1/*
2 * echainiv: Encrypted Chain IV Generator
3 *
4 * This generator generates an IV based on a sequence number by xoring it
5 * with a salt and then encrypting it with the same key as used to encrypt
6 * the plain text.  This algorithm requires that the block size be equal
7 * to the IV size.  It is mainly useful for CBC.
8 *
9 * This generator can only be used by algorithms where authentication
10 * is performed after encryption (i.e., authenc).
11 *
12 * Copyright (c) 2015 Herbert Xu <herbert@gondor.apana.org.au>
13 *
14 * This program is free software; you can redistribute it and/or modify it
15 * under the terms of the GNU General Public License as published by the Free
16 * Software Foundation; either version 2 of the License, or (at your option)
17 * any later version.
18 *
19 */
20
21#include <crypto/internal/geniv.h>
22#include <crypto/scatterwalk.h>
23#include <linux/err.h>
24#include <linux/init.h>
25#include <linux/kernel.h>
26#include <linux/mm.h>
27#include <linux/module.h>
28#include <linux/percpu.h>
29#include <linux/spinlock.h>
30#include <linux/string.h>
31
32#define MAX_IV_SIZE 16
33
34static DEFINE_PER_CPU(u32 [MAX_IV_SIZE / sizeof(u32)], echainiv_iv);
35
36/* We don't care if we get preempted and read/write IVs from the next CPU. */
37static void echainiv_read_iv(u8 *dst, unsigned size)
38{
39	u32 *a = (u32 *)dst;
40	u32 __percpu *b = echainiv_iv;
41
42	for (; size >= 4; size -= 4) {
43		*a++ = this_cpu_read(*b);
44		b++;
45	}
46}
47
48static void echainiv_write_iv(const u8 *src, unsigned size)
49{
50	const u32 *a = (const u32 *)src;
51	u32 __percpu *b = echainiv_iv;
52
53	for (; size >= 4; size -= 4) {
54		this_cpu_write(*b, *a);
55		a++;
56		b++;
57	}
58}
59
60static void echainiv_encrypt_complete2(struct aead_request *req, int err)
61{
62	struct aead_request *subreq = aead_request_ctx(req);
63	struct crypto_aead *geniv;
64	unsigned int ivsize;
65
66	if (err == -EINPROGRESS)
67		return;
68
69	if (err)
70		goto out;
71
72	geniv = crypto_aead_reqtfm(req);
73	ivsize = crypto_aead_ivsize(geniv);
74
75	echainiv_write_iv(subreq->iv, ivsize);
76
77	if (req->iv != subreq->iv)
78		memcpy(req->iv, subreq->iv, ivsize);
79
80out:
81	if (req->iv != subreq->iv)
82		kzfree(subreq->iv);
83}
84
85static void echainiv_encrypt_complete(struct crypto_async_request *base,
86					 int err)
87{
88	struct aead_request *req = base->data;
89
90	echainiv_encrypt_complete2(req, err);
91	aead_request_complete(req, err);
92}
93
94static int echainiv_encrypt(struct aead_request *req)
95{
96	struct crypto_aead *geniv = crypto_aead_reqtfm(req);
97	struct aead_geniv_ctx *ctx = crypto_aead_ctx(geniv);
98	struct aead_request *subreq = aead_request_ctx(req);
99	crypto_completion_t compl;
100	void *data;
101	u8 *info;
102	unsigned int ivsize = crypto_aead_ivsize(geniv);
103	int err;
104
105	if (req->cryptlen < ivsize)
106		return -EINVAL;
107
108	aead_request_set_tfm(subreq, ctx->child);
109
110	compl = echainiv_encrypt_complete;
111	data = req;
112	info = req->iv;
113
114	if (req->src != req->dst) {
115		struct blkcipher_desc desc = {
116			.tfm = ctx->null,
117		};
118
119		err = crypto_blkcipher_encrypt(
120			&desc, req->dst, req->src,
121			req->assoclen + req->cryptlen);
122		if (err)
123			return err;
124	}
125
126	if (unlikely(!IS_ALIGNED((unsigned long)info,
127				 crypto_aead_alignmask(geniv) + 1))) {
