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

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Message-ID: <alpine.DEB.2.20.1512221023550.2748@east.gentwo.org>
Date:	Tue, 22 Dec 2015 10:25:00 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	Dave Hansen <dave.hansen@...el.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 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.

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