ARM: Call syscall_trace_exit even when system call skipped

[keescook@chromium.org (Kees Cook)]

On Mon, Oct 8, 2018 at 4:00 AM, Eugene Syromyatnikov <evgsyr@gmail.com> wrote:
> From: Timothy E Baldwin <T.E.Baldwin99@members.leeds.ac.uk>
>
> On at least x86 and ARM64, and as documented in the ptrace man page
> a skipped system call will still cause a syscall exit ptrace stop.
>
> Previous to this commit 32-bit ARM did not, resulting in strace
> being confused when seccomp skips system calls.
>
> This change also impacts programs that use ptrace to skip system calls.
>
> Fixes: ad75b51459ae ("ARM: 7579/1: arch/allow a scno of -1 to not cause a SIGILL")
> Signed-off-by: Timothy E Baldwin <T.E.Baldwin99@members.leeds.ac.uk>
> Signed-off-by: Eugene Syromyatnikov <evgsyr@gmail.com>
> Reviewed-by: Kees Cook <keescook@chromium.org>
> Tested-by: Kees Cook <keescook@chromium.org>
> Tested-by: Eugene Syromyatnikov <evgsyr@gmail.com>
> ---
> KernelVersion: 4.19-rc7

Did this actually make it into the patch tracker? I don't see it in Incoming...

-Kees

> diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
> index 746565a..0465d65 100644
> --- a/arch/arm/kernel/entry-common.S
> +++ b/arch/arm/kernel/entry-common.S
> @@ -296,16 +296,15 @@ __sys_trace:
>         cmp     scno, #-1                       @ skip the syscall?
>         bne     2b
>         add     sp, sp, #S_OFF                  @ restore stack
> -       b       ret_slow_syscall
>
> -__sys_trace_return:
> -       str     r0, [sp, #S_R0 + S_OFF]!        @ save returned r0
> +__sys_trace_return_nosave:
> +       enable_irq_notrace
>         mov     r0, sp
>         bl      syscall_trace_exit
>         b       ret_slow_syscall
>
> -__sys_trace_return_nosave:
> -       enable_irq_notrace
> +__sys_trace_return:
> +       str     r0, [sp, #S_R0 + S_OFF]!        @ save returned r0
>         mov     r0, sp
>         bl      syscall_trace_exit
>         b       ret_slow_syscall
> --
> 2.1.4
>



-- 
Kees Cook
Pixel Security