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 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 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 } 128 129 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 } 188 189 static int decrypt_blob_key(u8 *key) 190 { 191 return do_dcp_crypto(key, key, false); 192 } 193 194 static int encrypt_blob_key(u8 *key) 195 { 196 return do_dcp_crypto(key, key, true); 197 } 198 199 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; 203 204 blen = calc_blob_len(p->key_len); 205 if (blen > MAX_BLOB_SIZE) 206 return -E2BIG; 207 208 b->fmt_version = DCP_BLOB_VERSION; 209 get_random_bytes(b->nonce, AES_KEYSIZE_128); 210 get_random_bytes(b->blob_key, AES_KEYSIZE_128); 211 212 ret = do_aead_crypto(p->key, b->payload, p->key_len, b->blob_key, 213 b->nonce, true); 214 if (ret) { 215 pr_err("Unable to encrypt blob payload: %i\n", ret); 216 return ret; 217 } 218 219 ret = encrypt_blob_key(b->blob_key); 220 if (ret) { 221 pr_err("Unable to encrypt blob key: %i\n", ret); 222 return ret; 223 } 224 225 b->payload_len = get_unaligned_le32(&p->key_len); 226 p->blob_len = blen; 227 return 0; 228 } 229 230 static int trusted_dcp_unseal(struct trusted_key_payload *p, char *datablob) 231 { 232 struct dcp_blob_fmt *b = (struct dcp_blob_fmt *)p->blob; 233 int blen, ret; 234 235 if (b->fmt_version != DCP_BLOB_VERSION) { 236 pr_err("DCP blob has bad version: %i, expected %i\n", 237 b->fmt_version, DCP_BLOB_VERSION); 238 ret = -EINVAL; 239 goto out; 240 } 241 242 p->key_len = le32_to_cpu(b->payload_len); 243 blen = calc_blob_len(p->key_len); 244 if (blen != p->blob_len) { 245 pr_err("DCP blob has bad length: %i != %i\n", blen, 246 p->blob_len); 247 ret = -EINVAL; 248 goto out; 249 } 250 251 ret = decrypt_blob_key(b->blob_key); 252 if (ret) { 253 pr_err("Unable to decrypt blob key: %i\n", ret); 254 goto out; 255 } 256 257 ret = do_aead_crypto(b->payload, p->key, p->key_len + DCP_BLOB_AUTHLEN, 258 b->blob_key, b->nonce, false); 259 if (ret) { 260 pr_err("Unwrap of DCP payload failed: %i\n", ret); 261 goto out; 262 } 263 264 ret = 0; 265 out: 266 return ret; 267 } 268 269 static int test_for_zero_key(void) 270 { 271 /* 272 * Encrypting a plaintext of all 0x55 bytes will yield 273 * this ciphertext in case the DCP test key is used. 274 */ 275 static const u8 bad[] = {0x9a, 0xda, 0xe0, 0x54, 0xf6, 0x3d, 0xfa, 0xff, 276 0x5e, 0xa1, 0x8e, 0x45, 0xed, 0xf6, 0xea, 0x6f}; 277 void *buf = NULL; 278 int ret = 0; 279 280 if (skip_zk_test) 281 goto out; 282 283 buf = kmalloc(AES_BLOCK_SIZE, GFP_KERNEL); 284 if (!buf) { 285 ret = -ENOMEM; 286 goto out; 287 } 288 289 memset(buf, 0x55, AES_BLOCK_SIZE); 290 291 ret = do_dcp_crypto(buf, buf, true); 292 if (ret) 293 goto out; 294 295 if (memcmp(buf, bad, AES_BLOCK_SIZE) == 0) { 296 pr_warn("Device neither in secure nor trusted mode!\n"); 297 ret = -EINVAL; 298 } 299 out: 300 kfree(buf); 301 return ret; 302 } 303 304 static int trusted_dcp_init(void) 305 { 306 int ret; 307 308 if (use_otp_key) 309 pr_info("Using DCP OTP key\n"); 310 311 ret = test_for_zero_key(); 312 if (ret) { 313 pr_warn("Test for zero'ed keys failed: %i\n", ret); 314 315 return -EINVAL; 316 } 317 318 return register_key_type(&key_type_trusted); 319 } 320 321 static void trusted_dcp_exit(void) 322 { 323 unregister_key_type(&key_type_trusted); 324 } 325 326 struct trusted_key_ops dcp_trusted_key_ops = { 327 .exit = trusted_dcp_exit, 328 .init = trusted_dcp_init, 329 .seal = trusted_dcp_seal, 330 .unseal = trusted_dcp_unseal, 331 .migratable = 0, 332 }; 333