linux-kernel - Re: [PATCH] slab: implement kmalloc guard

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Date:	Mon, 15 Sep 2014 11:11:34 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Mikulas Patocka <mpatocka@...hat.com>
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,
	"Alasdair G. Kergon" <agk@...hat.com>,
	Mike Snitzer <msnitzer@...hat.com>,
	Milan Broz <gmazyland@...il.com>, kkolasa@...soft.pl,
	dm-devel@...hat.com
Subject: Re: [PATCH] slab: implement kmalloc guard

On Thu, Sep 11, 2014 at 10:32:52PM -0400, Mikulas Patocka wrote:
> 
> 
> On Mon, 8 Sep 2014, Christoph Lameter wrote:
> 
> > On Mon, 8 Sep 2014, Mikulas Patocka wrote:
> > 
> > > I don't know what you mean. If someone allocates 10000 objects with sizes
> > > from 1 to 10000, you can't have 10000 slab caches - you can't have a slab
> > > cache for each used size. Also - you can't create a slab cache in
> > > interrupt context.
> > 
> > Oh you can create them up front on bootup. And I think only the small
> > sizes matter. Allocations >=8K are pushed to the page allocator anyways.
> 
> Only for SLUB. For SLAB, large allocations are still use SLAB caches up to 
> 4M. But anyway - having 8K preallocated slab caches is too much.
> 
> If you want to integrate this patch into the slab/slub subsystem, a better 
> solution would be to store the exact size requested with kmalloc along the 
> slab/slub object itself (before the preceding redzone). But it would 
> result in duplicating the work - you'd have to repeat the logic in this 
> patch three times - once for slab, once for slub and once for 
> kmalloc_large/kmalloc_large_node.
> 
> I don't know if it would be better than this patch.

Hello,

Out of bound write could be detected by kernel address asanitizer(KASan).
See following link.

https://lkml.org/lkml/2014/9/10/441

Although this patch also looks good to me, I think that KASan is
better than this, because it could detect out of bound write and
has more features for debugging.

Thanks.
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