* Re: [PATCH] powerpc/entry: Clear TIF_SYSCALL_RET before syscall error return
2026-08-28 5:38 [PATCH] powerpc/entry: Clear TIF_SYSCALL_RET before syscall error return Shrikanth Hegde
@ 2026-08-29 6:01 ` Shivaprasad G Bhat
2026-08-31 4:39 ` Mukesh Kumar Chaurasiya
2026-09-01 9:17 ` Venkat
2 siblings, 0 replies; 6+ messages in thread
From: Shivaprasad G Bhat @ 2026-08-29 6:01 UTC (permalink / raw)
To: Shrikanth Hegde, tglx, maddy, linuxppc-dev
Cc: linux-kernel, chleroy, mkchauras
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);
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH] powerpc/entry: Clear TIF_SYSCALL_RET before syscall error return
2026-08-28 5:38 [PATCH] powerpc/entry: Clear TIF_SYSCALL_RET before syscall error return Shrikanth Hegde
2026-08-29 6:01 ` Shivaprasad G Bhat
@ 2026-08-31 4:39 ` Mukesh Kumar Chaurasiya
2026-08-31 9:04 ` Shrikanth Hegde
2026-09-01 9:17 ` Venkat
2 siblings, 1 reply; 6+ messages in thread
From: Mukesh Kumar Chaurasiya @ 2026-08-31 4:39 UTC (permalink / raw)
To: Shrikanth Hegde; +Cc: tglx, maddy, linuxppc-dev, linux-kernel, chleroy, sbhat
On Fri, Aug 28, 2026 at 11:08:11AM +0530, 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>
> ---
> 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.
>
I think it is redundant as of now. The TIF_SYSCALL_RET flag is set when
error is set by the ptrace or seccomp, If the error value is set then
the syscall_enter_from_user_mode_randomize_stack will return false.
Hence the next check will become redundant.
I also see that TIF_SYSCALL_RET is also set when processing the ptrace
syscall, Which can leave the flag set for next syscall execution. Which
can again trigger the same issue.
Regards,
Mukesh
> 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
>
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH] powerpc/entry: Clear TIF_SYSCALL_RET before syscall error return
2026-08-31 4:39 ` Mukesh Kumar Chaurasiya
@ 2026-08-31 9:04 ` Shrikanth Hegde
2026-09-01 7:13 ` Mukesh Kumar Chaurasiya
0 siblings, 1 reply; 6+ messages in thread
From: Shrikanth Hegde @ 2026-08-31 9:04 UTC (permalink / raw)
To: Mukesh Kumar Chaurasiya
Cc: tglx, maddy, linuxppc-dev, linux-kernel, chleroy, sbhat
On 8/31/26 10:09 AM, Mukesh Kumar Chaurasiya wrote:
> On Fri, Aug 28, 2026 at 11:08:11AM +0530, 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>
>> ---
>> 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.
>>
> I think it is redundant as of now. The TIF_SYSCALL_RET flag is set when
> error is set by the ptrace or seccomp, If the error value is set then
> the syscall_enter_from_user_mode_randomize_stack will return false.
> Hence the next check will become redundant.
>
> I also see that TIF_SYSCALL_RET is also set when processing the ptrace
> syscall, Which can leave the flag set for next syscall execution. Which
> can again trigger the same issue.
>
I believe it is a pre-existing bug which can be fixed independent of this issue.
Since merge request broke the userspace it is better we fix it right away and
this pre-existing issue fix can be done subsequently.
No?
> Regards,
> Mukesh
>> 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
>>
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH] powerpc/entry: Clear TIF_SYSCALL_RET before syscall error return
2026-08-31 9:04 ` Shrikanth Hegde
@ 2026-09-01 7:13 ` Mukesh Kumar Chaurasiya
0 siblings, 0 replies; 6+ messages in thread
From: Mukesh Kumar Chaurasiya @ 2026-09-01 7:13 UTC (permalink / raw)
To: Shrikanth Hegde; +Cc: tglx, maddy, linuxppc-dev, linux-kernel, chleroy, sbhat
On Mon, Aug 31, 2026 at 02:34:10PM +0530, Shrikanth Hegde wrote:
>
>
> On 8/31/26 10:09 AM, Mukesh Kumar Chaurasiya wrote:
> > On Fri, Aug 28, 2026 at 11:08:11AM +0530, 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>
> > > ---
> > > 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.
> > >
> > I think it is redundant as of now. The TIF_SYSCALL_RET flag is set when
> > error is set by the ptrace or seccomp, If the error value is set then
> > the syscall_enter_from_user_mode_randomize_stack will return false.
> > Hence the next check will become redundant.
> >
> > I also see that TIF_SYSCALL_RET is also set when processing the ptrace
> > syscall, Which can leave the flag set for next syscall execution. Which
> > can again trigger the same issue.
> >
>
> I believe it is a pre-existing bug which can be fixed independent of this issue.
> Since merge request broke the userspace it is better we fix it right away and
> this pre-existing issue fix can be done subsequently.
>
> No?
>
Agreed.
Sure we can send that as a separate fix.
With that,
Reviewed-by: Mukesh Kumar Chaurasiya (IBM) <mkchauras@gmail.com>
Regards
Mukesh.
> > Regards,
> > Mukesh
> > > 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
> > >
>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] powerpc/entry: Clear TIF_SYSCALL_RET before syscall error return
2026-08-28 5:38 [PATCH] powerpc/entry: Clear TIF_SYSCALL_RET before syscall error return Shrikanth Hegde
2026-08-29 6:01 ` Shivaprasad G Bhat
2026-08-31 4:39 ` Mukesh Kumar Chaurasiya
@ 2026-09-01 9:17 ` Venkat
2 siblings, 0 replies; 6+ messages in thread
From: Venkat @ 2026-09-01 9:17 UTC (permalink / raw)
To: Shrikanth Hegde
Cc: tglx, maddy, linuxppc-dev, linux-kernel, chleroy, sbhat, mkchauras
> On 28 Aug 2026, at 11:08 AM, Shrikanth Hegde <sshegde@linux.ibm.com> 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: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Regards,
Venkat.
> 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
>
^ permalink raw reply [flat|nested] 6+ messages in thread