(uint64_t*)0x200000000360 = 0;
*(uint32_t*)0x200000000368 = 0;
*(uint32_t*)0x20000000036c = 0;
*(uint32_t*)0x200000000370 = 0;
*(uint32_t*)0x200000000374 = 0;
*(uint64_t*)0x200000000378 = 0;
*(uint64_t*)0x200000000380 = 0;
*(uint32_t*)0x200000000388 = 0;
*(uint32_t*)0x20000000038c = 0;
*(uint32_t*)0x200000000390 = 0;
syscall(__NR_bpf, /*cmd=*/5ul, /*arg=*/0x200000000300ul, /*size=*/0x80ul);
return 0;
}
Reply: **Analysis of the Bug**
The bug is located in the BPF verifier's backtracking and precision tracking logic. When verifying calls to certain helpers like `bpf_loop` or `bpf_set_retval`, the verifier explicitly marks their first argument (`BPF_REG_1`) as precise by calling `mark_chain_precision(env, BPF_REG_1)`. These helpers define their first argument type as `ARG_ANYTHING`.
During argument checking, `check_func_arg()` ensures that `ARG_ANYTHING` arguments are not pointers by calling `is_pointer_value()`. However, if the user has `CAP_PERFMON` privileges (which allows leaking kernel pointers), `env->allow_ptr_leaks` is set to `true`. When this flag is set, `is_pointer_value()` intentionally returns `false` even for pointer registers, allowing a pointer to be passed as `BPF_REG_1`.
When `mark_chain_precision()` is subsequently called on this pointer register, it invokes `bpf_mark_chain_precision()`, which contains the following sanity check:
```c
if (regno >= 0) {
reg = &func->regs[regno];
if (reg->type != SCALAR_VALUE) {
verifier_bug(env, "backtracking misuse");
return -EFAULT;
}
bt_set_reg(bt, regno);
}
```
Because the register holds a pointer type rather than a `SCALAR_VALUE`, the sanity check fails. This triggers the `verifier_bug()` macro, which emits a `BPF_WARN_ONCE` kernel warning and aborts the verification by returning `-EFAULT`.
**Security Impact**
* **Exploitable:** **False**. The verifier safely catches the unexpected state, emits a warning, and gracefully rejects the BPF program by returning `-EFAULT`. The program is never loaded or executed, meaning there is no memory corruption, privilege escalation, or information leak.
* **Denial of Service:** **False**. The bug only results in a single `WARN_ONCE` message in the kernel log and the rejection of the invalid BPF program. It does not crash the kernel, hang the system, or leak resources. (Note: Syzkaller treats WARNINGs as bugs, but in production environments without `panic_on_warn`, this is harmless).
* **Accessible From Unprivileged Processes:** **False**. Triggering this requires `CAP_PERFMON` to set `env->allow_ptr_leaks = true`, which a standard unprivileged user does not have.
* **Accessible From User Namespaces:** **True**. An unprivileged user can create a new user namespace, mount a BPF filesystem (`bpffs`) with delegation options, and create a BPF token. Because the user is root within their user namespace, the token will grant `CAP_PERFMON` for BPF operations, allowing them to bypass the pointer check and trigger the warning.
|
| 6/2 |
2026/09/04 08:34 |
llm |
expert |
0m
Model:
Tokens:
input: 13093
output: 29
thoughts: 79
Thoughts: Okay, let's dive into this syzkaller report.
**Analyzing a Potential BPF Backtracking Misuse**
Right, here's the report: `"verifier bug: backtracking misuse"` and the juicy bit, the warning in `kernel/bpf/backtrack.c:829`. That's a classic sign of something tricky happening within the BPF verifier. The stack trace, or at least the line number, is a good start. My initial thought is to go straight to that line and see what `bpf_mark_chain_precision` is doing around there. Hopefully, there's a comment or some context clues. This usually points to a subtle flaw in how the verifier handles the state of the program, particularly when backtracking or evaluating branches with potentially imprecise information. I'm expecting some kind of invalid assumption about the data or instruction set being tracked. Time to open the code and get to it.
|
| 7/2 |
2026/09/04 08:34 |
tool |
grepper |
0m
Error:
Args: map[Expression:WARNING: kernel/bpf/backtrack.c:829]
Results:
|
| 8/2 |
2026/09/04 08:34 |
llm |
expert |
0m
Model:
Tokens:
input: 13411
output: 38
thoughts: 22
Thoughts: Here's a summary of my immediate thought process, focusing on the provided directive:
**Analyzing Potential BPF Backtracking Issues**
Okay, so I'm diving into this BPF backtracking issue. The most logical starting point given the context is `kernel/bpf/backtrack.c`, specifically around line 829. My intuition tells me that's where the heart of the problem might be. I need to understand the control flow and data structures around that section of code to get a handle on the backtracking logic itself. This line number likely points to a particular function or block that implements or interacts with the potentially problematic backtracking mechanism. I'll need to carefully examine what's happening around that line to see how it works, if there is a bug, how to fix it, or how to provide an accurate reproduction of it.
|
| 9/2 |
2026/09/04 08:34 |
tool |
read-file |
0m
Args: map[File:kernel/bpf/backtrack.c FirstLine:800 LineCount:100]
Results: map[Contents: 800: struct bpf_verifier_state *starting_state,
801: int regno,
802: bool *changed)
803: {
804: struct bpf_verifier_state *st = starting_state;
805: struct backtrack_state *bt = &env->bt;
806: int first_idx = st->first_insn_idx;
807: int last_idx = starting_state->insn_idx;
808: int subseq_idx = -1;
809: struct bpf_func_state *func;
810: bool tmp, skip_first = true;
811: struct bpf_reg_state *reg;
812: int i, fr, err;
813:
814: if (!env->bpf_capable)
815: return 0;
816:
817: changed = changed ?: &tmp;
818: /* set frame number from which we are starting to backtrack */
819: bt_init(bt, starting_state->curframe);
820:
821: /* Do sanity checks against current state of register and/or stack
822: * slot, but don't set precise flag in current state, as precision
823: * tracking in the current state is unnecessary.
824: */
825: func = st->frame[bt->frame];
826: if (regno >= 0) {
827: reg = &func->regs[regno];
828: if (reg->type != SCALAR_VALUE) {
829: verifier_bug(env, "backtracking misuse");
830: return -EFAULT;
831: }
832: bt_set_reg(bt, regno);
833: }
834:
835: if (bt_empty(bt))
836: return 0;
837:
838: for (;;) {
839: DECLARE_BITMAP(mask, 64);
840: u32 history = st->jmp_history_cnt;
841: struct bpf_jmp_history_entry *hist;
842:
843: if (env->log.level & BPF_LOG_LEVEL2) {
844: verbose(env, "mark_precise: frame%d: last_idx %d first_idx %d subseq_idx %d \n",
845: bt->frame, last_idx, first_idx, subseq_idx);
846: }
847:
848: if (last_idx < 0) {
849: /* we are at the entry into subprog, which
850: * is expected for global funcs, but only if
851: * requested precise registers are R1-R5
852: * (which are global func's input arguments)
853: */
854: if (st->curframe == 0 &&
855: st->frame[0]->subprogno > 0 &&
856: st->frame[0]->callsite == BPF_MAIN_FUNC &&
857: bt_stack_mask(bt) == 0 &&
858: (bt_reg_mask(bt) & ~BPF_REGMASK_ARGS) == 0) {
859: bitmap_from_u64(mask, bt_reg_mask(bt));
860: for_each_set_bit(i, mask, 32) {
861: reg = &st->frame[0]->regs[i];
862: bt_clear_reg(bt, i);
863: if (reg->type == SCALAR_VALUE) {
864: reg->precise = true;
865: *changed = true;
866: }
867: }
868: return 0;
869: }
870:
871: verifier_bug(env, "backtracking func entry subprog %d reg_mask %x stack_mask %llx",
872: st->frame[0]->subprogno, bt_reg_mask(bt), bt_stack_mask(bt));
873: return -EFAULT;
874: }
875:
876: for (i = last_idx;;) {
877: if (skip_first) {
878: err = 0;
879: skip_first = false;
880: } else {
881: hist = get_jmp_hist_entry(st, history, i);
882: err = backtrack_insn(env, i, subseq_idx, hist, bt);
883: }
884: if (err == -ENOTSUPP) {
885: bpf_mark_all_scalars_precise(env, starting_state);
886: bt_reset(bt);
887: return 0;
888: } else if (err) {
889: return err;
890: }
891: if (bt_empty(bt))
892: /* Found assignment(s) into tracked register in this state.
893: * Since this state is already marked, just return.
894: * Nothing to be tracked further in the parent state.
895: */
896: return 0;
897: subseq_idx = i;
898: i = get_prev_insn_idx(st, i, &history);
899: if (i == -ENOENT)
]
|
| 10/2 |
2026/09/04 08:34 |
llm |
expert |
0m
Model:
Tokens:
input: 15231
output: 22
thoughts: 64
Thoughts: Here's my take on the bug and my thought process:
**Debugging the Precision Marking Function**
Okay, so the report indicates a bug, and it seems to be centered around a function. It's either `__mark_chain_precision` or `bpf_mark_chain_precision`. Hold on a minute... I need to verify that. My read of the code is `__mark_chain_precision`, but the report is showing `bpf_mark_chain_precision`. Let me double-check the exact function name right now to avoid wasting time later. Gotta nail down that function name *before* digging deeper. That's the first and most important step.
|
| 11/2 |
2026/09/04 08:35 |
tool |
grepper |
0m
Args: map[Expression:bpf_mark_chain_precision]
Results: map[Output:include/linux/bpf_verifier.h=1217=void bpf_clear_singular_ids(struct bpf_verifier_env *env, struct bpf_verifier_state *st);
include/linux/bpf_verifier.h:1218:int bpf_mark_chain_precision(struct bpf_verifier_env *env,
include/linux/bpf_verifier.h-1219- struct bpf_verifier_state *starting_state,
--
kernel/bpf/backtrack.c=665=void bpf_mark_all_scalars_precise(struct bpf_verifier_env *env,
--
kernel/bpf/backtrack.c-712-/*
kernel/bpf/backtrack.c:713: * bpf_mark_chain_precision() backtracks BPF program instruction sequence and
kernel/bpf/backtrack.c-714- * chain of verifier states making sure that register *regno* (if regno >= 0)
--
kernel/bpf/backtrack.c-798- */
kernel/bpf/backtrack.c:799:int bpf_mark_chain_precision(struct bpf_verifier_env *env,
kernel/bpf/backtrack.c-800- struct bpf_verifier_state *starting_state,
--
kernel/bpf/states.c=398=static void __clean_func_state(struct bpf_verifier_env *env,
--
kernel/bpf/states.c-451- * Can't replace with STACK_ZERO, because
kernel/bpf/states.c:452: * that requires bpf_mark_chain_precision().
kernel/bpf/states.c-453- */
--
kernel/bpf/states.c=1018=static int propagate_precision(struct bpf_verifier_env *env,
--
kernel/bpf/states.c-1066-
kernel/bpf/states.c:1067: err = bpf_mark_chain_precision(env, cur, -1, changed);
kernel/bpf/states.c-1068- if (err < 0)
--
kernel/bpf/verifier.c=3371=int mark_chain_precision(struct bpf_verifier_env *env, int regno)
kernel/bpf/verifier.c-3372-{
kernel/bpf/verifier.c:3373: return bpf_mark_chain_precision(env, env->cur_state, regno, NULL);
kernel/bpf/verifier.c-3374-}
--
kernel/bpf/verifier.c=3379=static int mark_chain_precision_batch(struct bpf_verifier_env *env,
--
kernel/bpf/verifier.c-3381-{
kernel/bpf/verifier.c:3382: return bpf_mark_chain_precision(env, starting_state, -1, NULL);
kernel/bpf/verifier.c-3383-}
]
|
| 12/2 |
2026/09/04 08:35 |
llm |
expert |
0m
Model:
Tokens:
input: 16223
output: 20
thoughts: 180
Thoughts: **Analyzing a Potential Backtracking Bug in the BPF Verifier**
Okay, so I'm looking at this `bpf_mark_chain_precision` function. Seems like that's the key piece involved here. I've pinpointed a potential bug within that function. Here's the snippet of code that's raising my concern:
```c
if (regno >= 0) {
reg = &func->regs[regno];
if (reg->type != SCALAR_VALUE) {
verifier_bug(env, "backtracking misuse");
return -EFAULT;
}
bt_set_reg(bt, regno);
}
```
The verifier calls `mark_chain_precision(env, regno)`, which, in turn, calls `bpf_mark_chain_precision(env, env->cur_state, regno, NULL)`. The problematic aspect is this conditional check: `if (reg->type != SCALAR_VALUE)`. If the register's type isn't `SCALAR_VALUE`, it calls `verifier_bug(env, "backtracking misuse")` and returns an error. This is a classic indicator of a potential issue when handling register types. It's a critical point in the backtracking mechanism, and the condition suggests a misuse of how the verifier is handling register states during its analysis.
Now, I need to dive deeper into the `verifier_bug` function to understand exactly how this error is being handled and what impact it has. Understanding the ramifications of this potential "backtracking misuse" is crucial to understanding the severity of the bug and how to correctly fix it. This is a common pattern in kernel verifiers - a state is assumed, but then not satisfied, which causes an error.
|
| 13/2 |
2026/09/04 08:35 |
tool |
grepper |
0m
Args: map[Expression:#define verifier_bug]
Results: map[Output:include/linux/bpf_verifier.h=1093=__printf(3, 4) void verbose_linfo(struct bpf_verifier_env *env,
--
include/linux/bpf_verifier.h-1096-
include/linux/bpf_verifier.h:1097:#define verifier_bug_if(cond, env, fmt, args...) \
include/linux/bpf_verifier.h-1098- ({ \
--
include/linux/bpf_verifier.h-1103- })
include/linux/bpf_verifier.h:1104:#define verifier_bug(env, fmt, args...) \
include/linux/bpf_verifier.h-1105- ({ \
]
|
| 14/2 |
2026/09/04 08:35 |
llm |
expert |
0m
Model:
Tokens:
input: 17007
output: 39
thoughts: 12
Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience:
**Analyzing the `verifier_bug` Definition**
Okay, so the initial thought is, "Let's dig into this `verifier_bug` concept." It's not something I'm intimately familiar with off the top of my head, so the first step is clearly a direct investigation. I need to establish a clear, concise definition to base any further analysis on. I'm likely thinking along the lines of, "What specific context does this term operate within? Is this related to formal verification, fuzzing, or perhaps static analysis? What are the key characteristics that differentiate a 'bug' in a verifier from a standard software bug?" My aim here is to get a solid grounding before I even consider specific scenarios or potential implications. The precise meaning, or even the common interpretations within a specific field, will heavily influence my next steps. This is foundational; I need to know precisely what we're dealing with before attempting to dissect the issue at all.
|
| 15/2 |
2026/09/04 08:35 |
tool |
read-file |
0m
Args: map[File:include/linux/bpf_verifier.h FirstLine:1090 LineCount:20]
Results: map[Contents:1090: void bpf_vlog_reset(struct bpf_verifier_log *log, u64 new_pos);
1091: int bpf_vlog_finalize(struct bpf_verifier_log *log, u32 *log_size_actual);
1092:
1093: __printf(3, 4) void verbose_linfo(struct bpf_verifier_env *env,
1094: u32 insn_off,
1095: const char *prefix_fmt, ...);
1096:
1097: #define verifier_bug_if(cond, env, fmt, args...) \
1098: ({ \
1099: bool __cond = (cond); \
1100: if (unlikely(__cond)) \
1101: verifier_bug(env, fmt " (" #cond ")", ##args); \
1102: (__cond); \
1103: })
1104: #define verifier_bug(env, fmt, args...) \
1105: ({ \
1106: BPF_WARN_ONCE(1, "verifier bug: " fmt "\n", ##args); \
1107: bpf_log(&env->log, "verifier bug: " fmt "\n", ##args); \
1108: })
1109:
]
|
| 16/2 |
2026/09/04 08:35 |
llm |
expert |
0m
Model:
Tokens:
input: 17655
output: 25
thoughts: 148
Thoughts: **Analyzing a BPF Verifier Bug**
Okay, so I've hit a `verifier_bug` which is immediately throwing a `BPF_WARN_ONCE`. That's a warning, not a hard stop, so I need to dig deeper. The verifier then rejects the BPF program with an `-EFAULT`. My initial thought is: is this exploitable? On the surface, if the verifier rejects the program, the program doesn't load, right? Seems safe.
But then I remember `bpf_mark_chain_precision` is called when the verifier tries to mark a register as precise. If that call fails, it also returns an `-EFAULT`. The caller is `mark_chain_precision`, which passes the error up. Now, where is `mark_chain_precision` called? I need to trace this back and check where `check_helper_call` comes into play. I'm going to follow the call stack from `mark_chain_precision` within `check_helper_call` to understand where this `-EFAULT` originates and how it impacts program loading, or if something sneaky is occurring before the rejection and potential exploitation.
|
| 17/2 |
2026/09/04 08:35 |
tool |
grepper |
0m
Error:
Args: map[Expression:mark_chain_precision.*check_helper_call]
Results:
|
| 18/2 |
2026/09/04 08:35 |
llm |
expert |
0m
Model:
Tokens:
input: 18092
output: 38
thoughts: 20
Thoughts: Here's a summary of my thought process, as if I were the one thinking it:
**Diving into the BPF Verifier**
Okay, time to get to the bottom of this. I need to take a look at the BPF verifier code again. Let's start with `kernel/bpf/verifier.c:10894`. I'm hoping that particular line will provide some key insight into the current issue, or perhaps just jog my memory about the relevant logic in that section. Time to see what we're working with here!
|
| 19/2 |
2026/09/04 08:35 |
tool |
read-file |
0m
Args: map[File:kernel/bpf/verifier.c FirstLine:10880 LineCount:30]
Results: map[Contents:10880: set_timer_callback_state);
10881: break;
10882: case BPF_FUNC_find_vma:
10883: err = push_callback_call(env, insn, insn_idx, meta.subprogno,
10884: set_find_vma_callback_state);
10885: break;
10886: case BPF_FUNC_snprintf:
10887: err = check_bpf_snprintf_call(env, regs);
10888: break;
10889: case BPF_FUNC_loop:
10890: update_loop_inline_state(env, meta.subprogno);
10891: /* Verifier relies on R1 value to determine if bpf_loop() iteration
10892: * is finished, thus mark it precise.
10893: */
10894: err = mark_chain_precision(env, BPF_REG_1);
10895: if (err)
10896: return err;
10897: if (cur_func(env)->callback_depth < reg_umax(®s[BPF_REG_1])) {
10898: err = push_callback_call(env, insn, insn_idx, meta.subprogno,
10899: set_loop_callback_state);
10900: } else {
10901: cur_func(env)->callback_depth = 0;
10902: if (env->log.level & BPF_LOG_LEVEL2)
10903: verbose(env, "frame%d bpf_loop iteration limit reached\n",
10904: env->cur_state->curframe);
10905: }
10906: break;
10907: case BPF_FUNC_dynptr_from_mem:
10908: if (regs[BPF_REG_1].type != PTR_TO_MAP_VALUE) {
10909: verbose(env, "Unsupported reg type %s for bpf_dynptr_from_mem data\n",
]
|
| 20/2 |
2026/09/04 08:35 |
llm |
expert |
0m
Model:
Tokens:
input: 18864
output: 23
thoughts: 114
Thoughts: **Analyzing the bpf_loop Function**
Okay, so I'm looking at how `BPF_FUNC_loop` interacts with the precision marking. Specifically, I see it calls `mark_chain_precision` with `BPF_REG_1` as an argument. The key here is, if the type of `regs[BPF_REG_1]` *isn't* a `SCALAR_VALUE`, `bpf_mark_chain_precision` is going to throw a `verifier_bug` and return `-EFAULT`. But now I'm pausing...is `regs[BPF_REG_1]` *always* guaranteed to be a `SCALAR_VALUE` when passed to `bpf_loop`? I need to verify that. Time to check the arguments and the calling conventions of `bpf_loop` itself. Gotta make sure this precision marking is robust.
|
| 21/2 |
2026/09/04 08:35 |
tool |
grepper |
0m
Args: map[Expression:BPF_CALL.*bpf_loop]
Results: map[Output:kernel/bpf/bpf_iter.c=717=const struct bpf_func_proto bpf_for_each_map_elem_proto = {
--
kernel/bpf/bpf_iter.c-726-
kernel/bpf/bpf_iter.c:727:BPF_CALL_4(bpf_loop, u32, nr_loops, void *, callback_fn, void *, callback_ctx,
kernel/bpf/bpf_iter.c-728- u64, flags)
]
|
| 22/2 |
2026/09/04 08:35 |
llm |
expert |
0m
Model:
Tokens:
input: 19336
output: 38
thoughts: 69
Thoughts: Here's my summary, as though I'm thinking through this myself:
**Analyzing `bpf_loop` Argument Verification**
Okay, so `bpf_loop`'s first argument is `u32 nr_loops`. That means `BPF_REG_1`, the register that should hold that value when the helper is called, *should* be a `SCALAR_VALUE`. Makes sense, so far. But something's niggling at me – I'm pretty sure the verifier does its argument checking *before* the `check_helper_call` function is even hit, right? Or am I misremembering the control flow here? I need to double-check that. Let's dig into `check_helper_call` and see exactly what's happening there to confirm or correct my understanding of the verification order and ensure this register is being validated as a scalar before the call proceeds. Let's see what `check_helper_call` reveals...
|
| 23/2 |
2026/09/04 08:35 |
tool |
read-file |
0m
Args: map[File:kernel/bpf/verifier.c FirstLine:10700 LineCount:50]
Results: map[Contents:10700: !env->cur_state->active_locks &&
10701: !env->cur_state->active_irq_id &&
10702: in_sleepable(env);
10703: }
10704:
10705: static const char *non_sleepable_context_description(struct bpf_verifier_env *env)
10706: {
10707: if (env->cur_state->active_rcu_locks)
10708: return "rcu_read_lock region";
10709: if (env->cur_state->active_preempt_locks)
10710: return "non-preemptible region";
10711: if (env->cur_state->active_irq_id)
10712: return "IRQ-disabled region";
10713: if (env->cur_state->active_locks)
10714: return "lock region";
10715: return "non-sleepable prog";
10716: }
10717:
10718: static int release_reg(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
10719: bool convert_rcu, bool release_dynptr)
10720: {
10721: int err = -EINVAL;
10722:
10723: if (bpf_register_is_null(reg))
10724: return 0;
10725:
10726: if (release_dynptr)
10727: err = unmark_stack_slots_dynptr(env, reg);
10728: else if (convert_rcu)
10729: err = ref_convert_alloc_rcu_protected(env, reg->id);
10730: else if (reg_is_referenced(env, reg))
10731: err = release_reference(env, reg->id);
10732:
10733: return err;
10734: }
10735:
10736: static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
10737: int *insn_idx_p)
10738: {
10739: enum bpf_prog_type prog_type = resolve_prog_type(env->prog);
10740: bool returns_cpu_specific_alloc_ptr = false;
10741: const struct bpf_func_proto *fn = NULL;
10742: enum bpf_return_type ret_type;
10743: enum bpf_type_flag ret_flag;
10744: struct bpf_reg_state *regs;
10745: struct bpf_call_arg_meta meta;
10746: const char *operation;
10747: int insn_idx = *insn_idx_p;
10748: bool changes_data;
10749: int i, err, func_id;
]
|
| 24/2 |
2026/09/04 08:35 |
llm |
expert |
0m
Model:
Tokens:
input: 20527
output: 39
thoughts: 22
Thoughts: Here's my take on those thoughts:
**Tracing the Call Stack: `check_func_arg` in Context**
Okay, so I'm digging into `check_helper_call` to understand its operation. My immediate goal is to figure out the specific locations where `check_func_arg` is actually invoked *within* this helper function. I need to understand its role in the bigger picture of the call validation. It's a targeted investigation; I'm not trying to reconstruct the entire execution flow from scratch, but pinpoint how `check_func_arg` is utilized. Ultimately, I'm trying to ensure I have a robust understanding of the validation routines.
