1 /* Copyright 2014 The Android Open Source Project 2 * 3 * Redistribution and use in source and binary forms, with or without 4 * modification, are permitted provided that the following conditions 5 * are met: 6 * 1. Redistributions of source code must retain the above copyright 7 * notice, this list of conditions and the following disclaimer. 8 * 2. Redistributions in binary form must reproduce the above copyright 9 * notice, this list of conditions and the following disclaimer in the 10 * documentation and/or other materials provided with the distribution. 11 * 12 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND ANY 13 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED 14 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE 15 * DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR ANY 16 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES 17 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 18 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND 19 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 20 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 21 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */ 22 23 #define LOG_TAG "keystore-engine" 24 #include <UniquePtr.h> 25 26 #include <pthread.h> 27 #include <sys/socket.h> 28 #include <stdarg.h> 29 #include <string.h> 30 #include <unistd.h> 31 32 #include <cutils/log.h> 33 34 #include <openssl/bn.h> 35 #include <openssl/ec.h> 36 #include <openssl/ec_key.h> 37 #include <openssl/ecdsa.h> 38 #include <openssl/engine.h> 39 #include <openssl/evp.h> 40 #include <openssl/rsa.h> 41 #include <openssl/x509.h> 42 43 #ifndef BACKEND_WIFI_HIDL 44 #include "keystore_backend_binder.h" 45 #else 46 #include "keystore_backend_hidl.h" 47 #endif 48 49 namespace { 50 extern const RSA_METHOD keystore_rsa_method; 51 extern const ECDSA_METHOD keystore_ecdsa_method; 52 53 /* key_id_dup is called when one of the RSA or EC_KEY objects is duplicated. */ 54 int key_id_dup(CRYPTO_EX_DATA* /* to */, 55 const CRYPTO_EX_DATA* /* from */, 56 void** from_d, 57 int /* index */, 58 long /* argl */, 59 void* /* argp */) { 60 char *key_id = reinterpret_cast<char *>(*from_d); 61 if (key_id != NULL) { 62 *from_d = strdup(key_id); 63 } 64 return 1; 65 } 66 67 /* key_id_free is called when one of the RSA, DSA or EC_KEY object is freed. */ 68 void key_id_free(void* /* parent */, 69 void* ptr, 70 CRYPTO_EX_DATA* /* ad */, 71 int /* index */, 72 long /* argl */, 73 void* /* argp */) { 74 char *key_id = reinterpret_cast<char *>(ptr); 75 free(key_id); 76 } 77 78 /* KeystoreEngine is a BoringSSL ENGINE that implements RSA and ECDSA by 79 * forwarding the requested operations to Keystore. */ 80 class KeystoreEngine { 81 public: 82 KeystoreEngine() 83 : rsa_index_(RSA_get_ex_new_index(0 /* argl */, 84 NULL /* argp */, 85 NULL /* new_func */, 86 key_id_dup, 87 key_id_free)), 88 ec_key_index_(EC_KEY_get_ex_new_index(0 /* argl */, 89 NULL /* argp */, 90 NULL /* new_func */, 91 key_id_dup, 92 key_id_free)), 93 engine_(ENGINE_new()) { 94 ENGINE_set_RSA_method( 95 engine_, &keystore_rsa_method, sizeof(keystore_rsa_method)); 96 ENGINE_set_ECDSA_method( 97 engine_, &keystore_ecdsa_method, sizeof(keystore_ecdsa_method)); 98 } 99 100 int rsa_ex_index() const { return rsa_index_; } 101 int ec_key_ex_index() const { return ec_key_index_; } 102 103 const ENGINE* engine() const { return engine_; } 