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Date: Tue, 5 Jan 2016 19:17:21 -0800
From: Laura Abbott <>
To: Kees Cook <>
Cc: Christoph Lameter <>, Pekka Enberg <>,
 David Rientjes <>, Joonsoo Kim <>,
 Andrew Morton <>, Linux-MM <>,
 LKML <>,
 "" <>
Subject: Re: [RFC][PATCH 0/7] Sanitization of slabs based on grsecurity/PaX

On 1/5/16 4:09 PM, Kees Cook wrote:
> On Tue, Dec 22, 2015 at 12:04 PM, Laura Abbott <> wrote:
>> On 12/22/15 8:08 AM, Christoph Lameter wrote:
>>> On Mon, 21 Dec 2015, Laura Abbott wrote:
>>>> The biggest change from PAX_MEMORY_SANTIIZE is that this feature
>>>> sanitizes
>>>> the SL[AOU]B allocators only. My plan is to work on the buddy allocator
>>>> santization after this series gets picked up. A side effect of this is
>>>> that allocations which go directly to the buddy allocator (i.e. large
>>>> allocations) aren't sanitized. I'd like feedback about whether it's worth
>>>> it to add sanitization on that path directly or just use the page
>>>> allocator sanitization when that comes in.
> This looks great! I love the added lkdtm tests, too. Very cool.
>>> I am not sure what the point of this patchset is. We have a similar effect
>>> to sanitization already in the allocators through two mechanisms:
>>> 1. Slab poisoning
>>> 2. Allocation with GFP_ZERO
>>> I do not think we need a third one. You could accomplish your goals much
>>> easier without this code churn by either
>>> 1. Improve the existing poisoning mechanism. Ensure that there are no
>>>      gaps. Security sensitive kernel slab caches can then be created with
>>>      the  POISONING flag set. Maybe add a Kconfig flag that enables
>>>      POISONING for each cache? What was the issue when you tried using
>>>      posining for sanitization?
>> The existing poisoning does work for sanitization but it's still a debug
>> feature. It seemed more appropriate to keep debug features and non-debug
>> features separate hence the separate option and configuration.
> What stuff is intertwined in the existing poisoning that makes it
> incompatible/orthogonal?

It's not the poisoning per se that's incompatible, it's how the poisoning is
set up. At least for slub, the current poisoning is part of SLUB_DEBUG which
enables other consistency checks on the allocator. Trying to pull out just
the poisoning for use when SLUB_DEBUG isn't on would result in roughly what
would be here anyway. I looked at trying to reuse some of the existing poisoning
and came to the conclusion it was less intrusive to the allocator to keep it


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