linux-kernel - Re: [PATCH] crypto: ctr: avoid VLA use

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Message-ID: <CAJHCu1+hKPTijqMO-bz5iB7fdmdxbh+xcpzW96tLYvOUBqhemg@mail.gmail.com>
Date:   Thu, 15 Mar 2018 11:42:25 +0100
From:   Salvatore Mesoraca <s.mesoraca16@...il.com>
To:     Herbert Xu <herbert@...dor.apana.org.au>
Cc:     linux-kernel@...r.kernel.org,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        linux-crypto@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH] crypto: ctr: avoid VLA use

2018-03-15 10:54 GMT+01:00 Herbert Xu <herbert@...dor.apana.org.au>:
> On Wed, Mar 14, 2018 at 02:17:30PM +0100, Salvatore Mesoraca wrote:
>> All ciphers implemented in Linux have a block size less than or
>> equal to 16 bytes and the most demanding hw require 16 bits
>> alignment for the block buffer.
>> We avoid 2 VLAs[1] by always allocating 16 bytes with 16 bits
>> alignment, unless the architecture support efficient unaligned
>> accesses.
>> We also check, at runtime, that our assumptions still stand,
>> possibly dynamically allocating a new buffer, just in case
>> something changes in the future.
>
> Please move the check to ctr instance creation time.  That is,
> if the underlying blocksize is greater than 16 bytes than simply
> fail the creation.

Good, I'll send a v2.
Thank you for your help,

Salvatore