1 /*
2  * ECDH helper functions - KPP wrappings
3  *
4  * Copyright (C) 2017 Intel Corporation
5  *
6  * This program is free software; you can redistribute it and/or modify
7  * it under the terms of the GNU General Public License version 2 as
8  * published by the Free Software Foundation;
9  *
10  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
11  * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
12  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT OF THIRD PARTY RIGHTS.
13  * IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) AND AUTHOR(S) BE LIABLE FOR ANY
14  * CLAIM, OR ANY SPECIAL INDIRECT OR CONSEQUENTIAL DAMAGES, OR ANY DAMAGES
15  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
16  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
17  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
18  *
19  * ALL LIABILITY, INCLUDING LIABILITY FOR INFRINGEMENT OF ANY PATENTS,
20  * COPYRIGHTS, TRADEMARKS OR OTHER RIGHTS, RELATING TO USE OF THIS
21  * SOFTWARE IS DISCLAIMED.
22  */
23 #include "ecdh_helper.h"
24 
25 #include <linux/scatterlist.h>
26 #include <crypto/ecdh.h>
27 
28 struct ecdh_completion {
29 	struct completion completion;
30 	int err;
31 };
32 
ecdh_complete(struct crypto_async_request * req,int err)33 static void ecdh_complete(struct crypto_async_request *req, int err)
34 {
35 	struct ecdh_completion *res = req->data;
36 
37 	if (err == -EINPROGRESS)
38 		return;
39 
40 	res->err = err;
41 	complete(&res->completion);
42 }
43 
swap_digits(u64 * in,u64 * out,unsigned int ndigits)44 static inline void swap_digits(u64 *in, u64 *out, unsigned int ndigits)
45 {
46 	int i;
47 
48 	for (i = 0; i < ndigits; i++)
49 		out[i] = __swab64(in[ndigits - 1 - i]);
50 }
51 
52 /* compute_ecdh_secret() - function assumes that the private key was
53  *                         already set.
54  * @tfm:          KPP tfm handle allocated with crypto_alloc_kpp().
55  * @public_key:   pair's ecc public key.
56  * secret:        memory where the ecdh computed shared secret will be saved.
57  *
58  * Return: zero on success; error code in case of error.
59  */
compute_ecdh_secret(struct crypto_kpp * tfm,const u8 public_key[64],u8 secret[32])60 int compute_ecdh_secret(struct crypto_kpp *tfm, const u8 public_key[64],
61 			u8 secret[32])
62 {
63 	struct kpp_request *req;
64 	u8 *tmp;
65 	struct ecdh_completion result;
66 	struct scatterlist src, dst;
67 	int err;
68 
69 	tmp = kmalloc(64, GFP_KERNEL);
70 	if (!tmp)
71 		return -ENOMEM;
72 
73 	req = kpp_request_alloc(tfm, GFP_KERNEL);
74 	if (!req) {
75 		err = -ENOMEM;
76 		goto free_tmp;
77 	}
78 
79 	init_completion(&result.completion);
80 
81 	swap_digits((u64 *)public_key, (u64 *)tmp, 4); /* x */
82 	swap_digits((u64 *)&public_key[32], (u64 *)&tmp[32], 4); /* y */
83 
84 	sg_init_one(&src, tmp, 64);
85 	sg_init_one(&dst, secret, 32);
86 	kpp_request_set_input(req, &src, 64);
87 	kpp_request_set_output(req, &dst, 32);
88 	kpp_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG,
89 				 ecdh_complete, &result);
90 	err = crypto_kpp_compute_shared_secret(req);
91 	if (err == -EINPROGRESS) {
92 		wait_for_completion(&result.completion);
93 		err = result.err;
94 	}
95 	if (err < 0) {
96 		pr_err("alg: ecdh: compute shared secret failed. err %d\n",
97 		       err);
98 		goto free_all;
99 	}
100 
101 	swap_digits((u64 *)secret, (u64 *)tmp, 4);
102 	memcpy(secret, tmp, 32);
103 
104 free_all:
105 	kpp_request_free(req);
106 free_tmp:
107 	kfree_sensitive(tmp);
108 	return err;
109 }
110 
111 /* set_ecdh_privkey() - set or generate ecc private key.
112  *
113  * Function generates an ecc private key in the crypto subsystem when receiving
114  * a NULL private key or sets the received key when not NULL.
