linux-kernel - Re: [PATCH 1/2] crypto: talitos - Work around SEC6 ERRATA (AES-CTR mode data size error)

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Date:   Thu, 21 Jan 2021 06:35:06 +0100
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:LINUX FOR POWERPC (32-BIT AND 64-BIT)" 
        <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH 1/2] crypto: talitos - Work around SEC6 ERRATA (AES-CTR
 mode data size error)



Le 20/01/2021 à 23:23, Ard Biesheuvel a écrit :
> On Wed, 20 Jan 2021 at 19:59, Christophe Leroy
> <christophe.leroy@...roup.eu> wrote:
>>
>> Talitos Security Engine AESU considers any input
>> data size that is not a multiple of 16 bytes to be an error.
>> This is not a problem in general, except for Counter mode
>> that is a stream cipher and can have an input of any size.
>>
>> Test Manager for ctr(aes) fails on 4th test vector which has
>> a length of 499 while all previous vectors which have a 16 bytes
>> multiple length succeed.
>>
>> As suggested by Freescale, round up the input data length to the
>> nearest 16 bytes.
>>
>> Fixes: 5e75ae1b3cef ("crypto: talitos - add new crypto modes")
>> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
> 
> Doesn't this cause the hardware to write outside the given buffer?


Only the input length is modified. Not the output length.

The ERRATA says:

The input data length (in the descriptor) can be rounded up to the nearest 16B. Set the
data-in length (in the descriptor) to include X bytes of data beyond the payload. Set the
data-out length to only output the relevant payload (don't need to output the padding).
SEC reads from memory are not destructive, so the extra bytes included in the AES-CTR
operation can be whatever bytes are contiguously trailing the payload.