Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932335AbaFYRCx (ORCPT ); Wed, 25 Jun 2014 13:02:53 -0400 Received: from mx1.redhat.com ([209.132.183.28]:32789 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755985AbaFYRCw (ORCPT ); Wed, 25 Jun 2014 13:02:52 -0400 Date: Wed, 25 Jun 2014 19:00:39 +0200 From: Oleg Nesterov To: Kees Cook Cc: LKML , Andy Lutomirski , "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: <20140625170039.GB14720@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> 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 06/25, Kees Cook wrote: > > On Wed, Jun 25, 2014 at 6:51 AM, Oleg Nesterov wrote: > > On 06/24, Kees Cook wrote: > >> > >> +static inline void seccomp_assign_mode(struct task_struct *task, > >> + unsigned long seccomp_mode) > >> +{ > >> + BUG_ON(!spin_is_locked(&task->sighand->siglock)); > >> + > >> + task->seccomp.mode = seccomp_mode; > >> + set_tsk_thread_flag(task, TIF_SECCOMP); > >> +} > > > > OK, but unless task == current this can race with secure_computing(). > > I think this needs smp_mb__before_atomic() and secure_computing() needs > > rmb() after test_bit(TIF_SECCOMP). > > > > Otherwise, can't __secure_computing() hit BUG() if it sees the old > > mode == SECCOMP_MODE_DISABLED ? > > > > Or seccomp_run_filters() can see ->filters == NULL and WARN(), > > smp_load_acquire() only serializes that LOAD with the subsequent memory > > operations. > > Hm, actually, now I'm worried about smp_load_acquire() being too slow > in run_filters(). > > The ordering must be: > - task->seccomp.filter must be valid before > - task->seccomp.mode is set, which must be valid before > - TIF_SECCOMP is set > > But I don't want to impact secure_computing(). What's the best way to > make sure this ordering is respected? Cough, confused... can't understand even after I read the email from Andy. We do not care if __secure_computing() misses the recently added filter, this can happen anyway, whatever we do. seccomp.mode is frozen after we set it != SECCOMP_MODE_DISABLED. So we should only worry if set_tsk_thread_flag(TIF_SECCOMP) actually changes this bit and makes __secure_computing() possible. If we add smp_mb__before_atomic() into seccomp_assign_mode() and rmb() at the start of __secure_computing() everything should be fine? 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/