linux-kernel - Re: [RFC 5/5] x86,seccomp: Add a seccomp fastpath

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Message-ID: <5398D7B4.5000303@zytor.com>
Date:	Wed, 11 Jun 2014 15:27:00 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andy Lutomirski <luto@...capital.net>
CC:	Alexei Starovoitov <alexei.starovoitov@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Kees Cook <keescook@...omium.org>,
	Will Drewry <wad@...omium.org>,
	Oleg Nesterov <oleg@...hat.com>, X86 ML <x86@...nel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>, linux-mips@...ux-mips.org,
	linux-arch <linux-arch@...r.kernel.org>,
	LSM List <linux-security-module@...r.kernel.org>
Subject: Re: [RFC 5/5] x86,seccomp: Add a seccomp fastpath

On 06/11/2014 03:22 PM, Andy Lutomirski wrote:
> On Wed, Jun 11, 2014 at 3:18 PM, H. Peter Anvin <hpa@...or.com> wrote:
>> On 06/11/2014 02:56 PM, Andy Lutomirski wrote:
>>>
>>> 13ns is with the simplest nonempty filter.  I hope that empty filters
>>> don't work.
>>>
>>
>> Why wouldn't they?
> 
> Is it permissible to fall off the end of a BPF program?  I'm getting
> EINVAL trying to install an actual empty filter.  The filter I tested
> with was:
> 

What I meant was that there has to be a well-defined behavior for the
program falling off the end anyway, and that that should be preserved.

I guess it is possible to require that all code paths must provably
reach a termination point.

	-hpa


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