diff options
| author | Tiezhu Yang <yangtiezhu@loongson.cn> | 2025-09-18 19:44:08 +0800 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2025-09-25 11:13:46 +0200 |
| commit | 040f278cc1a5f3d656e052d2835c3b00518edd2a (patch) | |
| tree | 80dadf878c43119265eabb7bd1773fee300dc646 | |
| parent | b6f29fa5f60367d91e606db64c12e7086423c2d5 (diff) | |
LoongArch: Fix unreliable stack for live patching
commit 677d4a52d4dc4a147d5e84af9ff207832578be70 upstream.
When testing the kernel live patching with "modprobe livepatch-sample",
there is a timeout over 15 seconds from "starting patching transition"
to "patching complete". The dmesg command shows "unreliable stack" for
user tasks in debug mode, here is one of the messages:
livepatch: klp_try_switch_task: bash:1193 has an unreliable stack
The "unreliable stack" is because it can not unwind from do_syscall()
to its previous frame handle_syscall(). It should use fp to find the
original stack top due to secondary stack in do_syscall(), but fp is
not used for some other functions, then fp can not be restored by the
next frame of do_syscall(), so it is necessary to save fp if task is
not current, in order to get the stack top of do_syscall().
Here are the call chains:
klp_enable_patch()
klp_try_complete_transition()
klp_try_switch_task()
klp_check_and_switch_task()
klp_check_stack()
stack_trace_save_tsk_reliable()
arch_stack_walk_reliable()
When executing "rmmod livepatch-sample", there exists a similar issue.
With this patch, it takes a short time for patching and unpatching.
Before:
# modprobe livepatch-sample
# dmesg -T | tail -3
[Sat Sep 6 11:00:20 2025] livepatch: 'livepatch_sample': starting patching transition
[Sat Sep 6 11:00:35 2025] livepatch: signaling remaining tasks
[Sat Sep 6 11:00:36 2025] livepatch: 'livepatch_sample': patching complete
# echo 0 > /sys/kernel/livepatch/livepatch_sample/enabled
# rmmod livepatch_sample
rmmod: ERROR: Module livepatch_sample is in use
# rmmod livepatch_sample
# dmesg -T | tail -3
[Sat Sep 6 11:06:05 2025] livepatch: 'livepatch_sample': starting unpatching transition
[Sat Sep 6 11:06:20 2025] livepatch: signaling remaining tasks
[Sat Sep 6 11:06:21 2025] livepatch: 'livepatch_sample': unpatching complete
After:
# modprobe livepatch-sample
# dmesg -T | tail -2
[Tue Sep 16 16:19:30 2025] livepatch: 'livepatch_sample': starting patching transition
[Tue Sep 16 16:19:31 2025] livepatch: 'livepatch_sample': patching complete
# echo 0 > /sys/kernel/livepatch/livepatch_sample/enabled
# rmmod livepatch_sample
# dmesg -T | tail -2
[Tue Sep 16 16:19:36 2025] livepatch: 'livepatch_sample': starting unpatching transition
[Tue Sep 16 16:19:37 2025] livepatch: 'livepatch_sample': unpatching complete
Cc: stable@vger.kernel.org # v6.9+
Fixes: 199cc14cb4f1 ("LoongArch: Add kernel livepatching support")
Reported-by: Xi Zhang <zhangxi@kylinos.cn>
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | arch/loongarch/kernel/stacktrace.c | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/arch/loongarch/kernel/stacktrace.c b/arch/loongarch/kernel/stacktrace.c index 9a038d1070d7..387dc4d3c486 100644 --- a/arch/loongarch/kernel/stacktrace.c +++ b/arch/loongarch/kernel/stacktrace.c @@ -51,12 +51,13 @@ int arch_stack_walk_reliable(stack_trace_consume_fn consume_entry, if (task == current) { regs->regs[3] = (unsigned long)__builtin_frame_address(0); regs->csr_era = (unsigned long)__builtin_return_address(0); + regs->regs[22] = 0; } else { regs->regs[3] = thread_saved_fp(task); regs->csr_era = thread_saved_ra(task); + regs->regs[22] = task->thread.reg22; } regs->regs[1] = 0; - regs->regs[22] = 0; for (unwind_start(&state, task, regs); !unwind_done(&state) && !unwind_error(&state); unwind_next_frame(&state)) { |