Messages in this thread | ![/](/images/icornerl.gif) | | Date | Thu, 10 Aug 2023 22:17:45 +0200 | From | "Arnd Bergmann" <> | Subject | Re: [PATCH v2 1/2] ARM: ptrace: Restore syscall restart tracing |
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On Thu, Aug 10, 2023, at 21:54, Kees Cook wrote: > Since commit 4e57a4ddf6b0 ("ARM: 9107/1: syscall: always store > thread_info->abi_syscall"), the seccomp selftests "syscall_restart" has > been broken. This was caused by the restart syscall not being stored to > "abi_syscall" during restart setup before branching to the "local_restart" > label. Tracers would see the wrong syscall, and scno would get overwritten > while returning from the TIF_WORK path. Add the missing store. >
> diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S > index bcc4c9ec3aa4..5c31e9de7a60 100644 > --- a/arch/arm/kernel/entry-common.S > +++ b/arch/arm/kernel/entry-common.S > @@ -90,6 +90,7 @@ slow_work_pending: > cmp r0, #0 > beq no_work_pending > movlt scno, #(__NR_restart_syscall - __NR_SYSCALL_BASE) > + str scno, [tsk, #TI_ABI_SYSCALL] @ make sure tracers see update > ldmia sp, {r0 - r6} @ have to reload r0 - r6 > b local_restart @ ... and off we go > ENDPROC(ret_fast_syscall)
Looks good to me, as in my previous reply this is safe for all cases with the current restartable syscalls, though it would be wrong if we had a restartblock version of epoll_wait on an OABI_COMPAT task, which needs to look at the high bits of the number to tell which structure layout to use.
I also looked at my original patch now and see what I did wrong there.
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
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