| 0/0 |
2026/07/25 00:56 |
flow |
assessment-security |
53m
Results: map[DenialOfService:false Explanation:Based on the analysis of the bug report and the kernel source code, here is the
assessment of the security impact:
**1. Nature of the Bug:**
The bug report shows a `WARN_ON_ONCE` being triggered in `ct_kernel_exit` and
`ct_kernel_enter` within `kernel/context_tracking.c`. The warning condition is
`WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user &&
!is_idle_task(current));`.
This warning is triggered because `ct_cpuidle_enter()` is being called from a
non-idle task. On ARM64, `cpu_suspend()` was modified to call
`ct_cpuidle_enter()` and `ct_cpuidle_exit()` directly. While `cpu_suspend()` is
primarily used for cpuidle (where it is correctly called from the idle task), it
is also used for system suspend (e.g., via `psci_system_suspend_enter`). During
system suspend, it is called in the context of the task that initiated the
suspend, which is not the idle task, thus triggering the debug warning.
**2. Exploitability & Denial of Service:**
This is purely a harmless warning caused by an overly strict assertion in a
debug configuration (`CONFIG_RCU_EQS_DEBUG`). It does not cause any memory
corruption, information leak, or control-flow hijack. Furthermore, it is a
`WARN_ON_ONCE` which simply prints a stack trace and continues execution without
halting the kernel or causing a denial of service. In production builds,
`CONFIG_RCU_EQS_DEBUG` is typically disabled, meaning the warning wouldn't even
trigger.
**3. Accessibility (Unprivileged / User Namespaces):**
To trigger this warning, a user must initiate a system suspend. The reproducer
does this by writing `"mem\n"` to `/sys/power/state`.
The `/sys/power/state` sysfs attribute is created with mode `0644` and is owned
by the global root (`GLOBAL_ROOT_UID`).
- An unprivileged user cannot write to this file.
- A process inside an unprivileged user namespace (even if it mounts its own
`sysfs` instance) cannot write to this file because `sysfs` inodes are always
owned by the global root. The process's `fsuid` (which is mapped to a non-zero
global UID) will not match the inode's UID (0), resulting in a permission denied
error.
Therefore, triggering this bug strictly requires global root privileges.
**Conclusion:**
The bug is a harmless debug warning that can only be triggered by a highly
privileged user (global root) initiating a system suspend. It has no security
impact, is not exploitable, does not cause a denial of service, and is
completely inaccessible to unprivileged users or from within user namespaces. Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:false UserNamespace:false VMGuestTrigger:false VMHostTrigger:false]
|
| 1/1 |
2026/07/25 00:56 |
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_mkdirat
#define __NR_mkdirat 34
#endif
#ifndef __NR_mmap
#define __NR_mmap 222
#endif
#ifndef __NR_mount
#define __NR_mount 40
#endif
#ifndef __NR_openat
#define __NR_openat 56
#endif
#ifndef __NR_write
#define __NR_write 64
#endif
uint64_t r[1] = {0xffffffffffffffff};
int main(void)
{
syscall(__NR_mmap, /*addr=*/0x1ffff000ul, /*len=*/0x1000, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x20000000ul, /*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=*/0x21000000ul, /*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)) {}
// mkdirat arguments: [
// fd: fd_dir (resource)
// path: ptr[in, buffer] {
// buffer: {2e 2f 73 79 73 00} (length 0x6)
// }
// mode: open_mode = 0x1ff (8 bytes)
// ]
memcpy((void*)0x20000040, "./sys\000", 6);
syscall(__NR_mkdirat, /*fd=*/0xffffff9c, /*path=*/0x20000040ul, /*mode=S_IXOTH|S_IWOTH|S_IROTH|S_IXGRP|S_IWGRP|S_IRGRP|S_IXUSR|S_IWUSR|0x100*/0x1fful);
// mount arguments: [
// src: nil
// dst: ptr[in, buffer] {
// buffer: {2e 2f 73 79 73 00} (length 0x6)
// }
// type: ptr[in, buffer] {
// buffer: {73 79 73 66 73 00} (length 0x6)
// }
// flags: mount_flags = 0x0 (8 bytes)
// data: nil
// ]
memcpy((void*)0x200000c0, "./sys\000", 6);
memcpy((void*)0x20000140, "sysfs\000", 6);
syscall(__NR_mount, /*src=*/0ul, /*dst=*/0x200000c0ul, /*type=*/0x20000140ul, /*flags=*/0ul, /*data=*/0ul);
// openat arguments: [
// fd: fd_dir (resource)
// file: ptr[in, buffer] {
// buffer: {2e 2f 73 79 73 2f 70 6f 77 65 72 2f 73 74 61 74 65 00} (length 0x12)
// }
// flags: open_flags = 0x2 (4 bytes)
// mode: open_mode = 0x0 (2 bytes)
// ]
// returns fd
memcpy((void*)0x20000180, "./sys/power/state\000", 18);
res = syscall(__NR_openat, /*fd=*/0xffffff9c, /*file=*/0x20000180ul, /*flags=O_RDWR*/2, /*mode=*/0);
if (res != -1)
r[0] = res;
// write arguments: [
// fd: fd (resource)
// buf: ptr[in, buffer] {
// buffer: {6d 65 6d 0a} (length 0x4)
// }
// count: len = 0x8 (8 bytes)
// ]
memcpy((void*)0x20000100, "mem\n", 4);
syscall(__NR_write, /*fd=*/r[0], /*buf=*/0x20000100ul, /*count=*/8ul);
return 0;
}
]
|
| 2/1 |
2026/07/25 00:56 |
action |
kernel-checkouter |
1m
Results: map[KernelSrc:/app/workdir/cache/src/e7f8564d804f224ae342b85c915ad8f153cc1e96]
|
| 3/1 |
2026/07/25 00:57 |
action |
kernel-builder |
22m
Results: map[KernelObj:/app/workdir/cache/build/db38d9148a088bff76fbfbe4bff3277332cd8957]
|
| 4/1 |
2026/07/25 01:19 |
action |
codesearch-prepare |
16m
Results: map[Index:codesearch-index]
|
| 5/1 |
2026/07/25 01:35 |
agent |
expert |
14m
Model:
Results: map[DenialOfService:false Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:false UserNamespace:false 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:
vhci_hcd vhci_hcd.1: suspend vhci_hcd
vhci_hcd vhci_hcd.0: suspend vhci_hcd
Disabling non-boot CPUs ...
psci: CPU1 killed (polled 0 ms)
------------[ cut here ]------------
WARNING: kernel/context_tracking.c:120 at ct_kernel_exit+0x1b4/0x1f4 kernel/context_tracking.c:118, CPU#0: syz.1.538/5484
Modules linked in:
CPU: 0 UID: 0 PID: 5484 Comm: syz.1.538 Not tainted syzkaller #0 PREEMPT
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/02/2026
pstate: 634003c5 (nZCv DAIF +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
pc : ct_kernel_exit+0x1b4/0x1f4 kernel/context_tracking.c:118
lr : instrument_atomic_read include/linux/instrumented.h:82 [inline]
lr : atomic_read include/linux/atomic/atomic-instrumented.h:32 [inline]
lr : ct_rcu_watching include/linux/context_tracking_state.h:91 [inline]
lr : ct_kernel_exit+0x13c/0x1f4 kernel/context_tracking.c:119
sp : ffff8000937075f0
x29: ffff8000937075f0 x28: dfff800000000000 x27: ffff800093707660
x26: 00000000000000c0 x25: ffff7000126e0ecc x24: ffff800088abf998
x23: ffff800088b0b6a0 x22: ffff0001ade38998 x21: ffff0001ade38998
x20: 0000000000000000 x19: 0000000000000005 x18: 00000000ffffffff
x17: ffff80008a791000 x16: 0000000000000005 x15: ffff80008a31ada0
x14: 0000000000000000 x13: 0000000000000001 x12: 0000000000000000
x11: 0000000000000000 x10: ffff600035bc7135 x9 : dfff800000000000
x8 : 0000000000000040 x7 : 0000000000000000 x6 : 000000000000003f
x5 : 0000000000000040 x4 : 0000000000000008 x3 : ffff8000868e6858
x2 : 0000000000000000 x1 : 0000000000000004 x0 : 0000000000000001
Call trace:
ct_kernel_exit+0x1b4/0x1f4 kernel/context_tracking.c:118 (P)
ct_idle_enter+0x24/0x38 kernel/context_tracking.c:299
ct_cpuidle_enter include/linux/cpuidle.h:134 [inline]
cpu_suspend+0x264/0x474 arch/arm64/kernel/suspend.c:140
psci_system_suspend_enter+0x4c/0x80 drivers/firmware/psci/psci.c:544
suspend_enter kernel/power/suspend.c:468 [inline]
suspend_devices_and_enter+0x88c/0xd0c kernel/power/suspend.c:533
enter_state kernel/power/suspend.c:618 [inline]
pm_suspend+0x498/0x698 kernel/power/suspend.c:644
state_store+0x14c/0x1fc kernel/power/main.c:819
kobj_attr_store+0x6c/0x90 lib/kobject.c:840
sysfs_kf_write+0xe0/0x108 fs/sysfs/file.c:145
kernfs_fop_write_iter+0x260/0x3b8 fs/kernfs/file.c:345
new_sync_write fs/read_write.c:595 [inline]
vfs_write+0x51c/0xa0c fs/read_write.c:687
ksys_write+0x12c/0x228 fs/read_write.c:739
__do_sys_write fs/read_write.c:750 [inline]
__se_sys_write fs/read_write.c:747 [inline]
__arm64_sys_write+0x7c/0x90 fs/read_write.c:747
__invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121
do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140
el0_svc+0x64/0x260 arch/arm64/kernel/entry-common.c:736
el0t_64_sync_handler+0x48/0x148 arch/arm64/kernel/entry-common.c:755
el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:594
irq event stamp: 60074
hardirqs last enabled at (60073): [<ffff80008690522c>] __raw_spin_unlock_irq include/linux/spinlock_api_smp.h:187 [inline]
hardirqs last enabled at (60073): [<ffff80008690522c>] _raw_spin_unlock_irq+0x30/0x80 kernel/locking/spinlock.c:206
hardirqs last disabled at (60074): [<ffff800080473cc0>] arch_suspend_disable_irqs+0x34/0x4c kernel/power/suspend.c:403
softirqs last enabled at (58694): [<ffff80008030ff18>] softirq_handle_end kernel/softirq.c:468 [inline]
softirqs last enabled at (58694): [<ffff80008030ff18>] handle_softirqs+0xc28/0xd98 kernel/softirq.c:650
softirqs last disabled at (58689): [<ffff8000800204c0>] __do_softirq+0x14/0x20 kernel/softirq.c:656
---[ end trace 0000000000000000 ]---
------------[ cut here ]------------
WARNING: kernel/context_tracking.c:165 at ct_kernel_enter+0x138/0x170 kernel/context_tracking.c:150, CPU#0: syz.1.538/5484
Modules linked in:
CPU: 0 UID: 0 PID: 5484 Comm: syz.1.538 Tainted: G W syzkaller #0 PREEMPT
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/02/2026
pstate: 600003c5 (nZCv DAIF -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : ct_kernel_enter+0x138/0x170 kernel/context_tracking.c:150
lr : instrument_atomic_read include/linux/instrumented.h:82 [inline]
lr : atomic_read include/linux/atomic/atomic-instrumented.h:32 [inline]
lr : ct_rcu_watching include/linux/context_tracking_state.h:91 [inline]
lr : ct_kernel_enter+0xc8/0x170 kernel/context_tracking.c:164
sp : ffff8000937075e0
x29: ffff8000937075e0 x28: dfff800000000000 x27: ffff800093707660
x26: 00000000000000c0 x25: ffff7000126e0ecc x24: 0000000100000000
x23: ffff800088b0b6a0 x22: ffff800088abf998 x21: ffff0001ade38998
x20: ffff0001ade38998 x19: 0000000000000000 x18: 00000000ffffffff
x17: 000000040044ffff x16: 041000f5b5503510 x15: 0000000000000000
x14: ffff0000d924ba80 x13: 0000000000000001 x12: 0000000000000000
x11: 0000000000000000 x10: ffff600035bc7135 x9 : dfff800000000000
x8 : 0000000000000040 x7 : 0000000000000000 x6 : 000000000000003f
x5 : 0000000000000040 x4 : 0000000000000000 x3 : ffff8000868e6a20
x2 : 0000000000000000 x1 : 0000000000000004 x0 : 0000000000000001
Call trace:
ct_kernel_enter+0x138/0x170 kernel/context_tracking.c:150 (P)
ct_idle_exit+0x24/0x48 kernel/context_tracking.c:317
ct_cpuidle_exit include/linux/cpuidle.h:144 [inline]
cpu_suspend+0x2dc/0x474 arch/arm64/kernel/suspend.c:158
psci_system_suspend_enter+0x4c/0x80 drivers/firmware/psci/psci.c:544
suspend_enter kernel/power/suspend.c:468 [inline]
suspend_devices_and_enter+0x88c/0xd0c kernel/power/suspend.c:533
enter_state kernel/power/suspend.c:618 [inline]
pm_suspend+0x498/0x698 kernel/power/suspend.c:644
state_store+0x14c/0x1fc kernel/power/main.c:819
kobj_attr_store+0x6c/0x90 lib/kobject.c:840
sysfs_kf_write+0xe0/0x108 fs/sysfs/file.c:145
kernfs_fop_write_iter+0x260/0x3b8 fs/kernfs/file.c:345
new_sync_write fs/read_write.c:595 [inline]
vfs_write+0x51c/0xa0c fs/read_write.c:687
ksys_write+0x12c/0x228 fs/read_write.c:739
__do_sys_write fs/read_write.c:750 [inline]
__se_sys_write fs/read_write.c:747 [inline]
__arm64_sys_write+0x7c/0x90 fs/read_write.c:747
__invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121
do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140
el0_svc+0x64/0x260 arch/arm64/kernel/entry-common.c:736
el0t_64_sync_handler+0x48/0x148 arch/arm64/kernel/entry-common.c:755
el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:594
irq event stamp: 60076
hardirqs last enabled at (60075): [<ffff800084649440>] psci_system_suspend_enter+0x4c/0x80 drivers/firmware/psci/psci.c:544
hardirqs last disabled at (60076): [<ffff800084649440>] psci_system_suspend_enter+0x4c/0x80 drivers/firmware/psci/psci.c:544
softirqs last enabled at (58694): [<ffff80008030ff18>] softirq_handle_end kernel/softirq.c:468 [inline]
softirqs last enabled at (58694): [<ffff80008030ff18>] handle_softirqs+0xc28/0xd98 kernel/softirq.c:650
softirqs last disabled at (58689): [<ffff8000800204c0>] __do_softirq+0x14/0x20 kernel/softirq.c:656
---[ end trace 0000000000000000 ]---
Enabling non-boot CPUs ...
