1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * Copyright (C) 2021 sigma star gmbh
4 */
5
6 #include <crypto/aead.h>
7 #include <crypto/aes.h>
8 #include <crypto/algapi.h>
9 #include <crypto/gcm.h>
10 #include <crypto/skcipher.h>
11 #include <keys/trusted-type.h>
12 #include <linux/key-type.h>
13 #include <linux/module.h>
14 #include <linux/printk.h>
15 #include <linux/random.h>
16 #include <linux/scatterlist.h>
17 #include <soc/fsl/dcp.h>
18
19 #define DCP_BLOB_VERSION 1
20 #define DCP_BLOB_AUTHLEN 16
21
22 /**
23 * DOC: dcp blob format
24 *
25 * The Data Co-Processor (DCP) provides hardware-bound AES keys using its
26 * AES encryption engine only. It does not provide direct key sealing/unsealing.
27 * To make DCP hardware encryption keys usable as trust source, we define
28 * our own custom format that uses a hardware-bound key to secure the sealing
29 * key stored in the key blob.
30 *
31 * Whenever a new trusted key using DCP is generated, we generate a random 128-bit
32 * blob encryption key (BEK) and 128-bit nonce. The BEK and nonce are used to
33 * encrypt the trusted key payload using AES-128-GCM.
34 *
35 * The BEK itself is encrypted using the hardware-bound key using the DCP's AES
36 * encryption engine with AES-128-ECB. The encrypted BEK, generated nonce,
37 * BEK-encrypted payload and authentication tag make up the blob format together
38 * with a version number, payload length and authentication tag.
39 */
40
41 /**
42 * struct dcp_blob_fmt - DCP BLOB format.
43 *
44 * @fmt_version: Format version, currently being %1.
45 * @blob_key: Random AES 128 key which is used to encrypt @payload,
46 * @blob_key itself is encrypted with OTP or UNIQUE device key in
47 * AES-128-ECB mode by DCP.
48 * @nonce: Random nonce used for @payload encryption.
49 * @payload_len: Length of the plain text @payload.
50 * @payload: The payload itself, encrypted using AES-128-GCM and @blob_key,
51 * GCM auth tag of size DCP_BLOB_AUTHLEN is attached at the end of it.
52 *
53 * The total size of a DCP BLOB is sizeof(struct dcp_blob_fmt) + @payload_len +
54 * DCP_BLOB_AUTHLEN.
55 */
56 struct dcp_blob_fmt {
57 __u8 fmt_version;
58 __u8 blob_key[AES_KEYSIZE_128];
59 __u8 nonce[AES_KEYSIZE_128];
60 __le32 payload_len;
61 __u8 payload[];
62 } __packed;
63
64 static bool use_otp_key;
65 module_param_named(dcp_use_otp_key, use_otp_key, bool, 0);
66 MODULE_PARM_DESC(dcp_use_otp_key, "Use OTP instead of UNIQUE key for sealing");
67
68 static bool skip_zk_test;
69 module_param_named(dcp_skip_zk_test, skip_zk_test, bool, 0);
70 MODULE_PARM_DESC(dcp_skip_zk_test, "Don't test whether device keys are zero'ed");
71
calc_blob_len(unsigned int payload_len)72 static unsigned int calc_blob_len(unsigned int payload_len)
73 {
74 return sizeof(struct dcp_blob_fmt) + payload_len + DCP_BLOB_AUTHLEN;
75 }
76
do_dcp_crypto(u8 * in,u8 * out,bool do_encrypt)77 static int do_dcp_crypto(u8 *in, u8 *out, bool do_encrypt)
78 {
79 struct skcipher_request *req = NULL;
80 struct scatterlist src_sg, dst_sg;
81 struct crypto_skcipher *tfm;
82 u8 paes_key[DCP_PAES_KEYSIZE];
83 DECLARE_CRYPTO_WAIT(wait);
84 int res = 0;
85
86 if (use_otp_key)
87 paes_key[0] = DCP_PAES_KEY_OTP;
88 else
89 paes_key[0] = DCP_PAES_KEY_UNIQUE;
90
91 tfm = crypto_alloc_skcipher("ecb-paes-dcp", CRYPTO_ALG_INTERNAL,
