Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753782AbaF0T5q (ORCPT ); Fri, 27 Jun 2014 15:57:46 -0400 Received: from mx1.redhat.com ([209.132.183.28]:65381 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751493AbaF0T5n (ORCPT ); Fri, 27 Jun 2014 15:57:43 -0400 Date: Fri, 27 Jun 2014 21:55:59 +0200 From: Oleg Nesterov To: Andy Lutomirski 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 Subject: Re: [PATCH v8 5/9] seccomp: split mode set routines Message-ID: <20140627195559.GA31661@redhat.com> References: <20140625173245.GA17695@redhat.com> <20140625175136.GA18185@redhat.com> <20140627192753.GA30752@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/27, Andy Lutomirski wrote: > > 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. I am just curious, does this 13ns overhead include the penalty from the slow syscall enter path triggered by TIF_SECCOMP ? > 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. Well, I am not going to insist... But imo it would be better to make it correct in a most simple way, then we can optimize this code and see if there is a noticeable difference. Not only we can change the ordering, we can remove the BUG_ON's and just accept the fact the __secure_computing() can race with sys_seccomp() from another thread. If nothing else, it would be much simpler to discuss this patch if it comes as a separate change. Oleg. -- 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/