crypto: arm64/aes-cts-cbc - factor out CBC en/decryption of a walk

The plain CBC driver and the CTS one share some code that iterates over
a scatterwalk and invokes the CBC asm code to do the processing. The
upcoming ESSIV/CBC mode will clone that pattern for the third time, so
let's factor it out first.
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

arch/arm64/crypto/aes-glue.c

@@ -186,46 +186,64 @@ static int ecb_decrypt(struct skcipher_request *req)
 	return err;
 }
 
-static int cbc_encrypt(struct skcipher_request *req)
+static int cbc_encrypt_walk(struct skcipher_request *req,
+			    struct skcipher_walk *walk)
 {
 	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
 	struct crypto_aes_ctx *ctx = crypto_skcipher_ctx(tfm);
-	int err, rounds = 6 + ctx->key_length / 4;
-	struct skcipher_walk walk;
+	int err = 0, rounds = 6 + ctx->key_length / 4;
 	unsigned int blocks;
 
-	err = skcipher_walk_virt(&walk, req, false);
-
-	while ((blocks = (walk.nbytes / AES_BLOCK_SIZE))) {
+	while ((blocks = (walk->nbytes / AES_BLOCK_SIZE))) {
 		kernel_neon_begin();
-		aes_cbc_encrypt(walk.dst.virt.addr, walk.src.virt.addr,
-				ctx->key_enc, rounds, blocks, walk.iv);
+		aes_cbc_encrypt(walk->dst.virt.addr, walk->src.virt.addr,
+				ctx->key_enc, rounds, blocks, walk->iv);
 		kernel_neon_end();
-		err = skcipher_walk_done(&walk, walk.nbytes % AES_BLOCK_SIZE);
+		err = skcipher_walk_done(walk, walk->nbytes % AES_BLOCK_SIZE);
 	}
 	return err;
 }
 
-static int cbc_decrypt(struct skcipher_request *req)
+static int cbc_encrypt(struct skcipher_request *req)
 {
-	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
-	struct crypto_aes_ctx *ctx = crypto_skcipher_ctx(tfm);
-	int err, rounds = 6 + ctx->key_length / 4;
 	struct skcipher_walk walk;
-	unsigned int blocks;
+	int err;
 
 	err = skcipher_walk_virt(&walk, req, false);
+	if (err)
+		return err;
+	return cbc_encrypt_walk(req, &walk);
+}
 
-	while ((blocks = (walk.nbytes / AES_BLOCK_SIZE))) {
+static int cbc_decrypt_walk(struct skcipher_request *req,
+			    struct skcipher_walk *walk)
+{
+	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
+	struct crypto_aes_ctx *ctx = crypto_skcipher_ctx(tfm);
+	int err = 0, rounds = 6 + ctx->key_length / 4;
+	unsigned int blocks;
+
+	while ((blocks = (walk->nbytes / AES_BLOCK_SIZE))) {
 		kernel_neon_begin();
-		aes_cbc_decrypt(walk.dst.virt.addr, walk.src.virt.addr,
-				ctx->key_dec, rounds, blocks, walk.iv);
+		aes_cbc_decrypt(walk->dst.virt.addr, walk->src.virt.addr,
+				ctx->key_dec, rounds, blocks, walk->iv);
 		kernel_neon_end();
-		err = skcipher_walk_done(&walk, walk.nbytes % AES_BLOCK_SIZE);
+		err = skcipher_walk_done(walk, walk->nbytes % AES_BLOCK_SIZE);
 	}
 	return err;
 }
 
+static int cbc_decrypt(struct skcipher_request *req)
+{
+	struct skcipher_walk walk;
+	int err;
+
+	err = skcipher_walk_virt(&walk, req, false);
+	if (err)
+		return err;
+	return cbc_decrypt_walk(req, &walk);
+}
+
 static int cts_cbc_init_tfm(struct crypto_skcipher *tfm)
 {
 	crypto_skcipher_set_reqsize(tfm, sizeof(struct cts_cbc_req_ctx));
@@ -251,22 +269,12 @@ static int cts_cbc_encrypt(struct skcipher_request *req)
 	}
 
 	if (cbc_blocks > 0) {
-		unsigned int blocks;
-
 		skcipher_request_set_crypt(&rctx->subreq, req->src, req->dst,
 					   cbc_blocks * AES_BLOCK_SIZE,
 					   req->iv);
 
-		err = skcipher_walk_virt(&walk, &rctx->subreq, false);
-
-		while ((blocks = (walk.nbytes / AES_BLOCK_SIZE))) {
-			kernel_neon_begin();
-			aes_cbc_encrypt(walk.dst.virt.addr, walk.src.virt.addr,
-					ctx->key_enc, rounds, blocks, walk.iv);
-			kernel_neon_end();
-			err = skcipher_walk_done(&walk,
-						 walk.nbytes % AES_BLOCK_SIZE);
-		}
+		err = skcipher_walk_virt(&walk, &rctx->subreq, false) ?:
+		      cbc_encrypt_walk(&rctx->subreq, &walk);
 		if (err)
 			return err;
 
@@ -316,22 +324,12 @@ static int cts_cbc_decrypt(struct skcipher_request *req)
 	}
 
 	if (cbc_blocks > 0) {
-		unsigned int blocks;
-
 		skcipher_request_set_crypt(&rctx->subreq, req->src, req->dst,
 					   cbc_blocks * AES_BLOCK_SIZE,
 					   req->iv);
 
-		err = skcipher_walk_virt(&walk, &rctx->subreq, false);
-
-		while ((blocks = (walk.nbytes / AES_BLOCK_SIZE))) {
-			kernel_neon_begin();
-			aes_cbc_decrypt(walk.dst.virt.addr, walk.src.virt.addr,
-					ctx->key_dec, rounds, blocks, walk.iv);
-			kernel_neon_end();
-			err = skcipher_walk_done(&walk,
-						 walk.nbytes % AES_BLOCK_SIZE);
-		}
+		err = skcipher_walk_virt(&walk, &rctx->subreq, false) ?:
+		      cbc_decrypt_walk(&rctx->subreq, &walk);
 		if (err)
 			return err;