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

[Christophe Leroy]

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.