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