Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754585AbaFKWcx (ORCPT ); Wed, 11 Jun 2014 18:32:53 -0400 Received: from mail-ob0-f179.google.com ([209.85.214.179]:47301 "EHLO mail-ob0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754234AbaFKWcu (ORCPT ); Wed, 11 Jun 2014 18:32:50 -0400 MIME-Version: 1.0 In-Reply-To: References: <9e11cd988a0f120606e37b5e275019754e2774da.1402517933.git.luto@amacapital.net> <5398D59A.3030900@zytor.com> <5398D7B4.5000303@zytor.com> Date: Wed, 11 Jun 2014 15:32:49 -0700 X-Google-Sender-Auth: IVpPnf4NeYmGACYKoUQRjO5i6qU Message-ID: Subject: Re: [RFC 5/5] x86,seccomp: Add a seccomp fastpath From: Kees Cook To: Andy Lutomirski Cc: "H. Peter Anvin" , Alexei Starovoitov , "linux-kernel@vger.kernel.org" , Will Drewry , Oleg Nesterov , X86 ML , "linux-arm-kernel@lists.infradead.org" , linux-mips@linux-mips.org, linux-arch , LSM List Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 11, 2014 at 3:28 PM, Andy Lutomirski wrote: > On Wed, Jun 11, 2014 at 3:27 PM, H. Peter Anvin wrote: >> On 06/11/2014 03:22 PM, Andy Lutomirski wrote: >>> On Wed, Jun 11, 2014 at 3:18 PM, H. Peter Anvin 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. >> > > Dunno. I haven't ever touched any of the actual BPF code. This whole > patchset only changes the code that invokes the BPF evaluator. Yes, this is how BPF works: runs to the end or exit early. With seccomp BPF specifically, the return value defaults to kill the process. If a filter was missing (NULL), or empty, or didn't explicitly return with a new value, the default (kill) should be taken. -Kees -- Kees Cook Chrome OS Security -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/