linux-kernel - Re: [kernel-hardening] [RFC][PATCH 6/7] mm: Add Kconfig option for slab sanitization

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Date:	Tue, 22 Dec 2015 09:22:47 -0800
From:	Dave Hansen <dave.hansen@...el.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	kernel-hardening@...ts.openwall.com,
	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Laura Abbott <laura@...bott.name>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>
Subject: Re: [kernel-hardening] [RFC][PATCH 6/7] mm: Add Kconfig option for
 slab sanitization

On 12/22/2015 08:25 AM, Christoph Lameter wrote:
> On Tue, 22 Dec 2015, Dave Hansen wrote:
>> On 12/21/2015 07:40 PM, Laura Abbott wrote:
>>> +	  The tradeoff is performance impact. The noticible impact can vary
>>> +	  and you are advised to test this feature on your expected workload
>>> +	  before deploying it
>>
>> What if instead of writing SLAB_MEMORY_SANITIZE_VALUE, we wrote 0's?
>> That still destroys the information, but it has the positive effect of
>> allowing a kzalloc() call to avoid zeroing the slab object.  It might
>> mitigate some of the performance impact.
> 
> We already write zeros in many cases or the object is initialized in a
> different. No one really wants an uninitialized object. The problem may be
> that a freed object is having its old content until reused. Which is
> something that poisoning deals with.

Or are you just saying that we should use the poisoning *code* that we
already have in slub?  Using the _code_ looks like a really good idea,
whether we're using it to write POISON_FREE, or 0's.  Something like the
attached patch?



View attachment "slub-poison-zeros.patch" of type "text/x-patch" (1547 bytes)