CPU1 is up
OOM killer enabled.
Restarting tasks: Starting
Restarting tasks: Done
random: crng reseeded on system resumption
PM: suspend exit
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_mkdirat
#define __NR_mkdirat 34
#endif
#ifndef __NR_mmap
#define __NR_mmap 222
#endif
#ifndef __NR_mount
#define __NR_mount 40
#endif
#ifndef __NR_openat
#define __NR_openat 56
#endif
#ifndef __NR_write
#define __NR_write 64
#endif
uint64_t r[1] = {0xffffffffffffffff};
int main(void)
{
syscall(__NR_mmap, /*addr=*/0x1ffff000ul, /*len=*/0x1000, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x20000000ul, /*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=*/0x21000000ul, /*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)) {}
// mkdirat arguments: [
// fd: fd_dir (resource)
// path: ptr[in, buffer] {
// buffer: {2e 2f 73 79 73 00} (length 0x6)
// }
// mode: open_mode = 0x1ff (8 bytes)
// ]
memcpy((void*)0x20000040, "./sys\000", 6);
syscall(__NR_mkdirat, /*fd=*/0xffffff9c, /*path=*/0x20000040ul, /*mode=S_IXOTH|S_IWOTH|S_IROTH|S_IXGRP|S_IWGRP|S_IRGRP|S_IXUSR|S_IWUSR|0x100*/0x1fful);
// mount arguments: [
// src: nil
// dst: ptr[in, buffer] {
// buffer: {2e 2f 73 79 73 00} (length 0x6)
// }
// type: ptr[in, buffer] {
// buffer: {73 79 73 66 73 00} (length 0x6)
// }
// flags: mount_flags = 0x0 (8 bytes)
// data: nil
// ]
memcpy((void*)0x200000c0, "./sys\000", 6);
memcpy((void*)0x20000140, "sysfs\000", 6);
syscall(__NR_mount, /*src=*/0ul, /*dst=*/0x200000c0ul, /*type=*/0x20000140ul, /*flags=*/0ul, /*data=*/0ul);
// openat arguments: [
// fd: fd_dir (resource)
// file: ptr[in, buffer] {
// buffer: {2e 2f 73 79 73 2f 70 6f 77 65 72 2f 73 74 61 74 65 00} (length 0x12)
// }
// flags: open_flags = 0x2 (4 bytes)
// mode: open_mode = 0x0 (2 bytes)
// ]
// returns fd
memcpy((void*)0x20000180, "./sys/power/state\000", 18);
res = syscall(__NR_openat, /*fd=*/0xffffff9c, /*file=*/0x20000180ul, /*flags=O_RDWR*/2, /*mode=*/0);
if (res != -1)
r[0] = res;
// write arguments: [
// fd: fd (resource)
// buf: ptr[in, buffer] {
// buffer: {6d 65 6d 0a} (length 0x4)
// }
// count: len = 0x8 (8 bytes)
// ]
memcpy((void*)0x20000100, "mem\n", 4);
syscall(__NR_write, /*fd=*/r[0], /*buf=*/0x20000100ul, /*count=*/8ul);
return 0;
}
Reply: Based on the analysis of the bug report and the kernel source code, here is the assessment of the security impact:
**1. Nature of the Bug:**
The bug report shows a `WARN_ON_ONCE` being triggered in `ct_kernel_exit` and `ct_kernel_enter` within `kernel/context_tracking.c`. The warning condition is `WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));`.
This warning is triggered because `ct_cpuidle_enter()` is being called from a non-idle task. On ARM64, `cpu_suspend()` was modified to call `ct_cpuidle_enter()` and `ct_cpuidle_exit()` directly. While `cpu_suspend()` is primarily used for cpuidle (where it is correctly called from the idle task), it is also used for system suspend (e.g., via `psci_system_suspend_enter`). During system suspend, it is called in the context of the task that initiated the suspend, which is not the idle task, thus triggering the debug warning.
**2. Exploitability & Denial of Service:**
This is purely a harmless warning caused by an overly strict assertion in a debug configuration (`CONFIG_RCU_EQS_DEBUG`). It does not cause any memory corruption, information leak, or control-flow hijack. Furthermore, it is a `WARN_ON_ONCE` which simply prints a stack trace and continues execution without halting the kernel or causing a denial of service. In production builds, `CONFIG_RCU_EQS_DEBUG` is typically disabled, meaning the warning wouldn't even trigger.
**3. Accessibility (Unprivileged / User Namespaces):**
To trigger this warning, a user must initiate a system suspend. The reproducer does this by writing `"mem\n"` to `/sys/power/state`.
The `/sys/power/state` sysfs attribute is created with mode `0644` and is owned by the global root (`GLOBAL_ROOT_UID`).
- An unprivileged user cannot write to this file.
- A process inside an unprivileged user namespace (even if it mounts its own `sysfs` instance) cannot write to this file because `sysfs` inodes are always owned by the global root. The process's `fsuid` (which is mapped to a non-zero global UID) will not match the inode's UID (0), resulting in a permission denied error.
Therefore, triggering this bug strictly requires global root privileges.
**Conclusion:**
The bug is a harmless debug warning that can only be triggered by a highly privileged user (global root) initiating a system suspend. It has no security impact, is not exploitable, does not cause a denial of service, and is completely inaccessible to unprivileged users or from within user namespaces.
|
| 6/2 |
2026/07/25 01:35 |
llm |
expert |
0m
Model:
Tokens:
input: 11289
output: 36
thoughts: 441
Thoughts: **Analyzing a Kernel Context Tracking Bug**
Okay, so I've got a bug report here, and it looks like we're dealing with two warnings originating from `kernel/context_tracking.c`. Specifically, they're pointing to lines 120 and 165 within that file. The reproducer seems straightforward: mount sysfs, open `./sys/power/state`, and write "mem\n" to it. This triggers a system suspend via `pm_suspend`.
Now, let's trace the execution path. The warnings are related to `ct_kernel_exit` and `ct_kernel_enter` from the call stack provided. Following the call trace it looks like `ct_kernel_exit` is the first function we encounter, followed by `ct_idle_enter`, `ct_cpuidle_enter` then `cpu_suspend` and then a journey through `psci_system_suspend_enter`, `suspend_enter`, `suspend_devices_and_enter`, and `enter_state`, ending in `pm_suspend`. Eventually the code appears to go through `state_store`.
My immediate thought is to dive into `kernel/context_tracking.c` and take a close look at the code around those flagged lines β 120 and 165. This should give me a solid clue. The relationship between context tracking, idle states, CPU suspend, and the power management process is what I am focused on now, as this seems to be where the issue is.
|
| 7/2 |
2026/07/25 01:35 |
tool |
read-file |
0m
Args: map[File:kernel/context_tracking.c FirstLine:100 LineCount:100]
Results: map[Contents: 100: * the possibility of usermode upcalls having messed up our count
101: * of interrupt nesting level during the prior busy period.
102: */
103: static void noinstr ct_kernel_exit(bool user, int offset)
104: {
105: struct context_tracking *ct = this_cpu_ptr(&context_tracking);
106:
107: WARN_ON_ONCE(ct_nmi_nesting() != CT_NESTING_IRQ_NONIDLE);
108: WRITE_ONCE(ct->nmi_nesting, 0);
109: WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
110: ct_nesting() == 0);
111: if (ct_nesting() != 1) {
112: // RCU will still be watching, so just do accounting and leave.
113: ct->nesting--;
114: return;
115: }
116:
117: instrumentation_begin();
118: lockdep_assert_irqs_disabled();
119: trace_rcu_watching(TPS("End"), ct_nesting(), 0, ct_rcu_watching());
120: WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));
121: rcu_preempt_deferred_qs(current);
122:
123: // instrumentation for the noinstr ct_kernel_exit_state()
124: instrument_atomic_write(&ct->state, sizeof(ct->state));
125:
126: instrumentation_end();
127: WRITE_ONCE(ct->nesting, 0); /* Avoid irq-access tearing. */
128: // RCU is watching here ...
129: ct_kernel_exit_state(offset);
130: // ... but is no longer watching here.
131: rcu_task_exit();
132: }
133:
134: /*
135: * Exit an RCU extended quiescent state, which can be either the
136: * idle loop or adaptive-tickless usermode execution.
137: *
138: * We crowbar the ->nmi_nesting field to CT_NESTING_IRQ_NONIDLE to
139: * allow for the possibility of usermode upcalls messing up our count of
140: * interrupt nesting level during the busy period that is just now starting.
141: */
142: static void noinstr ct_kernel_enter(bool user, int offset)
143: {
144: struct context_tracking *ct = this_cpu_ptr(&context_tracking);
145: long oldval;
146:
147: WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !raw_irqs_disabled());
148: oldval = ct_nesting();
149: WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && oldval < 0);
150: if (oldval) {
151: // RCU was already watching, so just do accounting and leave.
152: ct->nesting++;
153: return;
154: }
155: rcu_task_enter();
156: // RCU is not watching here ...
157: ct_kernel_enter_state(offset);
158: // ... but is watching here.
159: instrumentation_begin();
160:
161: // instrumentation for the noinstr ct_kernel_enter_state()
162: instrument_atomic_write(&ct->state, sizeof(ct->state));
163:
164: trace_rcu_watching(TPS("Start"), ct_nesting(), 1, ct_rcu_watching());
165: WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));
166: WRITE_ONCE(ct->nesting, 1);
167: WARN_ON_ONCE(ct_nmi_nesting());
168: WRITE_ONCE(ct->nmi_nesting, CT_NESTING_IRQ_NONIDLE);
169: instrumentation_end();
170: }
171:
172: /**
173: * ct_nmi_exit - inform RCU of exit from NMI context
174: *
175: * If we are returning from the outermost NMI handler that interrupted an
176: * RCU-idle period, update ct->state and ct->nmi_nesting
177: * to let the RCU grace-period handling know that the CPU is back to
178: * being RCU-idle.
179: *
180: * If you add or remove a call to ct_nmi_exit(), be sure to test
181: * with CONFIG_RCU_EQS_DEBUG=y.
182: */
183: void noinstr ct_nmi_exit(void)
184: {
185: struct context_tracking *ct = this_cpu_ptr(&context_tracking);
186:
187: instrumentation_begin();
188: /*
189: * Check for ->nmi_nesting underflow and bad CT state.
190: * (We are exiting an NMI handler, so RCU better be paying attention
191: * to us!)