|
| 25/2 |
2026/09/04 08:35 |
tool |
read-file |
0m
Args: map[File:kernel/bpf/verifier.c FirstLine:10750 LineCount:100]
Results: map[Contents:10750:
10751: /* find function prototype */
10752: func_id = insn->imm;
10753: err = bpf_get_helper_proto(env, insn->imm, &fn);
10754: if (err == -ERANGE) {
10755: verbose(env, "invalid func %s#%d\n", func_id_name(func_id), func_id);
10756: return -EINVAL;
10757: }
10758:
10759: if (err) {
10760: verbose(env, "program of this type cannot use helper %s#%d\n",
10761: func_id_name(func_id), func_id);
10762: operation = bpf_diag_fmt(env, "helper %s#%d", func_id_name(func_id), func_id);
10763: bpf_diag_policy(
10764: env, insn_idx, operation, "this program type does not allow the helper",
10765: "Use a helper allowed for this program type, or move the logic to a compatible program type.");
10766: return err;
10767: }
10768:
10769: /* eBPF programs must be GPL compatible to use GPL-ed functions */
10770: if (!env->prog->gpl_compatible && fn->gpl_only) {
10771: verbose(env, "cannot call GPL-restricted function from non-GPL compatible program\n");
10772: operation = bpf_diag_fmt(env, "helper %s#%d", func_id_name(func_id), func_id);
10773: bpf_diag_policy(
10774: env, insn_idx, operation,
10775: "this helper is restricted to GPL-compatible programs",
10776: "Use a GPL-compatible license, or replace the helper with one that is available to non-GPL programs.");
10777: return -EINVAL;
10778: }
10779:
10780: if (fn->allowed && !fn->allowed(env->prog)) {
10781: verbose(env, "helper call is not allowed in probe\n");
10782: operation = bpf_diag_fmt(env, "helper %s#%d", func_id_name(func_id), func_id);
10783: bpf_diag_policy(
10784: env, insn_idx, operation,
10785: "the helper-specific policy callback rejected this program",
10786: "Use the helper only from an allowed attach point or program configuration.");
10787: return -EINVAL;
10788: }
10789:
10790: /* With LD_ABS/IND some JITs save/restore skb from r1. */
10791: changes_data = bpf_helper_changes_pkt_data(func_id);
10792: if (changes_data && fn->arg1_type != ARG_PTR_TO_CTX) {
10793: verifier_bug(env, "func %s#%d: r1 != ctx", func_id_name(func_id), func_id);
10794: return -EFAULT;
10795: }
10796:
10797: memset(&meta, 0, sizeof(meta));
10798:
10799: err = check_func_proto(fn, &meta);
10800: if (err) {
10801: verifier_bug(env, "incorrect func proto %s#%d", func_id_name(func_id), func_id);
10802: return err;
10803: }
10804:
10805: if (fn->might_sleep && !in_sleepable_context(env)) {
10806: verbose(env, "sleepable helper %s#%d in %s\n", func_id_name(func_id), func_id,
10807: non_sleepable_context_description(env));
10808: operation = bpf_diag_fmt(env, "sleepable helper %s#%d",
10809: func_id_name(func_id), func_id);
10810: bpf_diag_ctx_forbidden(env, insn_idx, operation,
10811: "Move the helper call outside the critical section, or use a non-sleepable helper.");
10812: return -EINVAL;
10813: }
10814:
10815: /* Track non-sleepable context for helpers. */
10816: if (!in_sleepable_context(env))
10817: env->insn_aux_data[insn_idx].non_sleepable = true;
10818:
10819: meta.func_id = func_id;
10820: meta.fn = fn;
10821: /* check args */
10822: for (i = 0; i < MAX_BPF_FUNC_REG_ARGS; i++) {
10823: err = check_func_arg(env, i, &meta, insn_idx);
10824: if (err)
10825: return err;
10826: }
10827:
10828: err = record_func_map(env, &meta, func_id, insn_idx);
10829: if (err)
10830: return err;
10831:
10832: err = record_func_key(env, &meta, func_id, insn_idx);
10833: if (err)
10834: return err;
10835:
10836: regs = cur_regs(env);
10837:
10838: /* Mark slots with STACK_MISC in case of raw mode, stack offset
10839: * is inferred from register state.
10840: */
10841: for (i = 0; i < meta.arg_raw_mem.size; i++) {
10842: err = check_mem_access(env, insn_idx, regs + meta.arg_raw_mem.regno,
10843: argno_from_reg(meta.arg_raw_mem.regno), i, BPF_B,
10844: BPF_WRITE, -1, false, false);
10845: if (err)
10846: return err;
10847: }
10848:
10849: if (meta.release_regno) {
]
|
| 26/2 |
2026/09/04 08:35 |
llm |
expert |
0m
Model:
Tokens:
input: 22619
output: 19
thoughts: 122
Thoughts: **Analyzing the Argument Validation Logic**
Okay, so I'm stepping through this code, specifically looking at how arguments are validated. It seems like `check_func_arg` is the key function that's being used for all arguments passed to these functions. Right now I'm focusing on the `bpf_loop` function. I see that for `bpf_loop`, the first register, `BPF_REG_1`, represents `u32 nr_loops`. The expectation, from what I'm reading, is that `check_func_arg` should confirm that `BPF_REG_1` is a `SCALAR_VALUE`.
But... there's a disconnect. If `check_func_arg` rigidly enforces that `BPF_REG_1` *must* be a `SCALAR_VALUE`, how can it possibly be something else later when `mark_chain_precision` is called? That just doesn't make sense! There must be something I'm missing.
Time to dive deeper into `check_func_arg`. I need to understand exactly what `ARG_ANYTHING` means in the context of that function and how it might interact with the expected `SCALAR_VALUE` constraint. I need to trace this back. There's a subtle interaction here that is going to be key to unlocking the argument validation. I'll get to the bottom of this.
|
| 27/2 |
2026/09/04 08:35 |
tool |
grepper |
0m
Args: map[Expression:check_func_arg]
Results: map[Output:kernel/bpf/verifier.c=866=static bool is_dynptr_reg_valid_init(struct bpf_verifier_env *env, struct bpf_reg_state *reg)
--
kernel/bpf/verifier.c-873- * CONST_PTR_TO_DYNPTR already has fixed and var_off as 0 due to
kernel/bpf/verifier.c:874: * check_func_arg_reg_off's logic, so we don't need to check its
kernel/bpf/verifier.c-875- * offset and alignment.
--
kernel/bpf/verifier.c=4465=static int map_kptr_match_type(struct bpf_verifier_env *env,
--
kernel/bpf/verifier.c-4520- *
kernel/bpf/verifier.c:4521: * In the kptr_ref case, check_func_arg_reg_off already ensures reg->var_off
kernel/bpf/verifier.c-4522- * is zero. We must also ensure that btf_struct_ids_match does not walk
--
kernel/bpf/verifier.c=8416=reg_find_field_offset(const struct bpf_reg_state *reg, s32 off, u32 fields)
--
kernel/bpf/verifier.c-8431-
kernel/bpf/verifier.c:8432:static int __check_func_arg_reg_off(struct bpf_verifier_env *env,
kernel/bpf/verifier.c-8433- const struct bpf_reg_state *reg, argno_t argno,
--
kernel/bpf/verifier.c-8511-
kernel/bpf/verifier.c:8512:static int check_func_arg_reg_off(struct bpf_verifier_env *env,
kernel/bpf/verifier.c-8513- const struct bpf_reg_state *reg, argno_t argno,
--
kernel/bpf/verifier.c-8515-{
kernel/bpf/verifier.c:8516: return __check_func_arg_reg_off(env, reg, argno, arg_type, true);
kernel/bpf/verifier.c-8517-}
--
kernel/bpf/verifier.c=8642=static int process_map_ptr_arg(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
--
kernel/bpf/verifier.c-8679-
kernel/bpf/verifier.c:8680:static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
kernel/bpf/verifier.c-8681- struct bpf_call_arg_meta *meta,
--
kernel/bpf/verifier.c-8737-
kernel/bpf/verifier.c:8738: err = check_func_arg_reg_off(env, reg, argno, arg_type);
kernel/bpf/verifier.c-8739- if (err)
--
kernel/bpf/verifier.c=9572=static int setup_func_entry(struct bpf_verifier_env *env, int subprog, int callsite,
--
kernel/bpf/verifier.c-9619-
kernel/bpf/verifier.c:9620:static int btf_check_func_arg_match(struct bpf_verifier_env *env, int subprog,
kernel/bpf/verifier.c-9621- const struct btf *btf,
--
kernel/bpf/verifier.c-9672- } else if (arg->arg_type == ARG_PTR_TO_CTX) {
kernel/bpf/verifier.c:9673: ret = check_func_arg_reg_off(env, reg, argno, ARG_PTR_TO_CTX);
kernel/bpf/verifier.c-9674- if (ret < 0)
--
kernel/bpf/verifier.c-9684- } else if (base_type(arg->arg_type) == ARG_PTR_TO_MEM) {
kernel/bpf/verifier.c:9685: ret = check_func_arg_reg_off(env, reg, argno, ARG_DONTCARE);
kernel/bpf/verifier.c-9686- if (ret < 0)
--
kernel/bpf/verifier.c-9710- } else if (arg->arg_type == ARG_PTR_TO_DYNPTR) {
kernel/bpf/verifier.c:9711: ret = check_func_arg_reg_off(env, reg, argno, ARG_PTR_TO_DYNPTR);
kernel/bpf/verifier.c-9712- if (ret)
--
kernel/bpf/verifier.c-9729- bpf_subprog_name(env, subprog));
kernel/bpf/verifier.c:9730: err = err ?: check_func_arg_reg_off(env, reg, argno, arg->arg_type);
kernel/bpf/verifier.c-9731- if (err)
--
kernel/bpf/verifier.c=9750=static int btf_check_subprog_call(struct bpf_verifier_env *env, int subprog,
--
kernel/bpf/verifier.c-9767-
kernel/bpf/verifier.c:9768: err = btf_check_func_arg_match(env, subprog, btf, regs);
kernel/bpf/verifier.c-9769- /* Compiler optimizations can remove arguments from static functions
--
kernel/bpf/verifier.c=10736=static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
--
kernel/bpf/verifier.c-10822- for (i = 0; i < MAX_BPF_FUNC_REG_ARGS; i++) {
kernel/bpf/verifier.c:10823: err = check_func_arg(env, i, &meta, insn_idx);
kernel/bpf/verifier.c-10824- if (err)
--
kernel/bpf/verifier.c=12577=static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_call_arg_meta *meta,
--
kernel/bpf/verifier.c-12716- arg_type |= OBJ_RELEASE;
kernel/bpf/verifier.c:12717: ret = __check_func_arg_reg_off(env, reg, argno, arg_type,
kernel/bpf/verifier.c-12718- btf_id_fixed_off_ok);
]
|
| 28/2 |
2026/09/04 08:35 |
llm |
expert |
0m
Model:
Tokens:
input: 24805
output: 38
thoughts: 22
Thoughts: Here's my summary, as though I'm reading and thinking about the code:
**Diving into the BPF Verifier: `check_func_arg`**
Okay, time to dig into `kernel/bpf/verifier.c` and specifically, that `check_func_arg` function. I'm already anticipating this is where the magic happens, where the verifier digs into function arguments, ensuring they're safe and that any access within the function respects the established BPF rules.
I imagine this function is likely a workhorse. It probably gets called repeatedly, dealing with each argument passed to a BPF function. I'm expecting to see checks for things like:
* **Type Safety:** Ensuring arguments align with the expected type signatures of the BPF function. This is critical to prevent type confusion and memory corruption.
* **Pointer Validation:** Making certain that any pointer arguments point to valid memory regions accessible to the BPF program. This will probably involve tracking the provenance of the pointers and applying any necessary bounds checks.
* **Context and Permitted Actions:** I'm guessing this function will enforce restrictions on what arguments can be used for in the BPF program. For instance, read-only arguments may need to be treated differently from read-write.
* **Security:** This is probably where security vulnerabilities are prevented. I imagine that there are checks for out of bounds array access, and maybe invalid pointers.
* **State Tracking:** It's quite likely this is deeply intertwined with the verifier's overall state tracking. Changes to arguments, such as pointer dereferences or modifications, will need to be carefully reflected in the verifier's internal representation.
I'm ready to get down to details. Let's see how they've implemented this. This is the heart of keeping BPF safe.
|
| 29/2 |
2026/09/04 08:35 |
tool |
read-file |
0m
Args: map[File:kernel/bpf/verifier.c FirstLine:8680 LineCount:100]
Results: map[Contents:8680: static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
8681: struct bpf_call_arg_meta *meta,
8682: int insn_idx)
8683: {
8684: const struct bpf_func_proto *fn = meta->fn;
8685: u32 regno = BPF_REG_1 + arg;
8686: struct bpf_reg_state *reg = reg_state(env, regno);
8687: enum bpf_arg_type arg_type = fn->arg_type[arg];
8688: argno_t argno = argno_from_reg(regno);
8689: enum bpf_reg_type type = reg->type;
8690: u32 *arg_btf_id = NULL;
8691: u32 key_size;
8692: int err = 0;
8693:
8694: if (arg_type == ARG_DONTCARE)
8695: return 0;
8696:
8697: err = check_reg_arg(env, regno, SRC_OP);
8698: if (err)
8699: return err;
8700:
8701: if (arg_type == ARG_ANYTHING) {
8702: if (is_pointer_value(env, regno)) {
8703: verbose(env, "R%d leaks addr into helper function\n",
8704: regno);
8705: return -EACCES;
8706: }
8707: return 0;
8708: }
8709:
8710: if (type_is_pkt_pointer(type) &&
8711: !may_access_direct_pkt_data(env, fn, BPF_READ)) {
8712: verbose(env, "helper access to the packet is not allowed\n");
8713: return -EACCES;
8714: }
8715:
8716: if (base_type(arg_type) == ARG_PTR_TO_MAP_VALUE) {
8717: err = resolve_map_arg_type(env, meta, &arg_type);
8718: if (err)
8719: return err;
8720: }
8721:
8722: if (bpf_register_is_null(reg) && type_may_be_null(arg_type))
8723: /* A NULL register has a SCALAR_VALUE type, so skip
8724: * type checking.
8725: */
8726: goto skip_type_check;
8727:
8728: /* arg_btf_id and arg_size are in a union. */
8729: if (base_type(arg_type) == ARG_PTR_TO_BTF_ID ||
8730: base_type(arg_type) == ARG_PTR_TO_SPIN_LOCK)
8731: arg_btf_id = fn->arg_btf_id[arg];
8732:
8733: err = check_reg_type(env, reg, argno, arg_type, arg_btf_id, meta,
8734: func_id_name(meta->func_id));
8735: if (err)
8736: return err;
8737:
8738: err = check_func_arg_reg_off(env, reg, argno, arg_type);
8739: if (err)
8740: return err;
8741:
8742: skip_type_check:
8743: if (arg_type_is_release(arg_type) && !arg_type_is_dynptr(arg_type) &&
8744: !reg_is_referenced(env, reg) && !bpf_register_is_null(reg)) {
8745: verbose(env, "release helper %s expects referenced PTR_TO_BTF_ID passed to %s\n",
8746: func_id_name(meta->func_id), reg_arg_name(env, argno));
8747: bpf_diag_call_arg(
8748: env, insn_idx, argno, func_id_name(meta->func_id),
8749: "release helpers require a value that owns a live resource returned by a matching acquire helper",
8750: "Pass the resource-owning pointer returned by the matching acquire helper, and avoid calling the release helper after ownership has already been transferred or released.");
8751: return -EINVAL;
8752: }
8753:
8754: if (reg_is_referenced(env, reg))
8755: update_ref_obj(&meta->ref_obj, reg);
8756:
8757: switch (base_type(arg_type)) {
8758: case ARG_CONST_MAP_PTR:
8759: /* bpf_map_xxx(map_ptr) call: remember that map_ptr */
8760: err = process_map_ptr_arg(env, reg, argno, meta);
8761: if (err)
8762: return err;
8763: break;
8764: case ARG_PTR_TO_MAP_KEY:
8765: /* bpf_map_xxx(..., map_ptr, ..., key) call:
8766: * check that [key, key + map->key_size) are within
8767: * stack limits and initialized
8768: */
8769: if (!meta->map.ptr) {
8770: /* in function declaration map_ptr must come before
8771: * map_key, so that it's verified and known before
8772: * we have to check map_key here. Otherwise it means
8773: * that kernel subsystem misconfigured verifier
8774: */
8775: verifier_bug(env, "invalid map_ptr to access map->key");
8776: return -EFAULT;
8777: }
8778: key_size = meta->map.ptr->key_size;
8779: err = check_helper_mem_access(env, reg, argno, key_size, BPF_READ, false, NULL,
]
|
| 30/2 |
2026/09/04 08:35 |
llm |
expert |
0m
Model:
Tokens:
input: 27004
output: 20
thoughts: 36
Thoughts: Okay, here's my interpretation of those thoughts, summarized from my perspective as someone well-versed in this area:
**Analyzing `bpf_loop` Argument Handling**
Hmm, so I'm looking at `bpf_loop` and specifically focusing on how it handles its arguments. The key point here is that for the `nr_loops` parameter, the `arg_type` is defined as `ARG_ANYTHING`. Okay, that's interesting. It means there's a certain level of flexibility or, perhaps, a lack of strict type enforcement. I need to keep that in mind when examining the loop's implementation and how arguments interact with its logic. Now, let me quickly refresh my memory by double checking the `bpf_loop` prototype...
|
| 31/2 |
2026/09/04 08:36 |
tool |
grepper |
0m
Args: map[Expression:bpf_loop_proto]
Results: map[Output:include/linux/bpf.h=3938=extern const struct bpf_func_proto bpf_find_vma_proto;
include/linux/bpf.h:3939:extern const struct bpf_func_proto bpf_loop_proto;
include/linux/bpf.h-3940-extern const struct bpf_func_proto bpf_copy_from_user_task_proto;
--
kernel/bpf/bpf_iter.c=727=BPF_CALL_4(bpf_loop, u32, nr_loops, void *, callback_fn, void *, callback_ctx,
--
kernel/bpf/bpf_iter.c-752-
kernel/bpf/bpf_iter.c:753:const struct bpf_func_proto bpf_loop_proto = {
kernel/bpf/bpf_iter.c-754- .func = bpf_loop,
--
kernel/bpf/helpers.c=2067=bpf_base_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
--
kernel/bpf/helpers.c-2150- case BPF_FUNC_loop:
kernel/bpf/helpers.c:2151: return &bpf_loop_proto;
kernel/bpf/helpers.c-2152- case BPF_FUNC_user_ringbuf_drain:
]
|
| 32/2 |
2026/09/04 08:36 |
llm |
expert |
0m
Model:
Tokens:
input: 27592
output: 39
thoughts: 12
Thoughts: Okay, here's my attempt at summarizing the thought process, as though I were an expert:
**Diving into `bpf_loop_proto`**
Right, let's take a look at `bpf_loop_proto`. My initial reaction, knowing the usual context of BPF, is that this is likely a mechanism for creating some form of looping structure within a BPF program. I'm immediately trying to guess the intended purpose. Is it a general-purpose loop? Or is it targeted at a very specific use case, perhaps packet processing, system tracing, or something else entirely? Given how BPF can interact with the kernel, I'd guess that it's likely a controlled loop construct. You wouldn't want uncontrolled loops causing starvation within the kernel! The implications of uncontrolled looping are serious, and probably would require some form of bounded iteration. It could be a macro, a function wrapper, or something more sophisticated within the BPF VM itself. I'll need to look for any imposed restrictions. I'm keen to see how the looping construct interacts with the BPF verifier and any constraints it places on program execution to ensure safety. Ultimately, I'm expecting to understand its performance characteristics, possible caveats, and practical application scenarios.
|
| 33/2 |
2026/09/04 08:36 |
tool |
read-file |
0m
Args: map[File:kernel/bpf/bpf_iter.c FirstLine:750 LineCount:20]
Results: map[Contents: 750: return i;
751: }
752:
753: const struct bpf_func_proto bpf_loop_proto = {
754: .func = bpf_loop,
755: .gpl_only = false,
756: .ret_type = RET_INTEGER,
757: .arg1_type = ARG_ANYTHING,
758: .arg2_type = ARG_PTR_TO_FUNC,
759: .arg3_type = ARG_PTR_TO_STACK_OR_NULL,
760: .arg4_type = ARG_ANYTHING,
761: };
762:
763: struct bpf_iter_num_kern {
764: int cur; /* current value, inclusive */
765: int end; /* final value, exclusive */
766: } __aligned(8);
767:
768: __bpf_kfunc_start_defs();
769:
]
|
| 34/2 |
2026/09/04 08:36 |
llm |
expert |
0m
Model:
Tokens:
input: 28211
output: 19
thoughts: 129
Thoughts: **Analyzing Potential Security Risks in Function Arguments**
Okay, so I'm looking at this code and I see that `arg1_type` is set to `ARG_ANYTHING`. That's interesting, meaning the function can accept any type of argument. Now I'm in the `check_func_arg` function. Specifically, this block:
```c
if (arg_type == ARG_ANYTHING) {
if (is_pointer_value(env, regno)) {
verbose(env, "R%d leaks addr into helper function\n",
regno);
return -EACCES;
}
return 0;
}
```
My brain immediately goes to security concerns. With `ARG_ANYTHING`, the code explicitly calls `is_pointer_value` to check if the register `regno` holds a pointer value. The code is structured such that if it _is_ a pointer, then a violation is flagged, logging "R%d leaks addr into helper function" and returning -EACCES. This suggests there's a vulnerability if a pointer is passed to the function when it's not expected, likely because that could be leaking memory addresses or leading to other security-sensitive information leakage. That makes sense. I'll need to look at `is_pointer_value` next to fully understand the detection logic.
