linux-kernel - Re: [PATCH] crypto: caam - properly set IV after {en,de}crypt

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Message-ID: <VI1PR0401MB2591C51C446CFA129B50022298D20@VI1PR0401MB2591.eurprd04.prod.outlook.com>
Date:   Thu, 29 Jun 2017 10:19:01 +0000
From:   Horia Geantă <horia.geanta@....com>
To:     David Gstir <david@...ma-star.at>,
        Dan Douglass <dan.douglass@....com>,
        "herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>,
        "davem@...emloft.net" <davem@...emloft.net>
CC:     "richard@...ma-star.at" <richard@...ma-star.at>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH] crypto: caam - properly set IV after {en,de}crypt

On 6/28/2017 4:42 PM, Horia Geantă wrote:
> On 6/28/2017 4:27 PM, David Gstir wrote:
>> Certain cipher modes like CTS expect the IV (req->info) of
>> ablkcipher_request (or equivalently req->iv of skcipher_request) to
>> contain the last ciphertext block when the {en,de}crypt operation is done.
>> This is currently not the case for the CAAM driver which in turn breaks
>> e.g. cts(cbc(aes)) when the CAAM driver is enabled.
>>
>> This patch fixes the CAAM driver to properly set the IV after the
>> {en,de}crypt operation of ablkcipher finishes.
>>
>> This issue was revealed by the changes in the SW CTS mode in commit
>> 0605c41cc53ca ("crypto: cts - Convert to skcipher")
>>
>> Cc: <stable@...r.kernel.org> # 4.8+
>> Signed-off-by: David Gstir <david@...ma-star.at>
> Reviewed-by: Horia Geantă <horia.geanta@....com>
> 
Btw, instead of updating the IV in SW, CAAM engine could be programmed
to do it - by saving the Context Register of the AES accelerator.

Unfortunately this would require changes in quite a few places: shared
descriptor, HW S/G generation logic, IV dma (un)mapping and maybe others.

So it's better to have this fix now (which, considering size, is
appropriate for -stable) and later, if needed, offload IV updating in HW.

Regards,
Horia