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From: Ard Biesheuvel <ardb@kernel.org>
Date: Thu, 22 Feb 2024 00:37:45 +0100
Message-ID: <CAMj1kXH+k4Z_iowxp+t=yU4tQFwLYjQxAQ92bga-xeZxE734BA@mail.gmail.com>
Subject: Re: [PATCH] crypto: arm64/neonbs - fix out-of-bounds access on short input
To: Ard Biesheuvel <ardb+git@google.com>
Cc: linux-crypto@vger.kernel.org, herbert@gondor.apana.org.au, 
	stable@vger.kernel.org, syzbot+f1ceaa1a09ab891e1934@syzkaller.appspotmail.com
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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
>