192: */
193: WARN_ON_ONCE(ct_nmi_nesting() <= 0);
194: WARN_ON_ONCE(!rcu_is_watching_curr_cpu());
195:
196: /*
197: * If the nesting level is not 1, the CPU wasn't RCU-idle, so
198: * leave it in non-RCU-idle state.
199: */
]
|
| 8/2 |
2026/07/25 01:35 |
llm |
expert |
0m
Model:
Tokens:
input: 13815
output: 40
thoughts: 410
Thoughts: **Analyzing a Potentially Unusual Kernel Warning During System Suspend**
Okay, so I'm looking at this kernel warning: `WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));`. It seems like the issue is that `!is_idle_task(current)` is true, meaning the current task isn't the idle task. The current task is `syz.1.538` (PID 5484), so definitely *not* the idle task. The call trace points to `ct_idle_enter` being called, originating from `cpu_suspend`, which is itself called by `psci_system_suspend_enter`, and ultimately by `suspend_enter` during system suspend.
So, here's what's happening: the system is suspending, which is triggering a call to `ct_idle_enter`, but from a task other than the idle task. That feels wrong, because `ct_idle_enter` (or, more specifically, the `CONFIG_RCU_EQS_DEBUG` aspect of it) *expects* to be called from the idle task. But then, wait a second... `CONFIG_RCU_EQS_DEBUG` is a debug option, right? Yeah, this warning *only* happens when that debug configuration is enabled. In typical production builds, that's almost always disabled.
Let me quickly verify that. Okay, assuming it is disabled in production, this warning won't even *show* up. Even if it did, it's a `WARN_ON_ONCE`, meaning it logs a warning but it doesn't halt the kernel. Does this actually create any functional issues? Well, `ct_idle_enter` is transitioning the CPU to an RCU extended quiescent state, but we are also suspending and taking the CPU offline. I'll need to look at `arch/arm64/kernel/suspend.c` around line 140 to investigate further and see if there is any real interaction/problematic side effects.
|
| 9/2 |
2026/07/25 01:36 |
tool |
read-file |
0m
Args: map[File:arch/arm64/kernel/suspend.c FirstLine:120 LineCount:50]
Results: map[Contents: 120: *
121: * Strictly speaking the trace_hardirqs_off() here is superfluous,
122: * hardirqs should be firmly off by now. This really ought to use
123: * something like raw_local_daif_save().
124: */
125: flags = local_daif_save();
126:
127: /*
128: * Function graph tracer state gets inconsistent when the kernel
129: * calls functions that never return (aka suspend finishers) hence
130: * disable graph tracing during their execution.
131: */
132: pause_graph_tracing();
133:
134: /*
135: * Switch to using DAIF.IF instead of PMR in order to reliably
136: * resume if we're using pseudo-NMIs.
137: */
138: arm_cpuidle_save_irq_context(&context);
139:
140: ct_cpuidle_enter();
141:
142: if (__cpu_suspend_enter(&state)) {
143: /* Call the suspend finisher */
144: ret = fn(arg);
145:
146: /*
147: * Never gets here, unless the suspend finisher fails.
148: * Successful cpu_suspend() should return from cpu_resume(),
149: * returning through this code path is considered an error
150: * If the return value is set to 0 force ret = -EOPNOTSUPP
151: * to make sure a proper error condition is propagated
152: */
153: if (!ret)
154: ret = -EOPNOTSUPP;
155:
156: ct_cpuidle_exit();
157: } else {
158: ct_cpuidle_exit();
159: __cpu_suspend_exit();
160: }
161:
162: arm_cpuidle_restore_irq_context(&context);
163:
164: unpause_graph_tracing();
165:
166: /*
167: * Restore pstate flags. OS lock and mdscr have been already
168: * restored, so from this point onwards, debugging is fully
169: * reenabled if it was enabled when core started shutdown.
]
|
| 10/2 |
2026/07/25 01:36 |
llm |
expert |
0m
Model:
Tokens:
input: 15422
output: 47
thoughts: 396
Thoughts: **My Analysis of the `cpu_suspend` and `ct_cpuidle` Interaction**
Okay, so I'm looking at this code and immediately see that `cpu_suspend` is calling `ct_cpuidle_enter()` and `ct_cpuidle_exit()`. Right, and that `ct_cpuidle_enter()` is just a wrapper for `ct_idle_enter()`. Now, this whole thing is triggered during system suspend, specifically when we write to `/sys/power/state`, which is called through `psci_system_suspend_enter`. I see the calling task here isn't the idle task, which is a key observation.
My initial thought is that this is a bug. `ct_cpuidle_enter()` is *supposed* to be called from the idle task, right? But then I remember, `cpu_suspend` is used in both cpuidle *and* system suspend. When it's for cpuidle, the idle task is the caller, but during system suspend, the task initiating the suspend is calling it. Ah, so that means `ct_cpuidle_enter()` is being called from a non-idle task during system suspend, which makes perfect sense.
This immediately triggers the `WARN_ON_ONCE` in `ct_kernel_exit` and `ct_kernel_enter`. My concern now is, is this exploitable? After a quick look, it seems like the warning itself isn't a vulnerability. It's just a warning. And no, the warning itself isn't a denial of service either.
Then I start thinking about RCU. Does the fact that RCU is being put into an extended quiescent state from a non-idle task create any issues? Well, during system suspend, the CPU is going to sleep. Interrupts are disabled, we save the interrupt state using `local_daif_save()`. When it wakes up it's going to call `ct_cpuidle_exit()`. The more I look at this, the more this seems to be a known issue or just a benign warning, likely due to `CONFIG_RCU_EQS_DEBUG`. Maybe there isn't anything to really worry about here.
Time to search for any commits addressing this specific interaction. I'll need to check if this is already addressed.
|
| 11/2 |
2026/07/25 01:36 |
tool |
git-log |
10m
Error:
Args: map[CodeRegexp:ct_cpuidle_enter Count:10 SourcePath:arch/arm64/kernel/suspend.c]
Results:
|
| 12/2 |
2026/07/25 01:46 |
llm |
expert |
0m
Model:
Tokens:
input: 16405
output: 33
thoughts: 23
Thoughts: Okay, here's my interpretation of that thought process, tailored for an expert audience, and presented as if it were my own internal monologue:
**Investigating a Suspend Issue in the ARM64 Kernel**
Right, let's zero in on this suspend problem. Given the nature of the issue, and my understanding of the typical areas where these kinds of bugs surface, I'm going to start with a very targeted search. I'm thinking, "suspend" on an ARM64 system β the kernel's suspend code is the obvious first point. I know the standard file structure pretty well, so I'm going to assume the relevant code is likely going to be in `arch/arm64/kernel`. Itβs probably going to be related to suspend, so something like `suspend.c` is going to be a good bet, so letβs start with a path prefix search term of `PathPrefix="arch/arm64/kernel/suspend.c"`. That should get me on the right track pretty quickly. I expect this to narrow down my scope and allow me to find the related code. Let's see what turns up.
|
| 13/2 |
2026/07/25 01:46 |
tool |
git-log |
0m
Args: map[Count:10 PathPrefix:arch/arm64/kernel/suspend.c]
Results: map[Output:9533864816fb arm64/sme: Restore SME registers on exit from suspend
25693f177155 arm64: Avoid cpus_have_const_cap() for ARM64_HAS_DIT
54c8818aa283 arm64: Avoid cpus_have_const_cap() for ARM64_HAS_CNP
19235e472798 cpuidle, arm64: Fix the ARM64 cpuidle logic
01ab991fc0ee arm64: Enable data independent timing (DIT) in the kernel
973b9e373306 arm64: mte: move register initialization to C
1682c45b9206 arm64: mm: provide idmap pointer to cpu_replace_ttbr1()
dd671f16b1cd arm64: fix typos in comments
82868247897b arm64: kasan: mte: use a constant kernel GCR_EL1 value
77345ef70445 arm64: suspend: Use cpuidle context helpers in cpu_suspend()
]
|
| 14/2 |
2026/07/25 01:46 |
llm |
expert |
0m
Model:
Tokens:
input: 17012
output: 27
thoughts: 36
Thoughts: Okay, here's my interpretation of that.
**Analyzing Commit 19235e472798: ARM64 cpuidle Logic Fix**
Alright, let's dive into this specific commit: `19235e472798`. The description points to a fix related to the ARM64 architecture's `cpuidle` logic. Right off the bat, that gets my attention. `cpuidle` is crucial for power management on ARM64 systems, and issues here can have cascading effects on battery life, thermal performance, and overall system responsiveness. So, this warrants a closer look. I immediately start thinking about potential failure scenarios: were there unintended wake-ups? Incorrect idle states being entered? Were there regressions reported?
I'm mentally running through my mental checklist: I'll need to understand the specifics of the previous logic, the nature of the "fix," and how it impacts the interaction with the power management framework. I want to see if this commit addresses a known issue, a corner case that was missed during earlier testing, or perhaps some interaction with a specific hardware configuration. I'll probably be looking for the introduction of a new platform or a new mode of operation that was overlooked. I'll need to determine whether the fix adheres to ARM's specifications, or if there's any evidence of workarounds or kludges. I'll check how it integrates with the existing idle state management and whether it impacts scheduler behaviour. This is where the fun starts!
|
| 15/2 |
2026/07/25 01:46 |
tool |
git-show |
0m
Args:
Results: map[Output:commit 19235e47279894b033a3ec5cf2732de634862b3a
Author: Peter Zijlstra <peterz@infradead.org>
Date: Tue Jan 17 11:26:29 2023 +0100
cpuidle, arm64: Fix the ARM64 cpuidle logic
The recent cpuidle changes started triggering RCU splats on
Juno development boards:
| =============================
| WARNING: suspicious RCU usage
| -----------------------------
| include/trace/events/ipi.h:19 suspicious rcu_dereference_check() usage!
Fix cpuidle on ARM64:
- ... by introducing a new 'is_rcu' flag to the cpuidle helpers & make
ARM64 use it, as ARM64 wants to keep RCU active longer and wants to
do the ct_cpuidle_enter()/exit() dance itself.
- Also update the PSCI driver accordingly.
- This also removes the last known RCU_NONIDLE() user as a bonus.
Reported-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Sudeep Holla <sudeep.holla@arm.com>
Tested-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Link: https://lore.kernel.org/r/Y8Z31UbzG3LJgAXE@hirez.programming.kicks-ass.net
--
diff --git a/arch/arm64/kernel/cpuidle.c b/arch/arm64/kernel/cpuidle.c
index 41974a1a229a..42e19fff40ee 100644
--- a/arch/arm64/kernel/cpuidle.c
+++ b/arch/arm64/kernel/cpuidle.c
@@ -67,10 +67,10 @@ __cpuidle int acpi_processor_ffh_lpi_enter(struct acpi_lpi_state *lpi)
u32 state = lpi->address;
if (ARM64_LPI_IS_RETENTION_STATE(lpi->arch_flags))
- return CPU_PM_CPU_IDLE_ENTER_RETENTION_PARAM(psci_cpu_suspend_enter,
+ return CPU_PM_CPU_IDLE_ENTER_RETENTION_PARAM_RCU(psci_cpu_suspend_enter,
lpi->index, state);
else
- return CPU_PM_CPU_IDLE_ENTER_PARAM(psci_cpu_suspend_enter,
+ return CPU_PM_CPU_IDLE_ENTER_PARAM_RCU(psci_cpu_suspend_enter,
lpi->index, state);
}
#endif
diff --git a/arch/arm64/kernel/suspend.c b/arch/arm64/kernel/suspend.c
index e7163f31f716..0fbdf5fe64d8 100644
--- a/arch/arm64/kernel/suspend.c
+++ b/arch/arm64/kernel/suspend.c
@@ -4,6 +4,7 @@
#include <linux/slab.h>
#include <linux/uaccess.h>
#include <linux/pgtable.h>
+#include <linux/cpuidle.h>
#include <asm/alternative.h>
#include <asm/cacheflush.h>
#include <asm/cpufeature.h>
@@ -104,6 +105,10 @@ int cpu_suspend(unsigned long arg, int (*fn)(unsigned long))
* From this point debug exceptions are disabled to prevent
* updates to mdscr register (saved and restored along with
* general purpose registers) from kernel debuggers.
+ *
+ * Strictly speaking the trace_hardirqs_off() here is superfluous,
+ * hardirqs should be firmly off by now. This really ought to use
+ * something like raw_local_daif_save().
