1 /* 2 * Non-physical true random number generator based on timing jitter -- 3 * Jitter RNG standalone code. 4 * 5 * Copyright Stephan Mueller <smueller@chronox.de>, 2015 - 2023 6 * 7 * Design 8 * ====== 9 * 10 * See https://www.chronox.de/jent.html 11 * 12 * License 13 * ======= 14 * 15 * Redistribution and use in source and binary forms, with or without 16 * modification, are permitted provided that the following conditions 17 * are met: 18 * 1. Redistributions of source code must retain the above copyright 19 * notice, and the entire permission notice in its entirety, 20 * including the disclaimer of warranties. 21 * 2. Redistributions in binary form must reproduce the above copyright 22 * notice, this list of conditions and the following disclaimer in the 23 * documentation and/or other materials provided with the distribution. 24 * 3. The name of the author may not be used to endorse or promote 25 * products derived from this software without specific prior 26 * written permission. 27 * 28 * ALTERNATIVELY, this product may be distributed under the terms of 29 * the GNU General Public License, in which case the provisions of the GPL2 are 30 * required INSTEAD OF the above restrictions. (This clause is 31 * necessary due to a potential bad interaction between the GPL and 32 * the restrictions contained in a BSD-style copyright.) 33 * 34 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED 35 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 36 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ALL OF 37 * WHICH ARE HEREBY DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE 38 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 39 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT 40 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR 41 * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF 42 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 43 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE 44 * USE OF THIS SOFTWARE, EVEN IF NOT ADVISED OF THE POSSIBILITY OF SUCH 45 * DAMAGE. 46 */ 47 48 /* 49 * This Jitterentropy RNG is based on the jitterentropy library 50 * version 3.4.0 provided at https://www.chronox.de/jent.html 51 */ 52 53 #ifdef __OPTIMIZE__ 54 #error "The CPU Jitter random number generator must not be compiled with optimizations. See documentation. Use the compiler switch -O0 for compiling jitterentropy.c." 55 #endif 56 57 typedef unsigned long long __u64; 58 typedef long long __s64; 59 typedef unsigned int __u32; 60 typedef unsigned char u8; 61 #define NULL ((void *) 0) 62 63 /* The entropy pool */ 64 struct rand_data { 65 /* SHA3-256 is used as conditioner */ 66 #define DATA_SIZE_BITS 256 67 /* all data values that are vital to maintain the security 68 * of the RNG are marked as SENSITIVE. A user must not 69 * access that information while the RNG executes its loops to 70 * calculate the next random value. */ 71 void *hash_state; /* SENSITIVE hash state entropy pool */ 72 __u64 prev_time; /* SENSITIVE Previous time stamp */ 73 __u64 last_delta; /* SENSITIVE stuck test */ 74 __s64 last_delta2; /* SENSITIVE stuck test */ 75 76 unsigned int flags; /* Flags used to initialize */ 77 unsigned int osr; /* Oversample rate */ 78 #define JENT_MEMORY_ACCESSLOOPS 128 79 #define JENT_MEMORY_SIZE \ 80 (CONFIG_CRYPTO_JITTERENTROPY_MEMORY_BLOCKS * \ 81 CONFIG_CRYPTO_JITTERENTROPY_MEMORY_BLOCKSIZE) 82 unsigned char *mem; /* Memory access location with size of 83 * memblocks * memblocksize */ 84 unsigned int memlocation; /* Pointer to byte in *mem */ 85 unsigned int