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Date:   Mon, 26 Sep 2022 15:50:43 +0200
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Subject: Re: [PATCH v2 13/16] mempool: Use kmalloc_size_roundup() to match
 ksize() usage
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To:     Kees Cook <keescook@chromium.org>
Cc:     Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        "Ruhl, Michael J" <michael.j.ruhl@intel.com>,
        Hyeonggon Yoo <42.hyeyoo@gmail.com>,
        Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Alex Elder <elder@kernel.org>,
        Josef Bacik <josef@toxicpanda.com>,
        David Sterba <dsterba@suse.com>,
        Sumit Semwal <sumit.semwal@linaro.org>,
        =?UTF-8?Q?Christian_K=c3=b6nig?= <christian.koenig@amd.com>,
        Jesse Brandeburg <jesse.brandeburg@intel.com>,
        Daniel Micay <danielmicay@gmail.com>,
        Yonghong Song <yhs@fb.com>, Marco Elver <elver@google.com>,
        Miguel Ojeda <ojeda@kernel.org>, linux-kernel@vger.kernel.org,
        netdev@vger.kernel.org, linux-btrfs@vger.kernel.org,
        linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org,
        linaro-mm-sig@lists.linaro.org, linux-fsdevel@vger.kernel.org,
        intel-wired-lan@lists.osuosl.org, dev@openvswitch.org,
        x86@kernel.org, llvm@lists.linux.dev,
        linux-hardening@vger.kernel.org
References: <20220923202822.2667581-1-keescook@chromium.org>
 <20220923202822.2667581-14-keescook@chromium.org>
From:   Vlastimil Babka <vbabka@suse.cz>
In-Reply-To: <20220923202822.2667581-14-keescook@chromium.org>
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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@linux-foundation.org>
> Cc: linux-mm@kvack.org
> Signed-off-by: Kees Cook <keescook@chromium.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);