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 <redacted>
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(-)
From: Shivaprasad G Bhat <hidden> Date: 2026-08-29 06:01:49
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 <redacted>
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 <redacted>
Thanks,
Shivaprasad
quoted hunk
---
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(-)
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 <redacted>
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
On 8/31/26 10:09 AM, Mukesh Kumar Chaurasiya wrote:
On Fri, Aug 28, 2026 at 11:08:11AM +0530, Shrikanth Hegde wrote:
quoted
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 <redacted>
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?
On Mon, Aug 31, 2026 at 02:34:10PM +0530, Shrikanth Hegde wrote:
On 8/31/26 10:09 AM, Mukesh Kumar Chaurasiya wrote:
quoted
On Fri, Aug 28, 2026 at 11:08:11AM +0530, Shrikanth Hegde wrote:
quoted
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 <redacted>
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) <redacted>
Regards
Mukesh.
On 28 Aug 2026, at 11:08 AM, Shrikanth Hegde [off-list ref] 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 <redacted>
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(-)
On Fri, 28 Aug 2026 11:08:11 +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.
[...]