memblocks; /* Number of memory blocks in *mem */ 86 unsigned int memblocksize; /* Size of one memory block in bytes */ 87 unsigned int memaccessloops; /* Number of memory accesses per random 88 * bit generation */ 89 90 /* Repetition Count Test */ 91 unsigned int rct_count; /* Number of stuck values */ 92 93 /* Adaptive Proportion Test cutoff values */ 94 unsigned int apt_cutoff; /* Intermittent health test failure */ 95 unsigned int apt_cutoff_permanent; /* Permanent health test failure */ 96 #define JENT_APT_WINDOW_SIZE 512 /* Data window size */ 97 /* LSB of time stamp to process */ 98 #define JENT_APT_LSB 16 99 #define JENT_APT_WORD_MASK (JENT_APT_LSB - 1) 100 unsigned int apt_observations; /* Number of collected observations */ 101 unsigned int apt_count; /* APT counter */ 102 unsigned int apt_base; /* APT base reference */ 103 unsigned int health_failure; /* Record health failure */ 104 105 unsigned int apt_base_set:1; /* APT base reference set? */ 106 }; 107 108 /* Flags that can be used to initialize the RNG */ 109 #define JENT_DISABLE_MEMORY_ACCESS (1<<2) /* Disable memory access for more 110 * entropy, saves MEMORY_SIZE RAM for 111 * entropy collector */ 112 113 /* -- error codes for init function -- */ 114 #define JENT_ENOTIME 1 /* Timer service not available */ 115 #define JENT_ECOARSETIME 2 /* Timer too coarse for RNG */ 116 #define JENT_ENOMONOTONIC 3 /* Timer is not monotonic increasing */ 117 #define JENT_EVARVAR 5 /* Timer does not produce variations of 118 * variations (2nd derivation of time is 119 * zero). */ 120 #define JENT_ESTUCK 8 /* Too many stuck results during init. */ 121 #define JENT_EHEALTH 9 /* Health test failed during initialization */ 122 #define JENT_ERCT 10 /* RCT failed during initialization */ 123 #define JENT_EHASH 11 /* Hash self test failed */ 124 #define JENT_EMEM 12 /* Can't allocate memory for initialization */ 125 126 #define JENT_RCT_FAILURE 1 /* Failure in RCT health test. */ 127 #define JENT_APT_FAILURE 2 /* Failure in APT health test. */ 128 #define JENT_PERMANENT_FAILURE_SHIFT 16 129 #define JENT_PERMANENT_FAILURE(x) (x << JENT_PERMANENT_FAILURE_SHIFT) 130 #define JENT_RCT_FAILURE_PERMANENT JENT_PERMANENT_FAILURE(JENT_RCT_FAILURE) 131 #define JENT_APT_FAILURE_PERMANENT JENT_PERMANENT_FAILURE(JENT_APT_FAILURE) 132 133 /* 134 * The output n bits can receive more than n bits of min entropy, of course, 135 * but the fixed output of the conditioning function can only asymptotically 136 * approach the output size bits of min entropy, not attain that bound. Random 137 * maps will tend to have output collisions, which reduces the creditable 138 * output entropy (that is what SP 800-90B Section 3.1.5.1.2 attempts to bound). 139 * 140 * The value "64" is justified in Appendix A.4 of the current 90C draft, 141 * and aligns with NIST's in "epsilon" definition in this document, which is 142 * that a string can be considered "full entropy" if you can bound the min 143 * entropy in each bit of output to at least 1-epsilon, where epsilon is 144 * required to be <= 2^(-32). 145 */ 146 #define JENT_ENTROPY_SAFETY_FACTOR 64 147 148 #include <linux/fips.h> 149 #include <linux/minmax.h> 150 #include "jitterentropy.h" 151 152 /*************************************************************************** 153 * Adaptive Proportion Test 154 * 155 * This test complies with SP800-90B section 4.4.2. 156 ***************************************************************************/ 157 158 /* 159 * See the SP 800-90B comment #10b for the corrected cutoff for the SP 800-90B 160 * APT. 161 * https://www.untruth.org/~josh/sp80090b/UL%20SP800-90B-final%20comments%20v1.9%2020191212.pdf 162 * In the syntax of R, this is C = 2 + qbinom(1 − 2^(−30), 511, 2^(-1/osr)). 