crypto: cbcmac - remove unnecessary alignment logic

The cbcmac template is aligning a field in its desc context to the
alignmask of its underlying 'cipher', at runtime.  This is almost
entirely pointless, since cbcmac is already using the cipher API
functions that handle alignment themselves, and few ciphers set a
nonzero alignmask anyway.  Also, even without runtime alignment, an
alignment of at least 4 bytes can be guaranteed.

Thus, at best this code is optimizing for the rare case of ciphers that
set an alignmask >= 7, at the cost of hurting the common cases.

Therefore, remove the manual alignment code from cbcmac.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/ccm.c

@@ -56,6 +56,7 @@ struct cbcmac_tfm_ctx {
 
 struct cbcmac_desc_ctx {
 	unsigned int len;
+	u8 dg[];
 };
 
 static inline struct crypto_ccm_req_priv_ctx *crypto_ccm_reqctx(
@@ -785,10 +786,9 @@ static int crypto_cbcmac_digest_init(struct shash_desc *pdesc)
 {
 	struct cbcmac_desc_ctx *ctx = shash_desc_ctx(pdesc);
 	int bs = crypto_shash_digestsize(pdesc->tfm);
-	u8 *dg = (u8 *)ctx + crypto_shash_descsize(pdesc->tfm) - bs;
 
 	ctx->len = 0;
-	memset(dg, 0, bs);
+	memset(ctx->dg, 0, bs);
 
 	return 0;
 }
@@ -801,18 +801,17 @@ static int crypto_cbcmac_digest_update(struct shash_desc *pdesc, const u8 *p,
 	struct cbcmac_desc_ctx *ctx = shash_desc_ctx(pdesc);
 	struct crypto_cipher *tfm = tctx->child;
 	int bs = crypto_shash_digestsize(parent);
-	u8 *dg = (u8 *)ctx + crypto_shash_descsize(parent) - bs;
 
 	while (len > 0) {
 		unsigned int l = min(len, bs - ctx->len);
 
-		crypto_xor(dg + ctx->len, p, l);
+		crypto_xor(&ctx->dg[ctx->len], p, l);
 		ctx->len +=l;
 		len -= l;
 		p += l;
 
 		if (ctx->len == bs) {
-			crypto_cipher_encrypt_one(tfm, dg, dg);
+			crypto_cipher_encrypt_one(tfm, ctx->dg, ctx->dg);
 			ctx->len = 0;
 		}
 	}
@@ -827,12 +826,11 @@ static int crypto_cbcmac_digest_final(struct shash_desc *pdesc, u8 *out)
 	struct cbcmac_desc_ctx *ctx = shash_desc_ctx(pdesc);
 	struct crypto_cipher *tfm = tctx->child;
 	int bs = crypto_shash_digestsize(parent);
-	u8 *dg = (u8 *)ctx + crypto_shash_descsize(parent) - bs;
 
 	if (ctx->len)
-		crypto_cipher_encrypt_one(tfm, dg, dg);
+		crypto_cipher_encrypt_one(tfm, ctx->dg, ctx->dg);
 
-	memcpy(out, dg, bs);
+	memcpy(out, ctx->dg, bs);
 	return 0;
 }
 
@@ -889,8 +887,7 @@ static int cbcmac_create(struct crypto_template *tmpl, struct rtattr **tb)
 	inst->alg.base.cra_blocksize = 1;
 
 	inst->alg.digestsize = alg->cra_blocksize;
-	inst->alg.descsize = ALIGN(sizeof(struct cbcmac_desc_ctx),
-				   alg->cra_alignmask + 1) +
+	inst->alg.descsize = sizeof(struct cbcmac_desc_ctx) +
 			     alg->cra_blocksize;
 
 	inst->alg.base.cra_ctxsize = sizeof(struct cbcmac_tfm_ctx);