From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757880AbaFYRil (ORCPT ); Wed, 25 Jun 2014 13:38:41 -0400 Received: from mail-la0-f45.google.com ([209.85.215.45]:53174 "EHLO mail-la0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757837AbaFYRij (ORCPT ); Wed, 25 Jun 2014 13:38:39 -0400 MIME-Version: 1.0 In-Reply-To: <20140625173245.GA17695@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> From: Andy Lutomirski Date: Wed, 25 Jun 2014 10:38:17 -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 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. 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. --Andy