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

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Date:   Tue, 22 Dec 2020 20:04:22 -0800 (PST)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     tycho@...ho.pizza
CC:     schwab@...e.de, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org,
        Paul Walmsley <paul.walmsley@...ive.com>,
        david.abdurachmanov@...ive.com
Subject:     Re: [PATCH] riscv: return -ENOSYS for syscall -1

On Tue, 22 Dec 2020 08:22:19 PST (-0800), tycho@...ho.pizza wrote:
> 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>

Thanks, this is on fixes.