linux-kernel - Re: [PATCH] riscv: return -ENOSYS for syscall -1

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Date:   Tue, 22 Dec 2020 09:22:19 -0700
From:   Tycho Andersen <tycho@...ho.pizza>
To:     Andreas Schwab <schwab@...e.de>
Cc:     linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        David Abdurachmanov <david.abdurachmanov@...ive.com>
Subject: Re: [PATCH] riscv: return -ENOSYS for syscall -1

On Mon, Dec 21, 2020 at 11:52:00PM +0100, Andreas Schwab wrote:
> Properly return -ENOSYS for syscall -1 instead of leaving the return value
> uninitialized.  This fixes the strace teststuite.
> 
> Fixes: 5340627e3fe0 ("riscv: add support for SECCOMP and SECCOMP_FILTER")
> Signed-off-by: Andreas Schwab <schwab@...e.de>
> ---
>  arch/riscv/kernel/entry.S | 9 +--------
>  1 file changed, 1 insertion(+), 8 deletions(-)
> 
> diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
> index 524d918f3601..d07763001eb0 100644
> --- a/arch/riscv/kernel/entry.S
> +++ b/arch/riscv/kernel/entry.S
> @@ -186,14 +186,7 @@ check_syscall_nr:
>  	 * Syscall number held in a7.
>  	 * If syscall number is above allowed value, redirect to ni_syscall.
>  	 */
> -	bge a7, t0, 1f
> -	/*
> -	 * Check if syscall is rejected by tracer, i.e., a7 == -1.
> -	 * If yes, we pretend it was executed.
> -	 */
> -	li t1, -1
> -	beq a7, t1, ret_from_syscall_rejected
> -	blt a7, t1, 1f
> +	bgeu a7, t0, 1f

IIUC, this is all dead code anyway for the path where seccomp actually
rejects the syscall, since it should do the rejection directly in
handle_syscall_trace_enter(), which is called above this hunk. So it
seems good to me.

Reviewed-by: Tycho Andersen <tycho@...ho.pizza>