104 105 private: 106 const int rsa_index_; 107 const int ec_key_index_; 108 ENGINE* const engine_; 109 }; 110 111 pthread_once_t g_keystore_engine_once = PTHREAD_ONCE_INIT; 112 KeystoreEngine *g_keystore_engine; 113 KeystoreBackend *g_keystore_backend; 114 115 /* init_keystore_engine is called to initialize |g_keystore_engine|. This 116 * should only be called by |pthread_once|. */ 117 void init_keystore_engine() { 118 g_keystore_engine = new KeystoreEngine; 119 #ifndef BACKEND_WIFI_HIDL 120 g_keystore_backend = new KeystoreBackendBinder; 121 #else 122 g_keystore_backend = new KeystoreBackendHidl; 123 #endif 124 } 125 126 /* ensure_keystore_engine ensures that |g_keystore_engine| is pointing to a 127 * valid |KeystoreEngine| object and creates one if not. */ 128 void ensure_keystore_engine() { 129 pthread_once(&g_keystore_engine_once, init_keystore_engine); 130 } 131 132 /* Many OpenSSL APIs take ownership of an argument on success but don't free 133 * the argument on failure. This means we need to tell our scoped pointers when 134 * we've transferred ownership, without triggering a warning by not using the 135 * result of release(). */ 136 #define OWNERSHIP_TRANSFERRED(obj) \ 137 typeof ((obj).release()) _dummy __attribute__((unused)) = (obj).release() 138 139 const char* rsa_get_key_id(const RSA* rsa) { 140 return reinterpret_cast<char*>( 141 RSA_get_ex_data(rsa, g_keystore_engine->rsa_ex_index())); 142 } 143 144 /* rsa_private_transform takes a big-endian integer from |in|, calculates the 145 * d'th power of it, modulo the RSA modulus, and writes the result as a 146 * big-endian integer to |out|. Both |in| and |out| are |len| bytes long. It 147 * returns one on success and zero otherwise. */ 148 int rsa_private_transform(RSA *rsa, uint8_t *out, const uint8_t *in, size_t len) { 149 ALOGV("rsa_private_transform(%p, %p, %p, %u)", rsa, out, in, (unsigned) len); 150 151 ensure_keystore_engine(); 152 153 const char *key_id = rsa_get_key_id(rsa); 154 if (key_id == NULL) { 155 ALOGE("key had no key_id!"); 156 return 0; 157 } 158 159 uint8_t* reply = NULL; 160 size_t reply_len; 161 int32_t ret = g_keystore_backend->sign(key_id, in, len, &reply, &reply_len); 162 if (ret < 0) { 163 ALOGW("There was an error during rsa_decrypt: could not connect"); 164 return 0; 165 } else if (ret != 0) { 166 ALOGW("Error during sign from keystore: %d", ret); 167 return 0; 168 } else if (reply_len == 0 || reply == NULL) { 169 ALOGW("No valid signature returned"); 170 return 0; 171 } 172 173 if (reply_len > len) { 174 /* The result of the RSA operation can never be larger than the size of 175 * the modulus so we assume that the result has extra zeros on the 176 * left. This provides attackers with an oracle, but there's nothing 177 * that we can do about it here. */ 178 ALOGW("Reply len %zu greater than expected %zu", reply_len, len); 179 memcpy(out, &reply[reply_len - len], len); 180 } else if (reply_len < len) { 181 /* If the Keystore implementation returns a short value we assume that 182 * it's because it removed leading zeros from the left side. This is 183 * bad because it provides attackers with an oracle but we cannot do 184 * anything about a broken Keystore implementation here. */ 185 ALOGW("Reply len %zu lesser than expected %zu", reply_len, len); 186 memset(out, 0, len); 187 memcpy(out + len - reply_len, &reply[0], reply_len); 188 } else { 