|
| 35/2 |
2026/09/04 08:36 |
tool |
grepper |
0m
Args: map[Expression:is_pointer_value]
Results: map[Output:kernel/bpf/verifier.c=3398=static bool is_pointer_regtype(enum bpf_reg_type type)
--
kernel/bpf/verifier.c-3402-
kernel/bpf/verifier.c:3403:static bool __is_pointer_value(bool allow_ptr_leaks,
kernel/bpf/verifier.c-3404- const struct bpf_reg_state *reg)
--
kernel/bpf/verifier.c=3854=static int check_stack_read_fixed_off(struct bpf_verifier_env *env,
--
kernel/bpf/verifier.c-3966- */
kernel/bpf/verifier.c:3967: } else if (__is_pointer_value(env->allow_ptr_leaks, reg)) {
kernel/bpf/verifier.c-3968- /* If dst_regno==-1, the caller is asking us whether
--
kernel/bpf/verifier.c=4946=static int check_sock_access(struct bpf_verifier_env *env, int insn_idx,
--
kernel/bpf/verifier.c-4987-
kernel/bpf/verifier.c:4988:static bool is_pointer_value(struct bpf_verifier_env *env, int regno)
kernel/bpf/verifier.c-4989-{
kernel/bpf/verifier.c:4990: return __is_pointer_value(env->allow_ptr_leaks, reg_state(env, regno));
kernel/bpf/verifier.c-4991-}
--
kernel/bpf/verifier.c=6336=static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, struct bpf_reg_state *reg, argno_t argno,
--
kernel/bpf/verifier.c-6367- if (t == BPF_WRITE && value_regno >= 0 &&
kernel/bpf/verifier.c:6368: is_pointer_value(env, value_regno)) {
kernel/bpf/verifier.c-6369- verbose(env, "R%d leaks addr into map\n", value_regno);
--
kernel/bpf/verifier.c-6405- if (t == BPF_WRITE && value_regno >= 0 &&
kernel/bpf/verifier.c:6406: is_pointer_value(env, value_regno)) {
kernel/bpf/verifier.c-6407- verbose(env, "R%d leaks addr into mem\n", value_regno);
--
kernel/bpf/verifier.c-6428- if (t == BPF_WRITE && value_regno >= 0 &&
kernel/bpf/verifier.c:6429: is_pointer_value(env, value_regno)) {
kernel/bpf/verifier.c-6430- verbose(env, "R%d leaks addr into ctx\n", value_regno);
--
kernel/bpf/verifier.c-6481- if (t == BPF_WRITE && value_regno >= 0 &&
kernel/bpf/verifier.c:6482: is_pointer_value(env, value_regno)) {
kernel/bpf/verifier.c-6483- verbose(env, "R%d leaks addr into packet\n",
--
kernel/bpf/verifier.c-6491- if (t == BPF_WRITE && value_regno >= 0 &&
kernel/bpf/verifier.c:6492: is_pointer_value(env, value_regno)) {
kernel/bpf/verifier.c-6493- verbose(env, "R%d leaks addr into flow keys\n",
--
kernel/bpf/verifier.c=6670=static int check_atomic_rmw(struct bpf_verifier_env *env,
--
kernel/bpf/verifier.c-6699-
kernel/bpf/verifier.c:6700: if (is_pointer_value(env, aux_reg)) {
kernel/bpf/verifier.c-6701- verbose(env, "R%d leaks addr into mem\n", aux_reg);
--
kernel/bpf/verifier.c-6705-
kernel/bpf/verifier.c:6706: if (is_pointer_value(env, insn->src_reg)) {
kernel/bpf/verifier.c-6707- verbose(env, "R%d leaks addr into mem\n", insn->src_reg);
--
kernel/bpf/verifier.c=8680=static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
--
kernel/bpf/verifier.c-8701- if (arg_type == ARG_ANYTHING) {
kernel/bpf/verifier.c:8702: if (is_pointer_value(env, regno)) {
kernel/bpf/verifier.c-8703- verbose(env, "R%d leaks addr into helper function\n",
--
kernel/bpf/verifier.c=15780=static int check_alu_op(struct bpf_verifier_env *env, struct bpf_insn *insn)
--
kernel/bpf/verifier.c-15793-
kernel/bpf/verifier.c:15794: if (is_pointer_value(env, insn->dst_reg)) {
kernel/bpf/verifier.c-15795- verbose(env, "R%d pointer arithmetic prohibited\n",
--
kernel/bpf/verifier.c-15850- /* case: R1 = (s8, s16 s32)R2 */
kernel/bpf/verifier.c:15851: if (is_pointer_value(env, insn->src_reg)) {
kernel/bpf/verifier.c-15852- verbose(env,
--
kernel/bpf/verifier.c-15871- /* R1 = (u32) R2 */
kernel/bpf/verifier.c:15872: if (is_pointer_value(env, insn->src_reg)) {
kernel/bpf/verifier.c-15873- verbose(env,
--
kernel/bpf/verifier.c=16312=static int is_branch_taken(struct bpf_verifier_env *env, struct bpf_reg_state *reg1,
--
kernel/bpf/verifier.c-16317-
kernel/bpf/verifier.c:16318: if (__is_pointer_value(false, reg1) || __is_pointer_value(false, reg2)) {
kernel/bpf/verifier.c-16319- u64 val;
--
kernel/bpf/verifier.c=16803=static int check_cond_jmp_op(struct bpf_verifier_env *env,
--
kernel/bpf/verifier.c-16855- if (!(reg_is_pkt_pointer_any(dst_reg) && reg_is_pkt_pointer_any(src_reg)) &&
kernel/bpf/verifier.c:16856: is_pointer_value(env, insn->src_reg)) {
kernel/bpf/verifier.c-16857- verbose(env, "R%d pointer comparison prohibited\n",
--
kernel/bpf/verifier.c-16891- */
kernel/bpf/verifier.c:16892: if (!__is_pointer_value(false, dst_reg))
kernel/bpf/verifier.c-16893- err = mark_chain_precision(env, insn->dst_reg);
kernel/bpf/verifier.c-16894- if (BPF_SRC(insn->code) == BPF_X && !err &&
kernel/bpf/verifier.c:16895: !__is_pointer_value(false, src_reg))
kernel/bpf/verifier.c-16896- err = mark_chain_precision(env, insn->src_reg);
--
kernel/bpf/verifier.c-16987- if (!is_jmp32 && BPF_SRC(insn->code) == BPF_X &&
kernel/bpf/verifier.c:16988: __is_pointer_value(false, src_reg) && __is_pointer_value(false, dst_reg) &&
kernel/bpf/verifier.c-16989- base_type(src_reg->type) != PTR_TO_BTF_ID &&
--
kernel/bpf/verifier.c-17031- this_branch, other_branch) &&
kernel/bpf/verifier.c:17032: is_pointer_value(env, insn->dst_reg)) {
kernel/bpf/verifier.c-17033- verbose(env, "R%d pointer comparison prohibited\n",
--
kernel/bpf/verifier.c=17404=static int check_return_code(struct bpf_verifier_env *env, int regno, const char *reg_name)
--
kernel/bpf/verifier.c-17442-
kernel/bpf/verifier.c:17443: if (is_pointer_value(env, regno)) {
kernel/bpf/verifier.c-17444- verbose(env, "R%d leaks addr as return value\n", regno);
--
kernel/bpf/verifier.c=17489=static int check_global_subprog_return_code(struct bpf_verifier_env *env)
--
kernel/bpf/verifier.c-17505-
kernel/bpf/verifier.c:17506: if (is_pointer_value(env, BPF_REG_0)) {
kernel/bpf/verifier.c-17507- verbose(env, "R%d leaks addr as return value\n", BPF_REG_0);
]
|
| 36/2 |
2026/09/04 08:36 |
llm |
expert |
0m
Model:
Tokens:
input: 31241
output: 37
thoughts: 12
Thoughts: Okay, here's my interpretation of that thought process, tailored for an expert audience, and written in the first person:
**Analyzing the `__is_pointer_value` Macro**
Alright, let's dive into this `__is_pointer_value` macro. My first instinct, as always, is to think about the broader context. What language is this within? C or C++ likely, given the naming convention. What's the target platform? That might influence how it's implemented and optimized. I'm immediately trying to infer its purpose based on the name. It's clearly a test for something, and it's something pointer-related. But is it checking if a value *is* a pointer, if a value *represents* a pointer, or if a value has pointer semantics? The nuances here are important for understanding the intended use.
My mind immediately starts generating possible implementations. Is this a compile-time check using `sizeof` and type traits, possibly relying on the standard library? Maybe it's a runtime check involving bitwise operations, especially if we're dealing with memory addresses and potentially interpreting some integer as a pointer? I'm anticipating that if it's a runtime check, the implementation could be very platform-dependent, looking for certain alignment characteristics or bit patterns. I'm also considering the possibility of more complex, custom type system extensions if the environment is something unusual.
The underscore-underscore prefix is an indicator of implementation detail, so I need to be careful assuming anything. I would need to find the definition to understand the exact implementation strategy. A macro such as this could be checking whether a value is not 0, a pointer address must be a non-zero address to be valid. Or, this might be a static assertion using something like `static_assert` to detect an invalid pointer, such as a pointer to a const object. Or it could be a specialized construct for dealing with `void*`.
Ultimately, I need more information on how and where this macro is used to understand the complete picture. The macro name itself is not clear enough. Is it a language-intrinsic check, something custom-defined, or perhaps a wrapper around a more basic compiler intrinsic? The context is key.
|
| 37/2 |
2026/09/04 08:36 |
tool |
read-file |
0m
Args: map[File:kernel/bpf/verifier.c FirstLine:3398 LineCount:20]
Results: map[Contents:3398: static bool is_pointer_regtype(enum bpf_reg_type type)
3399: {
3400: return type != SCALAR_VALUE && type != NOT_INIT;
3401: }
3402:
3403: static bool __is_pointer_value(bool allow_ptr_leaks,
3404: const struct bpf_reg_state *reg)
3405: {
3406: if (allow_ptr_leaks)
3407: return false;
3408:
3409: return is_pointer_regtype(reg->type);
3410: }
3411:
3412: static void clear_scalar_id(struct bpf_reg_state *reg)
3413: {
3414: reg->id = 0;
3415: reg->delta = 0;
3416: }
3417:
]
|
| 38/2 |
2026/09/04 08:36 |
llm |
expert |
0m
Model:
Tokens:
input: 32032
output: 20
thoughts: 114
Thoughts: **My Reasoning on Pointer Leaks**
Okay, so we're looking at this `allow_ptr_leaks` flag, which is interesting. It seems like if `allow_ptr_leaks` is set to true, the `__is_pointer_value` function returns `false`. That means the `is_pointer_value(env, regno)` function will also return `false`, even when `reg->type` *is* a pointer type. That's a crucial point. It essentially bypasses our pointer checks in specific scenarios.
The big question now is, when does `allow_ptr_leaks` get set to true? We need to figure out the conditions that trigger this bypass. It appears this setting is linked to privileged users. Specifically, it's enabled for users with capabilities like CAP_PERFMON.
Therefore, my next step is clear: I need to trace where and how `allow_ptr_leaks` is being set within the code. Understanding the conditions for its activation is key to evaluating the overall security implications of this behavior.
|
| 39/2 |
2026/09/04 08:36 |
tool |
grepper |
0m
Args: map[Expression:allow_ptr_leaks]
Results: map[Output:include/linux/bpf.h=2860=bool bpf_token_capable(const struct bpf_token *token, int cap);
include/linux/bpf.h-2861-
include/linux/bpf.h:2862:static inline bool bpf_allow_ptr_leaks(const struct bpf_token *token)
include/linux/bpf.h-2863-{
--
include/linux/bpf_verifier.h=916=struct bpf_verifier_env {
--
include/linux/bpf_verifier.h-942- bool explore_alu_limits;
include/linux/bpf_verifier.h:943: bool allow_ptr_leaks;
include/linux/bpf_verifier.h-944- /* Allow access to uninitialized stack memory. Writes with fixed offset are
--
kernel/bpf/diagnostics.c=608=static void format_disasm_line(struct bpf_verifier_env *env, int insn_idx,
--
kernel/bpf/diagnostics.c-632-
kernel/bpf/diagnostics.c:633: print_bpf_insn(&cbs, insn, env->allow_ptr_leaks);
kernel/bpf/diagnostics.c-634- seq_buf_str(&ctx.seq);
--
kernel/bpf/disasm.c=186=void print_bpf_insn(const struct bpf_insn_cbs *cbs,
kernel/bpf/disasm.c-187- const struct bpf_insn *insn,
kernel/bpf/disasm.c:188: bool allow_ptr_leaks)
kernel/bpf/disasm.c-189-{
--
kernel/bpf/disasm.c-332-
kernel/bpf/disasm.c:333: if (is_ptr && !allow_ptr_leaks)
kernel/bpf/disasm.c-334- imm = 0;
--
kernel/bpf/disasm.h=37=void print_bpf_insn(const struct bpf_insn_cbs *cbs,
kernel/bpf/disasm.h-38- const struct bpf_insn *insn,
kernel/bpf/disasm.h:39: bool allow_ptr_leaks);
kernel/bpf/disasm.h-40-#endif
--
kernel/bpf/verifier.c=769=static void mark_reg_invalid(const struct bpf_verifier_env *env, struct bpf_reg_state *reg)
kernel/bpf/verifier.c-770-{
kernel/bpf/verifier.c:771: if (!env->allow_ptr_leaks)
kernel/bpf/verifier.c-772- bpf_mark_reg_not_init(env, reg);
--
kernel/bpf/verifier.c=1210=static bool is_stack_slot_special(const struct bpf_stack_state *stack)
--
kernel/bpf/verifier.c-1239- * - STACK_POISON, which truly forbids access to the slot.
kernel/bpf/verifier.c:1240: * Regardless of allow_ptr_leaks setting (i.e., privileged or unprivileged
kernel/bpf/verifier.c-1241- * mode), we won't promote STACK_INVALID to STACK_MISC. In privileged case it is
--
kernel/bpf/verifier.c=3324=void bpf_verbose_insn(struct bpf_verifier_env *env, struct bpf_insn *insn)
--
kernel/bpf/verifier.c-3331-
kernel/bpf/verifier.c:3332: print_bpf_insn(&cbs, insn, env->allow_ptr_leaks);
kernel/bpf/verifier.c-3333-}
--
kernel/bpf/verifier.c=3398=static bool is_pointer_regtype(enum bpf_reg_type type)
--
kernel/bpf/verifier.c-3402-
kernel/bpf/verifier.c:3403:static bool __is_pointer_value(bool allow_ptr_leaks,
kernel/bpf/verifier.c-3404- const struct bpf_reg_state *reg)
kernel/bpf/verifier.c-3405-{
kernel/bpf/verifier.c:3406: if (allow_ptr_leaks)
kernel/bpf/verifier.c-3407- return false;
--
kernel/bpf/verifier.c=3509=static int check_stack_write_fixed_off(struct bpf_verifier_env *env,
--
kernel/bpf/verifier.c-3524- */
kernel/bpf/verifier.c:3525: if (!env->allow_ptr_leaks &&
kernel/bpf/verifier.c-3526- bpf_is_spilled_reg(&state->stack[spi]) &&
--
kernel/bpf/verifier.c=3652=static int check_stack_write_var_off(struct bpf_verifier_env *env,
--
kernel/bpf/verifier.c-3697-
kernel/bpf/verifier.c:3698: if (!env->allow_ptr_leaks && *stype != STACK_MISC && *stype != STACK_ZERO) {
kernel/bpf/verifier.c-3699- /* Reject the write if range we may write to has not
--
kernel/bpf/verifier.c=3854=static int check_stack_read_fixed_off(struct bpf_verifier_env *env,
--
kernel/bpf/verifier.c-3966- */
kernel/bpf/verifier.c:3967: } else if (__is_pointer_value(env->allow_ptr_leaks, reg)) {
kernel/bpf/verifier.c-3968- /* If dst_regno==-1, the caller is asking us whether
--
kernel/bpf/verifier.c=4988=static bool is_pointer_value(struct bpf_verifier_env *env, int regno)
kernel/bpf/verifier.c-4989-{
kernel/bpf/verifier.c:4990: return __is_pointer_value(env->allow_ptr_leaks, reg_state(env, regno));
kernel/bpf/verifier.c-4991-}
--
kernel/bpf/verifier.c=5942=static int check_ptr_to_btf_access(struct bpf_verifier_env *env,
--
kernel/bpf/verifier.c-5954-
kernel/bpf/verifier.c:5955: if (!env->allow_ptr_leaks) {
kernel/bpf/verifier.c-5956- verbose(env,
--
kernel/bpf/verifier.c=6106=static int check_ptr_to_map_access(struct bpf_verifier_env *env,
--
kernel/bpf/verifier.c-6133-
kernel/bpf/verifier.c:6134: if (!env->allow_ptr_leaks) {
kernel/bpf/verifier.c-6135- verbose(env,
--
kernel/bpf/verifier.c=6836=static int check_stack_range_initialized(
--
kernel/bpf/verifier.c-6924- (state->stack[spi].spilled_ptr.type == SCALAR_VALUE ||
kernel/bpf/verifier.c:6925: env->allow_ptr_leaks)) {
kernel/bpf/verifier.c-6926- if (clobber) {
--
kernel/bpf/verifier.c=14417=static int sanitize_check_bounds(struct bpf_verifier_env *env,
--
kernel/bpf/verifier.c-14451- * If we return -EACCES, caller may want to try again treating pointer as a
kernel/bpf/verifier.c:14452: * scalar. So we only emit a diagnostic if !env->allow_ptr_leaks.
kernel/bpf/verifier.c-14453- */
kernel/bpf/verifier.c=14454=static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, struct bpf_insn *insn,
--
kernel/bpf/verifier.c-14482- /* 32-bit ALU ops on pointers produce (meaningless) scalars */
kernel/bpf/verifier.c:14483: if (opcode == BPF_SUB && env->allow_ptr_leaks) {
kernel/bpf/verifier.c-14484- __mark_reg_unknown(env, dst_reg);
--
kernel/bpf/verifier.c=15613=static int adjust_reg_min_max_vals(struct bpf_verifier_env *env,
--
kernel/bpf/verifier.c-15659- */
kernel/bpf/verifier.c:15660: if (opcode == BPF_SUB && env->allow_ptr_leaks) {
kernel/bpf/verifier.c-15661- mark_reg_unknown(env, regs, insn->dst_reg);
--
kernel/bpf/verifier.c=18638=static int check_map_prog_compatibility(struct bpf_verifier_env *env,
--
kernel/bpf/verifier.c-18724- }
kernel/bpf/verifier.c:18725: if (!env->allow_ptr_leaks || !env->bpf_capable) {
kernel/bpf/verifier.c-18726- verbose(env, "CAP_BPF and CAP_PERFMON are required to use arena\n");
--
kernel/bpf/verifier.c=21009=int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr,
--
kernel/bpf/verifier.c-21033-
kernel/bpf/verifier.c:21034: env->allow_ptr_leaks = bpf_allow_ptr_leaks(env->prog->aux->token);
kernel/bpf/verifier.c-21035- env->allow_uninit_stack = bpf_allow_uninit_stack(env->prog->aux->token);
]
|
| 40/2 |
2026/09/04 08:36 |
llm |
expert |
0m
Model:
Tokens:
input: 35073
output: 23
thoughts: 804
Thoughts: **My Analysis of a Potential Verifier Bug**
Okay, so I've been digging into this code and have identified a potential, albeit likely benign, issue in the BPF verifier. The scenario involves the `env->allow_ptr_leaks` flag, which, as I understand it, is only enabled for privileged users, usually those with `CAP_PERFMON`. When this flag is true, `is_pointer_value` is set to return `false` for pointer types. That's the crux.
This has an effect on the `check_func_arg` function for arguments of type `ARG_ANYTHING`. Because `is_pointer_value` returns `false`, `check_func_arg` would mistakenly *accept* a pointer register as a valid argument. This is where things start getting interesting.
Specifically, I’m looking at how this interacts with the `bpf_loop` helper. When `allow_ptr_leaks` is set and a pointer register is passed as the first argument (`BPF_REG_1`, which is effectively `nr_loops`), the verifier proceeds to call `mark_chain_precision`, which in turn calls `bpf_mark_chain_precision`.
Inside `bpf_mark_chain_precision`, there's a check on the register type: `if (reg->type != SCALAR_VALUE)`. Given the scenario I outlined, `reg->type` *is* a pointer type (not a `SCALAR_VALUE`). This, in turn, *triggers* `verifier_bug(env, "backtracking misuse")`! It's a bug.
So, in theory, I have a verifiable way to trigger this `verifier_bug`. Now the question: Is this a vulnerability?
Let's break down the consequences. The `verifier_bug` calls `BPF_WARN_ONCE` and returns `-EFAULT`. This means the verifier rejects the BPF program; it does *not* load. Thus, the only consequence is a warning in the kernel logs. In a typical production build (without `panic_on_warn` set, which is not the default), this doesn't lead to a kernel panic. It's just a warning.
Does it lead to memory corruption? No, the verifier just returns `-EFAULT` and cleans everything up. Denial of Service? Only if `panic_on_warn` is set, but, as I said, that is unusual. Any resource leaks? No, the verifier cleans everything up when it errors.
Based on this analysis, I'm confident that this issue is just a benign, although confusing, warning in the logs. This behavior is only accessible to privileged users, and all it does is reject a BPF program.
|
| 41/2 |
2026/09/04 08:36 |
tool |
grepper |
0m
Args: map[Expression:bpf_allow_ptr_leaks]
Results: map[Output:include/linux/bpf.h=2860=bool bpf_token_capable(const struct bpf_token *token, int cap);
include/linux/bpf.h-2861-
include/linux/bpf.h:2862:static inline bool bpf_allow_ptr_leaks(const struct bpf_token *token)
include/linux/bpf.h-2863-{
--
kernel/bpf/verifier.c=21009=int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr,
--
kernel/bpf/verifier.c-21033-
kernel/bpf/verifier.c:21034: env->allow_ptr_leaks = bpf_allow_ptr_leaks(env->prog->aux->token);
kernel/bpf/verifier.c-21035- env->allow_uninit_stack = bpf_allow_uninit_stack(env->prog->aux->token);
]
|
| 42/2 |
2026/09/04 08:36 |
llm |
expert |
0m
Model:
Tokens:
input: 36759
output: 37
thoughts: 15
Thoughts: Okay, let's dive into this `bpf_allow_ptr_leaks` thing.
**My Analysis of `bpf_allow_ptr_leaks`**
Alright, I'm going to take a look at this. Immediately, my expert brain kicks in, considering what this implies in the context of BPF. The name itself is intriguing. `allow_ptr_leaks`... That signals a deliberate decision, and that's the key: it's not a bug, it's a *feature*, or rather, a controlled relaxation of restrictions. I know BPF's security model is typically pretty tight, preventing unprivileged programs from accessing arbitrary kernel memory via pointers. So, this must be an exception to the rule, introduced for a specific purpose. My mind races. What are the *use cases* that necessitate this? What are the *trade-offs*? Is this related to tracing, observability, or something more specialized like network programming where direct memory access might be crucial for performance? Is this a knob I can enable and disable in different scenarios? Is there anything I can tweak, or is it either on or off?
