Re: [PATCH 2/2] crypto: blake2s - use memcpy_and_pad in __blake2s_init

[Eric Biggers <ebiggers@kernel.org>]

On Tue, Apr 14, 2026 at 05:49:04PM +0200, Thorsten Blum wrote:
> Use memcpy_and_pad() instead of memcpy() followed by memset() to
> simplify __blake2s_init(). Use sizeof(ctx->buf) instead of the macro
> BLAKE2S_BLOCK_SIZE.
> 
> Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
> ---
>  include/crypto/blake2s.h | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/include/crypto/blake2s.h b/include/crypto/blake2s.h
> index 648cb7824358..f0e0ce0b30a5 100644
> --- a/include/crypto/blake2s.h
> +++ b/include/crypto/blake2s.h
> @@ -70,9 +70,8 @@ static inline void __blake2s_init(struct blake2s_ctx *ctx, size_t outlen,
>  	ctx->buflen = 0;
>  	ctx->outlen = outlen;
>  	if (keylen) {
> -		memcpy(ctx->buf, key, keylen);
> -		memset(&ctx->buf[keylen], 0, BLAKE2S_BLOCK_SIZE - keylen);
> -		ctx->buflen = BLAKE2S_BLOCK_SIZE;
> +		memcpy_and_pad(ctx->buf, sizeof(ctx->buf), key, keylen, 0);
> +		ctx->buflen = sizeof(ctx->buf);

I'm wondering if this is actually better.  It's another helper function
to remember.  Also 'keylen' can be a compile-time constant here, and
compilers know what memcpy() and memset() do, so they will optimize the
code accordingly.  The helper function takes away the compiler's ability
to perform this optimization.  If this was already an out-of-line
function, it would be a bit more convincing.

- Eric