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

From: Christophe Leroy
Date: Thu Jan 21 2021 - 04:57:04 EST

Le 21/01/2021 à 08:31, Ard Biesheuvel a écrit :
On Thu, 21 Jan 2021 at 06:35, Christophe Leroy
<christophe.leroy@xxxxxxxxxx> wrote:

Le 20/01/2021 à 23:23, Ard Biesheuvel a écrit :
On Wed, 20 Jan 2021 at 19:59, Christophe Leroy
<christophe.leroy@xxxxxxxxxx> 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@xxxxxxxxxx>

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.

So what happens if the input is not 16 byte aligned, and rounding it
up causes it to extend across a page boundary into a page that is not
mapped by the IOMMU/SMMU?

What is the IOMMU/SMMU ?

The mpc8xx, mpc82xx and mpc83xx which embed the Talitos Security Engine don't have such thing, the security engine uses DMA and has direct access to the memory bus for reading and writing.