[PATCH v2] crypto: reduce minimum alignment of on-stack structures

[Eric Biggers]

On Fri, Jan 08, 2021 at 06:17:06PM +0100, Ard Biesheuvel wrote:
> diff --git a/include/crypto/skcipher.h b/include/crypto/skcipher.h
> index 6a733b171a5d..aa133dc3bf39 100644
> --- a/include/crypto/skcipher.h
> +++ b/include/crypto/skcipher.h
> @@ -128,7 +128,7 @@ struct skcipher_alg {
>  			     MAX_SYNC_SKCIPHER_REQSIZE + \
>  			     (!(sizeof((struct crypto_sync_skcipher *)1 == \
>  				       (typeof(tfm))1))) \
> -			    ] CRYPTO_MINALIGN_ATTR; \
> +			    ] __aligned(ARCH_SLAB_MINALIGN); \
>  	struct skcipher_request *name = (void *)__##name##_desc
>  

Are you sure this is okay?  __alignof__(struct skcipher_request) will still be
CRYPTO_MINALIGN_ATTR, since it contains a field with that alignment.  So
technically isn't the full alignment still needed, as the compiler can assume
that struct skcipher_request is CRYPTO_MINALIGN_ATTR-aligned?

- Eric