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

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Message-ID: <20160126070320.GB28254@js1304-P5Q-DELUXE>
Date:	Tue, 26 Jan 2016 16:03:20 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Laura Abbott <labbott@...oraproject.org>
Cc:	Christoph Lameter <cl@...ux.com>,
	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 Mon, Jan 25, 2016 at 05:15:10PM -0800, Laura Abbott wrote:
> Hi,
> 
> Based on the discussion from the series to add slab sanitization
> (lkml.kernel.org/g/<1450755641-7856-1-git-send-email-laura@...bott.name>)
> the existing SLAB_POISON mechanism already covers similar behavior.
> The performance of SLAB_POISON isn't very good. With hackbench -g 20 -l 1000
> on QEMU with one cpu:

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.

2) SLAB_POISON makes object size bigger so natural alignment will be
broken. For example, kmalloc(256) cache's size is 256 in normal
case but it would be 264 when SLAB_POISON is enabled. This causes
memory waste.

In fact, I'd prefer not reusing SLAB_POISON. It would make thing
simpler. But, it's up to Christoph.

Thanks.