1 files changed, 252 insertions, 0 deletions
diff --git a/crypto/cfb.c b/crypto/cfb.c
new file mode 100644
index 000000000..4e5219bbc
--- /dev/null
+++ b/crypto/cfb.c
@@ -0,0 +1,252 @@
+//SPDX-License-Identifier: GPL-2.0
+/*
+ * CFB: Cipher FeedBack mode
+ *
+ * Copyright (c) 2018 James.Bottomley@HansenPartnership.com
+ *
+ * CFB is a stream cipher mode which is layered on to a block
+ * encryption scheme.  It works very much like a one time pad where
+ * the pad is generated initially from the encrypted IV and then
+ * subsequently from the encrypted previous block of ciphertext.  The
+ * pad is XOR'd into the plain text to get the final ciphertext.
+ *
+ * The scheme of CFB is best described by wikipedia:
+ *
+ * https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#CFB
+ *
+ * Note that since the pad for both encryption and decryption is
+ * generated by an encryption operation, CFB never uses the block
+ * decryption function.
+ */
+
+#include <crypto/algapi.h>
+#include <crypto/internal/skcipher.h>
+#include <linux/err.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/string.h>
+
+static unsigned int crypto_cfb_bsize(struct crypto_skcipher *tfm)
+{
+	return crypto_cipher_blocksize(skcipher_cipher_simple(tfm));
+}
+
+static void crypto_cfb_encrypt_one(struct crypto_skcipher *tfm,
+					  const u8 *src, u8 *dst)
+{
+	crypto_cipher_encrypt_one(skcipher_cipher_simple(tfm), dst, src);
+}
+
+/* final encrypt and decrypt is the same */
+static void crypto_cfb_final(struct skcipher_walk *walk,
+			     struct crypto_skcipher *tfm)
+{
+	const unsigned long alignmask = crypto_skcipher_alignmask(tfm);
+	u8 tmp[MAX_CIPHER_BLOCKSIZE + MAX_CIPHER_ALIGNMASK];
+	u8 *stream = PTR_ALIGN(tmp + 0, alignmask + 1);
+	u8 *src = walk->src.virt.addr;
+	u8 *dst = walk->dst.virt.addr;
+	u8 *iv = walk->iv;
+	unsigned int nbytes = walk->nbytes;
+
+	crypto_cfb_encrypt_one(tfm, iv, stream);
+	crypto_xor_cpy(dst, stream, src, nbytes);
+}
+
+static int crypto_cfb_encrypt_segment(struct skcipher_walk *walk,
+				      struct crypto_skcipher *tfm)
+{
+	const unsigned int bsize = crypto_cfb_bsize(tfm);
+	unsigned int nbytes = walk->nbytes;
+	u8 *src = walk->src.virt.addr;
+	u8 *dst = walk->dst.virt.addr;
+	u8 *iv = walk->iv;
+
+	do {
+		crypto_cfb_encrypt_one(tfm, iv, dst);
+		crypto_xor(dst, src, bsize);
+		iv = dst;
+
+		src += bsize;
+		dst += bsize;
+	} while ((nbytes -= bsize) >= bsize);
+
+	memcpy(walk->iv, iv, bsize);
+
+	return nbytes;
+}
+
+static int crypto_cfb_encrypt_inplace(struct skcipher_walk *walk,
+				      struct crypto_skcipher *tfm)
+{
+	const unsigned int bsize = crypto_cfb_bsize(tfm);
+	unsigned int nbytes = walk->nbytes;
+	u8 *src = walk->src.virt.addr;
+	u8 *iv = walk->iv;
+	u8 tmp[MAX_CIPHER_BLOCKSIZE];
+
+	do {
+		crypto_cfb_encrypt_one(tfm, iv, tmp);
+		crypto_xor(src, tmp, bsize);
+		iv = src;
+
+		src += bsize;
+	} while ((nbytes -= bsize) >= bsize);
+
+	memcpy(walk->iv, iv, bsize);
+
+	return nbytes;
+}
+
+static int crypto_cfb_encrypt(struct skcipher_request *req)
+{
+	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
+	struct skcipher_walk walk;
+	unsigned int bsize = crypto_cfb_bsize(tfm);
+	int err;
+
+	err = skcipher_walk_virt(&walk, req, false);
+
+	while (walk.nbytes >= bsize) {
+		if (walk.src.virt.addr == walk.dst.virt.addr)