I need to understand the implications thoroughly before I consider using it. I'm already anticipating some of the crucial questions: What are the security guarantees that are *lost* by allowing pointer leaks? What mitigation strategies are in place to limit the damage that could be done if an attacker managed to exploit this? What are the potential consequences? How does the underlying BPF verifier handle this relaxation? Where in the code is it used, and why? I also have to keep in mind, I need to know the cost/benefit; how much performance are we trading for flexibility? I'm going to go deeper. Let's see how this is implemented.
|
| 43/2 |
2026/09/04 08:36 |
tool |
read-file |
0m
Args: map[File:include/linux/bpf.h FirstLine:2850 LineCount:30]
Results: map[Contents:2850: this_cpu_inc(*map->elem_count);
2851: }
2852:
2853: static inline void bpf_map_dec_elem_count(struct bpf_map *map)
2854: {
2855: this_cpu_dec(*map->elem_count);
2856: }
2857:
2858: extern int sysctl_unprivileged_bpf_disabled;
2859:
2860: bool bpf_token_capable(const struct bpf_token *token, int cap);
2861:
2862: static inline bool bpf_allow_ptr_leaks(const struct bpf_token *token)
2863: {
2864: return bpf_token_capable(token, CAP_PERFMON);
2865: }
2866:
2867: static inline bool bpf_allow_uninit_stack(const struct bpf_token *token)
2868: {
2869: return bpf_token_capable(token, CAP_PERFMON);
2870: }
2871:
2872: static inline bool bpf_bypass_spec_v1(const struct bpf_token *token)
2873: {
2874: return bpf_jit_bypass_spec_v1() ||
2875: cpu_mitigations_off() ||
2876: bpf_token_capable(token, CAP_PERFMON);
2877: }
2878:
2879: static inline bool bpf_bypass_spec_v4(const struct bpf_token *token)
]
|
| 44/2 |
2026/09/04 08:36 |
llm |
expert |
0m
Model:
Tokens:
input: 37655
output: 20
thoughts: 63
Thoughts: **Investigating BPF Pointer Leakage Restrictions**
Okay, so I'm looking at `bpf_allow_ptr_leaks` and the fact that it needs `CAP_PERFMON`. My immediate question is: can an unprivileged user actually get that capability within a user namespace? That's the crux of the matter, isn't it? To dig deeper, I need to understand what's happening internally – specifically, I need to check out `bpf_token_capable`. I know it's responsible for the capability checks, so that's where the next clue lies. Let's see what that code reveals. I need to understand this mechanism completely.
|
| 45/2 |
2026/09/04 08:37 |
tool |
grepper |
0m
Args: map[Expression:bpf_token_capable]
Results: map[Output:drivers/media/rc/bpf-lirc.c=83=lirc_mode2_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
--
drivers/media/rc/bpf-lirc.c-112- case BPF_FUNC_trace_printk:
drivers/media/rc/bpf-lirc.c:113: if (bpf_token_capable(prog->aux->token, CAP_PERFMON))
drivers/media/rc/bpf-lirc.c-114- return bpf_get_trace_printk_proto();
--
include/linux/bpf.h=2858=extern int sysctl_unprivileged_bpf_disabled;
include/linux/bpf.h-2859-
include/linux/bpf.h:2860:bool bpf_token_capable(const struct bpf_token *token, int cap);
include/linux/bpf.h-2861-
include/linux/bpf.h=2862=static inline bool bpf_allow_ptr_leaks(const struct bpf_token *token)
include/linux/bpf.h-2863-{
include/linux/bpf.h:2864: return bpf_token_capable(token, CAP_PERFMON);
include/linux/bpf.h-2865-}
--
include/linux/bpf.h=2867=static inline bool bpf_allow_uninit_stack(const struct bpf_token *token)
include/linux/bpf.h-2868-{
include/linux/bpf.h:2869: return bpf_token_capable(token, CAP_PERFMON);
include/linux/bpf.h-2870-}
--
include/linux/bpf.h=2872=static inline bool bpf_bypass_spec_v1(const struct bpf_token *token)
--
include/linux/bpf.h-2875- cpu_mitigations_off() ||
include/linux/bpf.h:2876: bpf_token_capable(token, CAP_PERFMON);
include/linux/bpf.h-2877-}
--
include/linux/bpf.h=2879=static inline bool bpf_bypass_spec_v4(const struct bpf_token *token)
--
include/linux/bpf.h-2882- cpu_mitigations_off() ||
include/linux/bpf.h:2883: bpf_token_capable(token, CAP_PERFMON);
include/linux/bpf.h-2884-}
--
include/linux/bpf.h=3354=static inline int bpf_obj_get_user(const char __user *pathname, int flags)
--
include/linux/bpf.h-3358-
include/linux/bpf.h:3359:static inline bool bpf_token_capable(const struct bpf_token *token, int cap)
include/linux/bpf.h-3360-{
--
include/linux/filter.h=1452=static inline bool bpf_jit_blinding_enabled(struct bpf_prog *prog)
--
include/linux/filter.h-1463- return false;
include/linux/filter.h:1464: if (bpf_jit_harden == 1 && bpf_token_capable(prog->aux->token, CAP_BPF))
include/linux/filter.h-1465- return false;
--
include/linux/lsm_hook_defs.h=453=LSM_HOOK(int, 0, bpf_token_cmd, const struct bpf_token *token, enum bpf_cmd cmd)
include/linux/lsm_hook_defs.h:454:LSM_HOOK(int, 0, bpf_token_capable, const struct bpf_token *token, int cap)
include/linux/lsm_hook_defs.h-455-#endif /* CONFIG_BPF_SYSCALL */
--
include/linux/security.h=2313=extern int security_bpf_token_cmd(const struct bpf_token *token, enum bpf_cmd cmd);
include/linux/security.h:2314:extern int security_bpf_token_capable(const struct bpf_token *token, int cap);
include/linux/security.h-2315-#else
--
include/linux/security.h=2359=static inline int security_bpf_token_cmd(const struct bpf_token *token, enum bpf_cmd cmd)
--
include/linux/security.h-2363-
include/linux/security.h:2364:static inline int security_bpf_token_capable(const struct bpf_token *token, int cap)
include/linux/security.h-2365-{
--
kernel/bpf/bpf_lsm.c=300=BTF_ID(func, bpf_lsm_bpf_token_cmd)
kernel/bpf/bpf_lsm.c:301:BTF_ID(func, bpf_lsm_bpf_token_capable)
kernel/bpf/bpf_lsm.c-302-BTF_ID(func, bpf_lsm_bprm_check_security)
--
kernel/bpf/core.c=670=void bpf_prog_kallsyms_add(struct bpf_prog *fp)
--
kernel/bpf/core.c-672- if (!bpf_prog_kallsyms_candidate(fp) ||
kernel/bpf/core.c:673: !bpf_token_capable(fp->aux->token, CAP_BPF))
kernel/bpf/core.c-674- return;
--
kernel/bpf/helpers.c=2067=bpf_base_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
--
kernel/bpf/helpers.c-2123-
kernel/bpf/helpers.c:2124: if (!bpf_token_capable(prog->aux->token, CAP_BPF))
kernel/bpf/helpers.c-2125- return NULL;
--
kernel/bpf/helpers.c-2191-
kernel/bpf/helpers.c:2192: if (!bpf_token_capable(prog->aux->token, CAP_PERFMON))
kernel/bpf/helpers.c-2193- return NULL;
--
kernel/bpf/syscall.c=1255=static int map_check_btf(struct bpf_map *map, struct bpf_token *token,
--
kernel/bpf/syscall.c-1284-
kernel/bpf/syscall.c:1285: if (!bpf_token_capable(token, CAP_BPF)) {
kernel/bpf/syscall.c-1286- ret = -EPERM;
--
kernel/bpf/syscall.c=1382=static int map_create_alloc(union bpf_attr *attr, bpfptr_t uattr, struct bpf_verifier_log *log,
--
kernel/bpf/syscall.c-1480- */
kernel/bpf/syscall.c:1481: if (sysctl_unprivileged_bpf_disabled && !bpf_token_capable(token, CAP_BPF))
kernel/bpf/syscall.c-1482- goto put_token;
--
kernel/bpf/syscall.c-1517- case BPF_MAP_TYPE_INSN_ARRAY:
kernel/bpf/syscall.c:1518: if (!bpf_token_capable(token, CAP_BPF))
kernel/bpf/syscall.c-1519- goto put_token;
--
kernel/bpf/syscall.c-1525- case BPF_MAP_TYPE_XSKMAP:
kernel/bpf/syscall.c:1526: if (!bpf_token_capable(token, CAP_NET_ADMIN))
kernel/bpf/syscall.c-1527- goto put_token;
--
kernel/bpf/syscall.c=2917=static int bpf_prog_load(union bpf_attr *attr, bpfptr_t uattr, struct bpf_log_attr *attr_log)
--
kernel/bpf/syscall.c-2959-
kernel/bpf/syscall.c:2960: bpf_cap = bpf_token_capable(token, CAP_BPF);
kernel/bpf/syscall.c-2961- err = -EPERM;
--
kernel/bpf/syscall.c-2987-
kernel/bpf/syscall.c:2988: if (is_net_admin_prog_type(type) && !bpf_token_capable(token, CAP_NET_ADMIN))
kernel/bpf/syscall.c-2989- goto put_token;
kernel/bpf/syscall.c:2990: if (is_perfmon_prog_type(type) && !bpf_token_capable(token, CAP_PERFMON))
kernel/bpf/syscall.c-2991- goto put_token;
--
kernel/bpf/syscall.c=4474=static int bpf_prog_attach_check_attach_type(const struct bpf_prog *prog,
--
kernel/bpf/syscall.c-4485- case BPF_PROG_TYPE_CGROUP_SKB:
kernel/bpf/syscall.c:4486: if (!bpf_token_capable(prog->aux->token, CAP_NET_ADMIN))
kernel/bpf/syscall.c-4487- /* cg-skb progs can be loaded by unpriv user.
--
kernel/bpf/syscall.c=5564=static int bpf_btf_load(const union bpf_attr *attr, bpfptr_t uattr, struct bpf_log_attr *attr_log)
--
kernel/bpf/syscall.c-5583-
kernel/bpf/syscall.c:5584: if (!bpf_token_capable(token, CAP_BPF)) {
kernel/bpf/syscall.c-5585- bpf_token_put(token);
--
kernel/bpf/syscall.c=5596=static int bpf_btf_get_fd_by_id(const union bpf_attr *attr)
--
kernel/bpf/syscall.c-5615-
kernel/bpf/syscall.c:5616: if (!bpf_token_capable(token, CAP_SYS_ADMIN)) {
kernel/bpf/syscall.c-5617- bpf_token_put(token);
--
kernel/bpf/syscall.c=6630=syscall_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
--
kernel/bpf/syscall.c-6633- case BPF_FUNC_sys_bpf:
kernel/bpf/syscall.c:6634: return !bpf_token_capable(prog->aux->token, CAP_PERFMON)
kernel/bpf/syscall.c-6635- ? NULL : &bpf_sys_bpf_proto;
--
kernel/bpf/token.c=12=static bool bpf_ns_capable(struct user_namespace *ns, int cap)
--
kernel/bpf/token.c-16-
kernel/bpf/token.c:17:bool bpf_token_capable(const struct bpf_token *token, int cap)
kernel/bpf/token.c-18-{
--
kernel/bpf/token.c-24- return false;
kernel/bpf/token.c:25: if (token && security_bpf_token_capable(token, cap) < 0)
kernel/bpf/token.c-26- return false;
--
kernel/bpf/verifier.c=21009=int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr,
--
kernel/bpf/verifier.c-21037- env->bypass_spec_v4 = bpf_bypass_spec_v4(env->prog->aux->token);
kernel/bpf/verifier.c:21038: env->bpf_capable = is_priv = bpf_token_capable(env->prog->aux->token, CAP_BPF);
kernel/bpf/verifier.c-21039- env->signature = attr->signature;
--
kernel/trace/bpf_trace.c=1274=bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
--
kernel/trace/bpf_trace.c-1298-
kernel/trace/bpf_trace.c:1299: if (!bpf_token_capable(prog->aux->token, CAP_SYS_ADMIN))
kernel/trace/bpf_trace.c-1300- return NULL;
--
net/core/filter.c=9156=static bool cg_skb_is_valid_access(int off, int size,
--
net/core/filter.c-9167- case bpf_ctx_range(struct __sk_buff, data_end):
net/core/filter.c:9168: if (!bpf_token_capable(prog->aux->token, CAP_BPF))
net/core/filter.c-9169- return false;
--
net/core/filter.c-9179- case bpf_ctx_range(struct __sk_buff, tstamp):
net/core/filter.c:9180: if (!bpf_token_capable(prog->aux->token, CAP_BPF))
net/core/filter.c-9181- return false;
--
net/core/filter.c=12361=bpf_sk_base_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
--
net/core/filter.c-12392-
net/core/filter.c:12393: if (!bpf_token_capable(prog->aux->token, CAP_PERFMON))
net/core/filter.c-12394- return NULL;
--
security/security.c=5422=int security_bpf_token_cmd(const struct bpf_token *token, enum bpf_cmd cmd)
--
security/security.c-5427-/**
security/security.c:5428: * security_bpf_token_capable() - Check if BPF token is allowed to delegate
security/security.c-5429- * requested BPF-related capability
--
security/security.c-5437- */
security/security.c:5438:int security_bpf_token_capable(const struct bpf_token *token, int cap)
security/security.c-5439-{
security/security.c:5440: return call_int_hook(bpf_token_capable, token, cap);
security/security.c-5441-}
--
security/selinux/hooks.c=7363=static int selinux_bpf_token_cmd(const struct bpf_token *token,
--
security/selinux/hooks.c-7384-
security/selinux/hooks.c:7385:static int selinux_bpf_token_capable(const struct bpf_token *token, int cap)
security/selinux/hooks.c-7386-{
--
security/selinux/hooks.c=7560=static struct security_hook_list selinux_hooks[] __ro_after_init = {
--
security/selinux/hooks.c-7844- LSM_HOOK_INIT(bpf_token_cmd, selinux_bpf_token_cmd),
security/selinux/hooks.c:7845: LSM_HOOK_INIT(bpf_token_capable, selinux_bpf_token_capable),
security/selinux/hooks.c-7846-#endif
--
tools/testing/selftests/bpf/prog_tests/token.c=750=static int userns_obj_priv_prog(int mnt_fd, struct token_lsm *lsm_skel)
--
tools/testing/selftests/bpf/prog_tests/token.c-773-
tools/testing/selftests/bpf/prog_tests/token.c:774: /* provide BPF token, but reject bpf_token_capable() with LSM */
tools/testing/selftests/bpf/prog_tests/token.c-775- lsm_skel->bss->reject_capable = true;
--
tools/testing/selftests/bpf/progs/token_lsm.c=12=int reject_cmd;
tools/testing/selftests/bpf/progs/token_lsm.c-13-
tools/testing/selftests/bpf/progs/token_lsm.c:14:SEC("lsm/bpf_token_capable")
tools/testing/selftests/bpf/progs/token_lsm.c-15-int BPF_PROG(token_capable, struct bpf_token *token, int cap)
]
|
| 46/2 |
2026/09/04 08:37 |
llm |
expert |
0m
Model:
Tokens:
input: 42354
output: 34
thoughts: 20
Thoughts: Here's a summary of my thinking, presented as if it were my thought process:
**Diving into `kernel/bpf/token.c`**
Okay, time to dig into the BPF tokenization code. Let's start with `kernel/bpf/token.c` and specifically focus our attention around line 17. That's a good starting point, likely where the core token structure definition or perhaps the initial setup functions are located. I'll need to understand how the BPF verifier interacts with and interprets these tokens at a foundational level. Knowing that will give me a better grasp of how more complex constructs are derived.
|
| 47/2 |
2026/09/04 08:37 |
tool |
read-file |
0m
Args: map[File:kernel/bpf/token.c FirstLine:1 LineCount:40]
Results: map[Contents: 1: // SPDX-License-Identifier: GPL-2.0
2: #include <linux/bpf.h>
3: #include <linux/vmalloc.h>
4: #include <linux/file.h>
5: #include <linux/fs.h>
6: #include <linux/kernel.h>
7: #include <linux/idr.h>
8: #include <linux/namei.h>
9: #include <linux/user_namespace.h>
10: #include <linux/security.h>
11:
12: static bool bpf_ns_capable(struct user_namespace *ns, int cap)
13: {
14: return ns_capable(ns, cap) || (cap != CAP_SYS_ADMIN && ns_capable(ns, CAP_SYS_ADMIN));
15: }
16:
17: bool bpf_token_capable(const struct bpf_token *token, int cap)
18: {
19: struct user_namespace *userns;
20:
21: /* BPF token allows ns_capable() level of capabilities */
22: userns = token ? token->userns : &init_user_ns;
23: if (!bpf_ns_capable(userns, cap))
24: return false;
25: if (token && security_bpf_token_capable(token, cap) < 0)
26: return false;
27: return true;
28: }
29:
30: void bpf_token_inc(struct bpf_token *token)
31: {
32: atomic64_inc(&token->refcnt);
33: }
34:
35: static void bpf_token_free(struct bpf_token *token)
36: {
37: security_bpf_token_free(token);
38: put_user_ns(token->userns);
39: kfree(token);
40: }
]
|
| 48/2 |
2026/09/04 08:37 |
llm |
expert |
0m
Model:
Tokens:
input: 43120
output: 20
thoughts: 193
Thoughts: **BPF Token Capability Analysis**
Okay, let's break this down. So `bpf_token_capable` is essentially doing a `ns_capable` check, specifically against the user namespace and a capability – in this case, `CAP_PERFMON`. Right, that makes sense. If a user spawns a user namespace, they automatically get all capabilities within *that* namespace. So, intuitively, `ns_capable` should return true for `CAP_PERFMON` in their own user namespace.
But hang on… I need to be more precise here. `bpf_token_capable` uses `token->userns` if a `token` is passed, otherwise it defaults to `&init_user_ns`. So, if a `token` isn't provided, it’s checking `ns_capable(&init_user_ns, CAP_PERFMON)`. That means the user needs to be root *in the initial namespace* to pass that check. That's the baseline.
Now, if a `token` *is* provided, it's checking against the token's user namespace: `ns_capable(token->userns, CAP_PERFMON)`. That's where things get interesting... I'm reminded of the newness of BPF tokens. The core question is: can an unprivileged user even *create* a BPF token? Because if they can, then they could effectively gain `CAP_PERFMON` (or other capabilities) within their own namespace through token manipulation. I need to dig into the `bpf_token_create` function to be sure.
|
| 49/2 |
2026/09/04 08:37 |
tool |
grepper |
0m
Args: map[Expression:bpf_token_create]
Results: map[Output:include/linux/bpf.h=2909=void bpf_token_put(struct bpf_token *token);
include/linux/bpf.h:2910:int bpf_token_create(union bpf_attr *attr);
include/linux/bpf.h-2911-struct bpf_token *bpf_token_get_from_fd(u32 ufd);
--
include/linux/lsm_hook_defs.h=449=LSM_HOOK(void, LSM_RET_VOID, bpf_prog_free, struct bpf_prog *prog)
include/linux/lsm_hook_defs.h:450:LSM_HOOK(int, 0, bpf_token_create, struct bpf_token *token, union bpf_attr *attr,
include/linux/lsm_hook_defs.h-451- const struct path *path)
--
include/linux/security.h=2309=extern void security_bpf_prog_free(struct bpf_prog *prog);
include/linux/security.h:2310:extern int security_bpf_token_create(struct bpf_token *token, union bpf_attr *attr,
include/linux/security.h-2311- const struct path *path);
--
include/linux/security.h=2347=static inline void security_bpf_prog_free(struct bpf_prog *prog)
--
include/linux/security.h-2349-
include/linux/security.h:2350:static inline int security_bpf_token_create(struct bpf_token *token, union bpf_attr *attr,
include/linux/security.h-2351- const struct path *path)
--
kernel/bpf/bpf_lsm.c=297=BTF_ID(func, bpf_lsm_bpf_prog_load)
kernel/bpf/bpf_lsm.c:298:BTF_ID(func, bpf_lsm_bpf_token_create)
kernel/bpf/bpf_lsm.c-299-BTF_ID(func, bpf_lsm_bpf_token_free)
--
kernel/bpf/syscall.c=6226=static int token_create(union bpf_attr *attr)
--
kernel/bpf/syscall.c-6234-
kernel/bpf/syscall.c:6235: return bpf_token_create(attr);
kernel/bpf/syscall.c-6236-}
--
kernel/bpf/token.c=107=const struct file_operations bpf_token_fops = {
--
kernel/bpf/token.c-111-
kernel/bpf/token.c:112:int bpf_token_create(union bpf_attr *attr)
kernel/bpf/token.c-113-{
--
kernel/bpf/token.c-187-
kernel/bpf/token.c:188: err = security_bpf_token_create(token, attr, &path);
kernel/bpf/token.c-189- if (err)
--
security/security.c=5370=int security_bpf_prog_load(struct bpf_prog *prog, union bpf_attr *attr,
--
security/security.c-5385-/**
security/security.c:5386: * security_bpf_token_create() - Check if creating of BPF token is allowed
security/security.c-5387- * @token: BPF token object
--
security/security.c-5395- */
security/security.c:5396:int security_bpf_token_create(struct bpf_token *token, union bpf_attr *attr,
security/security.c-5397- const struct path *path)
--
security/security.c-5404-
security/security.c:5405: rc = call_int_hook(bpf_token_create, token, attr, path);
security/security.c-5406- if (unlikely(rc))
--
security/selinux/hooks.c=7306=static int selinux_bpf_prog_load(struct bpf_prog *prog, union bpf_attr *attr,
--
security/selinux/hooks.c-7326-
security/selinux/hooks.c:7327:static int selinux_bpf_token_create(struct bpf_token *token,
security/selinux/hooks.c-7328- union bpf_attr *attr,
--
security/selinux/hooks.c=7560=static struct security_hook_list selinux_hooks[] __ro_after_init = {
--
security/selinux/hooks.c-7842- LSM_HOOK_INIT(bpf_prog_load, selinux_bpf_prog_load),
security/selinux/hooks.c:7843: LSM_HOOK_INIT(bpf_token_create, selinux_bpf_token_create),
security/selinux/hooks.c-7844- LSM_HOOK_INIT(bpf_token_cmd, selinux_bpf_token_cmd),
--
tools/lib/bpf/bpf.c=1411=int bpf_prog_bind_map(int prog_fd, int map_fd,
--
tools/lib/bpf/bpf.c-1429-
tools/lib/bpf/bpf.c:1430:int bpf_token_create(int bpffs_fd, struct bpf_token_create_opts *opts)
tools/lib/bpf/bpf.c-1431-{
--
tools/lib/bpf/bpf.c-1435-
tools/lib/bpf/bpf.c:1436: if (!OPTS_VALID(opts, bpf_token_create_opts))
tools/lib/bpf/bpf.c-1437- return libbpf_err(-EINVAL);
--
tools/lib/bpf/bpf.h=717=LIBBPF_API int bpf_prog_test_run_opts(int prog_fd,
--
tools/lib/bpf/bpf.h-719-
tools/lib/bpf/bpf.h:720:struct bpf_token_create_opts {
tools/lib/bpf/bpf.h-721- size_t sz; /* size of this struct for forward/backward compatibility */
--
tools/lib/bpf/bpf.h-724-};
tools/lib/bpf/bpf.h:725:#define bpf_token_create_opts__last_field flags
tools/lib/bpf/bpf.h-726-
tools/lib/bpf/bpf.h-727-/**
tools/lib/bpf/bpf.h:728: * @brief **bpf_token_create()** creates a new instance of BPF token derived
tools/lib/bpf/bpf.h-729- * from specified BPF FS mount point.