*/
flags = local_daif_save();
@@ -120,6 +125,8 @@ int cpu_suspend(unsigned long arg, int (*fn)(unsigned long))
*/
arm_cpuidle_save_irq_context(&context);
+ ct_cpuidle_enter();
+
if (__cpu_suspend_enter(&state)) {
/* Call the suspend finisher */
ret = fn(arg);
@@ -133,8 +140,11 @@ int cpu_suspend(unsigned long arg, int (*fn)(unsigned long))
*/
if (!ret)
ret = -EOPNOTSUPP;
+
+ ct_cpuidle_exit();
} else {
- RCU_NONIDLE(__cpu_suspend_exit());
+ ct_cpuidle_exit();
+ __cpu_suspend_exit();
}
arm_cpuidle_restore_irq_context(&context);
diff --git a/drivers/cpuidle/cpuidle-psci.c b/drivers/cpuidle/cpuidle-psci.c
index 4fc4e0381944..312a34ef28dc 100644
--- a/drivers/cpuidle/cpuidle-psci.c
+++ b/drivers/cpuidle/cpuidle-psci.c
@@ -69,16 +69,12 @@ static __cpuidle int __psci_enter_domain_idle_state(struct cpuidle_device *dev,
else
pm_runtime_put_sync_suspend(pd_dev);
- ct_cpuidle_enter();
-
state = psci_get_domain_state();
if (!state)
state = states[idx];
ret = psci_cpu_suspend_enter(state) ? -1 : idx;
- ct_cpuidle_exit();
-
if (s2idle)
dev_pm_genpd_resume(pd_dev);
else
@@ -192,7 +188,7 @@ static __cpuidle int psci_enter_idle_state(struct cpuidle_device *dev,
{
u32 *state = __this_cpu_read(psci_cpuidle_data.psci_states);
- return CPU_PM_CPU_IDLE_ENTER_PARAM(psci_cpu_suspend_enter, idx, state[idx]);
+ return CPU_PM_CPU_IDLE_ENTER_PARAM_RCU(psci_cpu_suspend_enter, idx, state[idx]);
}
static const struct of_device_id psci_idle_state_match[] = {
diff --git a/drivers/firmware/psci/psci.c b/drivers/firmware/psci/psci.c
index e7bcfca4159f..f3a044fa4652 100644
--- a/drivers/firmware/psci/psci.c
+++ b/drivers/firmware/psci/psci.c
@@ -462,11 +462,22 @@ int psci_cpu_suspend_enter(u32 state)
if (!psci_power_state_loses_context(state)) {
struct arm_cpuidle_irq_context context;
+ ct_cpuidle_enter();
arm_cpuidle_save_irq_context(&context);
ret = psci_ops.cpu_suspend(state, 0);
arm_cpuidle_restore_irq_context(&context);
+ ct_cpuidle_exit();
} else {
+ /*
+ * ARM64 cpu_suspend() wants to do ct_cpuidle_*() itself.
+ */
+ if (!IS_ENABLED(CONFIG_ARM64))
+ ct_cpuidle_enter();
+
ret = cpu_suspend(state, psci_suspend_finisher);
+
+ if (!IS_ENABLED(CONFIG_ARM64))
+ ct_cpuidle_exit();
}
return ret;
diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
index 630c879143c7..3183aeb7f5b4 100644
--- a/include/linux/cpuidle.h
+++ b/include/linux/cpuidle.h
@@ -307,7 +307,7 @@ extern s64 cpuidle_governor_latency_req(unsigned int cpu);
#define __CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, \
idx, \
state, \
- is_retention) \
+ is_retention, is_rcu) \
({ \
int __ret = 0; \
\
@@ -319,9 +319,11 @@ extern s64 cpuidle_governor_latency_req(unsigned int cpu);
if (!is_retention) \
__ret = cpu_pm_enter(); \
if (!__ret) { \
- ct_cpuidle_enter(); \
+ if (!is_rcu) \
+ ct_cpuidle_enter(); \
__ret = low_level_idle_enter(state); \
- ct_cpuidle_exit(); \
+ if (!is_rcu) \
+ ct_cpuidle_exit(); \
if (!is_retention) \
cpu_pm_exit(); \
} \
@@ -330,15 +332,21 @@ extern s64 cpuidle_governor_latency_req(unsigned int cpu);
})
#define CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx) \
- __CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx, idx, 0)
+ __CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx, idx, 0, 0)
#define CPU_PM_CPU_IDLE_ENTER_RETENTION(low_level_idle_enter, idx) \
- __CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx, idx, 1)
+ __CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx, idx, 1, 0)
#define CPU_PM_CPU_IDLE_ENTER_PARAM(low_level_idle_enter, idx, state) \
- __CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx, state, 0)
+ __CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx, state, 0, 0)
+
+#define CPU_PM_CPU_IDLE_ENTER_PARAM_RCU(low_level_idle_enter, idx, state) \
+ __CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx, state, 0, 1)
#define CPU_PM_CPU_IDLE_ENTER_RETENTION_PARAM(low_level_idle_enter, idx, state) \
- __CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx, state, 1)
+ __CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx, state, 1, 0)
+
+#define CPU_PM_CPU_IDLE_ENTER_RETENTION_PARAM_RCU(low_level_idle_enter, idx, state) \
+ __CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx, state, 1, 1)
#endif /* _LINUX_CPUIDLE_H */
]
|
| 16/2 |
2026/07/25 01:46 |
llm |
expert |
0m
Model:
Tokens:
input: 20564
output: 61
thoughts: 402
Thoughts: **Analyzing the CPU Suspend and RCU Interactions**
Okay, so this commit `19235e472798` on ARM64 introduced calls to `ct_cpuidle_enter()` and `ct_cpuidle_exit()` within `cpu_suspend()`. The commit message explains this is to manage RCU more actively on ARM64. But `cpu_suspend` is used for both CPU idle and system suspend, which makes me think there might be a problem.
I see that using `cpu_suspend` for system suspend triggers a warning, specifically: `WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));`. This is because during system suspend, the current task isn't the idle task, and that seems to trip up the debugging code with `CONFIG_RCU_EQS_DEBUG` enabled.
My initial thought is, "Is this a real issue?". It looks like it's just a warning. This debug warning is there to catch when RCU gets put into EQS from a non-idle task. In most cases, it signifies a problem, as it's typically the idle task (or user mode) that should be in EQS. However, during system suspend, the CPU is either going offline or entering a deeper sleep state. So it's perfectly acceptable for RCU to be in EQS, even if the current task isn't the idle task.
Thinking a little more deeply, if RCU is in EQS, it means RCU isn't watching this particular CPU. And if the CPU then does something that requires RCU β an interrupt, or calls RCU functions β that *would* be a bug. But, during system suspend, interrupts are disabled with `local_daif_save()`, and the CPU is about to be put to sleep. Therefore, RCU not watching this CPU at this point is completely fine. This suggests the warning is overly strict and overly conservative in its assumption that only the idle task can correctly enter EQS.
So, the warning is likely harmless but annoying. I should probably look to see if there's been any attempt to resolve this warning in the current codebase. I want to see if a fix has been attempted.
|
| 17/2 |
2026/07/25 01:46 |
tool |
git-log |
0m
Args: map[CodeRegexp:ct_cpuidle_enter Count:10 MessageRegexps:[suspend RCU] PathPrefix:arch/arm64/kernel/suspend.c]
Results:
|
| 18/2 |
2026/07/25 01:46 |
llm |
expert |
0m
Model:
Tokens:
input: 21530
output: 32
thoughts: 19
Thoughts: Okay, here's my interpretation of that thought process, tailored for an expert audience, and written in the first person:
**Investigating Potential Kernel Suspend/Resume Issues Related to `ct_kernel_exit`**
Alright, I'm thinking I need to zero in on some potential issues related to the interaction between the `ct_kernel_exit` function and system suspend/resume. Given what I know about the typical challenges with context teardown and power management, that combination has some serious potential for causing problems. My initial approach is going to be a targeted code search. I'll start by searching the commit history for any instances where `ct_kernel_exit` and "suspend" (or related terms like "resume," "hibernation," or "power management") are mentioned together. This should quickly highlight commits that specifically addressed potential race conditions, incorrect state handling, or unexpected behaviors in that area. This targeted approach is much more efficient than a broad search, and will let me focus my attention on code that's already known to be relevant, so I can save my time for the next investigation.
|
| 19/2 |
2026/07/25 01:46 |
tool |
git-log |
0m
Args: map[Count:10 MessageRegexps:[ct_kernel_exit suspend]]
Results:
|
| 20/2 |
2026/07/25 01:47 |
llm |
expert |
0m
Model:
Tokens:
input: 21825
output: 32
thoughts: 19
Thoughts: Okay, here's my take on those thoughts, framed as an expert's internal monologue:
**Investigating Potential Idle Task Suspend Issues**
Alright, time to dig into this potential issue. The initial hunch is there might be some interplay between `is_idle_task` and the `suspend` mechanisms. So, my immediate thought is to start with a targeted search. I need to zero in on commits where both of these keywords are present. This should help me identify code changes that directly touch this area. I'm expecting to find modifications related to task scheduling, power management, or possibly even race conditions that could occur when suspending an idle task. This search is a crucial first step to understand the context of the problem and to quickly narrow down the relevant code changes I need to scrutinize. I'm hoping it'll highlight any recent alterations that could have introduced a regression, or changes intended to mitigate existing bugs related to the interaction between idle tasks and the power management system. Let's see what the commit history reveals.
|
| 21/2 |
2026/07/25 01:47 |
tool |
git-log |
0m
Args: map[Count:10 MessageRegexps:[is_idle_task suspend]]
Results:
|
| 22/2 |
2026/07/25 01:47 |
llm |
expert |
0m
Model:
Tokens:
input: 22104
output: 30
thoughts: 17
Thoughts: Okay, here's my interpretation of that thought process, tailored for an expert audience, and presented as if it's coming from me:
**Diving into Context Tracking and Suspend**
Alright, time to dig into this. I'm thinking, let's zero in on some key areas where things might be getting hairy. The goal here is likely to understand a specific issue, perhaps a regression, performance bottleneck, or unexpected behavior related to context tracking or the suspend/resume cycle. So, my initial thought is, "Let's use the commit history as a starting point." I need to find the specific changes related to `context_tracking` and `suspend` as these are complex systems and likely interacting. The logic is, by filtering commits that touch both, I should quickly narrow down the most relevant modifications. I'm not looking for a needle in a haystack, I need a good starting point. This search will help refine my understanding of the problem space quickly, allowing me to focus on the most probable causes. It's a pragmatic and efficient approach for this stage of the investigation. Let's see what we can find.
|
| 23/2 |
2026/07/25 01:47 |
tool |
git-log |
0m
Args: map[Count:10 MessageRegexps:[context_tracking suspend]]
Results:
|
| 24/2 |
2026/07/25 01:47 |
llm |
expert |
0m
Model:
Tokens:
input: 22402
output: 34
thoughts: 21
Thoughts: Okay, here's my summary, presented as a stream of thought:
**Diving into the RCU Suspend Interaction**
Alright, time to dig in. My objective is clear: I need to understand the interplay between `RCU_EQS_DEBUG` and suspend/resume operations. Specifically, I need to see how they're related in the commit history. That means searching for commits where *both* keywords, `RCU_EQS_DEBUG` and `suspend`, are mentioned. I'm looking for evidence of interactions, potential debugging efforts, or maybe even fixes related to this specific area of the kernel. This search will be the foundation to allow me to form a hypothesis of the current state of interactions between these features and, if necessary, identify next steps in debugging.
|
| 25/2 |
2026/07/25 01:47 |
tool |
git-log |
0m
Args: map[Count:10 MessageRegexps:[RCU_EQS_DEBUG suspend]]
Results:
|
| 26/2 |
2026/07/25 01:48 |
llm |
expert |
0m
Model:
Tokens:
input: 22636
output: 47
thoughts: 31
Thoughts: Okay, here's my take on those thoughts, framed as an expert's internal monologue:
**Investigating Potential Context Tracking and Suspend Issues**
Alright, time to dive in. My initial thought is to narrow the search. Context tracking, that's definitely an area with potential gotchas, especially on ARM64. So, I'm thinking, let's start with `kernel/context_tracking.c`. That's a good place to start digging into core context switching logic, potential race conditions, or performance bottlenecks, all of which could manifest as suspend/resume problems. My instincts tell me we should also look at the architecture-specific side of things, particularly around power management. The suspend logic is intricate, so I'll also search in `arch/arm64/kernel/suspend.c`. This is where the hardware-level state is saved and restored, and that's often the root of the trickier issues. I'll need to look at commit histories to see how context tracking and suspend have evolved on arm64 in these files.
