crypto: xcbc - remove unnecessary alignment logic

The xcbc template is setting its alignmask to that of its underlying
'cipher'.  Yet, it doesn't care itself about how its inputs and outputs
are aligned, which is ostensibly the point of the alignmask.  Instead,
xcbc actually just uses its alignmask itself to runtime-align certain
fields in its tfm and desc contexts appropriately for its underlying
cipher.  That is almost entirely pointless too, though, since xcbc 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, this patch removes the manual alignment code from xcbc and
makes it stop setting an alignmask.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/xcbc.c

@@ -27,7 +27,7 @@ static u_int32_t ks[12] = {0x01010101, 0x01010101, 0x01010101, 0x01010101,
  */
 struct xcbc_tfm_ctx {
 	struct crypto_cipher *child;
-	u8 ctx[];
+	u8 consts[];
 };
 
 /*
@@ -43,7 +43,7 @@ struct xcbc_tfm_ctx {
  */
 struct xcbc_desc_ctx {
 	unsigned int len;
-	u8 ctx[];
+	u8 odds[];
 };
 
 #define XCBC_BLOCKSIZE	16
@@ -51,9 +51,8 @@ struct xcbc_desc_ctx {
 static int crypto_xcbc_digest_setkey(struct crypto_shash *parent,
 				     const u8 *inkey, unsigned int keylen)
 {
-	unsigned long alignmask = crypto_shash_alignmask(parent);
 	struct xcbc_tfm_ctx *ctx = crypto_shash_ctx(parent);
-	u8 *consts = PTR_ALIGN(&ctx->ctx[0], alignmask + 1);
+	u8 *consts = ctx->consts;
 	int err = 0;
 	u8 key1[XCBC_BLOCKSIZE];
 	int bs = sizeof(key1);
@@ -71,10 +70,9 @@ static int crypto_xcbc_digest_setkey(struct crypto_shash *parent,
 
 static int crypto_xcbc_digest_init(struct shash_desc *pdesc)
 {
-	unsigned long alignmask = crypto_shash_alignmask(pdesc->tfm);
 	struct xcbc_desc_ctx *ctx = shash_desc_ctx(pdesc);
 	int bs = crypto_shash_blocksize(pdesc->tfm);
-	u8 *prev = PTR_ALIGN(&ctx->ctx[0], alignmask + 1) + bs;
+	u8 *prev = &ctx->odds[bs];
 
 	ctx->len = 0;
 	memset(prev, 0, bs);
@@ -86,12 +84,11 @@ static int crypto_xcbc_digest_update(struct shash_desc *pdesc, const u8 *p,
 				     unsigned int len)
 {
 	struct crypto_shash *parent = pdesc->tfm;
-	unsigned long alignmask = crypto_shash_alignmask(parent);
 	struct xcbc_tfm_ctx *tctx = crypto_shash_ctx(parent);
 	struct xcbc_desc_ctx *ctx = shash_desc_ctx(pdesc);
 	struct crypto_cipher *tfm = tctx->child;
 	int bs = crypto_shash_blocksize(parent);
-	u8 *odds = PTR_ALIGN(&ctx->ctx[0], alignmask + 1);
+	u8 *odds = ctx->odds;
 	u8 *prev = odds + bs;
 
 	/* checking the data can fill the block */
@@ -132,13 +129,11 @@ static int crypto_xcbc_digest_update(struct shash_desc *pdesc, const u8 *p,
 static int crypto_xcbc_digest_final(struct shash_desc *pdesc, u8 *out)
 {
 	struct crypto_shash *parent = pdesc->tfm;
-	unsigned long alignmask = crypto_shash_alignmask(parent);
 	struct xcbc_tfm_ctx *tctx = crypto_shash_ctx(parent);
 	struct xcbc_desc_ctx *ctx = shash_desc_ctx(pdesc);
 	struct crypto_cipher *tfm = tctx->child;
 	int bs = crypto_shash_blocksize(parent);
-	u8 *consts = PTR_ALIGN(&tctx->ctx[0], alignmask + 1);
-	u8 *odds = PTR_ALIGN(&ctx->ctx[0], alignmask + 1);
+	u8 *odds = ctx->odds;
 	u8 *prev = odds + bs;
 	unsigned int offset = 0;
 
@@ -157,7 +152,7 @@ static int crypto_xcbc_digest_final(struct shash_desc *pdesc, u8 *out)
 	}
 
 	crypto_xor(prev, odds, bs);
-	crypto_xor(prev, consts + offset, bs);
+	crypto_xor(prev, &tctx->consts[offset], bs);
 
 	crypto_cipher_encrypt_one(tfm, out, prev);
 
@@ -191,7 +186,6 @@ static int xcbc_create(struct crypto_template *tmpl, struct rtattr **tb)
 	struct shash_instance *inst;
 	struct crypto_cipher_spawn *spawn;
 	struct crypto_alg *alg;
-	unsigned long alignmask;
 	u32 mask;
 	int err;
 
@@ -218,21 +212,15 @@ static int xcbc_create(struct crypto_template *tmpl, struct rtattr **tb)
 	if (err)
 		goto err_free_inst;
 
-	alignmask = alg->cra_alignmask | 3;
-	inst->alg.base.cra_alignmask = alignmask;
 	inst->alg.base.cra_priority = alg->cra_priority;
 	inst->alg.base.cra_blocksize = alg->cra_blocksize;
+	inst->alg.base.cra_ctxsize = sizeof(struct xcbc_tfm_ctx) +
+				     alg->cra_blocksize * 2;
 
 	inst->alg.digestsize = alg->cra_blocksize;
-	inst->alg.descsize = ALIGN(sizeof(struct xcbc_desc_ctx),
-				   crypto_tfm_ctx_alignment()) +
-			     (alignmask &
-			      ~(crypto_tfm_ctx_alignment() - 1)) +
+	inst->alg.descsize = sizeof(struct xcbc_desc_ctx) +
 			     alg->cra_blocksize * 2;
 
-	inst->alg.base.cra_ctxsize = ALIGN(sizeof(struct xcbc_tfm_ctx),
-					   alignmask + 1) +
-				     alg->cra_blocksize * 2;
 	inst->alg.base.cra_init = xcbc_init_tfm;
 	inst->alg.base.cra_exit = xcbc_exit_tfm;