[PATCH] powerpc/entry: Clear TIF_SYSCALL_RET before syscall error return

[PATCH] powerpc/entry: Clear TIF_SYSCALL_RET before syscall error return

[Shrikanth Hegde]

Shivaprasad reported a boot failure due to userspace processes crash on
abort() from libc.so.6. It was bisected to merge request
commit '3424d8c18a7d ("Merge tag  'core-entry-2026-08-17' of 
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip")'

Upon checking the merge, when syscall_enter_from_user_mode_randomize_stack
fails, which could happen when a tracer like seccomp or ptrace intercepts
and skips the syscall, the code returns to userspace immediately without
clearing the intermediate flag which was set.

When the next syscall is made, it immediately aborts the valid syscall
since the flag is still set. Hence clear the flag on occurrence of first
failure.

Reported-by: Shivaprasad G Bhat <sbhat@linux.ibm.com>
Closes: https://lore.kernel.org/all/e301014d-568f-4ed5-bc64-b8a85ca0b1e1@linux.ibm.com/
Fixes: 3424d8c18a7d ("Merge tag 'core-entry-2026-08-17' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip")
Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
---
PS: I have kept the block below since earlier code was checking it
regardless of result of syscall_enter_from_user_mode. If it turns out
to be a redundant, it can be removed later.

 arch/powerpc/kernel/syscall.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/syscall.c b/arch/powerpc/kernel/syscall.c
index 4916c205c4bb..fbefe1927b10 100644
--- a/arch/powerpc/kernel/syscall.c
+++ b/arch/powerpc/kernel/syscall.c
@@ -18,8 +18,10 @@ notrace long system_call_exception(struct pt_regs *regs, unsigned long r0)
 	long ret;
 	syscall_fn f;
 
-	if (unlikely(!syscall_enter_from_user_mode_randomize_stack(regs, &r0)))
+	if (unlikely(!syscall_enter_from_user_mode_randomize_stack(regs, &r0))) {
+		clear_thread_flag(TIF_SYSCALL_RET);
 		return syscall_get_error(current, regs);
+	}
 
 	if (unlikely(test_and_clear_thread_flag(TIF_SYSCALL_RET)))
 		return syscall_get_error(current, regs);
-- 
2.47.3

Re: [PATCH] powerpc/entry: Clear TIF_SYSCALL_RET before syscall error return

[Shivaprasad G Bhat]

On 8/28/26 11:08 AM, Shrikanth Hegde wrote:
> Shivaprasad reported a boot failure due to userspace processes crash on
> abort() from libc.so.6. It was bisected to merge request
> commit '3424d8c18a7d ("Merge tag  'core-entry-2026-08-17' of
> git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip")'
> 
> Upon checking the merge, when syscall_enter_from_user_mode_randomize_stack
> fails, which could happen when a tracer like seccomp or ptrace intercepts
> and skips the syscall, the code returns to userspace immediately without
> clearing the intermediate flag which was set.
> 
> When the next syscall is made, it immediately aborts the valid syscall
> since the flag is still set. Hence clear the flag on occurrence of first
> failure.
> 
> Reported-by: Shivaprasad G Bhat <sbhat@linux.ibm.com>
> Closes: https://lore.kernel.org/all/e301014d-568f-4ed5-bc64-b8a85ca0b1e1@linux.ibm.com/
> Fixes: 3424d8c18a7d ("Merge tag 'core-entry-2026-08-17' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip")
> Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>

Tested-by: Shivaprasad G Bhat <sbhat@linux.ibm.com>

Thanks,
Shivaprasad

> ---
> PS: I have kept the block below since earlier code was checking it
> regardless of result of syscall_enter_from_user_mode. If it turns out
> to be a redundant, it can be removed later.
> 
>   arch/powerpc/kernel/syscall.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/kernel/syscall.c b/arch/powerpc/kernel/syscall.c
> index 4916c205c4bb..fbefe1927b10 100644
> --- a/arch/powerpc/kernel/syscall.c
> +++ b/arch/powerpc/kernel/syscall.c
> @@ -18,8 +18,10 @@ notrace long system_call_exception(struct pt_regs *regs, unsigned long r0)
>   	long ret;
>   	syscall_fn f;
>   
> -	if (unlikely(!syscall_enter_from_user_mode_randomize_stack(regs, &r0)))
> +	if (unlikely(!syscall_enter_from_user_mode_randomize_stack(regs, &r0))) {
> +		clear_thread_flag(TIF_SYSCALL_RET);
>   		return syscall_get_error(current, regs);
> +	}
>   
>   	if (unlikely(test_and_clear_thread_flag(TIF_SYSCALL_RET)))
>   		return syscall_get_error(current, regs);