|
| 27/2 |
2026/07/25 01:48 |
tool |
git-log |
0m
Args: map[Count:10 MessageRegexps:[RCU suspend] PathPrefix:arch/arm64/kernel/suspend.c]
Results: map[Output:a2c42bbabbe2 arm64: spectre: Prevent lockdep splat on v4 mitigation enable path
]
|
| 28/2 |
2026/07/25 01:48 |
llm |
expert |
0m
Model:
Tokens:
input: 22979
output: 28
thoughts: 21
Thoughts: Here's my thought process, as if I were considering this myself:
**Investigating Context Tracking Warnings**
Okay, so we've got a potential issue flagged related to context tracking, and I need to figure out the history of the warning. My immediate instinct is to dive into the code itself. Since the warning is in `kernel/context_tracking.c`, that's where I need to start. The quickest way to get a handle on what might have changed recently is to look at the commit history directly. I want to see which commits touch that specific file (`kernel/context_tracking.c`) and, more importantly, *modify* something related to the warning itself. So, I need to focus my search on changes that could affect the warning's logic, its triggering conditions, or the text of the warning message. I'll need to define a search strategy that focuses on commits that modify the code to narrow my investigation.
|
| 29/2 |
2026/07/25 01:48 |
tool |
git-log |
0m
Args: map[Count:10 PathPrefix:kernel/context_tracking.c]
Results: map[Output:46e323599911 context_tracking: Remove rcu_task_trace_heavyweight_{enter,exit}()
59bed79ffdbc context_tracking: Make RCU watch ct_kernel_exit_state() warning
4f336dc07ece context_tracking, rcu: Rename rcu_dyntick trace event into rcu_watching
fda70207135b context_tracking, rcu: Rename rcu_dynticks_curr_cpu_in_eqs() into rcu_is_watching_curr_cpu()
b1b91fd1bece context_tracking, rcu: Rename rcu_dynticks_task*() into rcu_task*()
e1de43833622 context_tracking, rcu: Rename DYNTICK_IRQ_NONIDLE into CT_NESTING_IRQ_NONIDLE
8375cb260d7e context_tracking, rcu: Rename ct_dynticks_nmi_nesting() into ct_nmi_nesting()
dc5fface4b30 context_tracking, rcu: Rename struct context_tracking .dynticks_nmi_nesting into .nmi_nesting
1089c0078b69 context_tracking, rcu: Rename ct_dynticks_nesting() into ct_nesting()
bf66471987b4 context_tracking, rcu: Rename struct context_tracking .dynticks_nesting into .nesting
]
|
| 30/2 |
2026/07/25 01:48 |
llm |
expert |
0m
Model:
Tokens:
input: 23597
output: 30
thoughts: 372
Thoughts: **Analyzing a Kernel Warning During System Suspend**
Okay, let's break this down. I'm looking at a warning in `kernel/context_tracking.c`: `WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));`. Right, so this triggers when `CONFIG_RCU_EQS_DEBUG` is on, and the context isn't user space *and* it's not the idle task. Hmm, that rings a bell. Turns out this happens during system suspend on arm64. Specifically, `cpu_suspend` calls `ct_cpuidle_enter()`, which in turn leads to `ct_kernel_exit(false, ...)`. This happens from the task that *initiated* the suspend β the one writing to `/sys/power/state`, for example.
The immediate question is, is this a security issue? No, thankfully, it's just a warning. We're not talking about memory corruption, leaks, or privilege escalation. Okay, good.
Does it present a denial-of-service vulnerability? Well, in production builds, we typically disable `CONFIG_RCU_EQS_DEBUG`, so it's not a concern there. But let's confirm that. I'm assuming that debug options like `CONFIG_RCU_EQS_DEBUG` are not enabled in production builds. And even *if* it somehow *was* enabled, it's a `WARN_ON_ONCE`. It just prints a warning and keeps going. It *doesn't* stop the kernel unless we're talking about a debug/testing environment with `panic_on_warn` enabled, which is unlikely. So, no, not a denial-of-service issue.
And finally, is it accessible from unprivileged processes? The trigger is writing to `/sys/power/state`. So, the answer is, it likely depends on the permissions of `/sys/power/state`. I need to check those.
|
| 31/2 |
2026/07/25 01:48 |
tool |
grepper |
0m
Error:
Args: map[Expression:power/state PathPrefix:kernel/power/main.c]
Results:
|
| 32/2 |
2026/07/25 01:48 |
llm |
expert |
0m
Model:
Tokens:
input: 24452
output: 30
thoughts: 15
Thoughts: Here's a summary of my thought process:
**Investigating `/sys/power/state` Creation**
Okay, so I need to figure out the genesis of `/sys/power/state`. It's a critical file in the power management system, and understanding its creation is essential for debugging or modifying power-related behaviors. My initial approach is to trace its origin β to pinpoint where in the kernel it's brought into existence. I need to understand the underlying mechanisms. I am going to have to dive into the kernel source to find it.
|
| 33/2 |
2026/07/25 01:48 |
tool |
grepper |
0m
Error:
Args: map[Expression:"state" PathPrefix:kernel/power/main.c]
Results:
|
| 34/2 |
2026/07/25 01:48 |
llm |
expert |
0m
Model:
Tokens:
input: 24626
output: 35
thoughts: 18
Thoughts: Here's my thought process, as it stands:
**Navigating the Power Management Labyrinth**
Okay, so I'm diving into the kernel's power management aspects, and the first place I'm instinctively drawn to is `kernel/power/main.c`. That's where I expect to find the central handling of sysfs attributes related to power. I know from experience that this file is often the nexus for exposing controls and status information to userspace. I'm thinking I should start digging around in there for the typical sysfs entry points. I know I will be looking for the structure definitions, and associated handlers.
|
| 35/2 |
2026/07/25 01:48 |
tool |
read-file |
0m
Args: map[File:kernel/power/main.c FirstLine:800 LineCount:50]
Results: map[Contents: 800: const char *buf, size_t n)
801: {
802: suspend_state_t state;
803: int error;
804:
805: error = pm_autosleep_lock();
806: if (error)
807: return error;
808:
809: if (pm_autosleep_state() > PM_SUSPEND_ON) {
810: error = -EBUSY;
811: goto out;
812: }
813:
814: state = decode_state(buf, n);
815: if (state < PM_SUSPEND_MAX) {
816: if (state == PM_SUSPEND_MEM)
817: state = mem_sleep_current;
818:
819: error = pm_suspend(state);
820: } else if (state == PM_SUSPEND_MAX) {
821: error = hibernate();
822: } else {
823: error = -EINVAL;
824: }
825:
826: out:
827: pm_autosleep_unlock();
828: return error ? error : n;
829: }
830:
831: power_attr(state);
832:
833: #ifdef CONFIG_PM_SLEEP
834: /*
835: * The 'wakeup_count' attribute, along with the functions defined in
836: * drivers/base/power/wakeup.c, provides a means by which wakeup events can be
837: * handled in a non-racy way.
838: *
839: * If a wakeup event occurs when the system is in a sleep state, it simply is
840: * woken up. In turn, if an event that would wake the system up from a sleep
841: * state occurs when it is undergoing a transition to that sleep state, the
842: * transition should be aborted. Moreover, if such an event occurs when the
843: * system is in the working state, an attempt to start a transition to the
844: * given sleep state should fail during certain period after the detection of
845: * the event. Using the 'state' attribute alone is not sufficient to satisfy
846: * these requirements, because a wakeup event may occur exactly when 'state'
847: * is being written to and may be delivered to user space right before it is
848: * frozen, so the event will remain only partially processed until the system is
849: * woken up by another event. In particular, it won't cause the transition to
]
|
| 36/2 |
2026/07/25 01:48 |
llm |
expert |
0m
Model:
Tokens:
input: 25579
output: 31
thoughts: 28
Thoughts: Okay, here's my interpretation of that thought process, tailored for an expert audience, and written in the first person:
**Initial Attribute Creation**
Alright, so `power_attr(state);` is the key line here. My first thought is, "Right, that's the creation of a new attribute." It's likely constructing this attribute and associating it with the `state` object. I'm immediately picturing the underlying data structure, and what implications this has for memory management and potential conflicts if the state object already has an attribute with the same name.
My mind quickly jumps to the definition of `power_attr`. I need to understand what this function is actually *doing* under the hood. Is it dynamically allocating memory? Is it setting metadata? How are name collisions handled? Is it safe from concurrent access if `state` is shared across threads? Understanding that definition is going to dictate how I approach the rest of this system. I want to see how the attribute is being defined, which is vital.
|
| 37/2 |
2026/07/25 01:48 |
tool |
grepper |
0m
Args: map[Expression:define power_attr PathPrefix:kernel/power/power.h]
Results: map[Output:kernel/power/power.h=86=static inline bool hibernation_in_progress(void) { return false; }
--
kernel/power/power.h-88-
kernel/power/power.h:89:#define power_attr(_name) \
kernel/power/power.h-90-static struct kobj_attribute _name##_attr = { \
--
kernel/power/power.h-98-
kernel/power/power.h:99:#define power_attr_ro(_name) \
kernel/power/power.h-100-static struct kobj_attribute _name##_attr = { \
]
|
| 38/2 |
2026/07/25 01:48 |
llm |
expert |
0m
Model:
Tokens:
input: 26016
output: 34
thoughts: 19
Thoughts: Here's a summary of my thought process, as if I were the one thinking it:
**Diving into the Power Subsystem**
Alright, time to get my hands dirty with some power management code. I need to understand how this particular feature is implemented. Let's see... I'm thinking I should start digging into the core definitions. Let me take a look at `kernel/power/power.h` and see what's defined around line 89. That's usually a good starting point for exploring the power subsystem's fundamental structures or perhaps a key macro or enum. From there, I can start mapping out how this piece fits into the bigger picture. Hopefully, this section will point me in the direction of the relevant data structures or function prototypes I'm looking for. Let's see what's there...
|
| 39/2 |
2026/07/25 01:48 |
tool |
read-file |
0m
Args: map[File:kernel/power/power.h FirstLine:85 LineCount:20]
Results: map[Contents: 85:
86: static inline bool hibernation_in_progress(void) { return false; }
87: #endif /* !CONFIG_HIBERNATION */
88:
89: #define power_attr(_name) \
90: static struct kobj_attribute _name##_attr = { \
91: .attr = { \
92: .name = __stringify(_name), \
93: .mode = 0644, \
94: }, \
95: .show = _name##_show, \
96: .store = _name##_store, \
97: }
98:
99: #define power_attr_ro(_name) \
100: static struct kobj_attribute _name##_attr = { \
101: .attr = { \
102: .name = __stringify(_name), \
103: .mode = S_IRUGO, \
104: }, \
]
|
| 40/2 |
2026/07/25 01:48 |
llm |
expert |
0m
Model:
Tokens:
input: 26546
output: 34
thoughts: 617
Thoughts: **Analyzing the Reproducer and Sysfs Permissions**
Okay, so the mode is `0644`, meaning read access for everyone but only root can write. The reproducer runs as root, or at least in a user namespace where it *appears* as root. That's a key detail. The reproducer mounts `sysfs` in a new mount namespace, which is possible if it's in a new user namespace. Let's dig into the reproducer code itself to confirm what's happening.
Okay, I see the calls to `mkdirat`, `mount`, `openat`, and `write`. The question is, if it mounts `sysfs` within a user namespace, does it actually have write access to `/sys/power/state`? This is the core of the issue.
Let me think⦠sysfs files are owned by the global root (UID 0 in `init_user_ns`). If a process is within a user namespace, its UID 0 is mapped to a non-zero UID in the `init_user_ns`. So, even if the reproducer "thinks" it's root, when it mounts sysfs, the files *still* have the global root as owner. Therefore, a process in a user namespace shouldn't be able to write to `/sys/power/state` unless it's got *global* root privileges.
Hold on, syzkaller, the fuzzer, runs reproducers in a sandbox, right? Sometimes it uses `sandbox=none`, where it runs as root. Let me check the bug report⦠Ah, it says `UID: 0`. That confirms it's running as root, and in that configuration, it can write to this sysfs path.
If global root is required to write to `/sys/power/state`, then it's effectively inaccessible from unprivileged processes or within standard user namespaces, meaning the bug will be restricted to the "none" sandbox scenario. That's good to know, and the bug will be difficult to trigger. Let's verify sysfs behavior. I'm going to look at `fs/sysfs/mount.c`. The files are typically owned by `GLOBAL_ROOT_UID` and `GLOBAL_ROOT_GID`, as I suspected. This helps confirm the restrictions in place on a standard sysfs mount.
|
| 41/2 |
2026/07/25 01:48 |
tool |
read-file |
0m
Args: map[File:fs/sysfs/mount.c FirstLine:1 LineCount:50]
Results: map[Contents: 1: // SPDX-License-Identifier: GPL-2.0
2: /*
3: * fs/sysfs/symlink.c - operations for initializing and mounting sysfs
4: *
5: * Copyright (c) 2001-3 Patrick Mochel
6: * Copyright (c) 2007 SUSE Linux Products GmbH
7: * Copyright (c) 2007 Tejun Heo <teheo@suse.de>
8: *
9: * Please see Documentation/filesystems/sysfs.rst for more information.
