xref: /openbmc/linux/lib/digsig.c (revision b830f94f)
1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * Copyright (C) 2011 Nokia Corporation
4  * Copyright (C) 2011 Intel Corporation
5  *
6  * Author:
7  * Dmitry Kasatkin <dmitry.kasatkin@nokia.com>
8  *                 <dmitry.kasatkin@intel.com>
9  *
10  * File: sign.c
11  *	implements signature (RSA) verification
12  *	pkcs decoding is based on LibTomCrypt code
13  */
14 
15 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
16 
17 #include <linux/err.h>
18 #include <linux/module.h>
19 #include <linux/slab.h>
20 #include <linux/key.h>
21 #include <linux/crypto.h>
22 #include <crypto/hash.h>
23 #include <crypto/sha.h>
24 #include <keys/user-type.h>
25 #include <linux/mpi.h>
26 #include <linux/digsig.h>
27 
28 static struct crypto_shash *shash;
29 
30 static const char *pkcs_1_v1_5_decode_emsa(const unsigned char *msg,
31 						unsigned long  msglen,
32 						unsigned long  modulus_bitlen,
33 						unsigned long *outlen)
34 {
35 	unsigned long modulus_len, ps_len, i;
36 
37 	modulus_len = (modulus_bitlen >> 3) + (modulus_bitlen & 7 ? 1 : 0);
38 
39 	/* test message size */
40 	if ((msglen > modulus_len) || (modulus_len < 11))
41 		return NULL;
42 
43 	/* separate encoded message */
44 	if (msg[0] != 0x00 || msg[1] != 0x01)
45 		return NULL;
46 
47 	for (i = 2; i < modulus_len - 1; i++)
48 		if (msg[i] != 0xFF)
49 			break;
50 
51 	/* separator check */
52 	if (msg[i] != 0)
53 		/* There was no octet with hexadecimal value 0x00
54 		to separate ps from m. */
55 		return NULL;
56 
57 	ps_len = i - 2;
58 
59 	*outlen = (msglen - (2 + ps_len + 1));
60 
61 	return msg + 2 + ps_len + 1;
62 }
63 
64 /*
65  * RSA Signature verification with public key
66  */
67 static int digsig_verify_rsa(struct key *key,
68 		    const char *sig, int siglen,
69 		       const char *h, int hlen)
70 {
71 	int err = -EINVAL;
72 	unsigned long len;
73 	unsigned long mlen, mblen;
74 	unsigned nret, l;
75 	int head, i;
76 	unsigned char *out1 = NULL;
77 	const char *m;
78 	MPI in = NULL, res = NULL, pkey[2];
79 	uint8_t *p, *datap;
80 	const uint8_t *endp;
81 	const struct user_key_payload *ukp;
82 	struct pubkey_hdr *pkh;
83 
84 	down_read(&key->sem);
85 	ukp = user_key_payload_locked(key);
86 
87 	if (!ukp) {
88 		/* key was revoked before we acquired its semaphore */
89 		err = -EKEYREVOKED;
90 		goto err1;
91 	}
92 
93 	if (ukp->datalen < sizeof(*pkh))
94 		goto err1;
95 
96 	pkh = (struct pubkey_hdr *)ukp->data;
97 
98 	if (pkh->version != 1)
99 		goto err1;
100 
101 	if (pkh->algo != PUBKEY_ALGO_RSA)
102 		goto err1;
103 
104 	if (pkh->nmpi != 2)
105 		goto err1;
106 
107 	datap = pkh->mpi;
108 	endp = ukp->data + ukp->datalen;
109 
110 	for (i = 0; i < pkh->nmpi; i++) {
111 		unsigned int remaining = endp - datap;
112 		pkey[i] = mpi_read_from_buffer(datap, &remaining);
113 		if (IS_ERR(pkey[i])) {
114 			err = PTR_ERR(pkey[i]);
115 			goto err;
116 		}
117 		datap += remaining;
118 	}
119 
120 	mblen = mpi_get_nbits(pkey[0]);
121 	mlen = DIV_ROUND_UP(mblen, 8);
122 
123 	if (mlen == 0) {
124 		err = -EINVAL;
125 		goto err;
126 	}
127 
128 	err = -ENOMEM;
129 
130 	out1 = kzalloc(mlen, GFP_KERNEL);
131 	if (!out1)
132 		goto err;
133 
134 	nret = siglen;
135 	in = mpi_read_from_buffer(sig, &nret);
136 	if (IS_ERR(in)) {
137 		err = PTR_ERR(in);
138 		goto err;
