From mboxrd@z Thu Jan  1 00:00:00 1970
Received: with ECARTIS (v1.0.0; list linux-mips); Wed, 09 Jul 2014 20:57:28 +0200 (CEST)
Received: from mx1.redhat.com ([209.132.183.28]:43209 "EHLO mx1.redhat.com"
        rhost-flags-OK-OK-OK-OK) by eddie.linux-mips.org with ESMTP
        id S6861345AbaGIS5UB73pU (ORCPT <rfc822;linux-mips@linux-mips.org>);
        Wed, 9 Jul 2014 20:57:20 +0200
Received: from int-mx13.intmail.prod.int.phx2.redhat.com (int-mx13.intmail.prod.int.phx2.redhat.com [10.5.11.26])
        by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id s69IvAW8026742
        (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK);
        Wed, 9 Jul 2014 14:57:10 -0400
Received: from tranklukator.brq.redhat.com (dhcp-1-170.brq.redhat.com [10.34.1.170])
        by int-mx13.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with SMTP id s69Iv6L9024562;
        Wed, 9 Jul 2014 14:57:07 -0400
Received: by tranklukator.brq.redhat.com (nbSMTP-1.00) for uid 500
        oleg@redhat.com; Wed,  9 Jul 2014 20:55:52 +0200 (CEST)
Date:   Wed, 9 Jul 2014 20:55:49 +0200
From:   Oleg Nesterov <oleg@redhat.com>
To:     Kees Cook <keescook@chromium.org>
Cc:     linux-kernel@vger.kernel.org,
        Andy Lutomirski <luto@amacapital.net>,
        "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>,
        Alexei Starovoitov <ast@plumgrid.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Daniel Borkmann <dborkman@redhat.com>,
        Will Drewry <wad@chromium.org>,
        Julien Tinnes <jln@chromium.org>,
        David Drysdale <drysdale@google.com>,
        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
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>
User-Agent: Mutt/1.5.18 (2008-05-17)
X-Scanned-By: MIMEDefang 2.68 on 10.5.11.26
Return-Path: <oleg@redhat.com>
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: 41105
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: <mailto:ecartis@linux-mips.org?Subject=help>
List-unsubscribe: <mailto:ecartis@linux-mips.org?subject=unsubscribe%20linux-mips>
List-software: Ecartis version 1.0.0
List-Id: linux-mips <linux-mips.eddie.linux-mips.org>
X-List-ID: linux-mips <linux-mips.eddie.linux-mips.org>
List-subscribe: <mailto:ecartis@linux-mips.org?subject=subscribe%20linux-mips>
List-owner: <mailto:ralf@linux-mips.org>
List-post: <mailto:linux-mips@linux-mips.org>
List-archive: <http://www.linux-mips.org/archives/linux-mips/>
X-list: linux-mips

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.