ARM: ptrace: Restore syscall restart tracing

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.

Cc: Russell King <linux@armlinux.org.uk>
Cc: Arnd Bergmann <arnd@kernel.org>
Cc: Lecopzer Chen <lecopzer.chen@mediatek.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: linux-arm-kernel@lists.infradead.org
Fixes: 4e57a4ddf6b0 ("ARM: 9107/1: syscall: always store thread_info->abi_syscall")
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20230810195422.2304827-1-keescook@chromium.org
Signed-off-by: Kees Cook <keescook@chromium.org>

diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index bcc4c9ec3aa4ecdfb8027f55d87e1346db74705e..5c31e9de7a602e22a65f64c12cf2819be9fa56d6 100644 (file)
--- 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)