163 * (The original formula wasn't correct because the first symbol must 164 * necessarily have been observed, so there is no chance of observing 0 of these 165 * symbols.) 166 * 167 * For the alpha < 2^-53, R cannot be used as it uses a float data type without 168 * arbitrary precision. A SageMath script is used to calculate those cutoff 169 * values. 170 * 171 * For any value above 14, this yields the maximal allowable value of 512 172 * (by FIPS 140-2 IG 7.19 Resolution # 16, we cannot choose a cutoff value that 173 * renders the test unable to fail). 174 */ 175 static const unsigned int jent_apt_cutoff_lookup[15] = { 176 325, 422, 459, 477, 488, 494, 499, 502, 177 505, 507, 508, 509, 510, 511, 512 }; 178 static const unsigned int jent_apt_cutoff_permanent_lookup[15] = { 179 355, 447, 479, 494, 502, 507, 510, 512, 180 512, 512, 512, 512, 512, 512, 512 }; 181 #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0])) 182 183 static void jent_apt_init(struct rand_data *ec, unsigned int osr) 184 { 185 /* 186 * Establish the apt_cutoff based on the presumed entropy rate of 187 * 1/osr. 188 */ 189 if (osr >= ARRAY_SIZE(jent_apt_cutoff_lookup)) { 190 ec->apt_cutoff = jent_apt_cutoff_lookup[ 191 ARRAY_SIZE(jent_apt_cutoff_lookup) - 1]; 192 ec->apt_cutoff_permanent = jent_apt_cutoff_permanent_lookup[ 193 ARRAY_SIZE(jent_apt_cutoff_permanent_lookup) - 1]; 194 } else { 195 ec->apt_cutoff = jent_apt_cutoff_lookup[osr - 1]; 196 ec->apt_cutoff_permanent = 197 jent_apt_cutoff_permanent_lookup[osr - 1]; 198 } 199 } 200 /* 201 * Reset the APT counter 202 * 203 * @ec [in] Reference to entropy collector 204 */ 205 static void jent_apt_reset(struct rand_data *ec, unsigned int delta_masked) 206 { 207 /* Reset APT counter */ 208 ec->apt_count = 0; 209 ec->apt_base = delta_masked; 210 ec->apt_observations = 0; 211 } 212 213 /* 214 * Insert a new entropy event into APT 215 * 216 * @ec [in] Reference to entropy collector 217 * @delta_masked [in] Masked time delta to process 218 */ 219 static void jent_apt_insert(struct rand_data *ec, unsigned int delta_masked) 220 { 221 /* Initialize the base reference */ 222 if (!ec->apt_base_set) { 223 ec->apt_base = delta_masked; 224 ec->apt_base_set = 1; 225 return; 226 } 227 228 if (delta_masked == ec->apt_base) { 229 ec->apt_count++; 230 231 /* Note, ec->apt_count starts with one. */ 232 if (ec->apt_count >= ec->apt_cutoff_permanent) 233 ec->health_failure |= JENT_APT_FAILURE_PERMANENT; 234 else if (ec->apt_count >= ec->apt_cutoff) 235 ec->health_failure |= JENT_APT_FAILURE; 236 } 237 238 ec->apt_observations++; 239 240 if (ec->apt_observations >= JENT_APT_WINDOW_SIZE) 241 jent_apt_reset(ec, delta_masked); 242 } 243 244 /*************************************************************************** 245 * Stuck Test and its use as Repetition Count Test 246 * 247 * The Jitter RNG uses an enhanced version of the Repetition Count Test 248 * (RCT) specified in SP800-90B section 4.4.1. Instead of counting identical 249 * back-to-back values, the input to the RCT is the counting of the stuck 250 * values during the generation of one Jitter RNG output block. 251 * 252 * The RCT is applied with an alpha of 2^{-30} compliant to FIPS 140-2 IG 9.8. 