//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);