Re: [REGRESSION] x86/entry: Tracer no longer has opportunity to change the syscall number at entry via orig_ax

[Kyle Huey]

On Wed, Aug 19, 2020 at 12:44 PM Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
>
> On Wed, Aug 19 2020 at 10:14, Kyle Huey wrote:
> > tl;dr: after 27d6b4d14f5c3ab21c4aef87dd04055a2d7adf14 ptracer
> > modifications to orig_ax in a syscall entry trace stop are not honored
> > and this breaks our code.
>
> My fault and I have no idead why none of the silly test cases
> noticed. Fix below.

That'll do it, thanks.

- Kyle

> Thanks,
>
>         tglx
> ---
> diff --git a/kernel/entry/common.c b/kernel/entry/common.c
> index 9852e0d62d95..fcae019158ca 100644
> --- a/kernel/entry/common.c
> +++ b/kernel/entry/common.c
> @@ -65,7 +65,8 @@ static long syscall_trace_enter(struct pt_regs *regs, long syscall,
>
>         syscall_enter_audit(regs, syscall);
>
> -       return ret ? : syscall;
> +       /* The above might have changed the syscall number */
> +       return ret ? : syscall_get_nr(current, regs);
>  }
>
>  noinstr long syscall_enter_from_user_mode(struct pt_regs *regs, long syscall)