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Message-ID: <CAGXu5jLNeO-WmaQXp9z-+iw2sha-DXixtQ-fjQmahUkh0Hvxeg@mail.gmail.com>
Date: Wed, 26 Jul 2017 10:13:59 -0700
From: Kees Cook <keescook@...omium.org>
To: Christopher Lameter <cl@...ux.com>
Cc: Alexander Popov <alex.popov@...ux.com>, Andrew Morton <akpm@...ux-foundation.org>,
Pekka Enberg <penberg@...nel.org>, David Rientjes <rientjes@...gle.com>,
Joonsoo Kim <iamjoonsoo.kim@....com>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Ingo Molnar <mingo@...nel.org>, Josh Triplett <josh@...htriplett.org>,
Andy Lutomirski <luto@...nel.org>, Nicolas Pitre <nicolas.pitre@...aro.org>, Tejun Heo <tj@...nel.org>,
Daniel Mack <daniel@...que.org>, Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Sergey Senozhatsky <sergey.senozhatsky@...il.com>, Helge Deller <deller@....de>,
Rik van Riel <riel@...hat.com>, Linux-MM <linux-mm@...ck.org>, Tycho Andersen <tycho@...ker.com>,
LKML <linux-kernel@...r.kernel.org>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>
Subject: Re: [v3] mm: Add SLUB free list pointer obfuscation
On Wed, Jul 26, 2017 at 9:55 AM, Christopher Lameter <cl@...ux.com> wrote:
> On Wed, 26 Jul 2017, Kees Cook wrote:
>
>> >> 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?
>>
>> Do you mean do_slab_free()?
>
> Yes inserting these lines into do_slab_free() would simple ignore the
> double free operation in the fast path and that would be safe.
>
> Although in either case we are adding code to the fastpath...
While I'd like it unconditionally, I think Alexander's proposal was to
put it behind CONFIG_SLAB_FREELIST_HARDENED.
BTW, while I've got your attention, can you Ack the other patch? I
sent a v4 for the pointer obfuscation, which we really need:
https://lkml.org/lkml/2017/7/26/4
Thanks!
-Kees
--
Kees Cook
Pixel Security
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