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Date: Sun, 25 Jun 2017 12:56:21 -0700
From: Kees Cook <>
To: Christoph Lameter <>, Andrew Morton <>
Cc: Laura Abbott <>, Daniel Micay <>, 
	Pekka Enberg <>, David Rientjes <>, 
	Joonsoo Kim <>, "Paul E. McKenney" <>, 
	Ingo Molnar <>, Josh Triplett <>, 
	Andy Lutomirski <>, Nicolas Pitre <>, Tejun Heo <>, 
	Daniel Mack <>, Sebastian Andrzej Siewior <>, 
	Sergey Senozhatsky <>, Helge Deller <>, 
	Rik van Riel <>, LKML <>, 
	Linux-MM <>, 
	"" <>
Subject: Re: [PATCH v2] mm: Add SLUB free list pointer obfuscation

On Thu, Jun 22, 2017 at 6:50 PM, Kees Cook <> 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:

BTW, to quantify "nearly zero overhead", I ran multiple 200-run cycles
of "hackbench -g 20 -l 1000", and saw:

mean 10.11882499999999999995
variance .03320378329145728642
stdev .18221905304181911048

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 Cook
Pixel Security

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