| Message ID | 20260828053811.1042300-1-sshegde@linux.ibm.com (mailing list archive) |
|---|---|
| State | Under Review |
| Headers | show |
| Series | powerpc/entry: Clear TIF_SYSCALL_RET before syscall error return | expand |
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);
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 >
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 >>
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 > > > >
> 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 >
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);
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(-)