[PATCH] powerpc/ptrace: Do not return ENOSYS if invalid syscall

[Thadeu Lima de Souza Cascardo]

On Tue, Sep 10, 2019 at 10:01:22PM -0300, Thadeu Lima de Souza Cascardo wrote:
> If a tracer sets the syscall number to an invalid one, allow the return
> value set by the tracer to be returned the tracee.
> 
> The test for NR_syscalls is already at entry_64.S, and it's at
> do_syscall_trace_enter only to skip audit and trace.
> 
> After this, seccomp_bpf selftests complete just fine, as the failing test
> was using ptrace to change the syscall to return an error or a fake value,
> but were failing as it was always returning -ENOSYS.
> 
> Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo at canonical.com>
> ---
>  arch/powerpc/kernel/ptrace.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/kernel/ptrace.c b/arch/powerpc/kernel/ptrace.c
> index 8c92febf5f44..87315335f66a 100644
> --- a/arch/powerpc/kernel/ptrace.c
> +++ b/arch/powerpc/kernel/ptrace.c
> @@ -3316,7 +3316,7 @@ long do_syscall_trace_enter(struct pt_regs *regs)
>  
>  	/* Avoid trace and audit when syscall is invalid. */
>  	if (regs->gpr[0] >= NR_syscalls)
> -		goto skip;
> +		return regs->gpr[0];
>  
>  	if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
>  		trace_sys_enter(regs, regs->gpr[0]);

Ping? Any comments on this?

Thanks.
Cascardo.