linux-kernel - Re: [PATCH v3 1/3] mm/slub: Consider kfence case for get_orig

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Message-ID: <CAB=+i9TBMmq5EScWnNMHJAFqSxT3_wWkgJe20d3_w2D148gDVg@mail.gmail.com>
Date: Thu, 14 Nov 2024 22:38:47 +0900
From: Hyeonggon Yoo <42.hyeyoo@...il.com>
To: Feng Tang <feng.tang@...el.com>
Cc: Vlastimil Babka <vbabka@...e.cz>, Andrew Morton <akpm@...ux-foundation.org>, 
	Christoph Lameter <cl@...ux.com>, Pekka Enberg <penberg@...nel.org>, David Rientjes <rientjes@...gle.com>, 
	Joonsoo Kim <iamjoonsoo.kim@....com>, Roman Gushchin <roman.gushchin@...ux.dev>, 
	Andrey Konovalov <andreyknvl@...il.com>, Marco Elver <elver@...gle.com>, 
	Alexander Potapenko <glider@...gle.com>, Dmitry Vyukov <dvyukov@...gle.com>, 
	Danilo Krummrich <dakr@...nel.org>, Narasimhan.V@....com, linux-mm@...ck.org, 
	kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/3] mm/slub: Consider kfence case for get_orig_size()

On Thu, Oct 17, 2024 at 12:42 AM Feng Tang <feng.tang@...el.com> wrote:
>
> When 'orig_size' of kmalloc object is enabled by debug option, it
> should either contains the actual requested size or the cache's
> 'object_size'.
>
> But it's not true if that object is a kfence-allocated one, and the
> data at 'orig_size' offset of metadata could be zero or other values.
> This is not a big issue for current 'orig_size' usage, as init_object()
> and check_object() during alloc/free process will be skipped for kfence
> addresses. But it could cause trouble for other usage in future.
>
> Use the existing kfence helper kfence_ksize() which can return the
> real original request size.
>
> Signed-off-by: Feng Tang <feng.tang@...el.com>
> ---

Looks good to me,
Reviewed-by: Hyeonggon Yoo <42.hyeyoo@...il.com>

>  mm/slub.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/mm/slub.c b/mm/slub.c
> index af9a80071fe0..1d348899f7a3 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -768,6 +768,9 @@ static inline unsigned int get_orig_size(struct kmem_cache *s, void *object)
>  {
>         void *p = kasan_reset_tag(object);
>
> +       if (is_kfence_address(object))
> +               return kfence_ksize(object);
> +
>         if (!slub_debug_orig_size(s))
>                 return s->object_size;
>
> --
> 2.27.0
>