Re: [PATCH] crypto: arm64/neonbs - fix out-of-bounds access on short input

Ard Biesheuvel
2024-02-21T23:38:01Z

On Sat, 17 Feb 2024 at 17:12, Ard Biesheuvel <ardb+git@google.com> wrote:
>
> From: Ard Biesheuvel <ardb@kernel.org>
>
> The bit-sliced implementation of AES-CTR operates on blocks of 128
> bytes, and will fall back to the plain NEON version for tail blocks or
> inputs that are shorter than 128 bytes to begin with.
>
> It will call straight into the plain NEON asm helper, which performs all
> memory accesses in granules of 16 bytes (the size of a NEON register).
> For this reason, the associated plain NEON glue code will copy inputs
> shorter than 16 bytes into a temporary buffer, given that this is a rare
> occurrence and it is not worth the effort to work around this in the asm
> code.
>
> The fallback from the bit-sliced NEON version fails to take this into
> account, potentially resulting in out-of-bounds accesses. So clone the
> same workaround, and use a temp buffer for short in/outputs.
>
> Cc: <stable@vger.kernel.org>
> Reported-by: syzbot+f1ceaa1a09ab891e1934@syzkaller.appspotmail.com
> Tested-by: syzbot+f1ceaa1a09ab891e1934@syzkaller.appspotmail.com
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

Ping?

> ---
> arch/arm64/crypto/aes-neonbs-glue.c | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff --git a/arch/arm64/crypto/aes-neonbs-glue.c b/arch/arm64/crypto/aes-neonbs-glue.c
> index bac4cabef607..849dc41320db 100644
> --- a/arch/arm64/crypto/aes-neonbs-glue.c
> +++ b/arch/arm64/crypto/aes-neonbs-glue.c
> @@ -227,8 +227,19 @@ static int ctr_encrypt(struct skcipher_request *req)
> src += blocks * AES_BLOCK_SIZE;
> }
> if (nbytes && walk.nbytes == walk.total) {
> + u8 buf[AES_BLOCK_SIZE];
> + u8 *d = dst;
> +
> + if (unlikely(nbytes < AES_BLOCK_SIZE))
> + src = dst = memcpy(buf + sizeof(buf) - nbytes,
> + src, nbytes);
> +
> neon_aes_ctr_encrypt(dst, src, ctx->enc, ctx->key.rounds,
> nbytes, walk.iv);
> +
> + if (unlikely(nbytes < AES_BLOCK_SIZE))
> + memcpy(d, buf + sizeof(buf) - nbytes, nbytes);
> +
> nbytes = 0;
> }
> kernel_neon_end();
> --
> 2.44.0.rc0.258.g7320e95886-goog
>