128		info = kmalloc(ivsize, req->base.flags &
129				       CRYPTO_TFM_REQ_MAY_SLEEP ? GFP_KERNEL:
130								  GFP_ATOMIC);
131		if (!info)
132			return -ENOMEM;
133
134		memcpy(info, req->iv, ivsize);
135	}
136
137	aead_request_set_callback(subreq, req->base.flags, compl, data);
138	aead_request_set_crypt(subreq, req->dst, req->dst,
139			       req->cryptlen, info);
140	aead_request_set_ad(subreq, req->assoclen);
141
142	crypto_xor(info, ctx->salt, ivsize);
143	scatterwalk_map_and_copy(info, req->dst, req->assoclen, ivsize, 1);
144	echainiv_read_iv(info, ivsize);
145
146	err = crypto_aead_encrypt(subreq);
147	echainiv_encrypt_complete2(req, err);
148	return err;
149}
150
151static int echainiv_decrypt(struct aead_request *req)
152{
153	struct crypto_aead *geniv = crypto_aead_reqtfm(req);
154	struct aead_geniv_ctx *ctx = crypto_aead_ctx(geniv);
155	struct aead_request *subreq = aead_request_ctx(req);
156	crypto_completion_t compl;
157	void *data;
158	unsigned int ivsize = crypto_aead_ivsize(geniv);
159
160	if (req->cryptlen < ivsize)
161		return -EINVAL;
162
163	aead_request_set_tfm(subreq, ctx->child);
164
165	compl = req->base.complete;
166	data = req->base.data;
167
168	aead_request_set_callback(subreq, req->base.flags, compl, data);
169	aead_request_set_crypt(subreq, req->src, req->dst,
170			       req->cryptlen - ivsize, req->iv);
171	aead_request_set_ad(subreq, req->assoclen + ivsize);
172
173	scatterwalk_map_and_copy(req->iv, req->src, req->assoclen, ivsize, 0);
174
175	return crypto_aead_decrypt(subreq);
176}
177
178static int echainiv_aead_create(struct crypto_template *tmpl,
179				struct rtattr **tb)
180{
181	struct aead_instance *inst;
182	struct crypto_aead_spawn *spawn;
183	struct aead_alg *alg;
184	int err;
185
186	inst = aead_geniv_alloc(tmpl, tb, 0, 0);
187
188	if (IS_ERR(inst))
189		return PTR_ERR(inst);
190
191	spawn = aead_instance_ctx(inst);
192	alg = crypto_spawn_aead_alg(spawn);
193
194	err = -EINVAL;
195	if (inst->alg.ivsize & (sizeof(u32) - 1) ||
196	    inst->alg.ivsize > MAX_IV_SIZE)
197		goto free_inst;
198
199	inst->alg.encrypt = echainiv_encrypt;
200	inst->alg.decrypt = echainiv_decrypt;
201
202	inst->alg.init = aead_init_geniv;
203	inst->alg.exit = aead_exit_geniv;
204
205	inst->alg.base.cra_alignmask |= __alignof__(u32) - 1;
206	inst->alg.base.cra_ctxsize = sizeof(struct aead_geniv_ctx);
207	inst->alg.base.cra_ctxsize += inst->alg.ivsize;
208
209	inst->free = aead_geniv_free;
210
211	err = aead_register_instance(tmpl, inst);
212	if (err)
213		goto free_inst;
214
215out:
216	return err;
217
218free_inst:
219	aead_geniv_free(inst);
220	goto out;
221}
222
223static void echainiv_free(struct crypto_instance *inst)
224{
225	aead_geniv_free(aead_instance(inst));
226}
227
228static struct crypto_template echainiv_tmpl = {
229	.name = "echainiv",
230	.create = echainiv_aead_create,
231	.free = echainiv_free,
232	.module = THIS_MODULE,
233};
234
235static int __init echainiv_module_init(void)
236{
237	return crypto_register_template(&echainiv_tmpl);
238}
239
240static void __exit echainiv_module_exit(void)
241{
242	crypto_unregister_template(&echainiv_tmpl);
243}
244
245module_init(echainiv_module_init);
246module_exit(echainiv_module_exit);
247
248MODULE_LICENSE("GPL");
249MODULE_DESCRIPTION("Encrypted Chain IV Generator");
250MODULE_ALIAS_CRYPTO("echainiv");
251