Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753449AbaF0Tbl (ORCPT ); Fri, 27 Jun 2014 15:31:41 -0400 Received: from mail-lb0-f174.google.com ([209.85.217.174]:51405 "EHLO mail-lb0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750862AbaF0Tbi (ORCPT ); Fri, 27 Jun 2014 15:31:38 -0400 MIME-Version: 1.0 In-Reply-To: <20140627192753.GA30752@redhat.com> References: <20140625173245.GA17695@redhat.com> <20140625175136.GA18185@redhat.com> <20140627192753.GA30752@redhat.com> From: Andy Lutomirski Date: Fri, 27 Jun 2014 12:31:16 -0700 Message-ID: Subject: Re: [PATCH v8 5/9] seccomp: split mode set routines To: Oleg Nesterov Cc: Kees Cook , LKML , "Michael Kerrisk (man-pages)" , Alexei Starovoitov , Andrew Morton , Daniel Borkmann , Will Drewry , Julien Tinnes , David Drysdale , Linux API , "x86@kernel.org" , "linux-arm-kernel@lists.infradead.org" , linux-mips@linux-mips.org, linux-arch , linux-security-module 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 Fri, Jun 27, 2014 at 12:27 PM, Oleg Nesterov wrote: > On 06/27, Kees Cook wrote: >> >> It looks like SMP ARM issues dsb for rmb, which seems a bit expensive. >> http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0204g/CIHJFGFE.htm >> >> ... >> >> I really want to avoid adding anything to the secure_computing() >> execution path. :( > > I must have missed something but I do not understand your concerns. > > __secure_computing() is not trivial, and we are going to execute the > filters. Do you really think rmb() can add the noticeable difference? > > Not to mention that we can only get here if we take the slow syscall > enter path due to TIF_SECCOMP... > On my box, with my fancy multi-phase seccomp patches, the total seccomp overhead for a very short filter is about 13ns. Adding a full barrier would add several ns, I think. Admittedly, this is x86, not ARM, so comparisons here are completely bogus. And that read memory barrier doesn't even need an instruction on x86. But still, let's try to keep this fast. --Andy -- 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/