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

[Ard Biesheuvel <ardb@kernel.org>]

On Thu, 21 Jan 2021 at 06:35, Christophe Leroy
<christophe.leroy@csgroup.eu> wrote:
>
>
>
> Le 20/01/2021 à 23:23, Ard Biesheuvel a écrit :
> > On Wed, 20 Jan 2021 at 19:59, Christophe Leroy
> > <christophe.leroy@csgroup.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@csgroup.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.

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?