253 * 254 * During the counting operation, the Jitter RNG always calculates the RCT 255 * cut-off value of C. If that value exceeds the allowed cut-off value, 256 * the Jitter RNG output block will be calculated completely but discarded at 257 * the end. The caller of the Jitter RNG is informed with an error code. 258 ***************************************************************************/ 259 260 /* 261 * Repetition Count Test as defined in SP800-90B section 4.4.1 262 * 263 * @ec [in] Reference to entropy collector 264 * @stuck [in] Indicator whether the value is stuck 265 */ 266 static void jent_rct_insert(struct rand_data *ec, int stuck) 267 { 268 if (stuck) { 269 ec->rct_count++; 270 271 /* 272 * The cutoff value is based on the following consideration: 273 * alpha = 2^-30 or 2^-60 as recommended in SP800-90B. 274 * In addition, we require an entropy value H of 1/osr as this 275 * is the minimum entropy required to provide full entropy. 276 * Note, we collect (DATA_SIZE_BITS + ENTROPY_SAFETY_FACTOR)*osr 277 * deltas for inserting them into the entropy pool which should 278 * then have (close to) DATA_SIZE_BITS bits of entropy in the 279 * conditioned output. 280 * 281 * Note, ec->rct_count (which equals to value B in the pseudo 282 * code of SP800-90B section 4.4.1) starts with zero. Hence 283 * we need to subtract one from the cutoff value as calculated 284 * following SP800-90B. Thus C = ceil(-log_2(alpha)/H) = 30*osr 285 * or 60*osr. 286 */ 287 if ((unsigned int)ec->rct_count >= (60 * ec->osr)) { 288 ec->rct_count = -1; 289 ec->health_failure |= JENT_RCT_FAILURE_PERMANENT; 290 } else if ((unsigned int)ec->rct_count >= (30 * ec->osr)) { 291 ec->rct_count = -1; 292 ec->health_failure |= JENT_RCT_FAILURE; 293 } 294 } else { 295 /* Reset RCT */ 296 ec->rct_count = 0; 297 } 298 } 299 300 static inline __u64 jent_delta(__u64 prev, __u64 next) 301 { 302 #define JENT_UINT64_MAX (__u64)(~((__u64) 0)) 303 return (prev < next) ? (next - prev) : 304 (JENT_UINT64_MAX - prev + 1 + next); 305 } 306 307 /* 308 * Stuck test by checking the: 309 * 1st derivative of the jitter measurement (time delta) 310 * 2nd derivative of the jitter measurement (delta of time deltas) 311 * 3rd derivative of the jitter measurement (delta of delta of time deltas) 312 * 313 * All values must always be non-zero. 314 * 315 * @ec [in] Reference to entropy collector 316 * @current_delta [in] Jitter time delta 317 * 318 * @return 319 * 0 jitter measurement not stuck (good bit) 320 * 1 jitter measurement stuck (reject bit) 321 */ 322 static int jent_stuck(struct rand_data *ec, __u64 current_delta) 323 { 324 __u64 delta2 = jent_delta(ec->last_delta, current_delta); 325 __u64 delta3 = jent_delta(ec->last_delta2, delta2); 326 327 ec->last_delta = current_delta; 328 ec->last_delta2 = delta2; 329 330 /* 331 * Insert the result of the comparison of two back-to-back time 332 * deltas. 333 */ 334 jent_apt_insert(ec, current_delta); 335 336 if (!current_delta || !delta2 || !delta3) { 337 /* RCT with a stuck bit */ 338 jent_rct_insert(ec, 1); 339 return 1; 340 } 341 342 /* RCT with a non-stuck bit */ 343 jent_rct_insert(ec, 0); 344 345 return 0; 346 } 347 348 /* 349 * Report any health test failures 350 * 351 * @ec [in] Reference to entropy collector 352 * 353 * @return a bitmask indicating which tests failed 354 * 0 No health test failure 355 * 1 RCT failure 356 * 2 APT failure 357 * 1<<JENT_PERMANENT_FAILURE_SHIFT RCT permanent failure 358 * 2<<JENT_PERMANENT_FAILURE_SHIFT APT permanent failure 359 */ 360 static unsigned int jent_health_failure(struct rand_data *ec) 361 { 362 /* Test is only enabled in FIPS mode */ 363 if (!fips_enabled) 364 return 0; 365 366 return ec->health_failure; 367 } 368 369 /*************************************************************************** 370 * Noise sources 371 ***************************************************************************/ 372 373 /* 374 * Update of the loop count used for the next round of 375 * an entropy collection. 