92 CRYPTO_ALG_INTERNAL);
93 if (IS_ERR(tfm)) {
94 res = PTR_ERR(tfm);
95 tfm = NULL;
96 goto out;
97 }
98
99 req = skcipher_request_alloc(tfm, GFP_NOFS);
100 if (!req) {
101 res = -ENOMEM;
102 goto out;
103 }
104
105 skcipher_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG |
106 CRYPTO_TFM_REQ_MAY_SLEEP,
107 crypto_req_done, &wait);
108 res = crypto_skcipher_setkey(tfm, paes_key, sizeof(paes_key));
109 if (res < 0)
110 goto out;
111
112 sg_init_one(&src_sg, in, AES_KEYSIZE_128);
113 sg_init_one(&dst_sg, out, AES_KEYSIZE_128);
114 skcipher_request_set_crypt(req, &src_sg, &dst_sg, AES_KEYSIZE_128,
115 NULL);
116
117 if (do_encrypt)
118 res = crypto_wait_req(crypto_skcipher_encrypt(req), &wait);
119 else
120 res = crypto_wait_req(crypto_skcipher_decrypt(req), &wait);
121
122 out:
123 skcipher_request_free(req);
124 crypto_free_skcipher(tfm);
125
126 return res;
127 }
128
do_aead_crypto(u8 * in,u8 * out,size_t len,u8 * key,u8 * nonce,bool do_encrypt)129 static int do_aead_crypto(u8 *in, u8 *out, size_t len, u8 *key, u8 *nonce,
130 bool do_encrypt)
131 {
132 struct aead_request *aead_req = NULL;
133 struct scatterlist src_sg, dst_sg;
134 struct crypto_aead *aead;
135 int ret;
136
137 aead = crypto_alloc_aead("gcm(aes)", 0, CRYPTO_ALG_ASYNC);
138 if (IS_ERR(aead)) {
139 ret = PTR_ERR(aead);
140 goto out;
141 }
142
143 ret = crypto_aead_setauthsize(aead, DCP_BLOB_AUTHLEN);
144 if (ret < 0) {
145 pr_err("Can't set crypto auth tag len: %d\n", ret);
146 goto free_aead;
147 }
148
149 aead_req = aead_request_alloc(aead, GFP_KERNEL);
150 if (!aead_req) {
151 ret = -ENOMEM;
152 goto free_aead;
153 }
154
155 sg_init_one(&src_sg, in, len);
156 if (do_encrypt) {
157 /*
158 * If we encrypt our buffer has extra space for the auth tag.
159 */
160 sg_init_one(&dst_sg, out, len + DCP_BLOB_AUTHLEN);
161 } else {
162 sg_init_one(&dst_sg, out, len);
163 }
164
165 aead_request_set_crypt(aead_req, &src_sg, &dst_sg, len, nonce);
166 aead_request_set_callback(aead_req, CRYPTO_TFM_REQ_MAY_SLEEP, NULL,
167 NULL);
168 aead_request_set_ad(aead_req, 0);
169
170 if (crypto_aead_setkey(aead, key, AES_KEYSIZE_128)) {
171 pr_err("Can't set crypto AEAD key\n");
172 ret = -EINVAL;
173 goto free_req;
174 }
175
176 if (do_encrypt)
177 ret = crypto_aead_encrypt(aead_req);
178 else
179 ret = crypto_aead_decrypt(aead_req);
180
181 free_req:
182 aead_request_free(aead_req);
183 free_aead:
184 crypto_free_aead(aead);
185 out:
186 return ret;
187 }
188
decrypt_blob_key(u8 * encrypted_key,u8 * plain_key)189 static int decrypt_blob_key(u8 *encrypted_key, u8 *plain_key)
190 {
191 return do_dcp_crypto(encrypted_key, plain_key, false);
192 }
193
encrypt_blob_key(u8 * plain_key,u8 * encrypted_key)194 static int encrypt_blob_key(u8 *plain_key, u8 *encrypted_key)
195 {
196 return do_dcp_crypto(plain_key, encrypted_key, true);
197 }
198
trusted_dcp_seal(struct trusted_key_payload * p,char * datablob)199 static int trusted_dcp_seal(struct trusted_key_payload *p, char *datablob)
200 {
201 struct dcp_blob_fmt *b = (struct dcp_blob_fmt *)p->blob;
202 int blen, ret;
203 u8 plain_blob_key[AES_KEYSIZE_128];
204
205 blen = calc_blob_len(p->key_len);
206 if (blen > MAX_BLOB_SIZE)
207 return -E2BIG;
208
209 b->fmt_version = DCP_BLOB_VERSION;
