linux-kernel - Re: [RFC][PATCH 0/3] Speed up SLUB poisoning + disable checks

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Date:	Tue, 26 Jan 2016 09:01:31 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
cc:	Laura Abbott <labbott@...oraproject.org>,
	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com,
	Kees Cook <keescook@...omium.org>
Subject: Re: [RFC][PATCH 0/3] Speed up SLUB poisoning + disable checks

On Tue, 26 Jan 2016, Joonsoo Kim wrote:

> I doesn't follow up that discussion, but, I think that reusing
> SLAB_POISON for slab sanitization needs more changes. I assume that
> completeness and performance is matter for slab sanitization.
>
> 1) SLAB_POISON isn't applied to specific kmem_cache which has
> constructor or SLAB_DESTROY_BY_RCU flag. For debug, it's not necessary
> to be applied, but, for slab sanitization, it is better to apply it to
> all caches.

Those slabs can be legitimately accessed after the objects were freed. You
cannot sanitize nor poison.