10: */
11:
12: #include <linux/fs.h>
13: #include <linux/magic.h>
14: #include <linux/mount.h>
15: #include <linux/init.h>
16: #include <linux/slab.h>
17: #include <linux/user_namespace.h>
18: #include <linux/fs_context.h>
19: #include <net/net_namespace.h>
20:
21: #include "sysfs.h"
22:
23: static struct kernfs_root *sysfs_root;
24: struct kernfs_node *sysfs_root_kn;
25:
26: static void sysfs_fs_context_free(struct fs_context *fc)
27: {
28: struct kernfs_fs_context *kfc = fc->fs_private;
29:
30: if (kfc->ns_tag)
31: kobj_ns_drop(KOBJ_NS_TYPE_NET, kfc->ns_tag);
32: kernfs_free_fs_context(fc);
33: kfree(kfc);
34: }
35:
36: static const struct fs_context_operations sysfs_fs_context_ops = {
37: .free = sysfs_fs_context_free,
38: .get_tree = kernfs_get_tree,
39: };
40:
41: static int sysfs_init_fs_context(struct fs_context *fc)
42: {
43: struct kernfs_fs_context *kfc;
44: struct ns_common *ns;
45:
46: if (!(fc->sb_flags & SB_KERNMOUNT)) {
47: if (!kobj_ns_current_may_mount(KOBJ_NS_TYPE_NET))
48: return -EPERM;
49: }
50:
]
|
| 42/2 |
2026/07/25 01:48 |
llm |
expert |
0m
Model:
Tokens:
input: 28425
output: 42
thoughts: 16
Thoughts: Okay, here's my attempt at summarizing that thought process, keeping in mind I'm speaking to a fellow expert:
**Investigating `kobj_ns_current_may_mount`**
Alright, time to dive into this. The initial thought is to take a look at `kobj_ns_current_may_mount`. It's a key function in namespace management, and given the context I'm dealing with, it's a logical starting point. I need to refresh my understanding of its specific purpose and how it interacts with the broader kernel architecture. Perhaps there's an issue with how this function is used or what itβs evaluating that is contributing to the current problem. My initial assessment is it is likely involved in authorization and permissions when mounting something, so I'm going to dig into the details to understand itβs role.
|
| 43/2 |
2026/07/25 01:48 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/sysfs/mount.c Name:kobj_ns_current_may_mount]
Results: map[SourceCode:1074: bool kobj_ns_current_may_mount(enum kobj_ns_type type)
1075: {
1076: bool may_mount = true;
1077:
1078: spin_lock(&kobj_ns_type_lock);
1079: if (kobj_ns_type_is_valid(type) && kobj_ns_ops_tbl[type])
1080: may_mount = kobj_ns_ops_tbl[type]->current_may_mount();
1081: spin_unlock(&kobj_ns_type_lock);
1082:
1083: return may_mount;
1084: }
SourceFile:lib/kobject.c]
|
| 44/2 |
2026/07/25 01:48 |
llm |
expert |
0m
Model:
Tokens:
input: 28878
output: 40
thoughts: 28
Thoughts: Here's my take on the thought process, as if it were my own:
**Analyzing Namespace Mounting Restrictions**
Okay, so I'm digging into this kernel code and need to clarify the mounting permissions within different namespaces. Specifically, I'm focusing on the `KOBJ_NS_TYPE_NET` namespace type. I need to figure out what controls whether a mount operation is allowed. The key is to find out what function, if any, is used in that specific case.
It looks like the `current_may_mount` variable is the one to inspect. I need to understand what function is assigned to `current_may_mount` specifically when the namespace type is `KOBJ_NS_TYPE_NET`. Then I need to confirm whether `net_ns_may_mount` is the function that controls whether mount operations are allowed. If the assignment is `net_ns_may_mount`, then the allowed operations within the network namespace will be performed by that function.
|
| 45/2 |
2026/07/25 01:48 |
tool |
codesearch-definition-source |
0m
Error:
Args: map[ContextFile:net/core/net_namespace.c Name:net_ns_may_mount]
Results: map[SourceCode: SourceFile:]
|
| 46/2 |
2026/07/25 01:48 |
llm |
expert |
0m
Model:
Tokens:
input: 29174
output: 27
thoughts: 12
Thoughts: Here's my take on those thoughts:
**Analyzing the Search Query: `current_may_mount`**
Okay, so the prompt is just "Let's grep for `current_may_mount`". My immediate thought is, "What's the context here?" My expertise would have me immediately wondering about the system in question. Is this about filesystems? Kernel modules? Network mounts? What system am I working with?
Regardless, the implied action is clear: use the `grep` utility to search for the string "current_may_mount". This suggests we're probably looking through source code, configuration files, or system logs. The target is likely a codebase or set of configuration files where such a string might indicate the current status of something that *may* be mounted. The focus on `may_mount` suggests we are dealing with some condition or check pertaining to mount operations, potentially in a system that performs dynamic mounting, or has some level of user control over mounts. My experience tells me that such a string is highly specific and likely a good indicator to focus on. My mental file tree is starting to organize potential areas to investigate -- kernel internals, init scripts, or perhaps a filesystem management daemon. I'll need to run the `grep` command, analyze the output, and go from there. This is a solid starting point for a deeper investigation.
|
| 47/2 |
2026/07/25 01:48 |
tool |
grepper |
0m
Args: map[Expression:current_may_mount PathPrefix:net/]
Results: map[Output:net/core/net-sysfs.c=2139=static void remove_queue_kobjects(struct net_device *dev)
--
net/core/net-sysfs.c-2159-
net/core/net-sysfs.c:2160:static bool net_current_may_mount(void)
net/core/net-sysfs.c-2161-{
--
net/core/net-sysfs.c=2187=const struct kobj_ns_type_operations net_ns_type_operations = {
net/core/net-sysfs.c-2188- .type = KOBJ_NS_TYPE_NET,
net/core/net-sysfs.c:2189: .current_may_mount = net_current_may_mount,
net/core/net-sysfs.c-2190- .grab_current_ns = net_grab_current_ns,
]
|
| 48/2 |
2026/07/25 01:48 |
llm |
expert |
0m
Model:
Tokens:
input: 29743
output: 41
thoughts: 14
Thoughts: Okay, let's dive into this. Here's my take on those thoughts, as if they're my own:
**Analyzing `net_current_may_mount`**
Alright, let's focus on `net_current_may_mount`. Immediately, my brain starts to parse that name. "Net" suggests something related to networking, of course. "Current" implies a contextual aspect, likely referring to the present state or a specific network interface. And "may_mount"... that's the key. That implies this function is involved in determining whether or not a network resource is *allowed* to be mounted, or perhaps even actively attempting a mount operation.
My initial hypothesis is that this is a critical gatekeeper function. Itβs likely checking various conditions β perhaps security constraints, resource availability, network reachability, and maybe even user permissions β before permitting a network share or filesystem to be mounted. I'd need to dig into the surrounding code to understand the specific context, but that's my working theory based on the function name alone. Now, letβs see what we can find out... what questions do I have?
|
| 49/2 |
2026/07/25 01:48 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/core/net-sysfs.c Name:net_current_may_mount]
Results: map[SourceCode:2160: static bool net_current_may_mount(void)
2161: {
2162: struct net *net = current->nsproxy->net_ns;
2163:
2164: return ns_capable(net->user_ns, CAP_SYS_ADMIN);
2165: }
SourceFile:net/core/net-sysfs.c]
|
| 50/2 |
2026/07/25 01:48 |
llm |
expert |
0m
Model:
Tokens:
input: 30159
output: 38
thoughts: 114
Thoughts: **Examining Sysfs Mounting and Ownership**
Okay, so I'm digging into `sysfs` and how its mount behavior interacts with user namespaces, specifically considering potential security implications. It seems clear that a process needs `CAP_SYS_ADMIN` within the network namespace's user namespace to mount `sysfs`, which is expected. But this raises a crucial question: What about the ownership of the files created within `sysfs` after the mount?
My understanding is that when `sysfs` is mounted, the files that get created end up with ownership set to `GLOBAL_ROOT_UID` and `GLOBAL_ROOT_GID`, which is the default. This is problematic, if not correctly handled.
This is where things get interesting, because, as far as I can tell, the files are *not* automatically translated based on the user namespace, like we see in `userns` mounts. However, `sysfs` doesn't currently support ID-mapped mounts or user namespace-based ownership. We're essentially stuck with the global root. I need to understand how ownership is handled at a more granular level. Let's see how `kernfs_node` ownership is managed, to clarify the mechanisms here.
|
| 51/2 |
2026/07/25 01:49 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/kernfs/inode.c Name:kernfs_init_inode]
Results: map[SourceCode: 200: static void kernfs_init_inode(struct kernfs_node *kn, struct inode *inode)
201: {
202: kernfs_get(kn);
203: inode->i_private = kn;
204: inode->i_mapping->a_ops = &ram_aops;
205: inode->i_op = &kernfs_iops;
206: inode->i_generation = kernfs_gen(kn);
207:
208: set_default_inode_attr(inode, kn->mode);
209: kernfs_refresh_inode(kn, inode);
210:
211: /* initialize inode according to type */
212: switch (kernfs_type(kn)) {
213: case KERNFS_DIR:
214: inode->i_op = &kernfs_dir_iops;
215: inode->i_fop = &kernfs_dir_fops;
216: if (kn->flags & KERNFS_EMPTY_DIR)
217: make_empty_dir_inode(inode);
218: break;
219: case KERNFS_FILE:
220: inode->i_size = kn->attr.size;
221: inode->i_fop = &kernfs_file_fops;
222: break;
223: case KERNFS_LINK:
224: inode->i_op = &kernfs_symlink_iops;
225: break;
226: default:
227: BUG();
228: }
229:
230: unlock_new_inode(inode);
231: }
SourceFile:fs/kernfs/inode.c]
|
| 52/2 |
2026/07/25 01:49 |
llm |
expert |
0m
Model:
Tokens:
input: 31084
output: 38
thoughts: 12
Thoughts: Okay, let's dive into this. Here's my thought process on checking `kernfs_refresh_inode`, assuming I'm already well-versed in kernel file systems:
**Initial Thoughts on `kernfs_refresh_inode`**
Alright, `kernfs_refresh_inode`. That function's definitely a crucial piece in the kernfs puzzle, probably related to keeping inode metadata synchronized, especially after changes external to the kernfs structure itself. My immediate questions are: What triggers this refresh? Is it called proactively, or reactively? What sources of data are used to refresh the inode? Is it tied to something like sysfs? And, more importantly, are there any potential race conditions that jump out from the function name alone? My experience suggests this could be a point of performance bottleneck or subtle data corruption issues if not implemented correctly. I'll need to look at its call sites and internal workings to verify those assumptions. Okay, I'm ready. Let's dig in.
|
| 53/2 |
2026/07/25 01:49 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/kernfs/inode.c Name:kernfs_refresh_inode]
Results: map[SourceCode: 167: static void kernfs_refresh_inode(struct kernfs_node *kn, struct inode *inode)
168: {
169: struct kernfs_iattrs *attrs;
170:
171: inode->i_mode = kn->mode;
172: attrs = kernfs_iattrs_noalloc(kn);
173: if (attrs)
174: /*
175: * kernfs_node has non-default attributes get them from
176: * persistent copy in kernfs_node.
177: */
178: set_inode_attr(inode, attrs);
179:
180: if (kernfs_type(kn) == KERNFS_DIR && !(kn->flags & KERNFS_REMOVING))
181: set_nlink(inode, kn->dir.subdirs + 2);
182: }
SourceFile:fs/kernfs/inode.c]
|
| 54/2 |
2026/07/25 01:49 |
llm |
expert |
0m
Model:
Tokens:
input: 31625
output: 39
thoughts: 13
Thoughts: Okay, let's dive into this. Here's my thought process on checking `set_default_inode_attr`:
**Checking `set_default_inode_attr`**
Alright, so the task at hand is to analyze or work with `set_default_inode_attr`. My initial thought is to figure out the *context* here. Why are we looking at this function? What's the problem or the objective? Is it a debugging session, performance analysis, security audit, or something else entirely? Knowing the bigger picture will help me determine the most effective approach.
Next, I need to remind myself of the fundamental purpose of `set_default_inode_attr`. It's likely involved in setting default attributes or properties for an inode, right? That could be when creating a new file, directory, or other filesystem object. I need to refresh my memory on the data structures involved, like the `inode` itself, and any related structures such as the filesystem specific data.
I'll start by tracing the function's usage. Where is it called from? What's calling it? Is it within the VFS layer, a specific filesystem implementation, or somewhere else? I'll look at the call stack to see where the call originates and gain insight into its purpose. If I'm lucky, there will be comments that help explain what is going on.
