1 // SPDX-License-Identifier: GPL-2.0-or-later 2 /* 3 * PRNG: Pseudo Random Number Generator 4 * Based on NIST Recommended PRNG From ANSI X9.31 Appendix A.2.4 using 5 * AES 128 cipher 6 * 7 * (C) Neil Horman <nhorman@tuxdriver.com> 8 */ 9 10 #include <crypto/internal/rng.h> 11 #include <linux/err.h> 12 #include <linux/init.h> 13 #include <linux/module.h> 14 #include <linux/moduleparam.h> 15 #include <linux/string.h> 16 17 #define DEFAULT_PRNG_KEY "0123456789abcdef" 18 #define DEFAULT_PRNG_KSZ 16 19 #define DEFAULT_BLK_SZ 16 20 #define DEFAULT_V_SEED "zaybxcwdveuftgsh" 21 22 /* 23 * Flags for the prng_context flags field 24 */ 25 26 #define PRNG_FIXED_SIZE 0x1 27 #define PRNG_NEED_RESET 0x2 28 29 /* 30 * Note: DT is our counter value 31 * I is our intermediate value 32 * V is our seed vector 33 * See http://csrc.nist.gov/groups/STM/cavp/documents/rng/931rngext.pdf 34 * for implementation details 35 */ 36 37 38 struct prng_context { 39 spinlock_t prng_lock; 40 unsigned char rand_data[DEFAULT_BLK_SZ]; 41 unsigned char last_rand_data[DEFAULT_BLK_SZ]; 42 unsigned char DT[DEFAULT_BLK_SZ]; 43 unsigned char I[DEFAULT_BLK_SZ]; 44 unsigned char V[DEFAULT_BLK_SZ]; 45 u32 rand_data_valid; 46 struct crypto_cipher *tfm; 47 u32 flags; 48 }; 49 50 static int dbg; 51 52 static void hexdump(char *note, unsigned char *buf, unsigned int len) 53 { 54 if (dbg) { 55 printk(KERN_CRIT "%s", note); 56 print_hex_dump(KERN_CONT, "", DUMP_PREFIX_OFFSET, 57 16, 1, 58 buf, len, false); 59 } 60 } 61 62 #define dbgprint(format, args...) do {\ 63 if (dbg)\ 64 printk(format, ##args);\ 65 } while (0) 66 67 static void xor_vectors(unsigned char *in1, unsigned char *in2, 68 unsigned char *out, unsigned int size) 69 { 70 int i; 71 72 for (i = 0; i < size; i++) 73 out[i] = in1[i] ^ in2[i]; 74 75 } 76 /* 77 * Returns DEFAULT_BLK_SZ bytes of random data per call 78 * returns 0 if generation succeeded, <0 if something went wrong 79 */ 80 static int _get_more_prng_bytes(struct prng_context *ctx, int cont_test) 81 { 82 int i; 83 unsigned char tmp[DEFAULT_BLK_SZ]; 84 unsigned char *output = NULL; 85 86 87 dbgprint(KERN_CRIT "Calling _get_more_prng_bytes for context %p\n", 88 ctx); 89 90 hexdump("Input DT: ", ctx->DT, DEFAULT_BLK_SZ); 91 hexdump("Input I: ", ctx->I, DEFAULT_BLK_SZ); 92 hexdump("Input V: ", ctx->V, DEFAULT_BLK_SZ); 93 94 /* 95 * This algorithm is a 3 stage state machine 96 */ 97 for (i = 0; i < 3; i++) { 98 99 switch (i) { 100 case 0: 101 /* 102 * Start by encrypting the counter value 103 * This gives us an intermediate value I 104 */ 105 memcpy(tmp, ctx->DT, DEFAULT_BLK_SZ); 106 output = ctx->I; 107 hexdump("tmp stage 0: ", tmp, DEFAULT_BLK_SZ); 108 break; 109 case 1: 110 111 /* 112 * Next xor I with our secret vector V 113 * encrypt that result to obtain our 114 * pseudo random data which we output 115 */ 116 xor_vectors(ctx->I, ctx->V, tmp, DEFAULT_BLK_SZ); 117 hexdump("tmp stage 1: ", tmp, DEFAULT_BLK_SZ); 118 output = ctx->rand_data; 119 break; 120 case 2: 121 /* 122 * First check that we didn't produce the same 123 * random data that we did last time around through this 124 */ 125 if (!memcmp(ctx->rand_data, ctx->last_rand_data, 126 DEFAULT_BLK_SZ)) { 127 if (cont_test) { 128 panic("cprng %p Failed repetition check!