+			err = crypto_cfb_encrypt_inplace(&walk, tfm);
+		else
+			err = crypto_cfb_encrypt_segment(&walk, tfm);
+		err = skcipher_walk_done(&walk, err);
+	}
+
+	if (walk.nbytes) {
+		crypto_cfb_final(&walk, tfm);
+		err = skcipher_walk_done(&walk, 0);
+	}
+
+	return err;
+}
+
+static int crypto_cfb_decrypt_segment(struct skcipher_walk *walk,
+				      struct crypto_skcipher *tfm)
+{
+	const unsigned int bsize = crypto_cfb_bsize(tfm);
+	unsigned int nbytes = walk->nbytes;
+	u8 *src = walk->src.virt.addr;
+	u8 *dst = walk->dst.virt.addr;
+	u8 *iv = walk->iv;
+
+	do {
+		crypto_cfb_encrypt_one(tfm, iv, dst);
+		crypto_xor(dst, src, bsize);
+		iv = src;
+
+		src += bsize;
+		dst += bsize;
+	} while ((nbytes -= bsize) >= bsize);
+
+	memcpy(walk->iv, iv, bsize);
+
+	return nbytes;
+}
+
+static int crypto_cfb_decrypt_inplace(struct skcipher_walk *walk,
+				      struct crypto_skcipher *tfm)
+{
+	const unsigned int bsize = crypto_cfb_bsize(tfm);
+	unsigned int nbytes = walk->nbytes;
+	u8 *src = walk->src.virt.addr;
+	u8 * const iv = walk->iv;
+	u8 tmp[MAX_CIPHER_BLOCKSIZE];
+
+	do {
+		crypto_cfb_encrypt_one(tfm, iv, tmp);
+		memcpy(iv, src, bsize);
+		crypto_xor(src, tmp, bsize);
+		src += bsize;
+	} while ((nbytes -= bsize) >= bsize);
+
+	return nbytes;
+}
+
+static int crypto_cfb_decrypt_blocks(struct skcipher_walk *walk,
+				     struct crypto_skcipher *tfm)
+{
+	if (walk->src.virt.addr == walk->dst.virt.addr)
+		return crypto_cfb_decrypt_inplace(walk, tfm);
+	else
+		return crypto_cfb_decrypt_segment(walk, tfm);
+}
+
+static int crypto_cfb_decrypt(struct skcipher_request *req)
+{
+	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
+	struct skcipher_walk walk;
+	const unsigned int bsize = crypto_cfb_bsize(tfm);
+	int err;
+
+	err = skcipher_walk_virt(&walk, req, false);
+
+	while (walk.nbytes >= bsize) {
+		err = crypto_cfb_decrypt_blocks(&walk, tfm);
+		err = skcipher_walk_done(&walk, err);
+	}
+
+	if (walk.nbytes) {
+		crypto_cfb_final(&walk, tfm);
+		err = skcipher_walk_done(&walk, 0);
+	}
+
+	return err;
+}
+
+static int crypto_cfb_create(struct crypto_template *tmpl, struct rtattr **tb)
+{
+	struct skcipher_instance *inst;
+	struct crypto_alg *alg;
+	int err;
+
+	inst = skcipher_alloc_instance_simple(tmpl, tb);
+	if (IS_ERR(inst))
+		return PTR_ERR(inst);
+
+	alg = skcipher_ialg_simple(inst);
+
+	/* CFB mode is a stream cipher. */
+	inst->alg.base.cra_blocksize = 1;
+
+	/*
+	 * To simplify the implementation, configure the skcipher walk to only
+	 * give a partial block at the very end, never earlier.
+	 */
+	inst->alg.chunksize = alg->cra_blocksize;
+
+	inst->alg.encrypt = crypto_cfb_encrypt;
+	inst->alg.decrypt = crypto_cfb_decrypt;
+
+	err = skcipher_register_instance(tmpl, inst);
+	if (err)
+		inst->free(inst);
+
+	return err;
+}
+
+static struct crypto_template crypto_cfb_tmpl = {
+	.name = "cfb",
+	.create = crypto_cfb_create,
+	.module = THIS_MODULE,
+};
+
+static int __init crypto_cfb_module_init(void)
+{
+	return crypto_register_template(&crypto_cfb_tmpl);
+}
+
+static void __exit crypto_cfb_module_exit(void)
+{
+	crypto_unregister_template(&crypto_cfb_tmpl);
+}
+
+subsys_initcall(crypto_cfb_module_init);
+module_exit(crypto_cfb_module_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("CFB block cipher mode of operation");
+MODULE_ALIAS_CRYPTO("cfb");