Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757257AbaFYOv2 (ORCPT ); Wed, 25 Jun 2014 10:51:28 -0400 Received: from mail-ob0-f177.google.com ([209.85.214.177]:52820 "EHLO mail-ob0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756559AbaFYOvZ (ORCPT ); Wed, 25 Jun 2014 10:51:25 -0400 MIME-Version: 1.0 In-Reply-To: <20140625135121.GB7892@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> Date: Wed, 25 Jun 2014 07:51:25 -0700 X-Google-Sender-Auth: RCNeIVkYTQv2tceTvFHUOTo4kcM Message-ID: Subject: Re: [PATCH v8 5/9] seccomp: split mode set routines From: Kees Cook To: Oleg Nesterov 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 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 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? -Kees -- Kees Cook Chrome OS Security -- 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/