linux-kernel - Re: [PATCH mm] kfence: make compatible with kmemleak

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Message-ID: <20210317085225.GA12269@arm.com>
Date:   Wed, 17 Mar 2021 08:52:26 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Marco Elver <elver@...gle.com>
Cc:     akpm@...ux-foundation.org, glider@...gle.com, dvyukov@...gle.com,
        andreyknvl@...gle.com, jannh@...gle.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        kasan-dev@...glegroups.com, Luis Henriques <lhenriques@...e.de>
Subject: Re: [PATCH mm] kfence: make compatible with kmemleak

On Wed, Mar 17, 2021 at 09:47:40AM +0100, Marco Elver wrote:
> Because memblock allocations are registered with kmemleak, the KFENCE
> pool was seen by kmemleak as one large object. Later allocations through
> kfence_alloc() that were registered with kmemleak via
> slab_post_alloc_hook() would then overlap and trigger a warning.
> Therefore, once the pool is initialized, we can remove (free) it from
> kmemleak again, since it should be treated as allocator-internal and be
> seen as "free memory".
> 
> The second problem is that kmemleak is passed the rounded size, and not
> the originally requested size, which is also the size of KFENCE objects.
> To avoid kmemleak scanning past the end of an object and trigger a
> KFENCE out-of-bounds error, fix the size if it is a KFENCE object.
> 
> For simplicity, to avoid a call to kfence_ksize() in
> slab_post_alloc_hook() (and avoid new IS_ENABLED(CONFIG_DEBUG_KMEMLEAK)
> guard), just call kfence_ksize() in mm/kmemleak.c:create_object().
> 
> Reported-by: Luis Henriques <lhenriques@...e.de>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Signed-off-by: Marco Elver <elver@...gle.com>

Reviewed-by: Catalin Marinas <catalin.marinas@....com>