376 * 377 * Input: 378 * @bits is the number of low bits of the timer to consider 379 * @min is the number of bits we shift the timer value to the right at 380 * the end to make sure we have a guaranteed minimum value 381 * 382 * @return Newly calculated loop counter 383 */ 384 static __u64 jent_loop_shuffle(unsigned int bits, unsigned int min) 385 { 386 __u64 time = 0; 387 __u64 shuffle = 0; 388 unsigned int i = 0; 389 unsigned int mask = (1<<bits) - 1; 390 391 jent_get_nstime(&time); 392 393 /* 394 * We fold the time value as much as possible to ensure that as many 395 * bits of the time stamp are included as possible. 396 */ 397 for (i = 0; ((DATA_SIZE_BITS + bits - 1) / bits) > i; i++) { 398 shuffle ^= time & mask; 399 time = time >> bits; 400 } 401 402 /* 403 * We add a lower boundary value to ensure we have a minimum 404 * RNG loop count. 405 */ 406 return (shuffle + (1<<min)); 407 } 408 409 /* 410 * CPU Jitter noise source -- this is the noise source based on the CPU 411 * execution time jitter 412 * 413 * This function injects the individual bits of the time value into the 414 * entropy pool using a hash. 415 * 416 * ec [in] entropy collector 417 * time [in] time stamp to be injected 418 * stuck [in] Is the time stamp identified as stuck? 419 * 420 * Output: 421 * updated hash context in the entropy collector or error code 422 */ 423 static int jent_condition_data(struct rand_data *ec, __u64 time, int stuck) 424 { 425 #define SHA3_HASH_LOOP (1<<3) 426 struct { 427 int rct_count; 428 unsigned int apt_observations; 429 unsigned int apt_count; 430 unsigned int apt_base; 431 } addtl = { 432 ec->rct_count, 433 ec->apt_observations, 434 ec->apt_count, 435 ec->apt_base 436 }; 437 438 return jent_hash_time(ec->hash_state, time, (u8 *)&addtl, sizeof(addtl), 439 SHA3_HASH_LOOP, stuck); 440 } 441 442 /* 443 * Memory Access noise source -- this is a noise source based on variations in 444 * memory access times 445 * 446 * This function performs memory accesses which will add to the timing 447 * variations due to an unknown amount of CPU wait states that need to be 448 * added when accessing memory. The memory size should be larger than the L1 449 * caches as outlined in the documentation and the associated testing. 450 * 451 * The L1 cache has a very high bandwidth, albeit its access rate is usually 452 * slower than accessing CPU registers. Therefore, L1 accesses only add minimal 453 * variations as the CPU has hardly to wait. Starting with L2, significant 454 * variations are added because L2 typically does not belong to the CPU any more 455 * and therefore a wider range of CPU wait states is necessary for accesses. 456 * L3 and real memory accesses have even a wider range of wait states. However, 457 * to reliably access either L3 or memory, the ec->mem memory must be quite 458 * large which is usually not desirable. 