139 	}
140 
141 	res = mpi_alloc(mpi_get_nlimbs(in) * 2);
142 	if (!res)
143 		goto err;
144 
145 	err = mpi_powm(res, in, pkey[1], pkey[0]);
146 	if (err)
147 		goto err;
148 
149 	if (mpi_get_nlimbs(res) * BYTES_PER_MPI_LIMB > mlen) {
150 		err = -EINVAL;
151 		goto err;
152 	}
153 
154 	p = mpi_get_buffer(res, &l, NULL);
155 	if (!p) {
156 		err = -EINVAL;
157 		goto err;
158 	}
159 
160 	len = mlen;
161 	head = len - l;
162 	memset(out1, 0, head);
163 	memcpy(out1 + head, p, l);
164 
165 	kfree(p);
166 
167 	m = pkcs_1_v1_5_decode_emsa(out1, len, mblen, &len);
168 
169 	if (!m || len != hlen || memcmp(m, h, hlen))
170 		err = -EINVAL;
171 
172 err:
173 	mpi_free(in);
174 	mpi_free(res);
175 	kfree(out1);
176 	while (--i >= 0)
177 		mpi_free(pkey[i]);
178 err1:
179 	up_read(&key->sem);
180 
181 	return err;
182 }
183 
184 /**
185  * digsig_verify() - digital signature verification with public key
186  * @keyring:	keyring to search key in
187  * @sig:	digital signature
188  * @siglen:	length of the signature
189  * @data:	data
190  * @datalen:	length of the data
191  *
192  * Returns 0 on success, -EINVAL otherwise
193  *
194  * Verifies data integrity against digital signature.
195  * Currently only RSA is supported.
196  * Normally hash of the content is used as a data for this function.
197  *
198  */
199 int digsig_verify(struct key *keyring, const char *sig, int siglen,
200 						const char *data, int datalen)
201 {
202 	int err = -ENOMEM;
203 	struct signature_hdr *sh = (struct signature_hdr *)sig;
204 	struct shash_desc *desc = NULL;
205 	unsigned char hash[SHA1_DIGEST_SIZE];
206 	struct key *key;
207 	char name[20];
208 
209 	if (siglen < sizeof(*sh) + 2)
210 		return -EINVAL;
211 
212 	if (sh->algo != PUBKEY_ALGO_RSA)
213 		return -ENOTSUPP;
214 
215 	sprintf(name, "%llX", __be64_to_cpup((uint64_t *)sh->keyid));
216 
217 	if (keyring) {
218 		/* search in specific keyring */
219 		key_ref_t kref;
220 		kref = keyring_search(make_key_ref(keyring, 1UL),
221 				      &key_type_user, name, true);
222 		if (IS_ERR(kref))
223 			key = ERR_CAST(kref);
224 		else
225 			key = key_ref_to_ptr(kref);
226 	} else {
227 		key = request_key(&key_type_user, name, NULL);
228 	}
229 	if (IS_ERR(key)) {
230 		pr_err("key not found, id: %s\n", name);
231 		return PTR_ERR(key);
232 	}
233 
234 	desc = kzalloc(sizeof(*desc) + crypto_shash_descsize(shash),
235 		       GFP_KERNEL);
236 	if (!desc)
237 		goto err;
238 
239 	desc->tfm = shash;
240 
241 	crypto_shash_init(desc);
242 	crypto_shash_update(desc, data, datalen);
243 	crypto_shash_update(desc, sig, sizeof(*sh));
244 	crypto_shash_final(desc, hash);
245 
246 	kfree(desc);
247 
248 	/* pass signature mpis address */
249 	err = digsig_verify_rsa(key, sig + sizeof(*sh), siglen - sizeof(*sh),
250 			     hash, sizeof(hash));
251 
252 err:
253 	key_put(key);
254 
255 	return err ? -EINVAL : 0;
256 }
257 EXPORT_SYMBOL_GPL(digsig_verify);
258 
259 static int __init digsig_init(void)
260 {
261 	shash = crypto_alloc_shash("sha1", 0, 0);
262 	if (IS_ERR(shash)) {
263 		pr_err("shash allocation failed\n");
264 		return  PTR_ERR(shash);
265 	}
266 
267 	return 0;
268 
269 }
270 
271 static void __exit digsig_cleanup(void)
272 {
273 	crypto_free_shash(shash);
274 }
275 
276 module_init(digsig_init);
277 module_exit(digsig_cleanup);
278 
279 MODULE_LICENSE("GPL");
280