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 DECLARE_CRYPTO_WAIT(wait);
137
138 aead = crypto_alloc_aead("gcm(aes)", 0, CRYPTO_ALG_ASYNC);
139 if (IS_ERR(aead)) {
140 ret = PTR_ERR(aead);
141 goto out;
142 }
143
144 ret = crypto_aead_setauthsize(aead, DCP_BLOB_AUTHLEN);
145 if (ret < 0) {
146 pr_err("Can't set crypto auth tag len: %d\n", ret);
147 goto free_aead;
148 }
149
150 aead_req = aead_request_alloc(aead, GFP_KERNEL);
151 if (!aead_req) {
152 ret = -ENOMEM;
153 goto free_aead;
154 }
155
156 sg_init_one(&src_sg, in, len);
157 if (do_encrypt) {
158 /*
159 * If we encrypt our buffer has extra space for the auth tag.
160 */
161 sg_init_one(&dst_sg, out, len + DCP_BLOB_AUTHLEN);
162 } else {
163 sg_init_one(&dst_sg, out, len);
164 }
165
166 aead_request_set_crypt(aead_req, &src_sg, &dst_sg, len, nonce);
167 aead_request_set_callback(aead_req, CRYPTO_TFM_REQ_MAY_SLEEP,
168 crypto_req_done, &wait);
169 aead_request_set_ad(aead_req, 0);
170
171 if (crypto_aead_setkey(aead, key, AES_KEYSIZE_128)) {
172 pr_err("Can't set crypto AEAD key\n");
173 ret = -EINVAL;
174 goto free_req;
175 }
176
177 if (do_encrypt)
178 ret = crypto_wait_req(crypto_aead_encrypt(aead_req), &wait);
179 else
180 ret = crypto_wait_req(crypto_aead_decrypt(aead_req), &wait);
181
182 free_req:
183 aead_request_free(aead_req);
184 free_aead:
185 crypto_free_aead(aead);
186 out:
187 return ret;
188 }
189
decrypt_blob_key(u8 * encrypted_key,u8 * plain_key)190 static int decrypt_blob_key(u8 *encrypted_key, u8 *plain_key)
191 {
192 return do_dcp_crypto(encrypted_key, plain_key, false);
193 }
194
encrypt_blob_key(u8 * plain_key,u8 * encrypted_key)195 static int encrypt_blob_key(u8 *plain_key, u8 *encrypted_key)
196 {
197 return do_dcp_crypto(plain_key, encrypted_key, true);
198 }
199
trusted_dcp_seal(struct trusted_key_payload * p,char * datablob)200 static int trusted_dcp_seal(struct trusted_key_payload *p, char *datablob)
201 {
202 struct dcp_blob_fmt *b = (struct dcp_blob_fmt *)p->blob;
203 int blen, ret;
204 u8 plain_blob_key[AES_KEYSIZE_128];
205
206 blen = calc_blob_len(p->key_len);
207 if (blen > MAX_BLOB_SIZE)
208 return -E2BIG;
209
210 b->fmt_version = DCP_BLOB_VERSION;
211 get_random_bytes(b->nonce, AES_KEYSIZE_128);
212 get_random_bytes(plain_blob_key, AES_KEYSIZE_128);
213
214 ret = do_aead_crypto(p->key, b->payload, p->key_len, plain_blob_key,
215 b->nonce, true);
216 if (ret) {
217 pr_err("Unable to encrypt blob payload: %i\n", ret);
218 goto out;
219 }
220
221 ret = encrypt_blob_key(plain_blob_key, b->blob_key);
222 if (ret) {
223 pr_err("Unable to encrypt blob key: %i\n", ret);
224 goto out;
225 }
226
227 put_unaligned_le32(p->key_len, &b->payload_len);
228 p->blob_len = blen;
229 ret = 0;
230
231 out:
232 memzero_explicit(plain_blob_key, sizeof(plain_blob_key));
233
234 return ret;
235 }
236
trusted_dcp_unseal(struct trusted_key_payload * p,char * datablob)237 static int trusted_dcp_unseal(struct trusted_key_payload *p, char *datablob)
238 {
239 struct dcp_blob_fmt *b = (struct dcp_blob_fmt *)p->blob;
240 int blen, ret;
241 u8 plain_blob_key[AES_KEYSIZE_128];
242
243 if (b->fmt_version != DCP_BLOB_VERSION) {
244 pr_err("DCP blob has bad version: %i, expected %i\n",
245 b->fmt_version, DCP_BLOB_VERSION);
246 ret = -EINVAL;
247 goto out;
248 }
249
250 p->key_len = le32_to_cpu(b->payload_len);
251 blen = calc_blob_len(p->key_len);
252 if (blen != p->blob_len) {
253 pr_err("DCP blob has bad length: %i != %i\n", blen,
254 p->blob_len);
255 ret = -EINVAL;
256 goto out;
257 }
258
259 ret = decrypt_blob_key(b->blob_key, plain_blob_key);
260 if (ret) {
261 pr_err("Unable to decrypt blob key: %i\n", ret);
262 goto out;
263 }
264
265 ret = do_aead_crypto(b->payload, p->key, p->key_len + DCP_BLOB_AUTHLEN,
266 plain_blob_key, b->nonce, false);
267 if (ret) {
268 pr_err("Unwrap of DCP payload failed: %i\n", ret);
269 goto out;
270 }
271
272 ret = 0;
273 out:
274 memzero_explicit(plain_blob_key, sizeof(plain_blob_key));
275
276 return ret;
277 }
278
test_for_zero_key(void)279 static int test_for_zero_key(void)
280 {
281 /*
282 * Encrypting a plaintext of all 0x55 bytes will yield
283 * this ciphertext in case the DCP test key is used.
284 */
285 static const u8 bad[] = {0x9a, 0xda, 0xe0, 0x54, 0xf6, 0x3d, 0xfa, 0xff,
286 0x5e, 0xa1, 0x8e, 0x45, 0xed, 0xf6, 0xea, 0x6f};
287 void *buf = NULL;
288 int ret = 0;
289
290 if (skip_zk_test)
291 goto out;
292
293 buf = kmalloc(AES_BLOCK_SIZE, GFP_KERNEL);
294 if (!buf) {
295 ret = -ENOMEM;
296 goto out;
297 }
298
299 memset(buf, 0x55, AES_BLOCK_SIZE);
300
301 ret = do_dcp_crypto(buf, buf, true);
302 if (ret)
303 goto out;
304
305 if (memcmp(buf, bad, AES_BLOCK_SIZE) == 0) {
306 pr_warn("Device neither in secure nor trusted mode!\n");
307 ret = -EINVAL;
308 }
309 out:
310 kfree(buf);
311 return ret;
312 }
313
trusted_dcp_init(void)314 static int trusted_dcp_init(void)
315 {
316 int ret;
317
318 if (use_otp_key)
319 pr_info("Using DCP OTP key\n");
320
321 ret = test_for_zero_key();
322 if (ret) {
323 pr_warn("Test for zero'ed keys failed: %i\n", ret);
324
325 return -EINVAL;
326 }
327
328 return register_key_type(&key_type_trusted);
329 }
330
trusted_dcp_exit(void)331 static void trusted_dcp_exit(void)
332 {
333 unregister_key_type(&key_type_trusted);
334 }
335
336 struct trusted_key_ops dcp_trusted_key_ops = {
337 .exit = trusted_dcp_exit,
338 .init = trusted_dcp_init,
339 .seal = trusted_dcp_seal,
340 .unseal = trusted_dcp_unseal,
341 .migratable = 0,
342 };
343