--
tools/lib/bpf/bpf.h-740- */
tools/lib/bpf/bpf.h:741:LIBBPF_API int bpf_token_create(int bpffs_fd,
tools/lib/bpf/bpf.h:742: struct bpf_token_create_opts *opts);
tools/lib/bpf/bpf.h-743-
--
tools/lib/bpf/libbpf.c=5147=static int bpf_object_prepare_token(struct bpf_object *obj)
--
tools/lib/bpf/libbpf.c-5172-
tools/lib/bpf/libbpf.c:5173: token_fd = bpf_token_create(bpffs_fd, 0);
tools/lib/bpf/libbpf.c-5174- close(bpffs_fd);
--
tools/lib/bpf/libbpf.map=411=LIBBPF_1.4.0 {
--
tools/lib/bpf/libbpf.map-414- bpf_raw_tracepoint_open_opts;
tools/lib/bpf/libbpf.map:415: bpf_token_create;
tools/lib/bpf/libbpf.map-416- btf__new_split;
--
tools/testing/selftests/bpf/prog_tests/token.c=287=static void child(int sock_fd, struct bpffs_opts *opts, child_callback_fn callback)
--
tools/testing/selftests/bpf/prog_tests/token.c-389- /* create BPF token FD and pass it to parent for some extra checks */
tools/testing/selftests/bpf/prog_tests/token.c:390: token_fd = bpf_token_create(bpffs_fd, NULL);
tools/testing/selftests/bpf/prog_tests/token.c-391- if (!ASSERT_GT(token_fd, 0, "child_token_create")) {
--
tools/testing/selftests/bpf/prog_tests/token.c=506=static int userns_map_create(int mnt_fd, struct token_lsm *lsm_skel)
--
tools/testing/selftests/bpf/prog_tests/token.c-512- /* create BPF token from BPF FS mount */
tools/testing/selftests/bpf/prog_tests/token.c:513: token_fd = bpf_token_create(mnt_fd, NULL);
tools/testing/selftests/bpf/prog_tests/token.c-514- if (!ASSERT_GT(token_fd, 0, "token_create")) {
--
tools/testing/selftests/bpf/prog_tests/token.c=574=static int userns_btf_load(int mnt_fd, struct token_lsm *lsm_skel)
--
tools/testing/selftests/bpf/prog_tests/token.c-583- /* create BPF token from BPF FS mount */
tools/testing/selftests/bpf/prog_tests/token.c:584: token_fd = bpf_token_create(mnt_fd, NULL);
tools/testing/selftests/bpf/prog_tests/token.c-585- if (!ASSERT_GT(token_fd, 0, "token_create")) {
--
tools/testing/selftests/bpf/prog_tests/token.c=643=static int userns_prog_load(int mnt_fd, struct token_lsm *lsm_skel)
--
tools/testing/selftests/bpf/prog_tests/token.c-659- /* create BPF token from BPF FS mount */
tools/testing/selftests/bpf/prog_tests/token.c:660: token_fd = bpf_token_create(mnt_fd, NULL);
tools/testing/selftests/bpf/prog_tests/token.c-661- if (!ASSERT_GT(token_fd, 0, "token_create")) {
--
tools/testing/selftests/bpf/prog_tests/token.c=1108=static int userns_bpf_token_info(int mnt_fd, struct token_lsm *lsm_skel)
--
tools/testing/selftests/bpf/prog_tests/token.c-1114- /* create BPF token from BPF FS mount */
tools/testing/selftests/bpf/prog_tests/token.c:1115: token_fd = bpf_token_create(mnt_fd, NULL);
tools/testing/selftests/bpf/prog_tests/token.c-1116- if (!ASSERT_GT(token_fd, 0, "token_create")) {
]
|
| 50/2 |
2026/09/04 08:37 |
llm |
expert |
0m
Model:
Tokens:
input: 46765
output: 18
thoughts: 605
Thoughts: **My Assessment of the BPF Token Vulnerability**
Okay, so the initial thought is, can an unprivileged user actually create a BPF token? The core is the BPF filesystem, and I recall that `bpffs` *can* be mounted in a user namespace. This immediately triggers a line of reasoning: if it's in a user namespace, the token will be associated with that namespace. Crucially, `bpf_token_capable` then checks `ns_capable(token->userns, CAP_PERFMON)`. I know that I have `CAP_PERFMON` in my own user namespace, which means `bpf_token_capable(token, CAP_PERFMON)` *will* return true, and then I have `allow_ptr_leaks = true` using the BPF token.
So, where does that get me? Let's trace it. If `allow_ptr_leaks` is true, `is_pointer_value` returns false. This means I can pass a pointer to `bpf_loop`'s `nr_loops` argument because it is `ARG_ANYTHING`. Then, `check_helper_call` calls `mark_chain_precision(env, BPF_REG_1)`. This will then call `bpf_mark_chain_precision`, see that `reg->type != SCALAR_VALUE`, and trigger a `verifier_bug`. Now, *that* should give a kernel WARNING. But is it exploitable?
The verifier, thankfully, rejects the program with `-EFAULT`. No memory corruption, no privilege escalation, no information leak. It's just a WARNING. So, is there a denial of service (DoS) vulnerability here?
A WARNING in the kernel log could be triggered by an unprivileged user (assuming user namespaces are enabled), but usually, WARNINGs become DoS only if `panic_on_warn` is set, which is unlikely in production builds. And, even if a WARNING gets reported as a bug by syzkaller, there is no real impact.
Wait, `verifier_bug` uses `BPF_WARN_ONCE(1, ...)`! So, it's a `WARN_ONCE`, meaning the warning only happens once per boot. Therefore, it's not even a log spam DoS! That's good news.
Just to be absolutely sure, let me double check that `allow_ptr_leaks` can be true to allow passing pointers to other helpers that expect `ARG_ANYTHING`. The `is_pointer_value` function returns false, which is the key here. Yes, the path appears to work and open the same can of worms. Let's see what other helpers take `ARG_ANYTHING`.
|
| 51/2 |
2026/09/04 08:37 |
tool |
grepper |
0m
Args: map[Expression:ARG_ANYTHING]
Results: map[Output:
Full output is too long, showing 500 out of 1197 lines.
Use more precise expression if possible.
drivers/media/rc/bpf-lirc.c=50=static const struct bpf_func_proto rc_keydown_proto = {
--
drivers/media/rc/bpf-lirc.c-54- .arg1_type = ARG_PTR_TO_CTX,
drivers/media/rc/bpf-lirc.c:55: .arg2_type = ARG_ANYTHING,
drivers/media/rc/bpf-lirc.c:56: .arg3_type = ARG_ANYTHING,
drivers/media/rc/bpf-lirc.c:57: .arg4_type = ARG_ANYTHING,
drivers/media/rc/bpf-lirc.c-58-};
--
drivers/media/rc/bpf-lirc.c=73=static const struct bpf_func_proto rc_pointer_rel_proto = {
--
drivers/media/rc/bpf-lirc.c-77- .arg1_type = ARG_PTR_TO_CTX,
drivers/media/rc/bpf-lirc.c:78: .arg2_type = ARG_ANYTHING,
drivers/media/rc/bpf-lirc.c:79: .arg3_type = ARG_ANYTHING,
drivers/media/rc/bpf-lirc.c-80-};
--
include/linux/bpf.h=876=enum bpf_arg_type {
--
include/linux/bpf.h-895- ARG_PTR_TO_CTX, /* pointer to context */
include/linux/bpf.h:896: ARG_ANYTHING, /* any (initialized) argument is ok */
include/linux/bpf.h-897- ARG_PTR_TO_SPIN_LOCK, /* pointer to bpf_spin_lock */
--
kernel/bpf/backtrack.c=265=static int backtrack_insn(struct bpf_verifier_env *env, int idx, int subseq_idx,
--
kernel/bpf/backtrack.c-632- * that program doesn't care about specific value (e.g., when helper
kernel/bpf/backtrack.c:633: * takes register as ARG_ANYTHING parameter) is not safe.
kernel/bpf/backtrack.c-634- *
--
kernel/bpf/bpf_cgrp_storage.c=175=const struct bpf_func_proto bpf_cgrp_storage_get_proto = {
--
kernel/bpf/bpf_cgrp_storage.c-182- .arg3_type = ARG_PTR_TO_MAP_VALUE_OR_NULL,
kernel/bpf/bpf_cgrp_storage.c:183: .arg4_type = ARG_ANYTHING,
kernel/bpf/bpf_cgrp_storage.c-184-};
--
kernel/bpf/bpf_inode_storage.c=215=const struct bpf_func_proto bpf_inode_storage_get_proto = {
--
kernel/bpf/bpf_inode_storage.c-222- .arg3_type = ARG_PTR_TO_MAP_VALUE_OR_NULL,
kernel/bpf/bpf_inode_storage.c:223: .arg4_type = ARG_ANYTHING,
kernel/bpf/bpf_inode_storage.c-224-};
--
kernel/bpf/bpf_iter.c=717=const struct bpf_func_proto bpf_for_each_map_elem_proto = {
--
kernel/bpf/bpf_iter.c-723- .arg3_type = ARG_PTR_TO_STACK_OR_NULL,
kernel/bpf/bpf_iter.c:724: .arg4_type = ARG_ANYTHING,
kernel/bpf/bpf_iter.c-725-};
--
kernel/bpf/bpf_iter.c=753=const struct bpf_func_proto bpf_loop_proto = {
--
kernel/bpf/bpf_iter.c-756- .ret_type = RET_INTEGER,
kernel/bpf/bpf_iter.c:757: .arg1_type = ARG_ANYTHING,
kernel/bpf/bpf_iter.c-758- .arg2_type = ARG_PTR_TO_FUNC,
kernel/bpf/bpf_iter.c-759- .arg3_type = ARG_PTR_TO_STACK_OR_NULL,
kernel/bpf/bpf_iter.c:760: .arg4_type = ARG_ANYTHING,
kernel/bpf/bpf_iter.c-761-};
--
kernel/bpf/bpf_lsm.c=160=static const struct bpf_func_proto bpf_bprm_opts_set_proto = {
--
kernel/bpf/bpf_lsm.c-165- .arg1_btf_id = &bpf_bprm_opts_set_btf_ids[0],
kernel/bpf/bpf_lsm.c:166: .arg2_type = ARG_ANYTHING,
kernel/bpf/bpf_lsm.c-167-};
--
kernel/bpf/bpf_task_storage.c=238=const struct bpf_func_proto bpf_task_storage_get_proto = {
--
kernel/bpf/bpf_task_storage.c-245- .arg3_type = ARG_PTR_TO_MAP_VALUE_OR_NULL,
kernel/bpf/bpf_task_storage.c:246: .arg4_type = ARG_ANYTHING,
kernel/bpf/bpf_task_storage.c-247-};
--
kernel/bpf/btf.c=8016=int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog)
--
kernel/bpf/btf.c-8229- if (btf_type_is_int(t) || btf_is_any_enum(t)) {
kernel/bpf/btf.c:8230: sub->args[i].arg_type = ARG_ANYTHING;
kernel/bpf/btf.c-8231- continue;
--
kernel/bpf/btf.c=8749=const struct bpf_func_proto bpf_btf_find_by_name_kind_proto = {
--
kernel/bpf/btf.c-8754- .arg2_type = ARG_MEM_SIZE,
kernel/bpf/btf.c:8755: .arg3_type = ARG_ANYTHING,
kernel/bpf/btf.c:8756: .arg4_type = ARG_ANYTHING,
kernel/bpf/btf.c-8757-};
--
kernel/bpf/cgroup.c=1838=const struct bpf_func_proto bpf_get_local_storage_proto = {
--
kernel/bpf/cgroup.c-1842- .arg1_type = ARG_CONST_MAP_PTR,
kernel/bpf/cgroup.c:1843: .arg2_type = ARG_ANYTHING,
kernel/bpf/cgroup.c-1844-};
--
kernel/bpf/cgroup.c=1869=const struct bpf_func_proto bpf_set_retval_proto = {
--
kernel/bpf/cgroup.c-1872- .ret_type = RET_INTEGER,
kernel/bpf/cgroup.c:1873: .arg1_type = ARG_ANYTHING,
kernel/bpf/cgroup.c-1874-};
--
kernel/bpf/cgroup.c=2327=static const struct bpf_func_proto bpf_sysctl_get_name_proto = {
--
kernel/bpf/cgroup.c-2333- .arg3_type = ARG_MEM_SIZE,
kernel/bpf/cgroup.c:2334: .arg4_type = ARG_ANYTHING,
kernel/bpf/cgroup.c-2335-};
--
kernel/bpf/core.c=3197=const struct bpf_func_proto bpf_tail_call_proto = {
--
kernel/bpf/core.c-3205- .arg2_type = ARG_CONST_MAP_PTR,
kernel/bpf/core.c:3206: .arg3_type = ARG_ANYTHING,
kernel/bpf/core.c-3207-};
--
kernel/bpf/helpers.c=66=const struct bpf_func_proto bpf_map_update_elem_proto = {
--
kernel/bpf/helpers.c-73- .arg3_type = ARG_PTR_TO_MAP_VALUE,
kernel/bpf/helpers.c:74: .arg4_type = ARG_ANYTHING,
kernel/bpf/helpers.c-75-};
--
kernel/bpf/helpers.c=97=const struct bpf_func_proto bpf_map_push_elem_proto = {
--
kernel/bpf/helpers.c-103- .arg2_type = ARG_PTR_TO_MAP_VALUE,
kernel/bpf/helpers.c:104: .arg3_type = ARG_ANYTHING,
kernel/bpf/helpers.c-105-};
--
kernel/bpf/helpers.c=139=const struct bpf_func_proto bpf_map_lookup_percpu_elem_proto = {
--
kernel/bpf/helpers.c-145- .arg2_type = ARG_PTR_TO_MAP_KEY,
kernel/bpf/helpers.c:146: .arg3_type = ARG_ANYTHING,
kernel/bpf/helpers.c-147-};
--
kernel/bpf/helpers.c=440=const struct bpf_func_proto bpf_get_current_ancestor_cgroup_id_proto = {
--
kernel/bpf/helpers.c-443- .ret_type = RET_INTEGER,
kernel/bpf/helpers.c:444: .arg1_type = ARG_ANYTHING,
kernel/bpf/helpers.c-445-};
--
kernel/bpf/helpers.c=537=const struct bpf_func_proto bpf_strtol_proto = {
--
kernel/bpf/helpers.c-542- .arg2_type = ARG_MEM_SIZE,
kernel/bpf/helpers.c:543: .arg3_type = ARG_ANYTHING,
kernel/bpf/helpers.c-544- .arg4_type = ARG_PTR_TO_FIXED_SIZE_MEM | MEM_UNINIT | MEM_WRITE | MEM_ALIGNED,
--
kernel/bpf/helpers.c=565=const struct bpf_func_proto bpf_strtoul_proto = {
--
kernel/bpf/helpers.c-570- .arg2_type = ARG_MEM_SIZE,
kernel/bpf/helpers.c:571: .arg3_type = ARG_ANYTHING,
kernel/bpf/helpers.c-572- .arg4_type = ARG_PTR_TO_FIXED_SIZE_MEM | MEM_UNINIT | MEM_WRITE | MEM_ALIGNED,
--
kernel/bpf/helpers.c=623=const struct bpf_func_proto bpf_get_ns_current_pid_tgid_proto = {
--
kernel/bpf/helpers.c-626- .ret_type = RET_INTEGER,
kernel/bpf/helpers.c:627: .arg1_type = ARG_ANYTHING,
kernel/bpf/helpers.c:628: .arg2_type = ARG_ANYTHING,
kernel/bpf/helpers.c-629- .arg3_type = ARG_PTR_TO_UNINIT_MEM,
--
kernel/bpf/helpers.c=648=const struct bpf_func_proto bpf_event_output_data_proto = {
--
kernel/bpf/helpers.c-653- .arg2_type = ARG_CONST_MAP_PTR,
kernel/bpf/helpers.c:654: .arg3_type = ARG_ANYTHING,
kernel/bpf/helpers.c-655- .arg4_type = ARG_PTR_TO_MEM | MEM_RDONLY,
--
kernel/bpf/helpers.c=672=const struct bpf_func_proto bpf_copy_from_user_proto = {
--
kernel/bpf/helpers.c-678- .arg2_type = ARG_MEM_SIZE_OR_ZERO,
kernel/bpf/helpers.c:679: .arg3_type = ARG_ANYTHING,
kernel/bpf/helpers.c-680-};
--
kernel/bpf/helpers.c=703=const struct bpf_func_proto bpf_copy_from_user_task_proto = {
--
kernel/bpf/helpers.c-709- .arg2_type = ARG_MEM_SIZE_OR_ZERO,
kernel/bpf/helpers.c:710: .arg3_type = ARG_ANYTHING,
kernel/bpf/helpers.c-711- .arg4_type = ARG_PTR_TO_BTF_ID,
kernel/bpf/helpers.c-712- .arg4_btf_id = &btf_tracing_ids[BTF_TRACING_TYPE_TASK],
kernel/bpf/helpers.c:713: .arg5_type = ARG_ANYTHING
kernel/bpf/helpers.c-714-};
--
kernel/bpf/helpers.c=724=const struct bpf_func_proto bpf_per_cpu_ptr_proto = {
--
kernel/bpf/helpers.c-728- .arg1_type = ARG_PTR_TO_PERCPU_BTF_ID,
kernel/bpf/helpers.c:729: .arg2_type = ARG_ANYTHING,
kernel/bpf/helpers.c-730-};
--
kernel/bpf/helpers.c=1412=static const struct bpf_func_proto bpf_timer_init_proto = {
--
kernel/bpf/helpers.c-1417- .arg2_type = ARG_CONST_MAP_PTR,
kernel/bpf/helpers.c:1418: .arg3_type = ARG_ANYTHING,
kernel/bpf/helpers.c-1419-};
--
kernel/bpf/helpers.c=1556=static const struct bpf_func_proto bpf_timer_start_proto = {
--
kernel/bpf/helpers.c-1560- .arg1_type = ARG_PTR_TO_TIMER,
kernel/bpf/helpers.c:1561: .arg2_type = ARG_ANYTHING,
kernel/bpf/helpers.c:1562: .arg3_type = ARG_ANYTHING,
kernel/bpf/helpers.c-1563-};
--
kernel/bpf/helpers.c=1886=static const struct bpf_func_proto bpf_dynptr_from_mem_proto = {
--
kernel/bpf/helpers.c-1891- .arg2_type = ARG_MEM_SIZE_OR_ZERO,
kernel/bpf/helpers.c:1892: .arg3_type = ARG_ANYTHING,
kernel/bpf/helpers.c-1893- .arg4_type = ARG_PTR_TO_DYNPTR | DYNPTR_TYPE_LOCAL | MEM_UNINIT | MEM_WRITE,
--
kernel/bpf/helpers.c=1941=static const struct bpf_func_proto bpf_dynptr_read_proto = {
--
kernel/bpf/helpers.c-1947- .arg3_type = ARG_PTR_TO_DYNPTR,
kernel/bpf/helpers.c:1948: .arg4_type = ARG_ANYTHING,
kernel/bpf/helpers.c:1949: .arg5_type = ARG_ANYTHING,
kernel/bpf/helpers.c-1950-};
--
kernel/bpf/helpers.c=2000=static const struct bpf_func_proto bpf_dynptr_write_proto = {
--
kernel/bpf/helpers.c-2004- .arg1_type = ARG_PTR_TO_DYNPTR,
kernel/bpf/helpers.c:2005: .arg2_type = ARG_ANYTHING,
kernel/bpf/helpers.c-2006- .arg3_type = ARG_PTR_TO_MEM | MEM_RDONLY,
kernel/bpf/helpers.c-2007- .arg4_type = ARG_MEM_SIZE_OR_ZERO,
kernel/bpf/helpers.c:2008: .arg5_type = ARG_ANYTHING,
kernel/bpf/helpers.c-2009-};
--
kernel/bpf/helpers.c=2043=static const struct bpf_func_proto bpf_dynptr_data_proto = {
--
kernel/bpf/helpers.c-2047- .arg1_type = ARG_PTR_TO_DYNPTR,
kernel/bpf/helpers.c:2048: .arg2_type = ARG_ANYTHING,
kernel/bpf/helpers.c-2049- .arg3_type = ARG_CONST_ALLOC_SIZE_OR_ZERO,
--
kernel/bpf/helpers.c=2955=const struct bpf_func_proto bpf_current_task_under_cgroup_proto = {
--
kernel/bpf/helpers.c-2959- .arg1_type = ARG_CONST_MAP_PTR,
kernel/bpf/helpers.c:2960: .arg2_type = ARG_ANYTHING,
kernel/bpf/helpers.c-2961-};
--
kernel/bpf/ringbuf.c=551=const struct bpf_func_proto bpf_ringbuf_reserve_proto = {
--
kernel/bpf/ringbuf.c-555- .arg2_type = ARG_CONST_ALLOC_SIZE_OR_ZERO,
kernel/bpf/ringbuf.c:556: .arg3_type = ARG_ANYTHING,
kernel/bpf/ringbuf.c-557-};
--
kernel/bpf/ringbuf.c=593=const struct bpf_func_proto bpf_ringbuf_submit_proto = {
--
kernel/bpf/ringbuf.c-596- .arg1_type = ARG_PTR_TO_RINGBUF_MEM | OBJ_RELEASE,
kernel/bpf/ringbuf.c:597: .arg2_type = ARG_ANYTHING,
kernel/bpf/ringbuf.c-598-};
--
kernel/bpf/ringbuf.c=606=const struct bpf_func_proto bpf_ringbuf_discard_proto = {
--
kernel/bpf/ringbuf.c-609- .arg1_type = ARG_PTR_TO_RINGBUF_MEM | OBJ_RELEASE,
kernel/bpf/ringbuf.c:610: .arg2_type = ARG_ANYTHING,
kernel/bpf/ringbuf.c-611-};
--
kernel/bpf/ringbuf.c=632=const struct bpf_func_proto bpf_ringbuf_output_proto = {
--
kernel/bpf/ringbuf.c-637- .arg3_type = ARG_MEM_SIZE_OR_ZERO,
kernel/bpf/ringbuf.c:638: .arg4_type = ARG_ANYTHING,
kernel/bpf/ringbuf.c-639-};
--
kernel/bpf/ringbuf.c=663=const struct bpf_func_proto bpf_ringbuf_query_proto = {
--
kernel/bpf/ringbuf.c-666- .arg1_type = ARG_CONST_MAP_PTR,
kernel/bpf/ringbuf.c:667: .arg2_type = ARG_ANYTHING,
kernel/bpf/ringbuf.c-668-};
--
kernel/bpf/ringbuf.c=701=const struct bpf_func_proto bpf_ringbuf_reserve_dynptr_proto = {
--
kernel/bpf/ringbuf.c-704- .arg1_type = ARG_CONST_MAP_PTR,
kernel/bpf/ringbuf.c:705: .arg2_type = ARG_ANYTHING,
kernel/bpf/ringbuf.c:706: .arg3_type = ARG_ANYTHING,
kernel/bpf/ringbuf.c-707- .arg4_type = ARG_PTR_TO_DYNPTR | DYNPTR_TYPE_RINGBUF | MEM_UNINIT | MEM_WRITE,
--
kernel/bpf/ringbuf.c=722=const struct bpf_func_proto bpf_ringbuf_submit_dynptr_proto = {
--
kernel/bpf/ringbuf.c-725- .arg1_type = ARG_PTR_TO_DYNPTR | DYNPTR_TYPE_RINGBUF | OBJ_RELEASE,
kernel/bpf/ringbuf.c:726: .arg2_type = ARG_ANYTHING,
kernel/bpf/ringbuf.c-727-};
--
kernel/bpf/ringbuf.c=741=const struct bpf_func_proto bpf_ringbuf_discard_dynptr_proto = {
--
kernel/bpf/ringbuf.c-744- .arg1_type = ARG_PTR_TO_DYNPTR | DYNPTR_TYPE_RINGBUF | OBJ_RELEASE,
kernel/bpf/ringbuf.c:745: .arg2_type = ARG_ANYTHING,
kernel/bpf/ringbuf.c-746-};
--
kernel/bpf/ringbuf.c=873=const struct bpf_func_proto bpf_user_ringbuf_drain_proto = {
--
kernel/bpf/ringbuf.c-878- .arg3_type = ARG_PTR_TO_STACK_OR_NULL,
kernel/bpf/ringbuf.c:879: .arg4_type = ARG_ANYTHING,
kernel/bpf/ringbuf.c-880-};
--
kernel/bpf/stackmap.c=662=const struct bpf_func_proto bpf_get_stackid_proto = {
--
kernel/bpf/stackmap.c-667- .arg2_type = ARG_CONST_MAP_PTR,
kernel/bpf/stackmap.c:668: .arg3_type = ARG_ANYTHING,
kernel/bpf/stackmap.c-669-};
--
kernel/bpf/stackmap.c=736=const struct bpf_func_proto bpf_get_stackid_proto_pe = {
--
kernel/bpf/stackmap.c-741- .arg2_type = ARG_CONST_MAP_PTR,
kernel/bpf/stackmap.c:742: .arg3_type = ARG_ANYTHING,
kernel/bpf/stackmap.c-743-};
--
kernel/bpf/stackmap.c=859=const struct bpf_func_proto bpf_get_stack_proto = {
--
kernel/bpf/stackmap.c-865- .arg3_type = ARG_MEM_SIZE_OR_ZERO,
kernel/bpf/stackmap.c:866: .arg4_type = ARG_ANYTHING,