\n", 129 ctx); 130 } 131 132 printk(KERN_ERR 133 "ctx %p Failed repetition check!\n", 134 ctx); 135 136 ctx->flags |= PRNG_NEED_RESET; 137 return -EINVAL; 138 } 139 memcpy(ctx->last_rand_data, ctx->rand_data, 140 DEFAULT_BLK_SZ); 141 142 /* 143 * Lastly xor the random data with I 144 * and encrypt that to obtain a new secret vector V 145 */ 146 xor_vectors(ctx->rand_data, ctx->I, tmp, 147 DEFAULT_BLK_SZ); 148 output = ctx->V; 149 hexdump("tmp stage 2: ", tmp, DEFAULT_BLK_SZ); 150 break; 151 } 152 153 154 /* do the encryption */ 155 crypto_cipher_encrypt_one(ctx->tfm, output, tmp); 156 157 } 158 159 /* 160 * Now update our DT value 161 */ 162 for (i = DEFAULT_BLK_SZ - 1; i >= 0; i--) { 163 ctx->DT[i] += 1; 164 if (ctx->DT[i] != 0) 165 break; 166 } 167 168 dbgprint("Returning new block for context %p\n", ctx); 169 ctx->rand_data_valid = 0; 170 171 hexdump("Output DT: ", ctx->DT, DEFAULT_BLK_SZ); 172 hexdump("Output I: ", ctx->I, DEFAULT_BLK_SZ); 173 hexdump("Output V: ", ctx->V, DEFAULT_BLK_SZ); 174 hexdump("New Random Data: ", ctx->rand_data, DEFAULT_BLK_SZ); 175 176 return 0; 177 } 178 179 /* Our exported functions */ 180 static int get_prng_bytes(char *buf, size_t nbytes, struct prng_context *ctx, 181 int do_cont_test) 182 { 183 unsigned char *ptr = buf; 184 unsigned int byte_count = (unsigned int)nbytes; 185 int err; 186 187 188 spin_lock_bh(&ctx->prng_lock); 189 190 err = -EINVAL; 191 if (ctx->flags & PRNG_NEED_RESET) 192 goto done; 193 194 /* 195 * If the FIXED_SIZE flag is on, only return whole blocks of 196 * pseudo random data 197 */ 198 err = -EINVAL; 199 if (ctx->flags & PRNG_FIXED_SIZE) { 200 if (nbytes < DEFAULT_BLK_SZ) 201 goto done; 202 byte_count = DEFAULT_BLK_SZ; 203 } 204 205 /* 206 * Return 0 in case of success as mandated by the kernel 207 * crypto API interface definition. 208 */ 209 err = 0; 210 211 dbgprint(KERN_CRIT "getting %d random bytes for context %p\n", 212 byte_count, ctx); 213 214 215 remainder: 216 if (ctx->rand_data_valid == DEFAULT_BLK_SZ) { 217 if (_get_more_prng_bytes(ctx, do_cont_test) < 0) { 218 memset(buf, 0, nbytes); 219 err = -EINVAL; 220 goto done; 221 } 222 } 223 224 /* 225 * Copy any data less than an entire block 226 */ 227 if (byte_count < DEFAULT_BLK_SZ) { 228 empty_rbuf: 229 while (ctx->rand_data_valid < DEFAULT_BLK_SZ) { 230 *ptr = ctx->rand_data[ctx->rand_data_valid]; 231 ptr++; 232 byte_count--; 233 ctx->rand_data_valid++; 234 if (byte_count == 0) 235 goto done; 236 } 237 } 238 239 /* 240 * Now copy whole blocks 241 */ 242 for (; byte_count >= DEFAULT_BLK_SZ; byte_count -= DEFAULT_BLK_SZ) { 243 if (ctx->rand_data_valid == DEFAULT_BLK_SZ) { 244 if (_get_more_prng_bytes(ctx, do_cont_test) < 0) { 245 memset(buf, 0, nbytes); 246 err = -EINVAL; 247 goto done; 248 } 249 } 250 if (ctx->rand_data_valid > 0) 251 goto empty_rbuf; 252 memcpy(ptr, ctx->rand_data, DEFAULT_BLK_SZ); 253 ctx->rand_data_valid += DEFAULT_BLK_SZ; 254 ptr += DEFAULT_BLK_SZ; 255 } 256 257 /* 258 * Now go back and get any remaining partial block 259 */ 260 if (byte_count) 261 goto remainder; 262 263 done: 264 spin_unlock_bh(&ctx->prng_lock); 265 dbgprint(KERN_CRIT "returning %d from get_prng_bytes in context %p\n", 266 err, ctx); 267 return err; 268 } 269 270 static void free_prng_context(struct prng_context *ctx) 271 { 272 crypto_free_cipher(ctx->tfm); 273 } 274 275 static int reset_prng_context(struct prng_context *ctx, 276 const unsigned char *key, size_t klen, 277 const unsigned char *V, const unsigned char *DT) 278 { 279 int ret; 280 const unsigned char *prng_key; 281 282 spin_lock_bh(&ctx->prng_lock); 283 ctx->flags |= PRNG_NEED_RESET; 284 285 prng_key = (key != NULL) ? key : (unsigned char *)DEFAULT_PRNG_KEY; 286 287 if (!key) 288 klen = DEFAULT_PRNG_KSZ; 289 290 if (V) 291 memcpy(ctx->V, V, DEFAULT_BLK_SZ); 292 else 293 memcpy(ctx->V, DEFAULT_V_SEED, DEFAULT_BLK_SZ); 294 295 if (DT) 296 memcpy(ctx->DT, DT, DEFAULT_BLK_SZ); 297 else 298 memset(ctx->DT, 0, DEFAULT_BLK_SZ); 299 300 memset(ctx->rand_data, 0, DEFAULT_BLK_SZ); 301 memset(ctx->last_rand_data, 0, DEFAULT_BLK_SZ); 302 303 ctx->rand_data_valid = DEFAULT_BLK_SZ; 304 305 ret = crypto_cipher_setkey(ctx->tfm, prng_key, klen); 306 if (ret) { 307 dbgprint(KERN_CRIT "PRNG: setkey() failed flags=%x\n", 308 crypto_cipher_get_flags(ctx->tfm)); 309 goto out; 310 } 311 312 ret = 0; 313 ctx->flags &= ~PRNG_NEED_RESET; 314 out: 315 spin_unlock_bh(&ctx->prng_lock); 316 return ret; 317 } 318 319 static int cprng_init(struct crypto_tfm *tfm) 320 { 321 struct prng_context *ctx = crypto_tfm_ctx(tfm); 322 323 spin_lock_init(&ctx->prng_lock); 324 ctx->tfm = crypto_alloc_cipher("aes", 0, 0); 325 if (IS_ERR(ctx->tfm)) { 326 dbgprint(KERN_CRIT "Failed to alloc tfm for context %p\n", 327 ctx); 328 return PTR_ERR(ctx->tfm); 329 } 330 331 if (reset_prng_context(ctx, NULL, DEFAULT_PRNG_KSZ, NULL, NULL) < 0) 332 return -EINVAL; 333 334 /* 335 * after allocation, we should always force the user to reset 336 * so they don't inadvertently use the insecure default values 337 * without specifying them intentially 338 */ 339 ctx->flags |= PRNG_NEED_RESET; 340 return 0; 341 } 342 343 static void cprng_exit(struct crypto_tfm *tfm) 344 { 345 free_prng_context(crypto_tfm_ctx(tfm)); 346 } 347 348 static int cprng_get_random(struct crypto_rng *tfm, 349 const u8 *src, unsigned int slen, 350 u8 *rdata, unsigned int dlen) 351 { 352 struct prng_context *prng = crypto_rng_ctx(tfm); 353 354 return get_prng_bytes(rdata, dlen, prng, 0); 355 } 356 357 /* 358 * This is the cprng_registered reset method the seed value is 359 * interpreted as the tuple { V KEY DT} 360 * V and KEY are required during reset, and DT is optional, detected 361 * as being present by testing the length of the seed 362 */ 363 static int cprng_reset(struct crypto_rng *tfm, 364 