crypto: cfb - add support for Cipher FeedBack mode

TPM security routines require encryption and decryption with AES in
CFB mode, so add it to the Linux Crypto schemes.  CFB is basically 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.

https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#CFB

Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 353 insertions, 0 deletions

diff --git a/crypto/cfb.c b/crypto/cfb.c
new file mode 100644
index 000000000000..94ee39bed758
--- /dev/null
+++ b/crypto/cfb.c
@@ -0,0 +1,353 @@
+//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/slab.h>
+#include <linux/string.h>
+#include <linux/types.h>
+
+struct crypto_cfb_ctx {
+	struct crypto_cipher *child;
+};
+
+static unsigned int crypto_cfb_bsize(struct crypto_skcipher *tfm)
+{
+	struct crypto_cfb_ctx *ctx = crypto_skcipher_ctx(tfm);
+	struct crypto_cipher *child = ctx->child;
+
+	return crypto_cipher_blocksize(child);
+}
+
+static void crypto_cfb_encrypt_one(struct crypto_skcipher *tfm,
+					  const u8 *src, u8 *dst)
+{
+	struct crypto_cfb_ctx *ctx = crypto_skcipher_ctx(tfm);
+
+	crypto_cipher_encrypt_one(ctx->child, dst, src);
+}
+
+/* final encrypt and decrypt is the same */
+static void crypto_cfb_final(struct skcipher_walk *walk,
+			     struct crypto_skcipher *tfm)
+{
+	const unsigned int bsize = crypto_cfb_bsize(tfm);
+	const unsigned long alignmask = crypto_skcipher_alignmask(tfm);
+	u8 tmp[bsize + 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);
+		memcpy(iv, dst, bsize);
+
+		src += bsize;
+		dst += bsize;
+	} while ((nbytes -= bsize) >= 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[bsize];
+
+	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, iv, 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 *iv = walk->iv;
+	u8 tmp[bsize];
+
+	do {
+		crypto_cfb_encrypt_one(tfm, iv, tmp);
+		memcpy(iv, src, bsize);
+		crypto_xor(src, tmp, bsize);
+		src += bsize;
+	} while ((nbytes -= bsize) >= bsize);
+
+	memcpy(walk->iv, iv, 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_setkey(struct crypto_skcipher *parent, const u8 *key,
+			     unsigned int keylen)
+{
+	struct crypto_cfb_ctx *ctx = crypto_skcipher_ctx(parent);
+	struct crypto_cipher *child = ctx->child;
+	int err;
+
+	crypto_cipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
+	crypto_cipher_set_flags(child, crypto_skcipher_get_flags(parent) &
+				       CRYPTO_TFM_REQ_MASK);
+	err = crypto_cipher_setkey(child, key, keylen);
+	crypto_skcipher_set_flags(parent, crypto_cipher_get_flags(child) &
+					  CRYPTO_TFM_RES_MASK);
+	return err;
+}
+
+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_init_tfm(struct crypto_skcipher *tfm)
+{
+	struct skcipher_instance *inst = skcipher_alg_instance(tfm);
+	struct crypto_spawn *spawn = skcipher_instance_ctx(inst);
+	struct crypto_cfb_ctx *ctx = crypto_skcipher_ctx(tfm);
+	struct crypto_cipher *cipher;
+
+	cipher = crypto_spawn_cipher(spawn);
+	if (IS_ERR(cipher))
+		return PTR_ERR(cipher);
+
+	ctx->child = cipher;
+	return 0;
+}
+
+static void crypto_cfb_exit_tfm(struct crypto_skcipher *tfm)
+{
+	struct crypto_cfb_ctx *ctx = crypto_skcipher_ctx(tfm);
+
+	crypto_free_cipher(ctx->child);
+}
+
+static void crypto_cfb_free(struct skcipher_instance *inst)
+{
+	crypto_drop_skcipher(skcipher_instance_ctx(inst));
+	kfree(inst);
+}
+
+static int crypto_cfb_create(struct crypto_template *tmpl, struct rtattr **tb)
+{
+	struct skcipher_instance *inst;
+	struct crypto_attr_type *algt;
+	struct crypto_spawn *spawn;
+	struct crypto_alg *alg;
+	u32 mask;
+	int err;
+
+	err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_SKCIPHER);
+	if (err)
+		return err;
+
+	inst = kzalloc(sizeof(*inst) + sizeof(*spawn), GFP_KERNEL);
+	if (!inst)
+		return -ENOMEM;
+
+	algt = crypto_get_attr_type(tb);
+	err = PTR_ERR(algt);
+	if (IS_ERR(algt))
+		goto err_free_inst;
+
+	mask = CRYPTO_ALG_TYPE_MASK |
+		crypto_requires_off(algt->type, algt->mask,
+				    CRYPTO_ALG_NEED_FALLBACK);
+
+	alg = crypto_get_attr_alg(tb, CRYPTO_ALG_TYPE_CIPHER, mask);
+	err = PTR_ERR(alg);
+	if (IS_ERR(alg))
+		goto err_free_inst;
+
+	spawn = skcipher_instance_ctx(inst);
+	err = crypto_init_spawn(spawn, alg, skcipher_crypto_instance(inst),
+				CRYPTO_ALG_TYPE_MASK);
+	crypto_mod_put(alg);
+	if (err)
+		goto err_free_inst;
+
+	err = crypto_inst_setname(skcipher_crypto_instance(inst), "cfb", alg);
+	if (err)
+		goto err_drop_spawn;
+
+	inst->alg.base.cra_priority = alg->cra_priority;
+	/* we're a stream cipher independend of the crypto cra_blocksize */
+	inst->alg.base.cra_blocksize = 1;
+	inst->alg.base.cra_alignmask = alg->cra_alignmask;
+
+	inst->alg.ivsize = alg->cra_blocksize;
+	inst->alg.min_keysize = alg->cra_cipher.cia_min_keysize;
+	inst->alg.max_keysize = alg->cra_cipher.cia_max_keysize;
+
+	inst->alg.base.cra_ctxsize = sizeof(struct crypto_cfb_ctx);
+
+	inst->alg.init = crypto_cfb_init_tfm;
+	inst->alg.exit = crypto_cfb_exit_tfm;
+
+	inst->alg.setkey = crypto_cfb_setkey;
+	inst->alg.encrypt = crypto_cfb_encrypt;
+	inst->alg.decrypt = crypto_cfb_decrypt;
+
+	inst->free = crypto_cfb_free;
+
+	err = skcipher_register_instance(tmpl, inst);
+	if (err)
+		goto err_drop_spawn;
+
+out:
+	return err;
+
+err_drop_spawn:
+	crypto_drop_spawn(spawn);
+err_free_inst:
+	kfree(inst);
+	goto out;
+}
+
+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);
+}
+
+module_init(crypto_cfb_module_init);
+module_exit(crypto_cfb_module_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("CFB block cipher algorithm");
+MODULE_ALIAS_CRYPTO("cfb");