kernel/bpf/stackmap.c-867-};
--
kernel/bpf/stackmap.c=875=const struct bpf_func_proto bpf_get_stack_sleepable_proto = {
--
kernel/bpf/stackmap.c-881- .arg3_type = ARG_MEM_SIZE_OR_ZERO,
kernel/bpf/stackmap.c:882: .arg4_type = ARG_ANYTHING,
kernel/bpf/stackmap.c-883-};
--
kernel/bpf/stackmap.c=911=const struct bpf_func_proto bpf_get_task_stack_proto = {
--
kernel/bpf/stackmap.c-918- .arg3_type = ARG_MEM_SIZE_OR_ZERO,
kernel/bpf/stackmap.c:919: .arg4_type = ARG_ANYTHING,
kernel/bpf/stackmap.c-920-};
--
kernel/bpf/stackmap.c=928=const struct bpf_func_proto bpf_get_task_stack_sleepable_proto = {
--
kernel/bpf/stackmap.c-935- .arg3_type = ARG_MEM_SIZE_OR_ZERO,
kernel/bpf/stackmap.c:936: .arg4_type = ARG_ANYTHING,
kernel/bpf/stackmap.c-937-};
--
kernel/bpf/stackmap.c=1011=const struct bpf_func_proto bpf_get_stack_proto_pe = {
--
kernel/bpf/stackmap.c-1017- .arg3_type = ARG_MEM_SIZE_OR_ZERO,
kernel/bpf/stackmap.c:1018: .arg4_type = ARG_ANYTHING,
kernel/bpf/stackmap.c-1019-};
--
kernel/bpf/syscall.c=6568=static const struct bpf_func_proto bpf_sys_bpf_proto = {
--
kernel/bpf/syscall.c-6572- .ret_type = RET_INTEGER,
kernel/bpf/syscall.c:6573: .arg1_type = ARG_ANYTHING,
kernel/bpf/syscall.c-6574- .arg2_type = ARG_PTR_TO_MEM | MEM_RDONLY,
--
kernel/bpf/syscall.c=6594=static const struct bpf_func_proto bpf_sys_close_proto = {
--
kernel/bpf/syscall.c-6598- .ret_type = RET_INTEGER,
kernel/bpf/syscall.c:6599: .arg1_type = ARG_ANYTHING,
kernel/bpf/syscall.c-6600-};
--
kernel/bpf/syscall.c=6618=static const struct bpf_func_proto bpf_kallsyms_lookup_name_proto = {
--
kernel/bpf/syscall.c-6623- .arg2_type = ARG_MEM_SIZE_OR_ZERO,
kernel/bpf/syscall.c:6624: .arg3_type = ARG_ANYTHING,
kernel/bpf/syscall.c-6625- .arg4_type = ARG_PTR_TO_FIXED_SIZE_MEM | MEM_UNINIT | MEM_WRITE | MEM_ALIGNED,
--
kernel/bpf/task_iter.c=822=const struct bpf_func_proto bpf_find_vma_proto = {
--
kernel/bpf/task_iter.c-826- .arg1_btf_id = &btf_tracing_ids[BTF_TRACING_TYPE_TASK],
kernel/bpf/task_iter.c:827: .arg2_type = ARG_ANYTHING,
kernel/bpf/task_iter.c-828- .arg3_type = ARG_PTR_TO_FUNC,
kernel/bpf/task_iter.c-829- .arg4_type = ARG_PTR_TO_STACK_OR_NULL,
kernel/bpf/task_iter.c:830: .arg5_type = ARG_ANYTHING,
kernel/bpf/task_iter.c-831-};
--
kernel/bpf/verifier.c=8680=static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
--
kernel/bpf/verifier.c-8700-
kernel/bpf/verifier.c:8701: if (arg_type == ARG_ANYTHING) {
kernel/bpf/verifier.c-8702- if (is_pointer_value(env, regno)) {
--
kernel/bpf/verifier.c=9620=static int btf_check_func_arg_match(struct bpf_verifier_env *env, int subprog,
--
kernel/bpf/verifier.c-9660-
kernel/bpf/verifier.c:9661: if (arg->arg_type == ARG_ANYTHING) {
kernel/bpf/verifier.c-9662- if (reg->type != SCALAR_VALUE) {
--
kernel/bpf/verifier.c=11568=enum kfunc_ptr_arg_type {
--
kernel/bpf/verifier.c-11572- KF_ARG_CONST_ALLOC_SIZE_OR_ZERO,
kernel/bpf/verifier.c:11573: KF_ARG_ANYTHING,
kernel/bpf/verifier.c-11574- KF_ARG_PTR_TO_CTX,
--
kernel/bpf/verifier.c=11844=get_kfunc_arg_type(struct bpf_verifier_env *env, struct bpf_call_arg_meta *meta,
--
kernel/bpf/verifier.c-11864- return KF_ARG_CONST_ALLOC_SIZE_OR_ZERO;
kernel/bpf/verifier.c:11865: return KF_ARG_ANYTHING;
kernel/bpf/verifier.c-11866- }
--
kernel/bpf/verifier.c=12577=static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_call_arg_meta *meta,
--
kernel/bpf/verifier.c-12679- case KF_ARG_MEM_SIZE:
kernel/bpf/verifier.c:12680: case KF_ARG_ANYTHING:
kernel/bpf/verifier.c-12681- case KF_ARG_CONST_ALLOC_SIZE_OR_ZERO:
--
kernel/bpf/verifier.c-12743- break;
kernel/bpf/verifier.c:12744: case KF_ARG_ANYTHING:
kernel/bpf/verifier.c-12745- if (reg->type != SCALAR_VALUE) {
--
kernel/bpf/verifier.c=19300=static int do_check_common(struct bpf_verifier_env *env, int subprog)
--
kernel/bpf/verifier.c-19358- /* Also ensure the callback only has a single scalar argument. */
kernel/bpf/verifier.c:19359: if (sub->arg_cnt != 1 || sub->args[0].arg_type != ARG_ANYTHING) {
kernel/bpf/verifier.c-19360- verbose(env, "exception cb only supports single integer argument\n");
--
kernel/bpf/verifier.c-19371- mark_reg_known_zero(env, regs, i);
kernel/bpf/verifier.c:19372: } else if (arg->arg_type == ARG_ANYTHING) {
kernel/bpf/verifier.c-19373- reg->type = SCALAR_VALUE;
--
kernel/trace/bpf_trace.c=193=static const struct bpf_func_proto bpf_override_return_proto = {
--
kernel/trace/bpf_trace.c-197- .arg1_type = ARG_PTR_TO_CTX,
kernel/trace/bpf_trace.c:198: .arg2_type = ARG_ANYTHING,
kernel/trace/bpf_trace.c-199-};
--
kernel/trace/bpf_trace.c=219=const struct bpf_func_proto bpf_probe_read_user_proto = {
--
kernel/trace/bpf_trace.c-224- .arg2_type = ARG_MEM_SIZE_OR_ZERO,
kernel/trace/bpf_trace.c:225: .arg3_type = ARG_ANYTHING,
kernel/trace/bpf_trace.c-226-};
--
kernel/trace/bpf_trace.c=256=const struct bpf_func_proto bpf_probe_read_user_str_proto = {
--
kernel/trace/bpf_trace.c-261- .arg2_type = ARG_MEM_SIZE_OR_ZERO,
kernel/trace/bpf_trace.c:262: .arg3_type = ARG_ANYTHING,
kernel/trace/bpf_trace.c-263-};
--
kernel/trace/bpf_trace.c=271=const struct bpf_func_proto bpf_probe_read_kernel_proto = {
--
kernel/trace/bpf_trace.c-276- .arg2_type = ARG_MEM_SIZE_OR_ZERO,
kernel/trace/bpf_trace.c:277: .arg3_type = ARG_ANYTHING,
kernel/trace/bpf_trace.c-278-};
--
kernel/trace/bpf_trace.c=306=const struct bpf_func_proto bpf_probe_read_kernel_str_proto = {
--
kernel/trace/bpf_trace.c-311- .arg2_type = ARG_MEM_SIZE_OR_ZERO,
kernel/trace/bpf_trace.c:312: .arg3_type = ARG_ANYTHING,
kernel/trace/bpf_trace.c-313-};
--
kernel/trace/bpf_trace.c=326=static const struct bpf_func_proto bpf_probe_read_compat_proto = {
--
kernel/trace/bpf_trace.c-331- .arg2_type = ARG_MEM_SIZE_OR_ZERO,
kernel/trace/bpf_trace.c:332: .arg3_type = ARG_ANYTHING,
kernel/trace/bpf_trace.c-333-};
--
kernel/trace/bpf_trace.c=345=static const struct bpf_func_proto bpf_probe_read_compat_str_proto = {
--
kernel/trace/bpf_trace.c-350- .arg2_type = ARG_MEM_SIZE_OR_ZERO,
kernel/trace/bpf_trace.c:351: .arg3_type = ARG_ANYTHING,
kernel/trace/bpf_trace.c-352-};
--
kernel/trace/bpf_trace.c=380=static const struct bpf_func_proto bpf_probe_write_user_proto = {
--
kernel/trace/bpf_trace.c-383- .ret_type = RET_INTEGER,
kernel/trace/bpf_trace.c:384: .arg1_type = ARG_ANYTHING,
kernel/trace/bpf_trace.c-385- .arg2_type = ARG_PTR_TO_MEM | MEM_RDONLY,
--
kernel/trace/bpf_trace.c=555=static const struct bpf_func_proto bpf_seq_printf_btf_proto = {
--
kernel/trace/bpf_trace.c-562- .arg3_type = ARG_MEM_SIZE_OR_ZERO,
kernel/trace/bpf_trace.c:563: .arg4_type = ARG_ANYTHING,
kernel/trace/bpf_trace.c-564-};
--
kernel/trace/bpf_trace.c=604=const struct bpf_func_proto bpf_perf_event_read_proto = {
--
kernel/trace/bpf_trace.c-608- .arg1_type = ARG_CONST_MAP_PTR,
kernel/trace/bpf_trace.c:609: .arg2_type = ARG_ANYTHING,
kernel/trace/bpf_trace.c-610-};
--
kernel/trace/bpf_trace.c=629=static const struct bpf_func_proto bpf_perf_event_read_value_proto = {
--
kernel/trace/bpf_trace.c-633- .arg1_type = ARG_CONST_MAP_PTR,
kernel/trace/bpf_trace.c:634: .arg2_type = ARG_ANYTHING,
kernel/trace/bpf_trace.c-635- .arg3_type = ARG_PTR_TO_UNINIT_MEM,
--
kernel/trace/bpf_trace.c=725=static const struct bpf_func_proto bpf_perf_event_output_proto = {
--
kernel/trace/bpf_trace.c-730- .arg2_type = ARG_CONST_MAP_PTR,
kernel/trace/bpf_trace.c:731: .arg3_type = ARG_ANYTHING,
kernel/trace/bpf_trace.c-732- .arg4_type = ARG_PTR_TO_MEM | MEM_RDONLY,
--
kernel/trace/bpf_trace.c=913=const struct bpf_func_proto bpf_send_signal_proto = {
--
kernel/trace/bpf_trace.c-916- .ret_type = RET_INTEGER,
kernel/trace/bpf_trace.c:917: .arg1_type = ARG_ANYTHING,
kernel/trace/bpf_trace.c-918-};
--
kernel/trace/bpf_trace.c=925=const struct bpf_func_proto bpf_send_signal_thread_proto = {
--
kernel/trace/bpf_trace.c-928- .ret_type = RET_INTEGER,
kernel/trace/bpf_trace.c:929: .arg1_type = ARG_ANYTHING,
kernel/trace/bpf_trace.c-930-};
--
kernel/trace/bpf_trace.c=1051=const struct bpf_func_proto bpf_snprintf_btf_proto = {
--
kernel/trace/bpf_trace.c-1058- .arg4_type = ARG_MEM_SIZE,
kernel/trace/bpf_trace.c:1059: .arg5_type = ARG_ANYTHING,
kernel/trace/bpf_trace.c-1060-};
--
kernel/trace/bpf_trace.c=1235=static const struct bpf_func_proto bpf_get_func_arg_proto = {
--
kernel/trace/bpf_trace.c-1238- .arg1_type = ARG_PTR_TO_CTX,
kernel/trace/bpf_trace.c:1239: .arg2_type = ARG_ANYTHING,
kernel/trace/bpf_trace.c-1240- .arg3_type = ARG_PTR_TO_FIXED_SIZE_MEM | MEM_UNINIT | MEM_WRITE | MEM_ALIGNED,
--
kernel/trace/bpf_trace.c=1416=static const struct bpf_func_proto bpf_perf_event_output_proto_tp = {
--
kernel/trace/bpf_trace.c-1421- .arg2_type = ARG_CONST_MAP_PTR,
kernel/trace/bpf_trace.c:1422: .arg3_type = ARG_ANYTHING,
kernel/trace/bpf_trace.c-1423- .arg4_type = ARG_PTR_TO_MEM | MEM_RDONLY,
--
kernel/trace/bpf_trace.c=1441=static const struct bpf_func_proto bpf_get_stackid_proto_tp = {
--
kernel/trace/bpf_trace.c-1446- .arg2_type = ARG_CONST_MAP_PTR,
kernel/trace/bpf_trace.c:1447: .arg3_type = ARG_ANYTHING,
kernel/trace/bpf_trace.c-1448-};
--
kernel/trace/bpf_trace.c=1459=static const struct bpf_func_proto bpf_get_stack_proto_tp = {
--
kernel/trace/bpf_trace.c-1465- .arg3_type = ARG_MEM_SIZE_OR_ZERO,
kernel/trace/bpf_trace.c:1466: .arg4_type = ARG_ANYTHING,
]
|
| 52/2 |
2026/09/04 08:37 |
llm |
expert |
0m
Model:
Tokens:
input: 58575
output: 25
thoughts: 45
Thoughts: Okay, let me think this through.
**Analyzing the `bpf_loop` and `mark_chain_precision` Relationship**
Hmm, hold on a second. It just hit me. Is `bpf_loop` the *only* helper function that's calling `mark_chain_precision` on an `ARG_ANYTHING` argument? That seems...unusual. It warrants a closer look. Let me quickly go back and thoroughly re-examine the logic within `check_helper_call`. I need to confirm if this behavior is truly isolated to `bpf_loop`, or if I'm missing something in the broader context of helper function validation. I need to be absolutely certain of this; a potential oversight here could have wider implications on how arguments are handled and type safety. I'll need to go through it carefully.
|
| 53/2 |
2026/09/04 08:37 |
tool |
grepper |
0m
Error:
Args: map[Expression:mark_chain_precision.*check_helper_call]
Results:
|
| 54/2 |
2026/09/04 08:37 |
llm |
expert |
0m
Model:
Tokens:
input: 58836
output: 33
thoughts: 19
Thoughts: Here's a summary of my thought process, as if I were the one thinking it:
**Checking `check_helper_call` for `mark_chain_precision`**
Okay, I need to investigate the function `mark_chain_precision`. Let's start by looking into the `check_helper_call` function. I suspect there might be some interaction or dependency there, possibly related to how the precision of the chain is evaluated or managed. It's a common pattern to have helper functions that do the heavy lifting of validation or modification. My hypothesis is that `check_helper_call` is responsible for handling aspects of `mark_chain_precision`, specifically perhaps ensuring the call is correctly formatted, or verifying preconditions that need to be met before marking precision. This could involve input validation, data type checks, or even checking the context in which the precision is being marked. Time to dive in and see what the code reveals.
|
| 55/2 |
2026/09/04 08:37 |
tool |
grepper |
0m
Args: map[Expression:mark_chain_precision PathPrefix:kernel/bpf/verifier.c]
Results: map[Output:kernel/bpf/verifier.c=3338=void bpf_bt_sync_linked_regs(struct backtrack_state *bt, struct bpf_jmp_history_entry *hist)
--
kernel/bpf/verifier.c-3370-
kernel/bpf/verifier.c:3371:int mark_chain_precision(struct bpf_verifier_env *env, int regno)
kernel/bpf/verifier.c-3372-{
kernel/bpf/verifier.c:3373: return bpf_mark_chain_precision(env, env->cur_state, regno, NULL);
kernel/bpf/verifier.c-3374-}
kernel/bpf/verifier.c-3375-
kernel/bpf/verifier.c:3376:/* mark_chain_precision_batch() assumes that env->bt is set in the caller to
kernel/bpf/verifier.c-3377- * desired reg and stack masks across all relevant frames
kernel/bpf/verifier.c-3378- */
kernel/bpf/verifier.c:3379:static int mark_chain_precision_batch(struct bpf_verifier_env *env,
kernel/bpf/verifier.c-3380- struct bpf_verifier_state *starting_state)
kernel/bpf/verifier.c-3381-{
kernel/bpf/verifier.c:3382: return bpf_mark_chain_precision(env, starting_state, -1, NULL);
kernel/bpf/verifier.c-3383-}
--
kernel/bpf/verifier.c=3509=static int check_stack_write_fixed_off(struct bpf_verifier_env *env,
--
kernel/bpf/verifier.c-3615- */
kernel/bpf/verifier.c:3616: err = mark_chain_precision(env, value_regno);
kernel/bpf/verifier.c-3617- if (err)
--
kernel/bpf/verifier.c=3652=static int check_stack_write_var_off(struct bpf_verifier_env *env,
--
kernel/bpf/verifier.c-3760- /* backtracking doesn't work for STACK_ZERO yet. */
kernel/bpf/verifier.c:3761: err = mark_chain_precision(env, value_regno);
kernel/bpf/verifier.c-3762- if (err)
--
kernel/bpf/verifier.c=3784=static int mark_reg_stack_read(struct bpf_verifier_env *env,
--
kernel/bpf/verifier.c-3819- bpf_bt_set_frame_slot_mask(&env->bt, ptr_state->frameno, zero_spill_mask);
kernel/bpf/verifier.c:3820: return mark_chain_precision_batch(env, env->cur_state);
kernel/bpf/verifier.c-3821- }
--
kernel/bpf/verifier.c=4233=static int mark_stack_arg_precision(struct bpf_verifier_env *env, int arg_idx)
--
kernel/bpf/verifier.c-4238- bt_set_frame_stack_arg_slot(&env->bt, caller->frameno, spi);
kernel/bpf/verifier.c:4239: return mark_chain_precision_batch(env, env->cur_state);
kernel/bpf/verifier.c-4240-}
--
kernel/bpf/verifier.c=7057=static int check_mem_size_reg(struct bpf_verifier_env *env,
--
kernel/bpf/verifier.c-7121- if (regno >= 0)
kernel/bpf/verifier.c:7122: err = mark_chain_precision(env, regno);
kernel/bpf/verifier.c-7123- else
--
kernel/bpf/verifier.c=7168=static int process_const_alloc_mem_size(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
--
kernel/bpf/verifier.c-7189- if (regno >= 0)
kernel/bpf/verifier.c:7190: err = mark_chain_precision(env, regno);
kernel/bpf/verifier.c-7191- else
--
kernel/bpf/verifier.c=7202=static int process_const_arg(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
--
kernel/bpf/verifier.c-7218- if (regno >= 0)
kernel/bpf/verifier.c:7219: err = mark_chain_precision(env, regno);
kernel/bpf/verifier.c-7220- else
--
kernel/bpf/verifier.c=8580=static int get_constant_map_key(struct bpf_verifier_env *env,
--
kernel/bpf/verifier.c-8631- bpf_bt_set_frame_slot(&env->bt, key->frameno, spi);
kernel/bpf/verifier.c:8632: err = mark_chain_precision_batch(env, env->cur_state);
kernel/bpf/verifier.c-8633- if (err < 0)
--
kernel/bpf/verifier.c=10269=static int prepare_func_exit(struct bpf_verifier_env *env, int *insn_idx)
--
kernel/bpf/verifier.c-10297- /* we are going to rely on register's precise value */
kernel/bpf/verifier.c:10298: err = mark_chain_precision(env, BPF_REG_0);
kernel/bpf/verifier.c-10299- if (err)
--
kernel/bpf/verifier.c=10465=record_func_key(struct bpf_verifier_env *env, struct bpf_call_arg_meta *meta,
--
kernel/bpf/verifier.c-10489-
kernel/bpf/verifier.c:10490: err = mark_chain_precision(env, BPF_REG_3);
kernel/bpf/verifier.c-10491- if (err)
--
kernel/bpf/verifier.c=10635=static bool loop_flag_is_zero(struct bpf_verifier_env *env)
--
kernel/bpf/verifier.c-10640- if (reg_is_null)
kernel/bpf/verifier.c:10641: mark_chain_precision(env, BPF_REG_4);
kernel/bpf/verifier.c-10642-
--
kernel/bpf/verifier.c=10736=static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
--
kernel/bpf/verifier.c-10893- */
kernel/bpf/verifier.c:10894: err = mark_chain_precision(env, BPF_REG_1);
kernel/bpf/verifier.c-10895- if (err)
--
kernel/bpf/verifier.c-10944-
kernel/bpf/verifier.c:10945: err = mark_chain_precision(env, BPF_REG_1);
kernel/bpf/verifier.c-10946- if (err)
--
kernel/bpf/verifier.c=15613=static int adjust_reg_min_max_vals(struct bpf_verifier_env *env,
--
kernel/bpf/verifier.c-15672- */
kernel/bpf/verifier.c:15673: err = mark_chain_precision(env, insn->dst_reg);
kernel/bpf/verifier.c-15674- if (err)
--
kernel/bpf/verifier.c-15681- /* pointer += scalar */
kernel/bpf/verifier.c:15682: err = mark_chain_precision(env, insn->src_reg);
kernel/bpf/verifier.c-15683- if (err)
--
kernel/bpf/verifier.c-15687- /* if dst_reg is precise, src_reg should be precise as well */
kernel/bpf/verifier.c:15688: err = mark_chain_precision(env, insn->src_reg);
kernel/bpf/verifier.c-15689- if (err)
--
kernel/bpf/verifier.c=16803=static int check_cond_jmp_op(struct bpf_verifier_env *env,
--
kernel/bpf/verifier.c-16892- if (!__is_pointer_value(false, dst_reg))
kernel/bpf/verifier.c:16893: err = mark_chain_precision(env, insn->dst_reg);
kernel/bpf/verifier.c-16894- if (BPF_SRC(insn->code) == BPF_X && !err &&
kernel/bpf/verifier.c-16895- !__is_pointer_value(false, src_reg))
kernel/bpf/verifier.c:16896: err = mark_chain_precision(env, insn->src_reg);
kernel/bpf/verifier.c-16897- if (err)
--
kernel/bpf/verifier.c=17404=static int check_return_code(struct bpf_verifier_env *env, int regno, const char *reg_name)
--
kernel/bpf/verifier.c-17469-
kernel/bpf/verifier.c:17470: err = mark_chain_precision(env, regno);
kernel/bpf/verifier.c-17471- if (err)
]
|
| 56/2 |
2026/09/04 08:37 |
llm |
expert |
0m
Model:
Tokens:
input: 61646
output: 38
thoughts: 325
Thoughts: **Analyzing Precision Marking in BPF Helper Functions**
Okay, so I'm looking at how the BPF verifier handles precision marking within `check_helper_call`. I see that the `BPF_FUNC_loop` and `BPF_FUNC_user_ringbuf_drain` cases both call `mark_chain_precision` on `BPF_REG_1`. Now, in the `BPF_FUNC_loop` case, that makes sense because the verifier relies on the value of R1 to determine if the `bpf_loop()` iteration is finished and the value is `SCALAR_VALUE`.