189 memcpy(out, &reply[0], len); 190 } 191 192 ALOGV("rsa=%p keystore_rsa_priv_dec successful", rsa); 193 return 1; 194 } 195 196 const struct rsa_meth_st keystore_rsa_method = { 197 { 198 0 /* references */, 199 1 /* is_static */, 200 }, 201 NULL /* app_data */, 202 203 NULL /* init */, 204 NULL /* finish */, 205 206 NULL /* size */, 207 208 NULL /* sign */, 209 NULL /* verify */, 210 211 NULL /* encrypt */, 212 NULL /* sign_raw */, 213 NULL /* decrypt */, 214 NULL /* verify_raw */, 215 216 rsa_private_transform, 217 218 NULL /* mod_exp */, 219 NULL /* bn_mod_exp */, 220 221 RSA_FLAG_CACHE_PUBLIC | RSA_FLAG_OPAQUE, 222 223 NULL /* keygen */, 224 NULL /* multi_prime_keygen */, 225 NULL /* supports_digest */, 226 }; 227 228 const char* ecdsa_get_key_id(const EC_KEY* ec_key) { 229 return reinterpret_cast<char*>( 230 EC_KEY_get_ex_data(ec_key, g_keystore_engine->ec_key_ex_index())); 231 } 232 233 /* ecdsa_sign signs |digest_len| bytes from |digest| with |ec_key| and writes 234 * the resulting signature (an ASN.1 encoded blob) to |sig|. It returns one on 235 * success and zero otherwise. */ 236 static int ecdsa_sign(const uint8_t* digest, size_t digest_len, uint8_t* sig, 237 unsigned int* sig_len, EC_KEY* ec_key) { 238 ALOGV("ecdsa_sign(%p, %u, %p)", digest, (unsigned) digest_len, ec_key); 239 240 ensure_keystore_engine(); 241 242 const char *key_id = ecdsa_get_key_id(ec_key); 243 if (key_id == NULL) { 244 ALOGE("key had no key_id!"); 245 return 0; 246 } 247 248 size_t ecdsa_size = ECDSA_size(ec_key); 249 250 uint8_t* reply = NULL; 251 size_t reply_len; 252 int32_t ret = g_keystore_backend->sign( 253 key_id, digest, digest_len, &reply, &reply_len); 254 if (ret < 0) { 255 ALOGW("There was an error during ecdsa_sign: could not connect"); 256 return 0; 257 } else if (reply_len == 0 || reply == NULL) { 258 ALOGW("No valid signature returned"); 259 return 0; 260 } else if (reply_len > ecdsa_size) { 261 ALOGW("Signature is too large"); 262 return 0; 263 } 264 265 // Reviewer: should't sig_len be checked here? Or is it just assumed that it is at least ecdsa_size? 266 memcpy(sig, &reply[0], reply_len); 267 *sig_len = reply_len; 268 269 ALOGV("ecdsa_sign(%p, %u, %p) => success", digest, (unsigned)digest_len, 270 ec_key); 271 return 1; 272 } 273 274 const ECDSA_METHOD keystore_ecdsa_method = { 275 { 276 0 /* references */, 277 1 /* is_static */ 278 } /* common */, 279 NULL /* app_data */, 280 281 NULL /* init */, 282 NULL /* finish */, 283 NULL /* group_order_size */, 284 ecdsa_sign, 285 NULL /* verify */, 286 ECDSA_FLAG_OPAQUE, 287 }; 288 289 struct EVP_PKEY_Delete { 290 void operator()(EVP_PKEY* p) const { 291 EVP_PKEY_free(p); 292 } 293 }; 294 typedef UniquePtr<EVP_PKEY, EVP_PKEY_Delete> Unique_EVP_PKEY; 295 296 struct RSA_Delete { 297 void operator()(RSA* p) const { 298 RSA_free(p); 299 } 300 }; 301 typedef UniquePtr<RSA, RSA_Delete> Unique_RSA; 302 303 struct EC_KEY_Delete { 304 void operator()(EC_KEY* ec) const { 305 EC_KEY_free(ec); 306 } 307 }; 308 typedef UniquePtr<EC_KEY, EC_KEY_Delete> Unique_EC_KEY; 309 310 /* wrap_rsa returns an |EVP_PKEY| that contains an RSA key where the public 311 * part is taken from |public_rsa| and the private operations are forwarded to 312 * KeyStore and operate on the key named |key_id|. */ 313 static EVP_PKEY *wrap_rsa(const char *key_id, const RSA *public_rsa) { 314 Unique_RSA