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