From mboxrd@z Thu Jan 1 00:00:00 1970 From: Oleg Nesterov Subject: Re: [PATCH v9 09/11] seccomp: introduce writer locking Date: Wed, 9 Jul 2014 20:55:49 +0200 Message-ID: <20140709185549.GB4866@redhat.com> References: <1403911380-27787-1-git-send-email-keescook@chromium.org> <1403911380-27787-10-git-send-email-keescook@chromium.org> <20140709184215.GA4866@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20140709184215.GA4866@redhat.com> 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: Kees Cook Cc: linux-kernel@vger.kernel.org, Andy Lutomirski , "Michael Kerrisk (man-pages)" , Alexei Starovoitov , Andrew Morton , Daniel Borkmann , Will Drewry , Julien Tinnes , David Drysdale , linux-api@vger.kernel.org, x86@kernel.org, linux-arm-kernel@lists.infradead.org, linux-mips@linux-mips.org, linux-arch@vger.kernel.org, linux-security-module@vger.kernel.org List-Id: linux-arch.vger.kernel.org On 07/09, Oleg Nesterov wrote: > > On 06/27, Kees Cook wrote: > > > > static u32 seccomp_run_filters(int syscall) > > { > > - struct seccomp_filter *f; > > + struct seccomp_filter *f = ACCESS_ONCE(current->seccomp.filter); > > I am not sure... > > This is fine if this ->filter is the 1st (and only) one, in this case > we can rely on rmb() in the caller. > > But the new filter can be installed at any moment. Say, right after that > rmb() although this doesn't matter. Either we need smp_read_barrier_depends() > after that, or smp_load_acquire() like the previous version did? Wait... and it seems that seccomp_sync_threads() needs smp_store_release() when it sets thread->filter = current->filter by the same reason? OTOH. smp_store_release() in seccomp_attach_filter() can die, "current" doesn't need a barrier to serialize with itself. Oleg. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:35111 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932226AbaGIS5s (ORCPT ); Wed, 9 Jul 2014 14:57:48 -0400 Date: Wed, 9 Jul 2014 20:55:49 +0200 From: Oleg Nesterov Subject: Re: [PATCH v9 09/11] seccomp: introduce writer locking Message-ID: <20140709185549.GB4866@redhat.com> References: <1403911380-27787-1-git-send-email-keescook@chromium.org> <1403911380-27787-10-git-send-email-keescook@chromium.org> <20140709184215.GA4866@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140709184215.GA4866@redhat.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Kees Cook Cc: linux-kernel@vger.kernel.org, Andy Lutomirski , "Michael Kerrisk (man-pages)" , Alexei Starovoitov , Andrew Morton , Daniel Borkmann , Will Drewry , Julien Tinnes , David Drysdale , linux-api@vger.kernel.org, x86@kernel.org, linux-arm-kernel@lists.infradead.org, linux-mips@linux-mips.org, linux-arch@vger.kernel.org, linux-security-module@vger.kernel.org Message-ID: <20140709185549.l0YjQmTlyNmvFOnXVQi8mUU7sBXA1G5dPGHVTAVqs3s@z> On 07/09, Oleg Nesterov wrote: > > On 06/27, Kees Cook wrote: > > > > static u32 seccomp_run_filters(int syscall) > > { > > - struct seccomp_filter *f; > > + struct seccomp_filter *f = ACCESS_ONCE(current->seccomp.filter); > > I am not sure... > > This is fine if this ->filter is the 1st (and only) one, in this case > we can rely on rmb() in the caller. > > But the new filter can be installed at any moment. Say, right after that > rmb() although this doesn't matter. Either we need smp_read_barrier_depends() > after that, or smp_load_acquire() like the previous version did? Wait... and it seems that seccomp_sync_threads() needs smp_store_release() when it sets thread->filter = current->filter by the same reason? OTOH. smp_store_release() in seccomp_attach_filter() can die, "current" doesn't need a barrier to serialize with itself. Oleg.