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-rw-r--r--crypto/cfb.c254
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diff --git a/crypto/cfb.c b/crypto/cfb.c
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+// 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/cipher.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");
+MODULE_IMPORT_NS(CRYPTO_INTERNAL);