const u8 *seed, unsigned int slen) 365 { 366 struct prng_context *prng = crypto_rng_ctx(tfm); 367 const u8 *key = seed + DEFAULT_BLK_SZ; 368 const u8 *dt = NULL; 369 370 if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ) 371 return -EINVAL; 372 373 if (slen >= (2 * DEFAULT_BLK_SZ + DEFAULT_PRNG_KSZ)) 374 dt = key + DEFAULT_PRNG_KSZ; 375 376 reset_prng_context(prng, key, DEFAULT_PRNG_KSZ, seed, dt); 377 378 if (prng->flags & PRNG_NEED_RESET) 379 return -EINVAL; 380 return 0; 381 } 382 383 #ifdef CONFIG_CRYPTO_FIPS 384 static int fips_cprng_get_random(struct crypto_rng *tfm, 385 const u8 *src, unsigned int slen, 386 u8 *rdata, unsigned int dlen) 387 { 388 struct prng_context *prng = crypto_rng_ctx(tfm); 389 390 return get_prng_bytes(rdata, dlen, prng, 1); 391 } 392 393 static int fips_cprng_reset(struct crypto_rng *tfm, 394 const u8 *seed, unsigned int slen) 395 { 396 u8 rdata[DEFAULT_BLK_SZ]; 397 const u8 *key = seed + DEFAULT_BLK_SZ; 398 int rc; 399 400 struct prng_context *prng = crypto_rng_ctx(tfm); 401 402 if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ) 403 return -EINVAL; 404 405 /* fips strictly requires seed != key */ 406 if (!memcmp(seed, key, DEFAULT_PRNG_KSZ)) 407 return -EINVAL; 408 409 rc = cprng_reset(tfm, seed, slen); 410 411 if (!rc) 412 goto out; 413 414 /* this primes our continuity test */ 415 rc = get_prng_bytes(rdata, DEFAULT_BLK_SZ, prng, 0); 416 prng->rand_data_valid = DEFAULT_BLK_SZ; 417 418 out: 419 return rc; 420 } 421 #endif 422 423 static struct rng_alg rng_algs[] = { { 424 .generate = cprng_get_random, 425 .seed = cprng_reset, 426 .seedsize = DEFAULT_PRNG_KSZ + 2 * DEFAULT_BLK_SZ, 427 .base = { 428 .cra_name = "stdrng", 429 .cra_driver_name = "ansi_cprng", 430 .cra_priority = 100, 431 .cra_ctxsize = sizeof(struct prng_context), 432 .cra_module = THIS_MODULE, 433 .cra_init = cprng_init, 434 .cra_exit = cprng_exit, 435 } 436 #ifdef CONFIG_CRYPTO_FIPS 437 }, { 438 .generate = fips_cprng_get_random, 439 .seed = fips_cprng_reset, 440 .seedsize = DEFAULT_PRNG_KSZ + 2 * DEFAULT_BLK_SZ, 441 .base = { 442 .cra_name = "fips(ansi_cprng)", 443 .cra_driver_name = "fips_ansi_cprng", 444 .cra_priority = 300, 445 .cra_ctxsize = sizeof(struct prng_context), 446 .cra_module = THIS_MODULE, 447 .cra_init = cprng_init, 448 .cra_exit = cprng_exit, 449 } 450 #endif 451 } }; 452 453 /* Module initalization */ 454 static int __init prng_mod_init(void) 455 { 456 return crypto_register_rngs(rng_algs, ARRAY_SIZE(rng_algs)); 457 } 458 459 static void __exit prng_mod_fini(void) 460 { 461 crypto_unregister_rngs(rng_algs, ARRAY_SIZE(rng_algs)); 462 } 463 464 MODULE_LICENSE("GPL"); 465 MODULE_DESCRIPTION("Software Pseudo Random Number Generator"); 466 MODULE_AUTHOR("Neil Horman <nhorman@tuxdriver.com>"); 467 module_param(dbg, int, 0); 468 MODULE_PARM_DESC(dbg, "Boolean to enable debugging (0/1 == off/on)"); 469 subsys_initcall(prng_mod_init); 470 module_exit(prng_mod_fini); 471 MODULE_ALIAS_CRYPTO("stdrng"); 472 MODULE_ALIAS_CRYPTO("ansi_cprng"); 473