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From:   Peter Robinson <pbrobinson@gmail.com>
Date:   Fri, 31 May 2019 10:42:13 +0100
Message-ID: <CALeDE9PL0q7wGj6rJO03fzJZ4m5dnkLxvu4xgMhG0dNKWxxW2A@mail.gmail.com>
Subject: Re: [PATCH] crypto: ghash - fix unaligned memory access in ghash_setkey()
To:     Eric Biggers <ebiggers@kernel.org>
Cc:     linux-crypto@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        stable@vger.kernel.org
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On Thu, May 30, 2019 at 6:51 PM Eric Biggers <ebiggers@kernel.org> wrote:
>
> From: Eric Biggers <ebiggers@google.com>
>
> Changing ghash_mod_init() to be subsys_initcall made it start running
> before the alignment fault handler has been installed on ARM.  In kernel
> builds where the keys in the ghash test vectors happened to be
> misaligned in the kernel image, this exposed the longstanding bug that
> ghash_setkey() is incorrectly casting the key buffer (which can have any
> alignment) to be128 for passing to gf128mul_init_4k_lle().
>
> Fix this by memcpy()ing the key to a temporary buffer.
>
> Don't fix it by setting an alignmask on the algorithm instead because
> that would unnecessarily force alignment of the data too.
>
> Fixes: 2cdc6899a88e ("crypto: ghash - Add GHASH digest algorithm for GCM")
> Reported-by: Peter Robinson <pbrobinson@gmail.com>
Tested-by: Peter Robinson <pbrobinson@gmail.com>

That fixes the problems I was seeing, thanks for the quick response/fix.

Peter

> Cc: stable@vger.kernel.org
> Signed-off-by: Eric Biggers <ebiggers@google.com>
> ---
>  crypto/ghash-generic.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/crypto/ghash-generic.c b/crypto/ghash-generic.c
> index e6307935413c1..c8a347798eae6 100644
> --- a/crypto/ghash-generic.c
> +++ b/crypto/ghash-generic.c
> @@ -34,6 +34,7 @@ static int ghash_setkey(struct crypto_shash *tfm,
>                         const u8 *key, unsigned int keylen)
>  {
>         struct ghash_ctx *ctx = crypto_shash_ctx(tfm);
> +       be128 k;
>
>         if (keylen != GHASH_BLOCK_SIZE) {
>                 crypto_shash_set_flags(tfm, CRYPTO_TFM_RES_BAD_KEY_LEN);
> @@ -42,7 +43,12 @@ static int ghash_setkey(struct crypto_shash *tfm,
>
>         if (ctx->gf128)
>                 gf128mul_free_4k(ctx->gf128);
> -       ctx->gf128 = gf128mul_init_4k_lle((be128 *)key);
> +
> +       BUILD_BUG_ON(sizeof(k) != GHASH_BLOCK_SIZE);
> +       memcpy(&k, key, GHASH_BLOCK_SIZE); /* avoid violating alignment rules */
> +       ctx->gf128 = gf128mul_init_4k_lle(&k);
> +       memzero_explicit(&k, GHASH_BLOCK_SIZE);
> +
>         if (!ctx->gf128)
>                 return -ENOMEM;
>
> --
> 2.22.0.rc1.257.g3120a18244-goog
>