210 get_random_bytes(b->nonce, AES_KEYSIZE_128);
211 get_random_bytes(plain_blob_key, AES_KEYSIZE_128);
212
213 ret = do_aead_crypto(p->key, b->payload, p->key_len, plain_blob_key,
214 b->nonce, true);
215 if (ret) {
216 pr_err("Unable to encrypt blob payload: %i\n", ret);
217 goto out;
218 }
219
220 ret = encrypt_blob_key(plain_blob_key, b->blob_key);
221 if (ret) {
222 pr_err("Unable to encrypt blob key: %i\n", ret);
223 goto out;
224 }
225
226 put_unaligned_le32(p->key_len, &b->payload_len);
227 p->blob_len = blen;
228 ret = 0;
229
230 out:
231 memzero_explicit(plain_blob_key, sizeof(plain_blob_key));
232
233 return ret;
234 }
235
trusted_dcp_unseal(struct trusted_key_payload * p,char * datablob)236 static int trusted_dcp_unseal(struct trusted_key_payload *p, char *datablob)
237 {
238 struct dcp_blob_fmt *b = (struct dcp_blob_fmt *)p->blob;
239 int blen, ret;
240 u8 plain_blob_key[AES_KEYSIZE_128];
241
242 if (b->fmt_version != DCP_BLOB_VERSION) {
243 pr_err("DCP blob has bad version: %i, expected %i\n",
244 b->fmt_version, DCP_BLOB_VERSION);
245 ret = -EINVAL;
246 goto out;
247 }
248
249 p->key_len = le32_to_cpu(b->payload_len);
250 blen = calc_blob_len(p->key_len);
251 if (blen != p->blob_len) {
252 pr_err("DCP blob has bad length: %i != %i\n", blen,
253 p->blob_len);
254 ret = -EINVAL;
255 goto out;
256 }
257
258 ret = decrypt_blob_key(b->blob_key, plain_blob_key);
259 if (ret) {
260 pr_err("Unable to decrypt blob key: %i\n", ret);
261 goto out;
262 }
263
264 ret = do_aead_crypto(b->payload, p->key, p->key_len + DCP_BLOB_AUTHLEN,
265 plain_blob_key, b->nonce, false);
266 if (ret) {
267 pr_err("Unwrap of DCP payload failed: %i\n", ret);
268 goto out;
269 }
270
271 ret = 0;
272 out:
273 memzero_explicit(plain_blob_key, sizeof(plain_blob_key));
274
275 return ret;
276 }
277
test_for_zero_key(void)278 static int test_for_zero_key(void)
279 {
280 /*
281 * Encrypting a plaintext of all 0x55 bytes will yield
282 * this ciphertext in case the DCP test key is used.
283 */
284 static const u8 bad[] = {0x9a, 0xda, 0xe0, 0x54, 0xf6, 0x3d, 0xfa, 0xff,
285 0x5e, 0xa1, 0x8e, 0x45, 0xed, 0xf6, 0xea, 0x6f};
286 void *buf = NULL;
287 int ret = 0;
288
289 if (skip_zk_test)
290 goto out;
291
292 buf = kmalloc(AES_BLOCK_SIZE, GFP_KERNEL);
293 if (!buf) {
294 ret = -ENOMEM;
295 goto out;
296 }
297
298 memset(buf, 0x55, AES_BLOCK_SIZE);
299
300 ret = do_dcp_crypto(buf, buf, true);
301 if (ret)
302 goto out;
303
304 if (memcmp(buf, bad, AES_BLOCK_SIZE) == 0) {
305 pr_warn("Device neither in secure nor trusted mode!\n");
306 ret = -EINVAL;
307 }
308 out:
309 kfree(buf);
310 return ret;
311 }
312
trusted_dcp_init(void)313 static int trusted_dcp_init(void)
314 {
315 int ret;
316
317 if (use_otp_key)
318 pr_info("Using DCP OTP key\n");
319
320 ret = test_for_zero_key();
321 if (ret) {
322 pr_warn("Test for zero'ed keys failed: %i\n", ret);
323
324 return -EINVAL;
325 }
326
327 return register_key_type(&key_type_trusted);
328 }
329
trusted_dcp_exit(void)330 static void trusted_dcp_exit(void)
331 {
332 unregister_key_type(&key_type_trusted);
333 }
334
335 struct trusted_key_ops dcp_trusted_key_ops = {
336 .exit = trusted_dcp_exit,
337 .init = trusted_dcp_init,
338 .seal = trusted_dcp_seal,
339 .unseal = trusted_dcp_unseal,
340 .migratable = 0,
341 };
342