Re: [PATCH] s390/signal: Fix incorrect return address in signal frame

[Heiko Carstens <hca@linux.ibm.com>]

On Mon, Oct 12, 2026 at 03:50:03PM +0000, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [High] s390/signal: patch breaks -EINTR for -ERESTART_RESTARTBLOCK
> --
> 
> commit 158e48eb13e787b0b5c2f432c9056345d015870e
> Author: Heiko Carstens <hca@linux.ibm.com>
> 
> s390/signal: Fix incorrect return address in signal frame
> 
> This commit fixes an issue in arch_do_signal_or_restart() where a second call
> builds a signal frame with the wrong return address if the first call set up a
> vDSO system call restart. It addresses this by restoring psw.addr from
> arch_data before building the signal frame.
> 
> > diff --git a/arch/s390/kernel/signal.c b/arch/s390/kernel/signal.c
> > index 4874de5edea0a..25781d4a0ad0c 100644
> > --- a/arch/s390/kernel/signal.c
> > +++ b/arch/s390/kernel/signal.c
> > @@ -475,7 +475,10 @@ void arch_do_signal_or_restart(struct pt_regs *regs)
> >  		}
> >  		/* No longer in a system call */
> >  		clear_pt_regs_flag(regs, PIF_SYSCALL);
> > -
> > +		if (!(current->restart_block.arch_data & 1)) {
> > +			regs->psw.addr = current->restart_block.arch_data;
> > +			current->restart_block.arch_data = 1;
> > +		}
...
> The newly added code restores regs->psw.addr to the original return address,
> bypassing the vDSO stub. Without the vDSO stub executing sys_restart_syscall
> (which would return -EINTR), the syscall instead returns orig_gpr2.
> 
> Could this lead to system calls like nanosleep returning their first argument
> instead of -EINTR, breaking userspace error handling and POSIX compliance?

Correct. The whole point of this patch was to return -EINTR instead of
(incorrectly) restarting the system call, which is the most likely of the
unlikely scenarios. One could construct more obscure scenarios where user
space would end up with a SIGILL, but that's extremely unlikely.

Anyway, the -EINTR return code handling is broken with this patch.