459 * 460 * @ec [in] Reference to the entropy collector with the memory access data -- if 461 * the reference to the memory block to be accessed is NULL, this noise 462 * source is disabled 463 * @loop_cnt [in] if a value not equal to 0 is set, use the given value 464 * number of loops to perform the LFSR 465 */ 466 static void jent_memaccess(struct rand_data *ec, __u64 loop_cnt) 467 { 468 unsigned int wrap = 0; 469 __u64 i = 0; 470 #define MAX_ACC_LOOP_BIT 7 471 #define MIN_ACC_LOOP_BIT 0 472 __u64 acc_loop_cnt = 473 jent_loop_shuffle(MAX_ACC_LOOP_BIT, MIN_ACC_LOOP_BIT); 474 475 if (NULL == ec || NULL == ec->mem) 476 return; 477 wrap = ec->memblocksize * ec->memblocks; 478 479 /* 480 * testing purposes -- allow test app to set the counter, not 481 * needed during runtime 482 */ 483 if (loop_cnt) 484 acc_loop_cnt = loop_cnt; 485 486 for (i = 0; i < (ec->memaccessloops + acc_loop_cnt); i++) { 487 unsigned char *tmpval = ec->mem + ec->memlocation; 488 /* 489 * memory access: just add 1 to one byte, 490 * wrap at 255 -- memory access implies read 491 * from and write to memory location 492 */ 493 *tmpval = (*tmpval + 1) & 0xff; 494 /* 495 * Addition of memblocksize - 1 to pointer 496 * with wrap around logic to ensure that every 497 * memory location is hit evenly 498 */ 499 ec->memlocation = ec->memlocation + ec->memblocksize - 1; 500 ec->memlocation = ec->memlocation % wrap; 501 } 502 } 503 504 /*************************************************************************** 505 * Start of entropy processing logic 506 ***************************************************************************/ 507 /* 508 * This is the heart of the entropy generation: calculate time deltas and 509 * use the CPU jitter in the time deltas. The jitter is injected into the 510 * entropy pool. 511 * 512 * WARNING: ensure that ->prev_time is primed before using the output 513 * of this function! This can be done by calling this function 514 * and not using its result. 515 * 516 * @ec [in] Reference to entropy collector 517 * 518 * @return result of stuck test 519 */ 520 static int jent_measure_jitter(struct rand_data *ec, __u64 *ret_current_delta) 521 { 522 __u64 time = 0; 523 __u64 current_delta = 0; 524 int stuck; 525 526 /* Invoke one noise source before time measurement to add variations */ 527 jent_memaccess(ec, 0); 528 529 /* 530 * Get time stamp and calculate time delta to previous 531 * invocation to measure the timing variations 532 */ 533 jent_get_nstime(&time); 534 current_delta = jent_delta(ec->prev_time, time); 535 ec->prev_time = time; 536 537 /* Check whether we have a stuck measurement. */ 538 stuck = jent_stuck(ec, current_delta); 539 540 /* Now call the next noise sources which also injects the data */ 541 if (jent_condition_data(ec, current_delta, stuck)) 542 stuck = 1; 543 544 /* return the raw entropy value */ 545 if (ret_current_delta) 546 *ret_current_delta = current_delta; 547 548 return stuck; 549 } 550 551 /* 552 * Generator of one 64 bit random number 553 * Function fills rand_data->hash_state 554 * 555 * @ec [in] Reference to entropy collector 556 */ 557 static void jent_gen_entropy(struct rand_data *ec) 558 { 559 unsigned int k = 0, safety_factor = 0; 560 561 if (fips_enabled) 562 safety_factor = JENT_ENTROPY_SAFETY_FACTOR; 563 564 /* priming of the ->prev_time value */ 565 jent_measure_jitter(ec, NULL); 566 567 while (!jent_health_failure(ec)) { 568 /* If a stuck measurement is received, repeat measurement */ 569 if (jent_measure_jitter(ec, NULL)) 570 continue; 571 572 /* 573 * We multiply the loop value with ->osr to obtain the 574 * oversampling rate requested by the caller 575 */ 576 if (++k >= ((DATA_SIZE_BITS + safety_factor) * ec->osr)) 577 break; 578 } 579 } 580 581 /* 582 * Entry function: Obtain entropy for the caller. 583 * 584 * This function invokes the entropy gathering logic as often to generate 585 * as many bytes as requested by the caller. The entropy gathering logic 586 * creates 64 bit per invocation. 