crypto: keywrap - simplify code

The code is simplified by using two __be64 values for the operation
instead of using two arrays of u8. This allows to get rid of the memory
alignment code. In addition, the crypto_xor can be replaced with a
native XOR operation. Finally, the definition of the variables is
re-arranged such that the data structures come before simple variables
to potentially reduce memory space.
Signed-off-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/keywrap.c

@@ -93,18 +93,10 @@ struct crypto_kw_ctx {
 
 struct crypto_kw_block {
 #define SEMIBSIZE 8
-	u8 A[SEMIBSIZE];
-	u8 R[SEMIBSIZE];
+	__be64 A;
+	__be64 R;
 };
 
-/* convert 64 bit integer into its string representation */
-static inline void crypto_kw_cpu_to_be64(u64 val, u8 *buf)
-{
-	__be64 *a = (__be64 *)buf;
-
-	*a = cpu_to_be64(val);
-}
-
 /*
  * Fast forward the SGL to the "end" length minus SEMIBSIZE.
  * The start in the SGL defined by the fast-forward is returned with
@@ -139,17 +131,10 @@ static int crypto_kw_decrypt(struct blkcipher_desc *desc,
 	struct crypto_blkcipher *tfm = desc->tfm;
 	struct crypto_kw_ctx *ctx = crypto_blkcipher_ctx(tfm);
 	struct crypto_cipher *child = ctx->child;
-
-	unsigned long alignmask = max_t(unsigned long, SEMIBSIZE,
-					crypto_cipher_alignmask(child));
-	unsigned int i;
-
-	u8 blockbuf[sizeof(struct crypto_kw_block) + alignmask];
-	struct crypto_kw_block *block = (struct crypto_kw_block *)
-					PTR_ALIGN(blockbuf + 0, alignmask + 1);
-
-	u64 t = 6 * ((nbytes) >> 3);
+	struct crypto_kw_block block;
 	struct scatterlist *lsrc, *ldst;
+	u64 t = 6 * ((nbytes) >> 3);
+	unsigned int i;
 	int ret = 0;
 
 	/*
@@ -160,7 +145,7 @@ static int crypto_kw_decrypt(struct blkcipher_desc *desc,
 		return -EINVAL;
 
 	/* Place the IV into block A */
-	memcpy(block->A, desc->info, SEMIBSIZE);
+	memcpy(&block.A, desc->info, SEMIBSIZE);
 
 	/*
 	 * src scatterlist is read-only. dst scatterlist is r/w. During the
@@ -171,32 +156,27 @@ static int crypto_kw_decrypt(struct blkcipher_desc *desc,
 	ldst = dst;
 
 	for (i = 0; i < 6; i++) {
-		u8 tbe_buffer[SEMIBSIZE + alignmask];
-		/* alignment for the crypto_xor and the _to_be64 operation */
-		u8 *tbe = PTR_ALIGN(tbe_buffer + 0, alignmask + 1);
-		unsigned int tmp_nbytes = nbytes;
 		struct scatter_walk src_walk, dst_walk;
+		unsigned int tmp_nbytes = nbytes;
 
 		while (tmp_nbytes) {
 			/* move pointer by tmp_nbytes in the SGL */
 			crypto_kw_scatterlist_ff(&src_walk, lsrc, tmp_nbytes);
 			/* get the source block */
-			scatterwalk_copychunks(block->R, &src_walk, SEMIBSIZE,
+			scatterwalk_copychunks(&block.R, &src_walk, SEMIBSIZE,
 					       false);
 
-			/* perform KW operation: get counter as byte string */
-			crypto_kw_cpu_to_be64(t, tbe);
 			/* perform KW operation: modify IV with counter */
-			crypto_xor(block->A, tbe, SEMIBSIZE);
+			block.A ^= cpu_to_be64(t);
 			t--;
 			/* perform KW operation: decrypt block */
-			crypto_cipher_decrypt_one(child, (u8*)block,
-						  (u8*)block);
+			crypto_cipher_decrypt_one(child, (u8*)&block,
+						  (u8*)&block);
 
 			/* move pointer by tmp_nbytes in the SGL */
 			crypto_kw_scatterlist_ff(&dst_walk, ldst, tmp_nbytes);
 			/* Copy block->R into place */
-			scatterwalk_copychunks(block->R, &dst_walk, SEMIBSIZE,
+			scatterwalk_copychunks(&block.R, &dst_walk, SEMIBSIZE,
 					       true);
 
 			tmp_nbytes -= SEMIBSIZE;
@@ -208,11 +188,10 @@ static int crypto_kw_decrypt(struct blkcipher_desc *desc,
 	}
 