rsa(RSA_new_method(g_keystore_engine->engine())); 315 if (rsa.get() == NULL) { 316 return NULL; 317 } 318 319 char *key_id_copy = strdup(key_id); 320 if (key_id_copy == NULL) { 321 return NULL; 322 } 323 324 if (!RSA_set_ex_data(rsa.get(), g_keystore_engine->rsa_ex_index(), 325 key_id_copy)) { 326 free(key_id_copy); 327 return NULL; 328 } 329 330 rsa->n = BN_dup(public_rsa->n); 331 rsa->e = BN_dup(public_rsa->e); 332 if (rsa->n == NULL || rsa->e == NULL) { 333 return NULL; 334 } 335 336 Unique_EVP_PKEY result(EVP_PKEY_new()); 337 if (result.get() == NULL || 338 !EVP_PKEY_assign_RSA(result.get(), rsa.get())) { 339 return NULL; 340 } 341 OWNERSHIP_TRANSFERRED(rsa); 342 343 return result.release(); 344 } 345 346 /* wrap_ecdsa returns an |EVP_PKEY| that contains an ECDSA key where the public 347 * part is taken from |public_rsa| and the private operations are forwarded to 348 * KeyStore and operate on the key named |key_id|. */ 349 static EVP_PKEY *wrap_ecdsa(const char *key_id, const EC_KEY *public_ecdsa) { 350 Unique_EC_KEY ec(EC_KEY_new_method(g_keystore_engine->engine())); 351 if (ec.get() == NULL) { 352 return NULL; 353 } 354 355 if (!EC_KEY_set_group(ec.get(), EC_KEY_get0_group(public_ecdsa)) || 356 !EC_KEY_set_public_key(ec.get(), EC_KEY_get0_public_key(public_ecdsa))) { 357 return NULL; 358 } 359 360 char *key_id_copy = strdup(key_id); 361 if (key_id_copy == NULL) { 362 return NULL; 363 } 364 365 if (!EC_KEY_set_ex_data(ec.get(), g_keystore_engine->ec_key_ex_index(), 366 key_id_copy)) { 367 free(key_id_copy); 368 return NULL; 369 } 370 371 Unique_EVP_PKEY result(EVP_PKEY_new()); 372 if (result.get() == NULL || 373 !EVP_PKEY_assign_EC_KEY(result.get(), ec.get())) { 374 return NULL; 375 } 376 OWNERSHIP_TRANSFERRED(ec); 377 378 return result.release(); 379 } 380 381 } /* anonymous namespace */ 382 383 extern "C" { 384 385 EVP_PKEY* EVP_PKEY_from_keystore(const char* key_id) __attribute__((visibility("default"))); 386 387 /* EVP_PKEY_from_keystore returns an |EVP_PKEY| that contains either an RSA or 388 * ECDSA key where the public part of the key reflects the value of the key 389 * named |key_id| in Keystore and the private operations are forwarded onto 390 * KeyStore. */ 391 EVP_PKEY* EVP_PKEY_from_keystore(const char* key_id) { 392 ALOGV("EVP_PKEY_from_keystore(\"%s\")", key_id); 393 394 ensure_keystore_engine(); 395 396 uint8_t *pubkey = NULL; 397 size_t pubkey_len; 398 int32_t ret = g_keystore_backend->get_pubkey(key_id, &pubkey, &pubkey_len); 399 if (ret < 0) { 400 ALOGW("could not contact keystore"); 401 return NULL; 402 } else if (ret != 0 || pubkey == NULL) { 403 ALOGW("keystore reports error: %d", ret); 404 return NULL; 405 } 406 407 const uint8_t *inp = pubkey; 408 Unique_EVP_PKEY pkey(d2i_PUBKEY(NULL, &inp, pubkey_len)); 409 if (pkey.get() == NULL) { 410 ALOGW("Cannot convert pubkey"); 411 return NULL; 412 } 413 414 EVP_PKEY *result; 415 switch (EVP_PKEY_type(pkey->type)) { 416 case EVP_PKEY_RSA: { 417 Unique_RSA public_rsa(EVP_PKEY_get1_RSA(pkey.get())); 418 result = wrap_rsa(key_id, public_rsa.get()); 419 break; 420 } 421 case EVP_PKEY_EC: { 422 Unique_EC_KEY public_ecdsa(EVP_PKEY_get1_EC_KEY(pkey.get())); 423 result = wrap_ecdsa(key_id, public_ecdsa.get()); 424 break; 425 } 426 default: 427 ALOGE("Unsupported key type %d", EVP_PKEY_type(pkey->type)); 428 result = NULL; 429 } 430 431 return result; 432 } 433 434 } // extern "C" 435