587 * 588 * This function truncates the last 64 bit entropy value output to the exact 589 * size specified by the caller. 590 * 591 * @ec [in] Reference to entropy collector 592 * @data [in] pointer to buffer for storing random data -- buffer must already 593 * exist 594 * @len [in] size of the buffer, specifying also the requested number of random 595 * in bytes 596 * 597 * @return 0 when request is fulfilled or an error 598 * 599 * The following error codes can occur: 600 * -1 entropy_collector is NULL or the generation failed 601 * -2 Intermittent health failure 602 * -3 Permanent health failure 603 */ 604 int jent_read_entropy(struct rand_data *ec, unsigned char *data, 605 unsigned int len) 606 { 607 unsigned char *p = data; 608 609 if (!ec) 610 return -1; 611 612 while (len > 0) { 613 unsigned int tocopy, health_test_result; 614 615 jent_gen_entropy(ec); 616 617 health_test_result = jent_health_failure(ec); 618 if (health_test_result > JENT_PERMANENT_FAILURE_SHIFT) { 619 /* 620 * At this point, the Jitter RNG instance is considered 621 * as a failed instance. There is no rerun of the 622 * startup test any more, because the caller 623 * is assumed to not further use this instance. 624 */ 625 return -3; 626 } else if (health_test_result) { 627 /* 628 * Perform startup health tests and return permanent 629 * error if it fails. 630 */ 631 if (jent_entropy_init(0, 0, NULL, ec)) { 632 /* Mark the permanent error */ 633 ec->health_failure &= 634 JENT_RCT_FAILURE_PERMANENT | 635 JENT_APT_FAILURE_PERMANENT; 636 return -3; 637 } 638 639 return -2; 640 } 641 642 tocopy = min(DATA_SIZE_BITS / 8, len); 643 if (jent_read_random_block(ec->hash_state, p, tocopy)) 644 return -1; 645 646 len -= tocopy; 647 p += tocopy; 648 } 649 650 return 0; 651 } 652 653 /*************************************************************************** 654 * Initialization logic 655 ***************************************************************************/ 656 657 struct rand_data *jent_entropy_collector_alloc(unsigned int osr, 658 unsigned int flags, 659 void *hash_state) 660 { 661 struct rand_data *entropy_collector; 662 663 entropy_collector = jent_zalloc(sizeof(struct rand_data)); 664 if (!entropy_collector) 665 return NULL; 666 667 if (!(flags & JENT_DISABLE_MEMORY_ACCESS)) { 668 /* Allocate memory for adding variations based on memory 669 * access 670 */ 671 entropy_collector->mem = jent_kvzalloc(JENT_MEMORY_SIZE); 672 if (!entropy_collector->mem) { 673 jent_zfree(entropy_collector); 674 return NULL; 675 } 676 entropy_collector->memblocksize = 677 CONFIG_CRYPTO_JITTERENTROPY_MEMORY_BLOCKSIZE; 678 entropy_collector->memblocks = 679 CONFIG_CRYPTO_JITTERENTROPY_MEMORY_BLOCKS; 680 entropy_collector->memaccessloops = JENT_MEMORY_ACCESSLOOPS; 681 } 682 683 /* verify and set the oversampling rate */ 684 if (osr == 0) 685 osr = 1; /* H_submitter = 1 / osr */ 686 entropy_collector->osr = osr; 687 entropy_collector->flags = flags; 688 689 entropy_collector->hash_state = hash_state; 690 691 /* Initialize the APT */ 692 jent_apt_init(entropy_collector, osr); 693 694 /* fill the data pad with non-zero values */ 695 jent_gen_entropy(entropy_collector); 696 697 return entropy_collector; 698 } 699 700 void jent_entropy_collector_free(struct rand_data *entropy_collector) 701 { 702 jent_kvzfree(entropy_collector->mem, JENT_MEMORY_SIZE); 703 entropy_collector->mem = NULL; 704 jent_zfree(entropy_collector); 705 } 706 707 int jent_entropy_init(unsigned int osr, unsigned int flags, void *hash_state, 708 struct rand_data *p_ec) 709 { 710 /* 711 * If caller provides an allocated ec, reuse it which implies