Once I've got the surrounding code, I'll examine the function's implementation itself. What parameters does it take? What does it do with those parameters? Does it modify any global data or structures? Are there any potential race conditions or concurrency issues? I'll look for any potential bottlenecks or areas that need further optimization.
Finally, I'll need to consider any potential interactions this function might have with other parts of the filesystem. For instance, how does it interact with the allocation of disk blocks, the setting of permissions, or the handling of extended attributes? Understanding the interactions is critical for the overall health of the filesystem. I should also check the error handling; are there sufficient checks and graceful error conditions? This is all pretty standard operating procedure, but the devil is always in the details!
|
| 55/2 |
2026/07/25 01:49 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/kernfs/inode.c Name:set_default_inode_attr]
Results: map[SourceCode: 151: static inline void set_default_inode_attr(struct inode *inode, umode_t mode)
152: {
153: inode->i_mode = mode;
154: simple_inode_init_ts(inode);
155: }
SourceFile:fs/kernfs/inode.c]
|
| 56/2 |
2026/07/25 01:49 |
llm |
expert |
0m
Model:
Tokens:
input: 32239
output: 34
thoughts: 93
Thoughts: **Tracing the Origin of `i_uid` and `i_gid`**
Okay, so I'm trying to figure out where the user and group IDs, `i_uid` and `i_gid`, are actually initialized for inodes. This is a common point of confusion when digging into filesystem internals, so I need to nail this down. My initial thought was `new_inode` or perhaps `inode_init_always` β these are the likely candidates for inode setup. Let's see... is it `new_inode`? Nope, I seem to recall that one uses `current_fsuid()` and `current_fsgid()`. Wait, wasn't it `inode_init_always` that sets those values to zero? Right, I seem to remember that being the case. To confirm this, let me quickly double-check `fs/inode.c` and confirm exactly how `inode_init_always` works. Let's see if that clears it up.
|
| 57/2 |
2026/07/25 01:49 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/inode.c Name:inode_init_always]
Results: map[SourceCode:2943: static inline int inode_init_always(struct super_block *sb, struct inode *inode)
2944: {
2945: return inode_init_always_gfp(sb, inode, GFP_NOFS);
2946: }
SourceFile:include/linux/fs.h]
|
| 58/2 |
2026/07/25 01:49 |
llm |
expert |
0m
Model:
Tokens:
input: 32677
output: 37
thoughts: 14
Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience:
**Diving into `inode_init_always_gfp`**
Alright, let's take a closer look at `inode_init_always_gfp`. I need to understand its exact purpose and how it fits into the broader inode initialization scheme. My initial thought is it's likely a function dedicated to the initialization of inodes which are always allocated with a particular memory allocation flag, `GFP_...`. I'm especially interested in whether it handles any special cases or optimizations that aren't present in the more general inode initialization paths. I'll need to see if it's called during boot, or dynamically when resources are needed.
I'm thinking about the potential trade-offs here β performance vs. memory usage. If `inode_init_always_gfp` is optimized for a specific memory allocation policy, I'll want to quickly assess whether that policy is sensible in various kernel usage scenarios. I should consider how its used in conjunction with different filesystems. I'll probably also need to consider the broader context within the `inode` data structure initialization process, like where it fits within the context of other initialization functions. This is potentially interesting, but my overall goal is to understand how we can make things more efficient, or handle corner cases. So, what's its role, and how can we get rid of it.
|
| 59/2 |
2026/07/25 01:49 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/inode.c Name:inode_init_always_gfp]
Results: map[SourceCode: 213: /**
214: * inode_init_always_gfp - perform inode structure initialisation
215: * @sb: superblock inode belongs to
216: * @inode: inode to initialise
217: * @gfp: allocation flags
218: *
219: * These are initializations that need to be done on every inode
220: * allocation as the fields are not initialised by slab allocation.
221: * If there are additional allocations required @gfp is used.
222: */
223: int inode_init_always_gfp(struct super_block *sb, struct inode *inode, gfp_t gfp)
224: {
225: static const struct inode_operations empty_iops;
226: static const struct file_operations no_open_fops = {.open = no_open};
227: struct address_space *const mapping = &inode->i_data;
228:
229: inode->i_sb = sb;
230: inode->i_blkbits = sb->s_blocksize_bits;
231: inode->i_flags = 0;
232: inode_state_assign_raw(inode, 0);
233: atomic64_set(&inode->i_sequence, 0);
234: atomic_set(&inode->i_count, 1);
235: inode->i_op = &empty_iops;
236: inode->i_fop = &no_open_fops;
237: inode->i_ino = 0;
238: inode->__i_nlink = 1;
239: inode->i_opflags = 0;
240: if (sb->s_xattr)
241: inode->i_opflags |= IOP_XATTR;
242: if (sb->s_type->fs_flags & FS_MGTIME)
243: inode->i_opflags |= IOP_MGTIME;
244: i_uid_write(inode, 0);
245: i_gid_write(inode, 0);
246: atomic_set(&inode->i_writecount, 0);
247: inode->i_size = 0;
248: inode->i_write_hint = WRITE_LIFE_NOT_SET;
249: inode->i_blocks = 0;
250: inode->i_bytes = 0;
251: inode->i_generation = 0;
252: inode->i_pipe = NULL;
253: inode->i_cdev = NULL;
254: inode->i_link = NULL;
255: inode->i_dir_seq = 0;
256: inode->i_rdev = 0;
257: inode->dirtied_when = 0;
258:
259: #ifdef CONFIG_CGROUP_WRITEBACK
260: inode->i_wb_frn_winner = 0;
261: inode->i_wb_frn_avg_time = 0;
262: inode->i_wb_frn_history = 0;
263: #endif
264:
265: spin_lock_init(&inode->i_lock);
266: lockdep_set_class(&inode->i_lock, &sb->s_type->i_lock_key);
267:
268: init_rwsem(&inode->i_rwsem);
269: lockdep_set_class(&inode->i_rwsem, &sb->s_type->i_mutex_key);
270:
271: atomic_set(&inode->i_dio_count, 0);
272:
273: mapping->a_ops = &empty_aops;
274: mapping->host = inode;
275: mapping->flags = 0;
276: mapping->wb_err = 0;
277: atomic_set(&mapping->i_mmap_writable, 0);
278: mapping_set_gfp_mask(mapping, GFP_HIGHUSER_MOVABLE);
279: mapping->writeback_index = 0;
280: init_rwsem(&mapping->invalidate_lock);
281: lockdep_set_class_and_name(&mapping->invalidate_lock,
282: &sb->s_type->invalidate_lock_key,
283: "mapping.invalidate_lock");
284: if (sb->s_iflags & SB_I_STABLE_WRITES)
285: mapping_set_stable_writes(mapping);
286: inode->i_private = NULL;
287: inode->i_mapping = mapping;
288: INIT_HLIST_HEAD(&inode->i_dentry); /* buggered by rcu freeing */
289: #ifdef CONFIG_FS_POSIX_ACL
290: inode->i_acl = inode->i_default_acl = ACL_NOT_CACHED;
291: #endif
292:
293: #ifdef CONFIG_FSNOTIFY
294: inode->i_fsnotify_mask = 0;
295: #endif
296: inode->i_flctx = NULL;
297:
298: if (unlikely(security_inode_alloc(inode, gfp)))
299: return -ENOMEM;
300:
301: this_cpu_inc(nr_inodes);
302:
303: return 0;
304: }
SourceFile:fs/inode.c]
|
| 60/2 |
2026/07/25 01:49 |
llm |
expert |
0m
Model:
Tokens:
input: 34623
output: 33
thoughts: 706
Thoughts: **Analyzing Privilege Escalation via Sysfs and User Namespaces**
Okay, so I'm digging into this potential privilege escalation. Let's start with the basics: `/sys/power/state` is owned by root, specifically UID 0 and GID 0, thanks to `i_uid_write(inode, 0)` and `i_gid_write(inode, 0)`. The file's mode is `0644`, meaning only the owner can write to it.
Now, user namespaces complicate things. Inside a user namespace, the effective UID 0 is mapped to a non-zero UID in the initial user namespace. However, the `fsuid` of a process within a user namespace is mapped to *that namespace's* UID 0. The inode's UID remains the global root (0), and permission checks in `generic_permission` compare the inode's UID against the process's `fsuid`. Since they don't match (0 vs. the non-zero mapped UID), a process in an unprivileged user namespace *shouldn't* be able to write to `/sys/power/state`.
A caveat here: if a user namespace is created by root, and UID 0 maps to UID 0, it's effectively root. But for unprivileged namespaces, which is what we are focusing on, UID 0 *doesn't* map to 0.
Wait a second, can an unprivileged process *even mount* sysfs within a user namespace? It turns out it can if it has `CAP_SYS_ADMIN` in the network namespace's user namespace, and owns the network namespace. `net_current_may_mount` checks `ns_capable(net->user_ns, CAP_SYS_ADMIN)`. If an unprivileged user creates both a new user namespace and a new network namespace, *then* they can mount sysfs. However, even then, the files in sysfs are owned by the global root. So write access to `/sys/power/state` is still denied.
Let's verify this, I know Syzkaller should have root privileges, if it's running as root (UID 0 in `init_user_ns`) it can, of course, write to `/sys/power/state`. The bug report states `UID: 0`. Okay, so this bug requires global root privileges to trigger.
So, other methods of triggering system suspend? Possibly via `ioctl` on some device, or `rtc` wakealarms. But system suspend is, by its nature, a privileged operation.
Even if an unprivileged user could trigger this, the bug is a `WARN_ON_ONCE` within a debug option (`CONFIG_RCU_EQS_DEBUG`). It's not memory corruption, not an information leak, and not a denial of service (just a warning). The impact is exceedingly low.
Okay, now let's double-check if `CONFIG_RCU_EQS_DEBUG` is actually enabled in a production environment. It's usually disabled, so let's cross-reference that in `lib/Kconfig.debug`.
|
| 61/2 |
2026/07/25 01:49 |
tool |
read-file |
0m
Args: map[File:lib/Kconfig.debug FirstLine:1 LineCount:100]
Results: map[Contents: 1: # SPDX-License-Identifier: GPL-2.0-only
2: menu "Kernel hacking"
3:
4: menu "printk and dmesg options"
5:
6: config PRINTK_TIME
7: bool "Show timing information on printks"
8: depends on PRINTK
9: help
10: Selecting this option causes time stamps of the printk()
11: messages to be added to the output of the syslog() system
12: call and at the console.
13:
14: The timestamp is always recorded internally, and exported
15: to /dev/kmsg. This flag just specifies if the timestamp should
16: be included, not that the timestamp is recorded.
17:
18: The behavior is also controlled by the kernel command line
19: parameter printk.time=1. See Documentation/admin-guide/kernel-parameters.rst
20:
21: config PRINTK_CALLER
22: bool "Show caller information on printks"
23: depends on PRINTK
24: help
25: Selecting this option causes printk() to add a caller "thread id" (if
26: in task context) or a caller "processor id" (if not in task context)
27: to every message.
28:
29: This option is intended for environments where multiple threads
30: concurrently call printk() for many times, for it is difficult to
31: interpret without knowing where these lines (or sometimes individual
32: line which was divided into multiple lines due to race) came from.
33:
34: Since toggling after boot makes the code racy, currently there is
35: no option to enable/disable at the kernel command line parameter or
36: sysfs interface.
37:
38: config PRINTK_EXECUTION_CTX
39: bool
40: depends on PRINTK
41: help
42: This option extends struct printk_info to include extra execution
43: context in printk, such as task name and CPU number from where the
44: message originated. This is useful for correlating printk messages
45: with specific execution contexts.
46:
47: This is automatically enabled when a console driver that supports
48: execution context is selected.
49:
50: config STACKTRACE_BUILD_ID
51: bool "Show build ID information in stacktraces"
52: depends on PRINTK
53: help
54: Selecting this option adds build ID information for symbols in
55: stacktraces printed with the printk format '%p[SR]b'.
56:
57: This option is intended for distros where debuginfo is not easily
58: accessible but can be downloaded given the build ID of the vmlinux or
59: kernel module where the function is located.
60:
61: config CONSOLE_LOGLEVEL_DEFAULT
62: int "Default console loglevel (1-15)"
63: range 1 15
64: default "7"
65: help
66: Default loglevel to determine what will be printed on the console.
67:
68: Setting a default here is equivalent to passing in loglevel=<x> in
69: the kernel bootargs. loglevel=<x> continues to override whatever
70: value is specified here as well.
71:
72: Note: This does not affect the log level of un-prefixed printk()
73: usage in the kernel. That is controlled by the MESSAGE_LOGLEVEL_DEFAULT
74: option.