However, `bpf_user_ringbuf_drain` has `ARG_PTR_TO_MAP` as the `arg1_type`! So, `BPF_REG_1` is actually a pointer to a map, not a scalar. This means `mark_chain_precision` is being called with a register that isn't `SCALAR_VALUE` which seems like a potential bug. Specifically, `mark_chain_precision` calls `bpf_mark_chain_precision` which explicitly checks for `reg->type == SCALAR_VALUE`, but it's not being checked here.
The verifier should be complaining here, but it's not. I need to dig into `bpf_user_ringbuf_drain` within `check_helper_call` to understand why this isn't triggering a `verifier_bug`. This looks like a serious potential oversight in the precision tracking, and I need to investigate further.
|
| 57/2 |
2026/09/04 08:37 |
tool |
read-file |
0m
Args: map[File:kernel/bpf/verifier.c FirstLine:10940 LineCount:20]
Results: map[Contents:10940: return -EINVAL;
10941: }
10942: bpf_lsm_get_retval_range(env->prog, &range);
10943: }
10944:
10945: err = mark_chain_precision(env, BPF_REG_1);
10946: if (err)
10947: return err;
10948:
10949: if (!retval_range_within(range, r1)) {
10950: verbose_invalid_scalar(env, r1, range, "At bpf_set_retval", "R1");
10951: return -EINVAL;
10952: }
10953:
10954: break;
10955: }
10956: case BPF_FUNC_dynptr_write:
10957: {
10958: enum bpf_dynptr_type dynptr_type = meta.dynptr.type;
10959:
]
|
| 58/2 |
2026/09/04 08:37 |
llm |
expert |
0m
Model:
Tokens:
input: 62648
output: 22
thoughts: 39
Thoughts: Okay, here's my take on those thoughts, framed from an expert's perspective:
**Diving Deep into the BPF Function Call**
Alright, so I'm looking at this BPF code, and line 10945... aha! I see that's right inside `BPF_FUNC_set_retval`. Time to stop and make sure I know what I'm dealing with here. No point in assuming I know the ins and outs of this code block at a glance. Let's pull up the prototype for `BPF_FUNC_set_retval`. I need to review its argument types, return value (if any), and how it's intended to be used in this context before I start to unravel exactly what's happening. I need the full picture before moving on, no shortcuts!
|
| 59/2 |
2026/09/04 08:37 |
tool |
grepper |
0m
Args: map[Expression:bpf_set_retval_proto]
Results: map[Output:include/linux/bpf.h=3940=extern const struct bpf_func_proto bpf_copy_from_user_task_proto;
include/linux/bpf.h:3941:extern const struct bpf_func_proto bpf_set_retval_proto;
include/linux/bpf.h-3942-extern const struct bpf_func_proto bpf_get_retval_proto;
--
kernel/bpf/cgroup.c=1860=BPF_CALL_1(bpf_set_retval, int, retval)
--
kernel/bpf/cgroup.c-1868-
kernel/bpf/cgroup.c:1869:const struct bpf_func_proto bpf_set_retval_proto = {
kernel/bpf/cgroup.c-1870- .func = bpf_set_retval,
--
kernel/bpf/cgroup.c=2777=cgroup_common_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
--
kernel/bpf/cgroup.c-2815- default:
kernel/bpf/cgroup.c:2816: return &bpf_set_retval_proto;
kernel/bpf/cgroup.c-2817- }
--
kernel/bpf/core.c=3169=const struct bpf_func_proto bpf_seq_printf_btf_proto __weak;
kernel/bpf/core.c:3170:const struct bpf_func_proto bpf_set_retval_proto __weak;
kernel/bpf/core.c-3171-const struct bpf_func_proto bpf_get_retval_proto __weak;
]
|
| 60/2 |
2026/09/04 08:37 |
llm |
expert |
0m
Model:
Tokens:
input: 63336
output: 38
thoughts: 14
Thoughts: Okay, let's dive into this. Here's my perspective on this specific kernel function call:
**Understanding `bpf_set_retval_proto`**
Alright, so the function name, `bpf_set_retval_proto`, immediately suggests its purpose: setting a return value's protocol, specifically within the BPF (Berkeley Packet Filter) context. This means we're dealing with manipulating return values inside a BPF program, likely affecting how the kernel interprets or handles the results of that program. Given my experience, I'm already anticipating considerations like potential interactions with different network layers, different protocols, and whether this function pertains to socket filter programs, XDP, or something else entirely. It's likely involved in controlling how a BPF program affects data packets that are being processed. This kind of interaction between BPF and network data handling is what makes this so critical. What specifically is it setting? Is it related to the protocol number field in an IP header, or something more abstract? I'll need to dig deeper to pinpoint its exact application.
|
| 61/2 |
2026/09/04 08:38 |
tool |
read-file |
0m
Args: map[File:kernel/bpf/cgroup.c FirstLine:1865 LineCount:15]
Results: map[Contents:1865: ctx->retval = retval;
1866: return 0;
1867: }
1868:
1869: const struct bpf_func_proto bpf_set_retval_proto = {
1870: .func = bpf_set_retval,
1871: .gpl_only = false,
1872: .ret_type = RET_INTEGER,
1873: .arg1_type = ARG_ANYTHING,
1874: };
1875:
1876: static const struct bpf_func_proto *
1877: cgroup_dev_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
1878: {
1879: const struct bpf_func_proto *func_proto;
]
|
| 62/2 |
2026/09/04 08:38 |
llm |
expert |
0m
Model:
Tokens:
input: 63854
output: 37
thoughts: 1350
Thoughts: **Analysis of the `bpf_set_retval` Verifier Bug**
Okay, let's break this down systematically. I see that `bpf_set_retval` uses `arg1_type = ARG_ANYTHING`, and crucially, it calls `mark_chain_precision(env, BPF_REG_1)`. The core concern here is that, when `allow_ptr_leaks` is enabled, an unprivileged user (with a BPF token) could potentially pass a pointer to `bpf_set_retval` and, in turn, trigger a verification issue.
My initial assessment is that this is indeed a verifier bug, but it's *safely* handled. The verifier detects the type mismatch and correctly returns `-EFAULT`, rejecting the BPF program. Thus, even if the bug is present, the impact is limited to a kernel warning and program rejection. It doesn't appear to be exploitable in any traditional sense.
Let's address the denial-of-service aspect. Typically, a kernel warning isn't considered a denial of service unless `panic_on_warn` is set, which is unlikely in a production environment. However, since syzkaller flags it as a bug, we need to carefully assess. The critical aspect is that the code *handles* the condition where `reg->type` is not `SCALAR_VALUE` with `verifier_bug` and a `-EFAULT` return. The verifier gracefully aborts. The code explicitly prevents a crash or resource exhaustion. Therefore, while it's a bug, it does *not* cause a denial of service.
Now, let's explore accessibility: the bug isn't exploitable without either `CAP_PERFMON` or a BPF token. However, a user *can* trigger it from a user namespace. If they create a user namespace, mount bpffs, create a BPF token, and load a program with `allow_ptr_leaks = true`, they can certainly hit this warning. Therefore, the issue *is* accessible from user namespaces.
I revisited the `bpf_token_capable` check, and it's confirmed. In a user namespace, the user is root. Therefore, `ns_capable` will return true for `CAP_PERFMON`, or for `CAP_SYS_ADMIN`, thus allowing the trigger condition when a token is provided. `bpf_mark_chain_precision` will then flag the error.
Finally, I checked for other potential trigger pathways. `bpf_loop`, which uses `ARG_ANYTHING` for `nr_loops`, might seem like a candidate, but the reproducer is loading a `KPROBE` program, which requires `CAP_PERFMON` anyway. Since the bug is caught by the verifier, no further exploration is required. The verification process aborts. No other concerns.
In conclusion: this is a verifier bug, not exploitable for privilege escalation or denial of service in a general production setup, but it *is* triggerable by an unprivileged user within a user namespace if they have created a BPF token and enabled `allow_ptr_leaks`. The only outcome is a logged kernel warning, and the BPF program is rejected.
|
| 63/2 |
2026/09/04 08:38 |
tool |
read-file |
0m
Args: map[File:kernel/bpf/syscall.c FirstLine:2980 LineCount:30]
Results: map[Contents:2980: err = -E2BIG;
2981: goto put_token;
2982: }
2983: if (type != BPF_PROG_TYPE_SOCKET_FILTER &&
2984: type != BPF_PROG_TYPE_CGROUP_SKB &&
2985: !bpf_cap)
2986: goto put_token;
2987:
2988: if (is_net_admin_prog_type(type) && !bpf_token_capable(token, CAP_NET_ADMIN))
2989: goto put_token;
2990: if (is_perfmon_prog_type(type) && !bpf_token_capable(token, CAP_PERFMON))
2991: goto put_token;
2992:
2993: multi_func = is_tracing_multi(attr->expected_attach_type);
2994:
2995: /* attach_prog_fd/attach_btf_obj_fd can specify fd of either bpf_prog
2996: * or btf, we need to check which one it is
2997: */
2998: if (attr->attach_prog_fd) {
2999: dst_prog = bpf_prog_get(attr->attach_prog_fd);
3000: if (IS_ERR(dst_prog)) {
3001: dst_prog = NULL;
3002: attach_btf = btf_get_by_fd(attr->attach_btf_obj_fd);
3003: if (IS_ERR(attach_btf)) {
3004: err = -EINVAL;
3005: goto put_token;
3006: }
3007: if (!btf_is_kernel(attach_btf)) {
3008: /* attaching through specifying bpf_prog's BTF
3009: * objects directly might be supported eventually
]
|
| 64/2 |
2026/09/04 08:38 |
llm |
expert |
0m
Model:
Tokens:
input: 66473
output: 36
thoughts: 854
Thoughts: **Analyzing the BPF Perfmon Program Vulnerability**
Okay, so `BPF_PROG_TYPE_KPROBE` is, indeed, a perfmon program type. That's clear. And these types typically require `CAP_PERFMON` either through a token or directly. My initial thought was that the reproducer code was leveraging `bpf_token_fd`, but looking closer, that's not the case. It appears to be omitting the token entirely.
This immediately triggers a question: How is `CAP_PERFMON` being granted without the expected token mechanism? Then I remembered that syzkaller, which is generating this reproducer, often runs as root. And that's the key: it can run as root in either a user namespace *or* the init namespace.
My next step was to think through the implications. If syzkaller is running as root *within the init namespace*, then it will inherently possess `CAP_PERFMON`. This would directly explain why `allow_ptr_leaks` is true in this scenario.
I was then going through the implications of this. I then had to go back to `bpf_token_capable`.
I quickly realized that my initial thoughts were correct. I can also clearly see that the syzkaller instance is running as root.
But, I need to confirm whether an unprivileged user can trigger this. Without a token, the code checks `ns_capable(&init_user_ns, CAP_PERFMON)`. That's a solid guardrail, an unprivileged user cannot trigger this because it will always return false if in a user namespace. But, if a token *is* used, it's possible for an unprivileged user to exploit this. Now, can an unprivileged user create a token in a user namespace? This requires a further investigation of `bpf_token_create`.
|
| 65/2 |
2026/09/04 08:38 |
tool |
read-file |
0m
Args: map[File:kernel/bpf/token.c FirstLine:110 LineCount:50]
Results: map[Contents: 110: };
111:
112: int bpf_token_create(union bpf_attr *attr)
113: {
114: struct bpf_token *token __free(kfree) = NULL;
115: struct bpf_mount_opts *mnt_opts;
116: struct user_namespace *userns;
117: struct inode *inode;
118: CLASS(fd, f)(attr->token_create.bpffs_fd);
119: struct path path;
120: struct super_block *sb;
121: umode_t mode;
122: int err;
123:
124: if (fd_empty(f))
125: return -EBADF;
126:
127: path = fd_file(f)->f_path;
128: sb = path.dentry->d_sb;
129:
130: if (path.dentry != sb->s_root)
131: return -EINVAL;
132: if (sb->s_op != &bpf_super_ops)
133: return -EINVAL;
134: err = path_permission(&path, MAY_ACCESS);
135: if (err)
136: return err;
137:
138: userns = sb->s_user_ns;
139: /*
140: * Enforce that creators of BPF tokens are in the same user
141: * namespace as the BPF FS instance. This makes reasoning about
142: * permissions a lot easier and we can always relax this later.
143: */
144: if (current_user_ns() != userns)
145: return -EPERM;
146: if (!ns_capable(userns, CAP_BPF))
147: return -EPERM;
148:
149: /* Creating BPF token in init_user_ns doesn't make much sense. */
150: if (current_user_ns() == &init_user_ns)
151: return -EOPNOTSUPP;
152:
153: mnt_opts = sb->s_fs_info;
154: if (mnt_opts->delegate_cmds == 0 &&
155: mnt_opts->delegate_maps == 0 &&
156: mnt_opts->delegate_progs == 0 &&
157: mnt_opts->delegate_attachs == 0)
158: return -ENOENT; /* no BPF token delegation is set up */
159:
]
|
| 66/2 |
2026/09/04 08:38 |
llm |
expert |
0m
Model:
Tokens:
input: 68529
output: 31
thoughts: 99
Thoughts: **My BPF Token Creation Process**
Okay, so `bpf_token_create` needs the `current_user_ns()` to be different from `&init_user_ns`. That's straightforward: it *has* to be created within a user namespace. But, hang on... I recall something about `mnt_opts->delegate_cmds` and other options needing to be non-zero for this to work. How exactly are those initialized? Right, they're set when mounting `bpffs`. I need to refresh my memory on the mounting process. I'll go check `bpf_parse_param` in `kernel/bpf/inode.c`. That should give me the details I'm missing.
|
| 67/2 |
2026/09/04 08:38 |
tool |
grepper |
0m
Args: map[Expression:delegate_cmds PathPrefix:kernel/bpf/inode.c]
Results: map[Output:kernel/bpf/inode.c=778=static int bpf_show_options(struct seq_file *m, struct dentry *root)
--
kernel/bpf/inode.c-793-
kernel/bpf/inode.c:794: if (opts->delegate_cmds || opts->delegate_maps ||
kernel/bpf/inode.c-795- opts->delegate_progs || opts->delegate_attachs) {
--
kernel/bpf/inode.c-801- mask = (1ULL << __MAX_BPF_CMD) - 1;
kernel/bpf/inode.c:802: seq_print_delegate_opts(m, "delegate_cmds",
kernel/bpf/inode.c-803- info.btf, info.cmd_t, "BPF_",
kernel/bpf/inode.c:804: opts->delegate_cmds, mask);
kernel/bpf/inode.c-805-
--
kernel/bpf/inode.c=982=static const struct fs_parameter_spec bpf_fs_parameters[] = {
--
kernel/bpf/inode.c-985- fsparam_u32oct ("mode", OPT_MODE),
kernel/bpf/inode.c:986: fsparam_string ("delegate_cmds", OPT_DELEGATE_CMDS),
kernel/bpf/inode.c-987- fsparam_string ("delegate_maps", OPT_DELEGATE_MAPS),
--
kernel/bpf/inode.c=993=static int bpf_parse_param(struct fs_context *fc, struct fs_parameter *param)
--
kernel/bpf/inode.c-1066- case OPT_DELEGATE_CMDS:
kernel/bpf/inode.c:1067: delegate_msk = &opts->delegate_cmds;
kernel/bpf/inode.c-1068- enum_t = info.cmd_t;
--
kernel/bpf/inode.c=1245=static int bpf_init_fs_context(struct fs_context *fc)
--
kernel/bpf/inode.c-1257- /* start out with no BPF token delegation enabled */
kernel/bpf/inode.c:1258: opts->delegate_cmds = 0;
kernel/bpf/inode.c-1259- opts->delegate_maps = 0;
]
|
| 68/2 |
2026/09/04 08:38 |
llm |
expert |
0m
Model:
Tokens:
input: 69444
output: 37
thoughts: 53
Thoughts: **Investigating Unprivileged BPFfs Mounting for Token Creation**
Okay, so the documentation clearly states that `bpffs` requires `delegate_cmds=...` during mounting to enable token creation. My immediate question, as always, is about privilege. Can an unprivileged user actually mount `bpffs` with these options? That's the crux of the matter. We need to ascertain the feasibility of this and the potential security implications.
The best way to figure this out is to dive into the kernel code directly. Let's start by scrutinizing `bpf_init_fs_context`. This function is likely the linchpin; it's the gatekeeper for initialization and mounting. It's the place where the system either allows or denies the ability for unprivileged users to mount `bpffs` with the necessary delegation. Understanding its logic regarding capability checks and options handling is absolutely critical. We need to see if there are any obvious holes or if the system enforces the correct security boundaries. This is where the answer lies, and where I'll get to the bottom of this.
|
| 69/2 |
2026/09/04 08:38 |
tool |
read-file |
0m
Args: map[File:kernel/bpf/inode.c FirstLine:1240 LineCount:30]
Results: map[Contents:1240: };
1241:
1242: /*
1243: * Set up the filesystem mount context.
1244: */
1245: static int bpf_init_fs_context(struct fs_context *fc)
1246: {
1247: struct bpf_mount_opts *opts;
1248:
1249: opts = kzalloc_obj(struct bpf_mount_opts);
1250: if (!opts)
1251: return -ENOMEM;
1252:
1253: opts->mode = S_IRWXUGO;
1254: opts->uid = current_fsuid();
1255: opts->gid = current_fsgid();
1256:
1257: /* start out with no BPF token delegation enabled */
1258: opts->delegate_cmds = 0;
1259: opts->delegate_maps = 0;
1260: opts->delegate_progs = 0;
1261: opts->delegate_attachs = 0;
1262:
1263: fc->s_fs_info = opts;
1264: fc->ops = &bpf_context_ops;
1265: return 0;
1266: }
1267:
1268: static void bpf_kill_super(struct super_block *sb)
1269: {
]
|
| 70/2 |
2026/09/04 08:38 |
llm |
expert |
0m
Model:
Tokens:
input: 70175
output: 35
thoughts: 12
Thoughts: Here's a summary of my thought process, tailored for an expert like yourself:
**bpffs Mounting Privileges: A Security Angle**
Okay, so the question immediately pops: Can Joe User, a regular unprivileged guy, just go ahead and mount a `bpffs` filesystem? That's the crux of it. My initial concern is security, naturally. If it's as simple as `mount bpffs`, we've got a potential vulnerability on our hands. The implications are significant; BPF (Berkeley Packet Filter) can do some powerful, low-level stuff, and allowing unrestrained access to that sort of machinery, even indirectly through a filesystem, would be a major red flag.
I'm thinking about the potential for malicious actors to leverage BPF programs within `bpffs` to inject code, manipulate kernel behavior, or gain unauthorized access to system resources. Are there any restrictions? Is it tied into capabilities or perhaps specific user namespaces? Are there inherent dangers in allowing untrusted code to run within the kernel, even if indirectly through a filesystem interface? It's all about risk mitigation. We need to dissect the implementation, understand how permissions are handled, and verify the access control mechanisms. We need to be able to fully comprehend how and if these restrictions are actually implemented.
I'm mentally running through the kernel documentation, maybe some relevant `man` pages, and any existing security advisories related to BPF and filesystems. What are the best practices here? What are the standard security precautions? It really seems that the default "no" should be the starting point here, it would seem prudent to assume there would be some security implications of allowing standard users to mount it. I need to get to the bottom of this.
|
| 71/2 |
2026/09/04 08:38 |
tool |
grepper |
0m
Args: map[Expression:FS_USERNS_MOUNT PathPrefix:kernel/bpf/inode.c]
Results: map[Output:kernel/bpf/inode.c=1277=static struct file_system_type bpf_fs_type = {
--
kernel/bpf/inode.c-1282- .kill_sb = bpf_kill_super,
kernel/bpf/inode.c:1283: .fs_flags = FS_USERNS_MOUNT,
kernel/bpf/inode.c-1284-};
]
|
| 72/2 |
2026/09/04 08:38 |
llm |
expert |
0m
Model:
Tokens:
input: 70705
output: 38
thoughts: 395
Thoughts: **My Assessment of the BPF Vulnerability**
Okay, so `FS_USERNS_MOUNT` is confirmed, meaning an unprivileged user can indeed create a user namespace and mount `bpffs` with those `delegate_` flags. That lets them create a BPF token and load a program. Since they're in a user namespace, they automatically have `CAP_PERFMON` there, meaning the `bpf_token_capable` check passes, and `allow_ptr_leaks` is true. This triggers that known `verifier_bug`.
But, is this actually exploitable? I have to analyze this carefully.
Right, the key point is it's just a WARNING and ultimately returns `-EFAULT`. So, is there any way to bypass the verifier *entirely*? No, the verifier *does* reject the program. Is there memory corruption? Nope, it's a clean error path. Therefore, it's *not* exploitable in a classic sense.
Is it a DoS? A warning alone isn't a denial-of-service in production kernels, unless `panic_on_warn` is set, and that's not typical.
So, I'm going to mark this down as:
* Exploitable: False
* DenialOfService: False
* Unprivileged: False (it *needs* user namespaces, even if it's considered unprivileged within them)
* UserNamespace: True
* VMGuestTrigger: False
* VMHostTrigger: False
* NetworkTrigger: False
* RemoteTrigger: False
* PeripheralTrigger: False
* FilesystemTrigger: False
One more thing though, I have to make sure that even though this particular `verifier_bug` isn't exploitable, the `allow_ptr_leaks` being true doesn't enable bypassing the verifier in *other* ways. If `allow_ptr_leaks` is true, `is_pointer_value` returns false. And that has implications for pointer arithmetic checks. I'll need to double-check `check_alu_op` to be sure.
|
| 73/2 |
2026/09/04 08:38 |
tool |
read-file |
0m
Args: map[File:kernel/bpf/verifier.c FirstLine:15780 LineCount:50]
Results: map[Contents:15780: static int check_alu_op(struct bpf_verifier_env *env, struct bpf_insn *insn)
15781: {
15782: struct bpf_reg_state *regs = cur_regs(env);
15783: u8 opcode = BPF_OP(insn->code);
15784: int err;
15785:
15786: bpf_diag_mod_begin(env, ®s[insn->dst_reg], NULL, BPF_DIAG_MOD_WRITE);
15787:
15788: if (opcode == BPF_END || opcode == BPF_NEG) {
15789: /* check src operand */
15790: err = check_reg_arg(env, insn->dst_reg, SRC_OP);
15791: if (err)
15792: return err;
15793:
15794: if (is_pointer_value(env, insn->dst_reg)) {
15795: verbose(env, "R%d pointer arithmetic prohibited\n",
15796: insn->dst_reg);
15797: return -EACCES;
15798: }
15799:
15800: /* check dest operand */
15801: if (regs[insn->dst_reg].type == SCALAR_VALUE) {
15802: err = check_reg_arg(env, insn->dst_reg, DST_OP_NO_MARK);
15803: err = err ?: adjust_scalar_min_max_vals(env, insn,
15804: ®s[insn->dst_reg],
15805: regs[insn->dst_reg]);
15806: } else {
15807: err = check_reg_arg(env, insn->dst_reg, DST_OP);
15808: }
15809: if (err)
15810: return err;
15811:
15812: } else if (opcode == BPF_MOV) {
15813:
15814: if (BPF_SRC(insn->code) == BPF_X) {
15815: if (insn->off == BPF_ADDR_SPACE_CAST) {
15816: if (!env->prog->aux->arena) {
15817: verbose(env, "addr_space_cast insn can only be used in a program that has an associated arena\n");
15818: return -EINVAL;
15819: }
15820: }
15821:
15822: /* check src operand */
15823: err = check_reg_arg(env, insn->src_reg, SRC_OP);
15824: if (err)
15825: return err;
15826: }
15827:
15828: /* check dest operand, mark as required later */
15829: err = check_reg_arg(env, insn->dst_reg, DST_OP_NO_MARK);
]
|
| 74/2 |
2026/09/04 08:38 |
llm |
expert |
0m
Model:
Tokens:
input: 72489
output: 37
thoughts: 272
Thoughts: **My Analysis of Pointer Operations and Their Impact**
Okay, so I'm digging into this code and the interaction between pointer handling and the `allow_ptr_leaks` flag is really interesting. If `allow_ptr_leaks` is set, `is_pointer_value` returns false. That means, crucially, that we're allowing `BPF_END` and `BPF_NEG` to operate on pointers! That's a potential vulnerability point, so let's understand the implications of applying `BPF_END` or `BPF_NEG` to a pointer.
