linux-hardening - Re: [PATCH 03/12] net: ipa: Proactively round up to kmalloc bucket size

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Message-ID: <4d75a9fd-1b94-7208-9de8-5a0102223e68@ieee.org>
Date:   Thu, 22 Sep 2022 08:45:19 -0500
From:   Alex Elder <elder@...e.org>
To:     Kees Cook <keescook@...omium.org>, Vlastimil Babka <vbabka@...e.cz>
Cc:     Alex Elder <elder@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        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>,
        Jacob Shin <jacob.shin@....com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.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, linux-wireless@...r.kernel.org,
        llvm@...ts.linux.dev, linux-hardening@...r.kernel.org
Subject: Re: [PATCH 03/12] net: ipa: Proactively round up to kmalloc bucket
 size

On 9/21/22 10:10 PM, Kees Cook wrote:
> Instead of discovering the kmalloc bucket size _after_ allocation, round
> up proactively so the allocation is explicitly made for the full size,
> allowing the compiler to correctly reason about the resulting size of
> the buffer through the existing __alloc_size() hint.
> 
> Cc: Alex Elder <elder@...nel.org>
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: Eric Dumazet <edumazet@...gle.com>
> Cc: Jakub Kicinski <kuba@...nel.org>
> Cc: Paolo Abeni <pabeni@...hat.com>
> Cc: netdev@...r.kernel.org
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>   drivers/net/ipa/gsi_trans.c | 7 +++++--
>   1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ipa/gsi_trans.c b/drivers/net/ipa/gsi_trans.c
> index 18e7e8c405be..cec968854dcf 100644
> --- a/drivers/net/ipa/gsi_trans.c
> +++ b/drivers/net/ipa/gsi_trans.c
> @@ -89,6 +89,7 @@ int gsi_trans_pool_init(struct gsi_trans_pool *pool, size_t size, u32 count,
>   			u32 max_alloc)
>   {
>   	void *virt;
> +	size_t allocate;

I don't care about this but the reverse Christmas tree
convention would put the "allocate" variable definition
above "virt".

Whether you fix that or not, this patch looks good to me.

Reviewed-by: Alex Elder <elder@...aro.org>

>   	if (!size)
>   		return -EINVAL;
> @@ -104,13 +105,15 @@ int gsi_trans_pool_init(struct gsi_trans_pool *pool, size_t size, u32 count,
>   	 * If there aren't enough entries starting at the free index,
>   	 * we just allocate free entries from the beginning of the pool.
>   	 */
> -	virt = kcalloc(count + max_alloc - 1, size, GFP_KERNEL);
> +	allocate = size_mul(count + max_alloc - 1, size);
> +	allocate = kmalloc_size_roundup(allocate);
> +	virt = kzalloc(allocate, GFP_KERNEL);
>   	if (!virt)
>   		return -ENOMEM;
>   
>   	pool->base = virt;
>   	/* If the allocator gave us any extra memory, use it */
> -	pool->count = ksize(pool->base) / size;
> +	pool->count = allocate / size;
>   	pool->free = 0;
>   	pool->max_alloc = max_alloc;
>   	pool->size = size;