75:
76: config CONSOLE_LOGLEVEL_QUIET
77: int "quiet console loglevel (1-15)"
78: range 1 15
79: default "4"
80: help
81: loglevel to use when "quiet" is passed on the kernel commandline.
82:
83: When "quiet" is passed on the kernel commandline this loglevel
84: will be used as the loglevel. IOW passing "quiet" will be the
85: equivalent of passing "loglevel=<CONSOLE_LOGLEVEL_QUIET>"
86:
87: config MESSAGE_LOGLEVEL_DEFAULT
88: int "Default message log level (1-7)"
89: range 1 7
90: default "4"
91: help
92: Default log level for printk statements with no specified priority.
93:
94: This was hard-coded to KERN_WARNING since at least 2.6.10 but folks
95: that are auditing their logs closely may want to set it to a lower
96: priority.
97:
98: Note: This does not affect what message level gets printed on the console
99: by default. To change that, use loglevel=<x> in the kernel bootargs,
100: or pick a different CONSOLE_LOGLEVEL_DEFAULT configuration value.
]
|
| 62/2 |
2026/07/25 01:49 |
llm |
expert |
0m
Model:
Tokens:
input: 37454
output: 34
thoughts: 14
Thoughts: Okay, here's my summarized thought process, presented as if I were thinking it:
**Digging into the RCU Code**
Right, let's get down to brass tacks. I need to understand what's going on with this RCU stuff, specifically, I've got a hunch there's a problem related to debugging. So, first thing, I'm going to start with a grep. A good, old-fashioned grep. Specifically, I'm thinking I should look for the string `RCU_EQS_DEBUG`. That's a strong indicator of debugging output or functionality. This keyword is probably going to lead me to the relevant areas of the code base. I'm going to follow the trail of this particular string and see where it goes. This should give me a good entry point to start tracing the execution and hopefully understand this debug mechanism.
|
| 63/2 |
2026/07/25 01:49 |
tool |
grepper |
0m
Error:
Args: map[Expression:config RCU_EQS_DEBUG PathPrefix:lib/Kconfig.debug]
Results:
|
| 64/2 |
2026/07/25 01:49 |
llm |
expert |
0m
Model:
Tokens:
input: 37701
output: 22
thoughts: 13
Thoughts: Okay, here's my summarized thought process, presented as if I were thinking it:
**Locating the Definition of RCU_EQS_DEBUG**
Alright, I need to get my bearings here. The code I'm looking at mentions `RCU_EQS_DEBUG`. My immediate question is: where is *that* defined? I can't really analyze its behavior or understand its purpose in the current context without knowing its actual value, what it represents, and potentially any dependencies it has. This is basic debugging 101, really. So, I need to trace this macro back to its source. Time to start digging through headers and source files until I find the damn thing. Let's get to it!
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tool |
grepper |
0m
Args: map[Expression:config RCU_EQS_DEBUG]
Results: map[Output:kernel/rcu/Kconfig.debug=178=config RCU_TRACE
--
kernel/rcu/Kconfig.debug-189-
kernel/rcu/Kconfig.debug:190:config RCU_EQS_DEBUG
kernel/rcu/Kconfig.debug-191- bool "Provide debugging asserts for adding NO_HZ support to an arch"
]
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llm |
expert |
0m
Model:
Tokens:
input: 37993
output: 37
thoughts: 22
Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience:
**Diving into RCU Debug Configuration**
Okay, so I need to get a handle on the RCU debug configuration options. My instinct tells me that the key settings will be defined within the Kconfig files, and based on past experience I'm going to focus on `kernel/rcu/Kconfig.debug`. I think that around line 190 should be a good starting point. I want to see how the debug features are enabled, what dependencies they have, and perhaps what the default values are. Let's see what gems we can unearth there. Hopefully I can find something useful for the task at hand.
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tool |
read-file |
0m
Args: map[File:kernel/rcu/Kconfig.debug FirstLine:185 LineCount:20]
Results: map[Contents: 185: event tracing.
186:
187: Say Y here if you want to enable RCU tracing
188: Say N if you are unsure.
189:
190: config RCU_EQS_DEBUG
191: bool "Provide debugging asserts for adding NO_HZ support to an arch"
192: depends on DEBUG_KERNEL
193: help
194: This option provides consistency checks in RCU's handling of
195: NO_HZ. These checks have proven quite helpful in detecting
196: bugs in arch-specific NO_HZ code.
197:
198: Say N here if you need ultimate kernel/user switch latencies
199: Say Y if you are unsure
200:
201: config RCU_STRICT_GRACE_PERIOD
202: bool "Provide debug RCU implementation with short grace periods"
203: depends on DEBUG_KERNEL && RCU_EXPERT && NR_CPUS <= 4 && !TINY_RCU
204: default n
]
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llm |
expert |
0m
Model:
Tokens:
input: 38518
output: 66
thoughts: 969
Thoughts: **Analysis of the Potential Bug in RCU_EQS_DEBUG**
Okay, so the code has a `WARN_ON_ONCE` construct, suggesting it's designed as a debugging check. The "Say Y if you are unsure" message strongly hints this `RCU_EQS_DEBUG` is a debug feature, likely controlled by `DEBUG_KERNEL`. In a production build, `DEBUG_KERNEL` might be enabled, but `RCU_EQS_DEBUG` is specifically a debug assert. Even if enabled, it only triggers a warning, not a crash.
The trigger point seems to be writing to `/sys/power/state`. However, this requires global root privileges. That's a key point. This means it's inaccessible to unprivileged processes and definitely cannot be triggered from within a user namespace. It's not exploitable. It doesn't cause any denial-of-service, just a warning. This isn't triggered by the usual suspect vectors: no VM guest, host, network, remote, peripheral, or filesystem triggers are involved.
Let me recap:
* The root cause is a `WARN_ON_ONCE` call within `ct_kernel_exit` and `ct_kernel_enter`.
* The warning is triggered when `CONFIG_RCU_EQS_DEBUG` is set, and `ct_cpuidle_enter()` is called from a task that's not idle.
* On ARM64, this happens during a system suspend because `cpu_suspend()` calls `ct_cpuidle_enter()`. The crucial part is that `ct_cpuidle_enter()` is called from the task initiating the suspend, like writing to `/sys/power/state`.
* Writing to `/sys/power/state` demands global root privileges (UID 0 within the `init_user_ns`) because the file is owned by `GLOBAL_ROOT_UID` and has mode `0644`.
* Processes within a user namespace simply cannot access the file because their `fsuid` won't match `GLOBAL_ROOT_UID`.
* The issue is definitely not exploitable, it won't cause any DoS, and is not accessible by unprivileged programs or user namespaces.
I should also check other potential ways to trigger system suspend.
I need to confirm there aren't any other avenues.
System suspend can be started by:
* Writing to `/sys/power/state` (requires root).
* `ioctl` on `/dev/rtc` (RTC_WKALM_SET, etc.)? No, that just sets wake alarms, it does not start the suspend.
* ACPI events? Those are handled by kernel threads or root processes (acpid).
* `systemd-logind` also starts suspend when the lid is closed, but it's running as root.
Are there any unprivileged methods to trigger a system suspend? No, the system suspend operation requires high privileges.
I need to quickly confirm if `sysfs` can be mounted within a user namespace and whether that changes the ownership of `/sys/power/state`. As I found earlier, `sysfs` does not support idmapped mounts or userns ownership. The inodes are always created with `GLOBAL_ROOT_UID` and `GLOBAL_ROOT_GID`. So, even if I mount it within a user namespace, the files are still owned by global root. If a user namespace process has a non-zero uid mapped to the global root, or if it has UID 0 mapped to the global root, then that means the user namespace was created by global root, thus, the process is already privileged. This confirms that this potential bug is not accessible by unprivileged processes or user namespaces.
One last thing, let me briefly check for any other call paths to `cpu_suspend` on ARM64.
`cpu_suspend` is called by:
* `psci_system_suspend_enter` (system suspend)
* `psci_cpu_suspend_enter` (cpuidle)
* `acpi_processor_ffh_lpi_enter` (cpuidle)
When it's called from cpuidle, it's called from an idle task, so `is_idle_task(current)` is true, meaning the warning is not triggered. When it's called from a system suspend, the function is called from the task which started the suspend, thus is not an idle task, and the warning is triggered. So the only way to trigger the warning is via system suspend. And system suspend requires root.
Final Conclusion:
* Exploitable: False
* DenialOfService: False
* Unprivileged: False
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tool |
set-results |
0m
Args: map[DenialOfService:false Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:false UserNamespace:false VMGuestTrigger:false VMHostTrigger:false]
Results: map[DenialOfService:false Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:false UserNamespace:false VMGuestTrigger:false VMHostTrigger:false]
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llm |
expert |
0m
Model:
Tokens:
input: 40642
output: 629
thoughts: 348
Thoughts: **Final Thoughts on the Context Tracking Bug**
Okay, the analysis is done, and it's pretty clear-cut. Time to finalize the response. Let me lay out my thinking:
The core of the issue boils down to a `WARN_ON_ONCE` in `ct_kernel_exit` and `ct_kernel_enter` within `kernel/context_tracking.c`. The warning arises when `CONFIG_RCU_EQS_DEBUG` is enabled and we see `ct_cpuidle_enter()` being invoked from a task that's *not* the idle task.
Now, on ARM64, the kernel uses `cpu_suspend()` which, crucially, calls `ct_cpuidle_enter()`. Here's where it gets interesting: `cpu_suspend()` is used for *both* CPU idle and system suspend. In the case of CPU idle, `cpu_suspend()` is initiated by the idle task itself, so no warning is generated. But, when it's used for system suspend, `cpu_suspend()` is triggered by the process initiating the suspend β like, say, writing to `/sys/power/state`. And *that* process isn't the idle task, hence the warning.
I think I see the implications now. Triggering a system suspend requires a write to `/sys/power/state`. This file's permissions are locked down β owned by `GLOBAL_ROOT_UID` with mode `0644`. So, we're talking about global root privileges required to even *get* to the point where the warning appears. This means an unprivileged process or a process running inside a user namespace (where uid 0 might map to a non-zero global uid) can't touch that file and can't cause the warning.
So, in the end, it really doesn't worry me. It's a warning related to a debug option (`CONFIG_RCU_EQS_DEBUG`). There's no chance of memory corruption, information leakage, or a denial of service. The file and permissions are such that it's unexploitable and has no security ramifications. It is more of a minor annoyance at worst.
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action |
format-explanation |
0m
Results: map[Explanation:Based on the analysis of the bug report and the kernel source code, here is the
assessment of the security impact:
**1. Nature of the Bug:**
The bug report shows a `WARN_ON_ONCE` being triggered in `ct_kernel_exit` and
`ct_kernel_enter` within `kernel/context_tracking.c`. The warning condition is
`WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user &&
!is_idle_task(current));`.
This warning is triggered because `ct_cpuidle_enter()` is being called from a
non-idle task. On ARM64, `cpu_suspend()` was modified to call
`ct_cpuidle_enter()` and `ct_cpuidle_exit()` directly. While `cpu_suspend()` is
primarily used for cpuidle (where it is correctly called from the idle task), it
is also used for system suspend (e.g., via `psci_system_suspend_enter`). During
system suspend, it is called in the context of the task that initiated the
suspend, which is not the idle task, thus triggering the debug warning.
**2. Exploitability & Denial of Service:**
This is purely a harmless warning caused by an overly strict assertion in a
debug configuration (`CONFIG_RCU_EQS_DEBUG`). It does not cause any memory
corruption, information leak, or control-flow hijack. Furthermore, it is a
`WARN_ON_ONCE` which simply prints a stack trace and continues execution without
halting the kernel or causing a denial of service. In production builds,
`CONFIG_RCU_EQS_DEBUG` is typically disabled, meaning the warning wouldn't even
trigger.
**3. Accessibility (Unprivileged / User Namespaces):**
To trigger this warning, a user must initiate a system suspend. The reproducer
does this by writing `"mem\n"` to `/sys/power/state`.
The `/sys/power/state` sysfs attribute is created with mode `0644` and is owned
by the global root (`GLOBAL_ROOT_UID`).
- An unprivileged user cannot write to this file.
- A process inside an unprivileged user namespace (even if it mounts its own
`sysfs` instance) cannot write to this file because `sysfs` inodes are always
owned by the global root. The process's `fsuid` (which is mapped to a non-zero
global UID) will not match the inode's UID (0), resulting in a permission denied
error.
Therefore, triggering this bug strictly requires global root privileges.
**Conclusion:**
The bug is a harmless debug warning that can only be triggered by a highly
privileged user (global root) initiating a system suspend. It has no security
impact, is not exploitable, does not cause a denial of service, and is
completely inaccessible to unprivileged users or from within user namespaces.]
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