Right, the code block:
```c
if (regs[insn->dst_reg].type == SCALAR_VALUE) {
err = check_reg_arg(env, insn->dst_reg, DST_OP_NO_MARK);
err = err ?: adjust_scalar_min_max_vals(env, insn,
®s[insn->dst_reg],
regs[insn->dst_reg]);
} else {
err = check_reg_arg(env, insn->dst_reg, DST_OP);
}
```
If the destination register (`regs[insn->dst_reg]`) is already a scalar value, we perform the check with `DST_OP_NO_MARK` and then adjust min/max values. But what happens if it *isn't*? It looks like we call `check_reg_arg(env, insn->dst_reg, DST_OP)` instead. Which is the case when it's a pointer. That's key. Now, I need to know what `check_reg_arg` with `DST_OP` actually does. My hunch is that this is where we transition the value's type. I need to dive into the implementation of `check_reg_arg` to confirm whether or not it's changing the register's type to `SCALAR_VALUE`.
|
| 75/2 |
2026/09/04 08:39 |
tool |
read-file |
0m
Args: map[File:kernel/bpf/verifier.c FirstLine:7290 LineCount:50]
Results: map[Contents:7290: }
7291:
7292: rec = reg_btf_record(reg);
7293: if (!btf_record_has_field(rec, is_res_lock ? BPF_RES_SPIN_LOCK : BPF_SPIN_LOCK)) {
7294: verbose(env, "%s '%s' has no valid %s_lock\n", map ? "map" : "local",
7295: map ? map->name : "kptr", lock_str);
7296: return -EINVAL;
7297: }
7298: spin_lock_off = is_res_lock ? rec->res_spin_lock_off : rec->spin_lock_off;
7299: if (spin_lock_off != val) {
7300: verbose(env, "off %lld doesn't point to 'struct %s_lock' that is at %d\n",
7301: val, lock_str, spin_lock_off);
7302: return -EINVAL;
7303: }
7304: if (is_lock) {
7305: void *ptr;
7306: int type;
7307:
7308: if (map)
7309: ptr = map;
7310: else
7311: ptr = btf;
7312:
7313: if (!is_res_lock && cur->active_locks) {
7314: lock = find_lock_state(cur, REF_TYPE_LOCK, 0, NULL);
7315: if (lock) {
7316: verbose(env,
7317: "Locking two bpf_spin_locks are not allowed\n");
7318: bpf_diag_lock(
7319: env, env->insn_idx, "nested spin lock",
7320: "This path already holds a bpf_spin_lock. The verifier allows only one regular BPF spin lock at a time.",
7321: "Unlock the current bpf_spin_lock before taking another one.", lock);
7322: return -EINVAL;
7323: }
7324: } else if (is_res_lock && cur->active_locks) {
7325: lock = find_lock_state(cur, REF_TYPE_RES_LOCK | REF_TYPE_RES_LOCK_IRQ,
7326: reg->id, ptr);
7327: if (lock) {
7328: verbose(env, "Acquiring the same lock again, AA deadlock detected\n");
7329: bpf_diag_lock(
7330: env, env->insn_idx, "recursive resource spin lock",
7331: "This path already holds the same resource spin lock. Taking it again would deadlock.",
7332: "Avoid reacquiring the same resource spin lock before it is unlocked.", lock);
7333: return -EINVAL;
7334: }
7335: }
7336:
7337: if (is_res_lock && is_irq)
7338: type = REF_TYPE_RES_LOCK_IRQ;
7339: else if (is_res_lock)
]
|
| 76/2 |
2026/09/04 08:39 |
llm |
expert |
0m
Model:
Tokens:
input: 74114
output: 33
thoughts: 13
Thoughts: Okay, here's my attempt at summarizing that thought process, keeping in mind I'm speaking to a fellow expert:
**Navigating the Codebase: A Quick Check**
Right, let me just pause here. Before I get too deep into this logic, I need to make sure I'm remembering the argument validation correctly. Hang on, I need to double-check that `check_reg_arg` function. I *think* I've got the validation strategy right, but it's always worth a quick look to confirm. No point in continuing if I'm building on a shaky foundation, even a minor oversight there could introduce some nasty bugs later on. Better safe than sorry when you're dealing with critical argument validation like this. Okay, let me go and verify that function... then I can come back to what I was working on.
|
| 77/2 |
2026/09/04 08:39 |
tool |
grepper |
0m
Args: map[Expression:check_reg_arg PathPrefix:kernel/bpf/verifier.c]
Results: map[Output:kernel/bpf/verifier.c=3168=static void mark_stack_slots_scratched(struct bpf_verifier_env *env,
--
kernel/bpf/verifier.c-3176-
kernel/bpf/verifier.c:3177:static int __check_reg_arg(struct bpf_verifier_env *env, struct bpf_reg_state *regs, u32 regno,
kernel/bpf/verifier.c-3178- enum bpf_reg_arg_type t)
--
kernel/bpf/verifier.c-3208-
kernel/bpf/verifier.c:3209:static int check_reg_arg(struct bpf_verifier_env *env, u32 regno,
kernel/bpf/verifier.c-3210- enum bpf_reg_arg_type t)
--
kernel/bpf/verifier.c-3214-
kernel/bpf/verifier.c:3215: return __check_reg_arg(env, state->regs, regno, t);
kernel/bpf/verifier.c-3216-}
--
kernel/bpf/verifier.c=6585=static int check_load_mem(struct bpf_verifier_env *env, struct bpf_insn *insn,
--
kernel/bpf/verifier.c-6596- if (is_stack_arg_ldx(insn)) {
kernel/bpf/verifier.c:6597: err = check_reg_arg(env, insn->dst_reg, DST_OP_NO_MARK);
kernel/bpf/verifier.c-6598- if (err)
--
kernel/bpf/verifier.c-6603- /* check src operand */
kernel/bpf/verifier.c:6604: err = check_reg_arg(env, insn->src_reg, SRC_OP);
kernel/bpf/verifier.c-6605- if (err)
--
kernel/bpf/verifier.c-6608- /* check dst operand */
kernel/bpf/verifier.c:6609: err = check_reg_arg(env, insn->dst_reg, DST_OP_NO_MARK);
kernel/bpf/verifier.c-6610- if (err)
--
kernel/bpf/verifier.c=6632=static int check_store_reg(struct bpf_verifier_env *env, struct bpf_insn *insn,
--
kernel/bpf/verifier.c-6642- if (is_stack_arg_stx(insn)) {
kernel/bpf/verifier.c:6643: err = check_reg_arg(env, insn->src_reg, SRC_OP);
kernel/bpf/verifier.c-6644- if (err)
--
kernel/bpf/verifier.c-6649- /* check src1 operand */
kernel/bpf/verifier.c:6650: err = check_reg_arg(env, insn->src_reg, SRC_OP);
kernel/bpf/verifier.c-6651- if (err)
--
kernel/bpf/verifier.c-6654- /* check src2 operand */
kernel/bpf/verifier.c:6655: err = check_reg_arg(env, insn->dst_reg, SRC_OP);
kernel/bpf/verifier.c-6656- if (err)
--
kernel/bpf/verifier.c=6670=static int check_atomic_rmw(struct bpf_verifier_env *env,
--
kernel/bpf/verifier.c-6682- /* check src1 operand */
kernel/bpf/verifier.c:6683: err = check_reg_arg(env, insn->src_reg, SRC_OP);
kernel/bpf/verifier.c-6684- if (err)
--
kernel/bpf/verifier.c-6687- /* check src2 operand */
kernel/bpf/verifier.c:6688: err = check_reg_arg(env, insn->dst_reg, SRC_OP);
kernel/bpf/verifier.c-6689- if (err)
--
kernel/bpf/verifier.c-6695-
kernel/bpf/verifier.c:6696: err = check_reg_arg(env, aux_reg, SRC_OP);
kernel/bpf/verifier.c-6697- if (err)
--
kernel/bpf/verifier.c-6720- /* check and record load of old value */
kernel/bpf/verifier.c:6721: err = check_reg_arg(env, load_reg, DST_OP);
kernel/bpf/verifier.c-6722- if (err)
--
kernel/bpf/verifier.c=6755=static int check_atomic_load(struct bpf_verifier_env *env,
--
kernel/bpf/verifier.c-6759-
kernel/bpf/verifier.c:6760: err = check_reg_arg(env, insn->src_reg, SRC_OP);
kernel/bpf/verifier.c-6761- if (err)
--
kernel/bpf/verifier.c=8680=static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
--
kernel/bpf/verifier.c-8696-
kernel/bpf/verifier.c:8697: err = check_reg_arg(env, regno, SRC_OP);
kernel/bpf/verifier.c-8698- if (err)
--
kernel/bpf/verifier.c=9538=static void clear_caller_saved_regs(struct bpf_verifier_env *env,
--
kernel/bpf/verifier.c-9547- bpf_mark_reg_not_init(env, ®s[caller_saved[i]]);
kernel/bpf/verifier.c:9548: __check_reg_arg(env, regs, caller_saved[i], DST_OP_NO_MARK);
kernel/bpf/verifier.c-9549- }
--
kernel/bpf/verifier.c=9572=static int setup_func_entry(struct bpf_verifier_env *env, int subprog, int callsite,
--
kernel/bpf/verifier.c-9608-
kernel/bpf/verifier.c:9609: /* only increment it after check_reg_arg() finished */
kernel/bpf/verifier.c-9610- state->curframe++;
--
kernel/bpf/verifier.c=10736=static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
--
kernel/bpf/verifier.c-11002- bpf_mark_reg_not_init(env, ®s[caller_saved[i]]);
kernel/bpf/verifier.c:11003: check_reg_arg(env, caller_saved[i], DST_OP_NO_MARK);
kernel/bpf/verifier.c-11004- }
--
kernel/bpf/verifier.c=15780=static int check_alu_op(struct bpf_verifier_env *env, struct bpf_insn *insn)
--
kernel/bpf/verifier.c-15789- /* check src operand */
kernel/bpf/verifier.c:15790: err = check_reg_arg(env, insn->dst_reg, SRC_OP);
kernel/bpf/verifier.c-15791- if (err)
--
kernel/bpf/verifier.c-15801- if (regs[insn->dst_reg].type == SCALAR_VALUE) {
kernel/bpf/verifier.c:15802: err = check_reg_arg(env, insn->dst_reg, DST_OP_NO_MARK);
kernel/bpf/verifier.c-15803- err = err ?: adjust_scalar_min_max_vals(env, insn,
--
kernel/bpf/verifier.c-15806- } else {
kernel/bpf/verifier.c:15807: err = check_reg_arg(env, insn->dst_reg, DST_OP);
kernel/bpf/verifier.c-15808- }
--
kernel/bpf/verifier.c-15822- /* check src operand */
kernel/bpf/verifier.c:15823: err = check_reg_arg(env, insn->src_reg, SRC_OP);
kernel/bpf/verifier.c-15824- if (err)
--
kernel/bpf/verifier.c-15828- /* check dest operand, mark as required later */
kernel/bpf/verifier.c:15829: err = check_reg_arg(env, insn->dst_reg, DST_OP_NO_MARK);
kernel/bpf/verifier.c-15830- if (err)
--
kernel/bpf/verifier.c-15927- /* check src1 operand */
kernel/bpf/verifier.c:15928: err = check_reg_arg(env, insn->src_reg, SRC_OP);
kernel/bpf/verifier.c-15929- if (err)
--
kernel/bpf/verifier.c-15933- /* check src2 operand */
kernel/bpf/verifier.c:15934: err = check_reg_arg(env, insn->dst_reg, SRC_OP);
kernel/bpf/verifier.c-15935- if (err)
--
kernel/bpf/verifier.c-15954- /* check dest operand */
kernel/bpf/verifier.c:15955: err = check_reg_arg(env, insn->dst_reg, DST_OP_NO_MARK);
kernel/bpf/verifier.c-15956- err = err ?: adjust_reg_min_max_vals(env, insn);
--
kernel/bpf/verifier.c=16803=static int check_cond_jmp_op(struct bpf_verifier_env *env,
--
kernel/bpf/verifier.c-16842- /* check src2 operand */
kernel/bpf/verifier.c:16843: err = check_reg_arg(env, insn->dst_reg, SRC_OP);
kernel/bpf/verifier.c-16844- if (err)
--
kernel/bpf/verifier.c-16849- /* check src1 operand */
kernel/bpf/verifier.c:16850: err = check_reg_arg(env, insn->src_reg, SRC_OP);
kernel/bpf/verifier.c-16851- if (err)
--
kernel/bpf/verifier.c=17043=static int check_ld_imm(struct bpf_verifier_env *env, struct bpf_insn *insn)
--
kernel/bpf/verifier.c-17055-
kernel/bpf/verifier.c:17056: err = check_reg_arg(env, insn->dst_reg, DST_OP);
kernel/bpf/verifier.c-17057- if (err)
--
kernel/bpf/verifier.c=17180=static int check_ld_abs(struct bpf_verifier_env *env, struct bpf_insn *insn)
--
kernel/bpf/verifier.c-17197- /* check whether implicit source operand (register R6) is readable */
kernel/bpf/verifier.c:17198: err = check_reg_arg(env, ctx_reg, SRC_OP);
kernel/bpf/verifier.c-17199- if (err)
--
kernel/bpf/verifier.c-17217- /* check explicit source operand */
kernel/bpf/verifier.c:17218: err = check_reg_arg(env, insn->src_reg, SRC_OP);
kernel/bpf/verifier.c-17219- if (err)
--
kernel/bpf/verifier.c-17231- bpf_mark_reg_not_init(env, ®s[caller_saved[i]]);
kernel/bpf/verifier.c:17232: check_reg_arg(env, caller_saved[i], DST_OP_NO_MARK);
kernel/bpf/verifier.c-17233- }
--
kernel/bpf/verifier.c=17404=static int check_return_code(struct bpf_verifier_env *env, int regno, const char *reg_name)
--
kernel/bpf/verifier.c-17438- */
kernel/bpf/verifier.c:17439: err = check_reg_arg(env, regno, SRC_OP);
kernel/bpf/verifier.c-17440- if (err)
--
kernel/bpf/verifier.c=17489=static int check_global_subprog_return_code(struct bpf_verifier_env *env)
--
kernel/bpf/verifier.c-17497-
kernel/bpf/verifier.c:17498: err = check_reg_arg(env, BPF_REG_0, SRC_OP);
kernel/bpf/verifier.c-17499- if (err)
--
kernel/bpf/verifier.c=18103=static int do_check_insn(struct bpf_verifier_env *env, bool *do_print_state)
--
kernel/bpf/verifier.c-18134-
kernel/bpf/verifier.c:18135: err = check_reg_arg(env, insn->dst_reg, SRC_OP);
kernel/bpf/verifier.c-18136- if (err)
]
|
| 78/2 |
2026/09/04 08:39 |
llm |
expert |
0m
Model:
Tokens:
input: 77961
output: 66
thoughts: 809
Thoughts: **Analysis of the BPF Verifier Bug**
Okay, so let me break this down. That `check_reg_arg` function is the key. Specifically, that line `mark_reg_unknown(env, regs, regno)` when the destination operand is a destination operand (`DST_OP`). So, in the presence of `allow_ptr_leaks`, operations like `BPF_NEG` and `BPF_SUB` on a pointer simply convert them to a `SCALAR_VALUE`, effectively neutralizing them as pointers that could be dereferenced later, making the program safe. This is, in essence, what `CAP_PERFMON` is *intended* to allow: the controlled leaking of pointers to user space by turning them into scalars that cannot be dereferenced..
The real vulnerability lies in the interaction between `allow_ptr_leaks` and `bpf_loop` or `bpf_set_retval`. These functions call `mark_chain_precision` on an `ARG_ANYTHING` argument. This argument *could* be a pointer if `allow_ptr_leaks` is set. And `mark_chain_precision` expects a scalar, which will cause the verifier to throw a `verifier_bug` exception and reject the program. This is known and has been fixed. Either by checking the register's scalar status before calling `mark_chain_precision`, or skipping it altogether for pointers. This means the security impact is practically nothing – it's just a warning.
Now, let's assess the exploitability. It's *not* exploitable in a meaningful way. It's not a denial-of-service, it's not unprivileged and it requires `CAP_PERFMON`, or a BPF token. BPF tokens require user namespaces, making the vulnerability user-namespace specific, not a VM-related attack, or anything triggered remotely or via peripherals.
The catch is, can an unprivileged user trigger this at all? No. The `bpf_token_create` function *explicitly* requires a user namespace via the `current_user_ns() != &init_user_ns` check. Even if an unprivileged user has `CAP_PERFMON`, it doesn't change the fact they're still unprivileged without a user namespace. So, my assessment boils down to this:
- Exploitable: False
- DenialOfService: False
- Unprivileged: False
- UserNamespace: True
- VMGuestTrigger: False
- VMHostTrigger: False
- NetworkTrigger: False
- RemoteTrigger: False
- PeripheralTrigger: False
- FilesystemTrigger: False
I'm comfortable with this. Let's call `set-results`.
|
| 79/2 |
2026/09/04 08:39 |
tool |
set-results |
0m
Args: map[DenialOfService:false Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:false UserNamespace:true VMGuestTrigger:false VMHostTrigger:false]
Results: map[DenialOfService:false Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:false UserNamespace:true VMGuestTrigger:false VMHostTrigger:false]
|
| 80/2 |
2026/09/04 08:39 |
llm |
expert |
0m
Model:
Tokens:
input: 79484
output: 655
thoughts: 572
Thoughts: **Final Thoughts on the BPF Verifier Bug**
Okay, the analysis is complete. Time to draft the final response. This comes down to a bug within the BPF verifier's backtracking logic. Essentially, the verifier has a problem when it encounters `bpf_loop` or `bpf_set_retval` helpers. The root cause lies in how `mark_chain_precision` is called, specifically when it attempts to handle the first argument (`BPF_REG_1`). These helpers declare their first arguments as `ARG_ANYTHING`.
Normally, a check in `check_func_arg` prevents the use of pointers as `ARG_ANYTHING` arguments through `is_pointer_value()`. However, the presence of `CAP_PERFMON` (or its equivalent BPF token), allows the verifier to permit pointers where they shouldn't be. Specifically, setting `env->allow_ptr_leaks` to `true`, causes `is_pointer_value()` to return false even for pointers. This is where things get interesting. When `mark_chain_precision` gets called on a pointer register, it eventually calls `bpf_mark_chain_precision`, which contains a sanity check that, at runtime, confirms the register type. The problem is that the sanity check checks `if (reg->type != SCALAR_VALUE)`. In this case, since a pointer is passed as a `BPF_REG_1`, the check fails. It then emits a `verifier_bug` (which translates to a kernel `WARNING`) and returns `-EFAULT`.
**So, the security implications are as follows:**
* **Exploitable?** No, thankfully. The verifier safely catches this unexpected state and rejects the BPF program. No memory corruption, privilege escalation, or information leaks. No real harm, just a warning and a program rejection.
* **Denial of Service?** No. This isn't a crash. The impact is limited to a single `WARN_ONCE` in the kernel logs and the rejection of the BPF program.
* **User Namespace Impact?** It's nuanced. An unprivileged user can't trigger this directly without the `CAP_PERFMON` capability, obviously. However, the user namespace mechanism does create a potential attack vector. A user *can* create a user namespace, mount `bpffs` with delegation options, and create a BPF token. Since they are root within that namespace, the token *will* effectively grant them `CAP_PERFMON` for BPF. This means it is, in effect, accessible from a user namespace.
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Results: map[Explanation:**Analysis of the Bug**
The bug is located in the BPF verifier's backtracking and precision tracking
logic. When verifying calls to certain helpers like `bpf_loop` or
`bpf_set_retval`, the verifier explicitly marks their first argument
(`BPF_REG_1`) as precise by calling `mark_chain_precision(env, BPF_REG_1)`.
These helpers define their first argument type as `ARG_ANYTHING`.
During argument checking, `check_func_arg()` ensures that `ARG_ANYTHING`
arguments are not pointers by calling `is_pointer_value()`. However, if the user
has `CAP_PERFMON` privileges (which allows leaking kernel pointers),
`env->allow_ptr_leaks` is set to `true`. When this flag is set,
`is_pointer_value()` intentionally returns `false` even for pointer registers,
allowing a pointer to be passed as `BPF_REG_1`.
When `mark_chain_precision()` is subsequently called on this pointer register,
it invokes `bpf_mark_chain_precision()`, which contains the following sanity
check:
```c
if (regno >= 0) {
reg = &func->regs[regno];
if (reg->type != SCALAR_VALUE) {
verifier_bug(env, "backtracking misuse");
return -EFAULT;
}
bt_set_reg(bt, regno);
}
```
Because the register holds a pointer type rather than a `SCALAR_VALUE`, the
sanity check fails. This triggers the `verifier_bug()` macro, which emits a
`BPF_WARN_ONCE` kernel warning and aborts the verification by returning
`-EFAULT`.
**Security Impact**
* **Exploitable:** **False**. The verifier safely catches the unexpected state,
emits a warning, and gracefully rejects the BPF program by returning `-EFAULT`.
The program is never loaded or executed, meaning there is no memory corruption,
privilege escalation, or information leak.
* **Denial of Service:** **False**. The bug only results in a single `WARN_ONCE`
message in the kernel log and the rejection of the invalid BPF program. It does
not crash the kernel, hang the system, or leak resources. (Note: Syzkaller
treats WARNINGs as bugs, but in production environments without `panic_on_warn`,
this is harmless).
* **Accessible From Unprivileged Processes:** **False**. Triggering this
requires `CAP_PERFMON` to set `env->allow_ptr_leaks = true`, which a standard
unprivileged user does not have.
* **Accessible From User Namespaces:** **True**. An unprivileged user can create
a new user namespace, mount a BPF filesystem (`bpffs`) with delegation options,
and create a BPF token. Because the user is root within their user namespace,
the token will grant `CAP_PERFMON` for BPF operations, allowing them to bypass
the pointer check and trigger the warning.]
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