From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Wed, 25 Jun 2014 19:53:02 +0200 (CEST) Received: from mx1.redhat.com ([209.132.183.28]:54903 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by eddie.linux-mips.org with ESMTP id S6859932AbaFYRw6aMBxj (ORCPT ); Wed, 25 Jun 2014 19:52:58 +0200 Received: from int-mx09.intmail.prod.int.phx2.redhat.com (int-mx09.intmail.prod.int.phx2.redhat.com [10.5.11.22]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id s5PHqh46008384 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 25 Jun 2014 13:52:44 -0400 Received: from tranklukator.brq.redhat.com (dhcp-1-125.brq.redhat.com [10.34.1.125]) by int-mx09.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with SMTP id s5PHqd1D027604; Wed, 25 Jun 2014 13:52:40 -0400 Received: by tranklukator.brq.redhat.com (nbSMTP-1.00) for uid 500 oleg@redhat.com; Wed, 25 Jun 2014 19:51:41 +0200 (CEST) Date: Wed, 25 Jun 2014 19:51:36 +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: <20140625175136.GA18185@redhat.com> References: <1403642893-23107-1-git-send-email-keescook@chromium.org> <1403642893-23107-6-git-send-email-keescook@chromium.org> <20140625135121.GB7892@redhat.com> <20140625173245.GA17695@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) X-Scanned-By: MIMEDefang 2.68 on 10.5.11.22 Return-Path: X-Envelope-To: <"|/home/ecartis/ecartis -s linux-mips"> (uid 0) X-Orcpt: rfc822;linux-mips@linux-mips.org Original-Recipient: rfc822;linux-mips@linux-mips.org X-archive-position: 40825 X-ecartis-version: Ecartis v1.0.0 Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org X-original-sender: oleg@redhat.com Precedence: bulk List-help: List-unsubscribe: List-software: Ecartis version 1.0.0 List-Id: linux-mips X-List-ID: linux-mips List-subscribe: List-owner: List-post: List-archive: X-list: linux-mips On 06/25, Andy Lutomirski wrote: > > On Wed, Jun 25, 2014 at 10:32 AM, Oleg Nesterov wrote: > > On 06/25, Andy Lutomirski wrote: > >> > >> Write the filter, then smp_mb (or maybe a weaker barrier is okay), > >> then set the bit. > > > > Yes, exactly, this is what I meant. Plas rmb() in __secure_computing(). > > > > But I still can't understand the rest of your discussion about the > > ordering we need ;) > > Let me try again from scratch. > > Currently there are three relevant variables: TIF_SECCOMP, > seccomp.mode, and seccomp.filter. __secure_computing needs > seccomp.mode and seccomp.filter to be in sync, and it wants (but > doesn't really need) TIF_SECCOMP to be in sync as well. > > My suggestion is to rearrange it a bit. Move mode into seccomp.filter > (so that filter == NULL implies no seccomp) and don't check > TIF_SECCOMP in secure_computing. Then turning on seccomp is entirely > atomic except for the fact that the seccomp hooks won't be called if > filter != NULL but !TIF_SECCOMP. This removes all ordering > requirements. Ah, got it, thanks. Perhaps I missed somehing, but to me this looks like unnecessary complication at first glance. We alredy have TIF_SECCOMP, we need it anyway, and we should only care about the case when this bit is actually set, so that we can race with the 1st call of __secure_computing(). Otherwise we are fine: we can miss the new filter anyway, ->mode can't be changed it is already nonzero. > Alternatively, __secure_computing could still BUG_ON(!seccomp.filter). > In that case, filter needs to be set before TIF_SECCOMP is set, but > that's straightforward. Yep. And this is how seccomp_assign_mode() already works? It is called after we change ->filter chain, it changes ->mode before set(TIF_SECCOMP) just it lacks a barrier. Oleg. From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx1.redhat.com ([209.132.183.28]:54903 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by eddie.linux-mips.org with ESMTP id S6859932AbaFYRw6aMBxj (ORCPT ); Wed, 25 Jun 2014 19:52:58 +0200 Date: Wed, 25 Jun 2014 19:51:36 +0200 From: Oleg Nesterov Subject: Re: [PATCH v8 5/9] seccomp: split mode set routines Message-ID: <20140625175136.GA18185@redhat.com> References: <1403642893-23107-1-git-send-email-keescook@chromium.org> <1403642893-23107-6-git-send-email-keescook@chromium.org> <20140625135121.GB7892@redhat.com> <20140625173245.GA17695@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Return-Path: Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org List-help: List-unsubscribe: List-software: Ecartis version 1.0.0 List-subscribe: List-owner: List-post: List-archive: 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 Message-ID: <20140625175136.c94QKkSXF9rsXKCWD1PMxGY2g0O1o6qcpy8fmd0pjDg@z> On 06/25, Andy Lutomirski wrote: > > On Wed, Jun 25, 2014 at 10:32 AM, Oleg Nesterov wrote: > > On 06/25, Andy Lutomirski wrote: > >> > >> Write the filter, then smp_mb (or maybe a weaker barrier is okay), > >> then set the bit. > > > > Yes, exactly, this is what I meant. Plas rmb() in __secure_computing(). > > > > But I still can't understand the rest of your discussion about the > > ordering we need ;) > > Let me try again from scratch. > > Currently there are three relevant variables: TIF_SECCOMP, > seccomp.mode, and seccomp.filter. __secure_computing needs > seccomp.mode and seccomp.filter to be in sync, and it wants (but > doesn't really need) TIF_SECCOMP to be in sync as well. > > My suggestion is to rearrange it a bit. Move mode into seccomp.filter > (so that filter == NULL implies no seccomp) and don't check > TIF_SECCOMP in secure_computing. Then turning on seccomp is entirely > atomic except for the fact that the seccomp hooks won't be called if > filter != NULL but !TIF_SECCOMP. This removes all ordering > requirements. Ah, got it, thanks. Perhaps I missed somehing, but to me this looks like unnecessary complication at first glance. We alredy have TIF_SECCOMP, we need it anyway, and we should only care about the case when this bit is actually set, so that we can race with the 1st call of __secure_computing(). Otherwise we are fine: we can miss the new filter anyway, ->mode can't be changed it is already nonzero. > Alternatively, __secure_computing could still BUG_ON(!seccomp.filter). > In that case, filter needs to be set before TIF_SECCOMP is set, but > that's straightforward. Yep. And this is how seccomp_assign_mode() already works? It is called after we change ->filter chain, it changes ->mode before set(TIF_SECCOMP) just it lacks a barrier. Oleg.