115  *
116  * @tfm:           KPP tfm handle allocated with crypto_alloc_kpp().
117  * @private_key:   user's ecc private key. When not NULL, the key is expected
118  *                 in little endian format.
119  *
120  * Return: zero on success; error code in case of error.
121  */
set_ecdh_privkey(struct crypto_kpp * tfm,const u8 private_key[32])122 int set_ecdh_privkey(struct crypto_kpp *tfm, const u8 private_key[32])
123 {
124 	u8 *buf, *tmp = NULL;
125 	unsigned int buf_len;
126 	int err;
127 	struct ecdh p = {0};
128 
129 	if (private_key) {
130 		tmp = kmalloc(32, GFP_KERNEL);
131 		if (!tmp)
132 			return -ENOMEM;
133 		swap_digits((u64 *)private_key, (u64 *)tmp, 4);
134 		p.key = tmp;
135 		p.key_size = 32;
136 	}
137 
138 	buf_len = crypto_ecdh_key_len(&p);
139 	buf = kmalloc(buf_len, GFP_KERNEL);
140 	if (!buf) {
141 		err = -ENOMEM;
142 		goto free_tmp;
143 	}
144 
145 	err = crypto_ecdh_encode_key(buf, buf_len, &p);
146 	if (err)
147 		goto free_all;
148 
149 	err = crypto_kpp_set_secret(tfm, buf, buf_len);
150 	/* fall through */
151 free_all:
152 	kfree_sensitive(buf);
153 free_tmp:
154 	kfree_sensitive(tmp);
155 	return err;
156 }
157 
158 /* generate_ecdh_public_key() - function assumes that the private key was
159  *                              already set.
160  *
161  * @tfm:          KPP tfm handle allocated with crypto_alloc_kpp().
162  * @public_key:   memory where the computed ecc public key will be saved.
163  *
164  * Return: zero on success; error code in case of error.
165  */
generate_ecdh_public_key(struct crypto_kpp * tfm,u8 public_key[64])166 int generate_ecdh_public_key(struct crypto_kpp *tfm, u8 public_key[64])
167 {
168 	struct kpp_request *req;
169 	u8 *tmp;
170 	struct ecdh_completion result;
171 	struct scatterlist dst;
172 	int err;
173 
174 	tmp = kmalloc(64, GFP_KERNEL);
175 	if (!tmp)
176 		return -ENOMEM;
177 
178 	req = kpp_request_alloc(tfm, GFP_KERNEL);
179 	if (!req) {
180 		err = -ENOMEM;
181 		goto free_tmp;
182 	}
183 
184 	init_completion(&result.completion);
185 	sg_init_one(&dst, tmp, 64);
186 	kpp_request_set_input(req, NULL, 0);
187 	kpp_request_set_output(req, &dst, 64);
188 	kpp_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG,
189 				 ecdh_complete, &result);
190 
191 	err = crypto_kpp_generate_public_key(req);
192 	if (err == -EINPROGRESS) {
193 		wait_for_completion(&result.completion);
194 		err = result.err;
195 	}
196 	if (err < 0)
197 		goto free_all;
198 
199 	/* The public key is handed back in little endian as expected by
200 	 * the Security Manager Protocol.
201 	 */
202 	swap_digits((u64 *)tmp, (u64 *)public_key, 4); /* x */
203 	swap_digits((u64 *)&tmp[32], (u64 *)&public_key[32], 4); /* y */
204 
205 free_all:
206 	kpp_request_free(req);
207 free_tmp:
208 	kfree(tmp);
209 	return err;
210 }
211 
212 /* generate_ecdh_keys() - generate ecc key pair.
213  *
214  * @tfm:          KPP tfm handle allocated with crypto_alloc_kpp().
215  * @public_key:   memory where the computed ecc public key will be saved.
216  *
217  * Return: zero on success; error code in case of error.
218  */
generate_ecdh_keys(struct crypto_kpp * tfm,u8 public_key[64])219 int generate_ecdh_keys(struct crypto_kpp *tfm, u8 public_key[64])
220 {
221 	int err;
222 
223 	err = set_ecdh_privkey(tfm, NULL);
224 	if (err)
225 		return err;
226 
227 	return generate_ecdh_public_key(tfm, public_key);
228 }
229