Re: [RFC/RFT PATCH 07/15] crypto: arm64/aes-neonbs - fix returning final keystream block

[Ard Biesheuvel]

On Wed, 23 Jan 2019 at 23:52, Eric Biggers <ebiggers@xxxxxxxxxx> wrote:
>
> From: Eric Biggers <ebiggers@xxxxxxxxxx>
>
> The arm64 NEON bit-sliced implementation of AES-CTR fails the improved
> skcipher tests because it sometimes produces the wrong ciphertext.  The
> bug is that the final keystream block isn't returned from the assembly
> code when the number of non-final blocks is zero.  This can happen if
> the input data ends a few bytes after a page boundary.  In this case the
> last bytes get "encrypted" by XOR'ing them with uninitialized memory.
>
> Fix the assembly code to return the final keystream block when needed.
>
> Fixes: 88a3f582bea9 ("crypto: arm64/aes - don't use IV buffer to return final keystream block")
> Cc: <stable@xxxxxxxxxxxxxxx> # v4.11+
> Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>

Reviewed-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>

> ---
>  arch/arm64/crypto/aes-neonbs-core.S | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/crypto/aes-neonbs-core.S b/arch/arm64/crypto/aes-neonbs-core.S
> index e613a87f8b53..8432c8d0dea6 100644
> --- a/arch/arm64/crypto/aes-neonbs-core.S
> +++ b/arch/arm64/crypto/aes-neonbs-core.S
> @@ -971,18 +971,22 @@ CPU_LE(   rev             x8, x8          )
>
>  8:     next_ctr        v0
>         st1             {v0.16b}, [x24]
> -       cbz             x23, 0f
> +       cbz             x23, .Lctr_done
>
>         cond_yield_neon 98b
>         b               99b
>
> -0:     frame_pop
> +.Lctr_done:
> +       frame_pop
>         ret
>
>         /*
>          * If we are handling the tail of the input (x6 != NULL), return the
>          * final keystream block back to the caller.
>          */
> +0:     cbz             x25, 8b
> +       st1             {v0.16b}, [x25]
> +       b               8b
>  1:     cbz             x25, 8b
>         st1             {v1.16b}, [x25]
>         b               8b
> --
> 2.20.1.321.g9e740568ce-goog
>