that the 712 * health test entropy data is used to further still the available 713 * entropy pool. 714 */ 715 struct rand_data *ec = p_ec; 716 int i, time_backwards = 0, ret = 0, ec_free = 0; 717 unsigned int health_test_result; 718 719 if (!ec) { 720 ec = jent_entropy_collector_alloc(osr, flags, hash_state); 721 if (!ec) 722 return JENT_EMEM; 723 ec_free = 1; 724 } else { 725 /* Reset the APT */ 726 jent_apt_reset(ec, 0); 727 /* Ensure that a new APT base is obtained */ 728 ec->apt_base_set = 0; 729 /* Reset the RCT */ 730 ec->rct_count = 0; 731 /* Reset intermittent, leave permanent health test result */ 732 ec->health_failure &= (~JENT_RCT_FAILURE); 733 ec->health_failure &= (~JENT_APT_FAILURE); 734 } 735 736 /* We could perform statistical tests here, but the problem is 737 * that we only have a few loop counts to do testing. These 738 * loop counts may show some slight skew and we produce 739 * false positives. 740 * 741 * Moreover, only old systems show potentially problematic 742 * jitter entropy that could potentially be caught here. But 743 * the RNG is intended for hardware that is available or widely 744 * used, but not old systems that are long out of favor. Thus, 745 * no statistical tests. 746 */ 747 748 /* 749 * We could add a check for system capabilities such as clock_getres or 750 * check for CONFIG_X86_TSC, but it does not make much sense as the 751 * following sanity checks verify that we have a high-resolution 752 * timer. 753 */ 754 /* 755 * TESTLOOPCOUNT needs some loops to identify edge systems. 100 is 756 * definitely too little. 757 * 758 * SP800-90B requires at least 1024 initial test cycles. 759 */ 760 #define TESTLOOPCOUNT 1024 761 #define CLEARCACHE 100 762 for (i = 0; (TESTLOOPCOUNT + CLEARCACHE) > i; i++) { 763 __u64 start_time = 0, end_time = 0, delta = 0; 764 765 /* Invoke core entropy collection logic */ 766 jent_measure_jitter(ec, &delta); 767 end_time = ec->prev_time; 768 start_time = ec->prev_time - delta; 769 770 /* test whether timer works */ 771 if (!start_time || !end_time) { 772 ret = JENT_ENOTIME; 773 goto out; 774 } 775 776 /* 777 * test whether timer is fine grained enough to provide 778 * delta even when called shortly after each other -- this 779 * implies that we also have a high resolution timer 780 */ 781 if (!delta || (end_time == start_time)) { 782 ret = JENT_ECOARSETIME; 783 goto out; 784 } 785 786 /* 787 * up to here we did not modify any variable that will be 788 * evaluated later, but we already performed some work. Thus we 789 * already have had an impact on the caches, branch prediction, 790 * etc. with the goal to clear it to get the worst case 791 * measurements. 792 */ 793 if (i < CLEARCACHE) 794 continue; 795 796 /* test whether we have an increasing timer */ 797 if (!(end_time > start_time)) 798 time_backwards++; 799 } 800 801 /* 802 * we allow up to three times the time running backwards. 803 * CLOCK_REALTIME is affected by adjtime and NTP operations. Thus, 804 * if such an operation just happens to interfere with our test, it 805 * should not fail. The value of 3 should cover the NTP case being 806 * performed during our test run. 807 */ 808 if (time_backwards > 3) { 809 ret = JENT_ENOMONOTONIC; 810 goto out; 811 } 812 813 /* Did we encounter a health test failure? */ 814 health_test_result = jent_health_failure(ec); 815 if (health_test_result) { 816 ret = (health_test_result & JENT_RCT_FAILURE) ? JENT_ERCT : 817 JENT_EHEALTH; 818 goto out; 819 } 820 821 out: 822 if (ec_free) 823 jent_entropy_collector_free(ec); 824 825 return ret; 826 } 827