Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1751779AbdGZOln (ORCPT <rfc822;w@1wt.eu>);
        Wed, 26 Jul 2017 10:41:43 -0400
Received: from resqmta-ch2-10v.sys.comcast.net ([69.252.207.42]:47594 "EHLO
        resqmta-ch2-10v.sys.comcast.net" rhost-flags-OK-OK-OK-OK)
        by vger.kernel.org with ESMTP id S1751756AbdGZOlk (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Wed, 26 Jul 2017 10:41:40 -0400
Date: Wed, 26 Jul 2017 09:08:01 -0500 (CDT)
From: Christopher Lameter <cl@linux.com>
X-X-Sender: cl@nuc-kabylake
To: Kees Cook <keescook@chromium.org>
cc: Alexander Popov <alex.popov@linux.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Ingo Molnar <mingo@kernel.org>, Josh Triplett <josh@joshtriplett.org>,
        Andy Lutomirski <luto@kernel.org>,
        Nicolas Pitre <nicolas.pitre@linaro.org>, Tejun Heo <tj@kernel.org>,
        Daniel Mack <daniel@zonque.org>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Helge Deller <deller@gmx.de>, Rik van Riel <riel@redhat.com>,
        Linux-MM <linux-mm@kvack.org>, Tycho Andersen <tycho@docker.com>,
        LKML <linux-kernel@vger.kernel.org>,
        "kernel-hardening@lists.openwall.com" 
        <kernel-hardening@lists.openwall.com>
Subject: Re: [v3] mm: Add SLUB free list pointer obfuscation
In-Reply-To: <CAGXu5jKRDhvqj0TU10W10hsdixN2P+hHzpYfSVvOFZy=hW72Mg@mail.gmail.com>
Message-ID: <alpine.DEB.2.20.1707260906230.6341@nuc-kabylake>
References: <20170706002718.GA102852@beast> <cdd42a1b-ce15-df8c-6bd1-b0943275986f@linux.com> <CAGXu5jKRDhvqj0TU10W10hsdixN2P+hHzpYfSVvOFZy=hW72Mg@mail.gmail.com>
User-Agent: Alpine 2.20 (DEB 67 2015-01-07)
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
X-CMAE-Envelope: MS4wfGO1K7M5Mh/B8Gll7leJOMLrl2oS0tSxCmRZOqzFc4fyv06+UCtbm1lgM5Tg7sgPszEzlx2m70X3GQHC6dorojETdO3ukErEo6VM46nwaceTpUrD7zoW
 tiDSYuE/8H9Wl3nh1coOXMu9mtLpGGedPJVFuaPcH8aijSi/VLyz+lvav1YJ6Kpt63LyfnqJBFHNydK6DbkKdWvhi+tU3D2C6YfvJ9Q0Qg/BPvPOzvqeg6CO
 dAlEGvxne6jPBVWfUnKnPTJVZnzcnJyvKHTyzj/fz9c6aC8NK9++T9lGdgHqnSXBKu6N0gbknuQgt4+k91eSFNJUKD1Od7phRb0q5msRlVHnpTVTFg3eR7Tp
 IE/XEGYvNATLiwhFhFVqypzVkt0lYhyWT/VTXMLB+RCGeMqNIQ2vBqjYD9eS0MS8rvzM8Uh/FvlAfx5medTXBPqap1v+RTZiC1jhHYEdqh2kbHkia+FYku4Z
 9pWRuXSpsn35j4eVWNd6FF2j8bP5z/MpFFSpvsuB90ws820fEvfHED7kg7PG/w+byibrNTgtJdLwckon+ov4STU7/563siN9jDB2gYcJEres5ZHZ9Dt6ULYI
 0aAimrQeTdEm4aBZ2fn8TyChDN9ZpVGslQSaRvaSPYLSLE8VxOEpHZbdu4r0NLlNvg+IiU2HtRBxNgS2ktnu9e6PFjmCYrPHBqycQn8LQVyfyVTegnuGaETf
 HpbEXYDOO5Iq82U6sYALy1cEewAOpHmoJuslmOMLa3DJHKwqZl8JrXy3VEPofd5uHZ0L5QMkPDbaXgmnRWTcgEUjA2MwV/4k
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 761
Lines: 21

On Tue, 25 Jul 2017, Kees Cook wrote:

> > @@ -290,6 +290,10 @@ static inline void set_freepointer(struct kmem_cache *s,
> > void *object, void *fp)
> >  {
> >         unsigned long freeptr_addr = (unsigned long)object + s->offset;
> >
> > +#ifdef CONFIG_SLAB_FREELIST_HARDENED
> > +       BUG_ON(object == fp); /* naive detection of double free or corruption */
> > +#endif
> > +
> >         *(void **)freeptr_addr = freelist_ptr(s, fp, freeptr_addr);
>
> What happens if, instead of BUG_ON, we do:
>
> if (unlikely(WARN_RATELIMIT(object == fp, "double-free detected"))
>         return;

This may work for the free fastpath but the set_freepointer function is
use in multiple other locations. Maybe just add this to the fastpath
instead of to this fucnction?