 	/* Perform authentication check */
-	if (crypto_memneq("\xA6\xA6\xA6\xA6\xA6\xA6\xA6\xA6", block->A,
-			  SEMIBSIZE))
+	if (block.A != cpu_to_be64(0xa6a6a6a6a6a6a6a6))
 		ret = -EBADMSG;
 
-	memzero_explicit(block, sizeof(struct crypto_kw_block));
+	memzero_explicit(&block, sizeof(struct crypto_kw_block));
 
 	return ret;
 }
@@ -224,17 +203,10 @@ static int crypto_kw_encrypt(struct blkcipher_desc *desc,
 	struct crypto_blkcipher *tfm = desc->tfm;
 	struct crypto_kw_ctx *ctx = crypto_blkcipher_ctx(tfm);
 	struct crypto_cipher *child = ctx->child;
-
-	unsigned long alignmask = max_t(unsigned long, SEMIBSIZE,
-					crypto_cipher_alignmask(child));
-	unsigned int i;
-
-	u8 blockbuf[sizeof(struct crypto_kw_block) + alignmask];
-	struct crypto_kw_block *block = (struct crypto_kw_block *)
-					PTR_ALIGN(blockbuf + 0, alignmask + 1);
-
-	u64 t = 1;
+	struct crypto_kw_block block;
 	struct scatterlist *lsrc, *ldst;
+	u64 t = 1;
+	unsigned int i;
 
 	/*
 	 * Require at least 2 semiblocks (note, the 3rd semiblock that is
@@ -249,7 +221,7 @@ static int crypto_kw_encrypt(struct blkcipher_desc *desc,
 	 * Place the predefined IV into block A -- for encrypt, the caller
 	 * does not need to provide an IV, but he needs to fetch the final IV.
 	 */
-	memcpy(block->A, "\xA6\xA6\xA6\xA6\xA6\xA6\xA6\xA6", SEMIBSIZE);
+	block.A = cpu_to_be64(0xa6a6a6a6a6a6a6a6);
 
 	/*
 	 * src scatterlist is read-only. dst scatterlist is r/w. During the
@@ -260,30 +232,26 @@ static int crypto_kw_encrypt(struct blkcipher_desc *desc,
 	ldst = dst;
 
 	for (i = 0; i < 6; i++) {
-		u8 tbe_buffer[SEMIBSIZE + alignmask];
-		u8 *tbe = PTR_ALIGN(tbe_buffer + 0, alignmask + 1);
-		unsigned int tmp_nbytes = nbytes;
 		struct scatter_walk src_walk, dst_walk;
+		unsigned int tmp_nbytes = nbytes;
 
 		scatterwalk_start(&src_walk, lsrc);
 		scatterwalk_start(&dst_walk, ldst);
 
 		while (tmp_nbytes) {
 			/* get the source block */
-			scatterwalk_copychunks(block->R, &src_walk, SEMIBSIZE,
+			scatterwalk_copychunks(&block.R, &src_walk, SEMIBSIZE,
 					       false);
 
 			/* perform KW operation: encrypt block */
-			crypto_cipher_encrypt_one(child, (u8 *)block,
-						  (u8 *)block);
-			/* perform KW operation: get counter as byte string */
-			crypto_kw_cpu_to_be64(t, tbe);
+			crypto_cipher_encrypt_one(child, (u8 *)&block,
+						  (u8 *)&block);
 			/* perform KW operation: modify IV with counter */
-			crypto_xor(block->A, tbe, SEMIBSIZE);
+			block.A ^= cpu_to_be64(t);
 			t++;
 
 			/* Copy block->R into place */
-			scatterwalk_copychunks(block->R, &dst_walk, SEMIBSIZE,
+			scatterwalk_copychunks(&block.R, &dst_walk, SEMIBSIZE,
 					       true);
 
 			tmp_nbytes -= SEMIBSIZE;
@@ -295,9 +263,9 @@ static int crypto_kw_encrypt(struct blkcipher_desc *desc,
 	}
 
 	/* establish the IV for the caller to pick up */
-	memcpy(desc->info, block->A, SEMIBSIZE);
+	memcpy(desc->info, &block.A, SEMIBSIZE);
 
-	memzero_explicit(block, sizeof(struct crypto_kw_block));
+	memzero_explicit(&block, sizeof(struct crypto_kw_block));
 
 	return 0;
 }