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Date: Sun, 25 Jun 2017 12:56:21 -0700
From: Kees Cook <keescook@...omium.org>
To: Christoph Lameter <cl@...ux.com>, Andrew Morton <akpm@...ux-foundation.org>
Cc: Laura Abbott <labbott@...hat.com>, Daniel Micay <danielmicay@...il.com>,
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>, LKML <linux-kernel@...r.kernel.org>,
Linux-MM <linux-mm@...ck.org>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH v2] mm: Add SLUB free list pointer obfuscation
On Thu, Jun 22, 2017 at 6:50 PM, Kees Cook <keescook@...omium.org> wrote:
> This SLUB free list pointer obfuscation code is modified from Brad
> Spengler/PaX Team's code in the last public patch of grsecurity/PaX based
> on my understanding of the code. Changes or omissions from the original
> code are mine and don't reflect the original grsecurity/PaX code.
>
> This adds a per-cache random value to SLUB caches that is XORed with
> their freelist pointers. This adds nearly zero overhead and frustrates the
> very common heap overflow exploitation method of overwriting freelist
> pointers. A recent example of the attack is written up here:
> http://cyseclabs.com/blog/cve-2016-6187-heap-off-by-one-exploit
BTW, to quantify "nearly zero overhead", I ran multiple 200-run cycles
of "hackbench -g 20 -l 1000", and saw:
before:
mean 10.11882499999999999995
variance .03320378329145728642
stdev .18221905304181911048
after:
mean 10.12654000000000000014
variance .04700556623115577889
stdev .21680767106160192064
The difference gets lost in the noise, but if the above is sensible,
it's 0.07% slower. ;)
-Kees
--
Kees Cook
Pixel Security
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