Re: [PATCH v5 8/8] crypto, x86/sha: Eliminate casts on asm implementations

[Eric Biggers]

On Wed, Nov 13, 2019 at 10:25:16AM -0800, Kees Cook wrote:
> In order to avoid CFI function prototype mismatches, this removes the
> casts on assembly implementations of sha1/256/512 accelerators. The
> safety checks from BUILD_BUG_ON() remain.
> 
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> ---
>  arch/x86/crypto/sha1_ssse3_glue.c   | 61 ++++++++++++-----------------
>  arch/x86/crypto/sha256_ssse3_glue.c | 31 +++++++--------
>  arch/x86/crypto/sha512_ssse3_glue.c | 28 ++++++-------
>  3 files changed, 50 insertions(+), 70 deletions(-)
> 
> diff --git a/arch/x86/crypto/sha1_ssse3_glue.c b/arch/x86/crypto/sha1_ssse3_glue.c
> index 639d4c2fd6a8..a151d899f37a 100644
> --- a/arch/x86/crypto/sha1_ssse3_glue.c
> +++ b/arch/x86/crypto/sha1_ssse3_glue.c
> @@ -27,11 +27,8 @@
>  #include <crypto/sha1_base.h>
>  #include <asm/simd.h>
>  
> -typedef void (sha1_transform_fn)(u32 *digest, const char *data,
> -				unsigned int rounds);
> -
>  static int sha1_update(struct shash_desc *desc, const u8 *data,
> -			     unsigned int len, sha1_transform_fn *sha1_xform)
> +			     unsigned int len, sha1_block_fn *sha1_xform)
>  {
>  	struct sha1_state *sctx = shash_desc_ctx(desc);
>  
> @@ -39,48 +36,44 @@ static int sha1_update(struct shash_desc *desc, const u8 *data,
>  	    (sctx->count % SHA1_BLOCK_SIZE) + len < SHA1_BLOCK_SIZE)
>  		return crypto_sha1_update(desc, data, len);
>  
> -	/* make sure casting to sha1_block_fn() is safe */
> +	/* make sure sha1_block_fn() use in generic routines is safe */
>  	BUILD_BUG_ON(offsetof(struct sha1_state, state) != 0);

This update to the comment makes no sense, since sha1_block_fn() is obviously
safe in the helpers, and this says nothing about the assembly functions.
Instead this should say something like:

	/*
	 * Make sure that struct sha1_state begins directly with the 160-bit
	 * SHA1 internal state, as this is what the assembly functions expect.
	 */

Likewise for SHA-256 and SHA-512, except for those it would be a 256-bit and
512-bit internal state respectively.

> -asmlinkage void sha1_transform_ssse3(u32 *digest, const char *data,
> -				     unsigned int rounds);
> +asmlinkage void sha1_transform_ssse3(struct sha1_state *digest,
> +				     u8 const *data, int rounds);

'u8 const' is unconventional.  Please use 'const u8' instead.

Also, this function prototype is also given in a comment in the corresponding
assembly file.  Can you please update that too, and also leave a comment in the
assembly file like "struct sha1_state is assumed to begin with u32 state[5]."?

Likewise for all the other SHA-1, and SHA-256, and SHA-512 assembly functions,
except it would be u32 state[8] for SHA-256 and u64 state[8] for SHA-512.

- Eric