linux-kernel - Re: [PATCH v2 13/16] mempool: Use kmalloc_size

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Message-ID: <f4fc52c4-7c18-1d76-0c7a-4058ea2486b9@suse.cz>
Date:   Mon, 26 Sep 2022 15:50:43 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Kees Cook <keescook@...omium.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        "Ruhl, Michael J" <michael.j.ruhl@...el.com>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Alex Elder <elder@...nel.org>,
        Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Christian König <christian.koenig@....com>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Daniel Micay <danielmicay@...il.com>,
        Yonghong Song <yhs@...com>, Marco Elver <elver@...gle.com>,
        Miguel Ojeda <ojeda@...nel.org>, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, linux-btrfs@...r.kernel.org,
        linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linaro-mm-sig@...ts.linaro.org, linux-fsdevel@...r.kernel.org,
        intel-wired-lan@...ts.osuosl.org, dev@...nvswitch.org,
        x86@...nel.org, llvm@...ts.linux.dev,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2 13/16] mempool: Use kmalloc_size_roundup() to match
 ksize() usage

On 9/23/22 22:28, Kees Cook wrote:
> Round up allocations with kmalloc_size_roundup() so that mempool's use
> of ksize() is always accurate and no special handling of the memory is
> needed by KASAN, UBSAN_BOUNDS, nor FORTIFY_SOURCE.
> 
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: linux-mm@...ck.org
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>   mm/mempool.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/mempool.c b/mm/mempool.c
> index 96488b13a1ef..0f3107b28e6b 100644
> --- a/mm/mempool.c
> +++ b/mm/mempool.c
> @@ -526,7 +526,7 @@ EXPORT_SYMBOL(mempool_free_slab);
>    */
>   void *mempool_kmalloc(gfp_t gfp_mask, void *pool_data)
>   {
> -	size_t size = (size_t)pool_data;
> +	size_t size = kmalloc_size_roundup((size_t)pool_data);

Hm it is kinda wasteful to call into kmalloc_size_roundup for every 
allocation that has the same input. We could do it just once in 
mempool_init_node() for adjusting pool->pool_data ?

But looking more closely, I wonder why poison_element() and 
kasan_unpoison_element() in mm/mempool.c even have to use 
ksize()/__ksize() and not just operate on the requested size (again, 
pool->pool_data). If no kmalloc mempool's users use ksize() to write 
beyond requested size, then we don't have to unpoison/poison that area 
either?

>   	return kmalloc(size, gfp_mask);
>   }
>   EXPORT_SYMBOL(mempool_kmalloc);