linux-kernel - Re: [PATCH] mm/slub: support left red zone

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Message-ID: <alpine.DEB.2.20.1602050300130.13917@east.gentwo.org>
Date:	Fri, 5 Feb 2016 03:06:30 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/slub: support left red zone

On Thu, 4 Feb 2016, Joonsoo Kim wrote:

> On Thu, Feb 04, 2016 at 03:15:50PM +0900, Joonsoo Kim wrote:
> > SLUB already has red zone debugging feature. But, it is only positioned
> > at the end of object(aka right red zone) so it cannot catch left oob.
> > Although current object's right red zone acts as left red zone of
> > previous object, first object in a slab cannot take advantage of
>
> Oops... s/previous/next.
>
> > this effect. This patch explicitly add left red zone to each objects
> > to detect left oob more precisely.


An access before the first object is an access outside of the page
boundaries of a page allocated by the page allocator for the slab
allocator since the first object starts at offset 0.



And the page allocator debugging methods can catch that case.


Do we really need this code?