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 57typedef unsigned long long __u64; 58typedef long long __s64; 59typedef unsigned int __u32; 60typedef unsigned char u8; 61#define NULL ((void *) 0) 62 63/* The entropy pool */ 64struct 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 "jitterentropy.h" 150 151/*************************************************************************** 152 * Adaptive Proportion Test 153 * 154 * This test complies with SP800-90B section 4.4.2. 155 ***************************************************************************/ 156 157/* 158 * See the SP 800-90B comment #10b for the corrected cutoff for the SP 800-90B 159 * APT. 160 * http://www.untruth.org/~josh/sp80090b/UL%20SP800-90B-final%20comments%20v1.9%2020191212.pdf 161 * In in the syntax of R, this is C = 2 + qbinom(1 ��� 2^(���30), 511, 2^(-1/osr)). 162 * (The original formula wasn't correct because the first symbol must 163 * necessarily have been observed, so there is no chance of observing 0 of these 164 * symbols.) 165 * 166 * For the alpha < 2^-53, R cannot be used as it uses a float data type without 167 * arbitrary precision. A SageMath script is used to calculate those cutoff 168 * values. 169 * 170 * For any value above 14, this yields the maximal allowable value of 512 171 * (by FIPS 140-2 IG 7.19 Resolution # 16, we cannot choose a cutoff value that 172 * renders the test unable to fail). 173 */ 174static const unsigned int jent_apt_cutoff_lookup[15] = { 175 325, 422, 459, 477, 488, 494, 499, 502, 176 505, 507, 508, 509, 510, 511, 512 }; 177static const unsigned int jent_apt_cutoff_permanent_lookup[15] = { 178 355, 447, 479, 494, 502, 507, 510, 512, 179 512, 512, 512, 512, 512, 512, 512 }; 180#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0])) 181 182static void jent_apt_init(struct rand_data *ec, unsigned int osr) 183{ 184 /* 185 * Establish the apt_cutoff based on the presumed entropy rate of 186 * 1/osr. 187 */ 188 if (osr >= ARRAY_SIZE(jent_apt_cutoff_lookup)) { 189 ec->apt_cutoff = jent_apt_cutoff_lookup[ 190 ARRAY_SIZE(jent_apt_cutoff_lookup) - 1]; 191 ec->apt_cutoff_permanent = jent_apt_cutoff_permanent_lookup[ 192 ARRAY_SIZE(jent_apt_cutoff_permanent_lookup) - 1]; 193 } else { 194 ec->apt_cutoff = jent_apt_cutoff_lookup[osr - 1]; 195 ec->apt_cutoff_permanent = 196 jent_apt_cutoff_permanent_lookup[osr - 1]; 197 } 198} 199/* 200 * Reset the APT counter 201 * 202 * @ec [in] Reference to entropy collector 203 */ 204static void jent_apt_reset(struct rand_data *ec, unsigned int delta_masked) 205{ 206 /* Reset APT counter */ 207 ec->apt_count = 0; 208 ec->apt_base = delta_masked; 209 ec->apt_observations = 0; 210} 211 212/* 213 * Insert a new entropy event into APT 214 * 215 * @ec [in] Reference to entropy collector 216 * @delta_masked [in] Masked time delta to process 217 */ 218static void jent_apt_insert(struct rand_data *ec, unsigned int delta_masked) 219{ 220 /* Initialize the base reference */ 221 if (!ec->apt_base_set) { 222 ec->apt_base = delta_masked; 223 ec->apt_base_set = 1; 224 return; 225 } 226 227 if (delta_masked == ec->apt_base) { 228 ec->apt_count++; 229 230 /* Note, ec->apt_count starts with one. */ 231 if (ec->apt_count >= ec->apt_cutoff_permanent) 232 ec->health_failure |= JENT_APT_FAILURE_PERMANENT; 233 else if (ec->apt_count >= ec->apt_cutoff) 234 ec->health_failure |= JENT_APT_FAILURE; 235 } 236 237 ec->apt_observations++; 238 239 if (ec->apt_observations >= JENT_APT_WINDOW_SIZE) 240 jent_apt_reset(ec, delta_masked); 241} 242 243/*************************************************************************** 244 * Stuck Test and its use as Repetition Count Test 245 * 246 * The Jitter RNG uses an enhanced version of the Repetition Count Test 247 * (RCT) specified in SP800-90B section 4.4.1. Instead of counting identical 248 * back-to-back values, the input to the RCT is the counting of the stuck 249 * values during the generation of one Jitter RNG output block. 250 * 251 * The RCT is applied with an alpha of 2^{-30} compliant to FIPS 140-2 IG 9.8. 252 * 253 * During the counting operation, the Jitter RNG always calculates the RCT 254 * cut-off value of C. If that value exceeds the allowed cut-off value, 255 * the Jitter RNG output block will be calculated completely but discarded at 256 * the end. The caller of the Jitter RNG is informed with an error code. 257 ***************************************************************************/ 258 259/* 260 * Repetition Count Test as defined in SP800-90B section 4.4.1 261 * 262 * @ec [in] Reference to entropy collector 263 * @stuck [in] Indicator whether the value is stuck 264 */ 265static void jent_rct_insert(struct rand_data *ec, int stuck) 266{ 267 if (stuck) { 268 ec->rct_count++; 269 270 /* 271 * The cutoff value is based on the following consideration: 272 * alpha = 2^-30 or 2^-60 as recommended in SP800-90B. 273 * In addition, we require an entropy value H of 1/osr as this 274 * is the minimum entropy required to provide full entropy. 275 * Note, we collect (DATA_SIZE_BITS + ENTROPY_SAFETY_FACTOR)*osr 276 * deltas for inserting them into the entropy pool which should 277 * then have (close to) DATA_SIZE_BITS bits of entropy in the 278 * conditioned output. 279 * 280 * Note, ec->rct_count (which equals to value B in the pseudo 281 * code of SP800-90B section 4.4.1) starts with zero. Hence 282 * we need to subtract one from the cutoff value as calculated 283 * following SP800-90B. Thus C = ceil(-log_2(alpha)/H) = 30*osr 284 * or 60*osr. 285 */ 286 if ((unsigned int)ec->rct_count >= (60 * ec->osr)) { 287 ec->rct_count = -1; 288 ec->health_failure |= JENT_RCT_FAILURE_PERMANENT; 289 } else if ((unsigned int)ec->rct_count >= (30 * ec->osr)) { 290 ec->rct_count = -1; 291 ec->health_failure |= JENT_RCT_FAILURE; 292 } 293 } else { 294 /* Reset RCT */ 295 ec->rct_count = 0; 296 } 297} 298 299static inline __u64 jent_delta(__u64 prev, __u64 next) 300{ 301#define JENT_UINT64_MAX (__u64)(~((__u64) 0)) 302 return (prev < next) ? (next - prev) : 303 (JENT_UINT64_MAX - prev + 1 + next); 304} 305 306/* 307 * Stuck test by checking the: 308 * 1st derivative of the jitter measurement (time delta) 309 * 2nd derivative of the jitter measurement (delta of time deltas) 310 * 3rd derivative of the jitter measurement (delta of delta of time deltas) 311 * 312 * All values must always be non-zero. 313 * 314 * @ec [in] Reference to entropy collector 315 * @current_delta [in] Jitter time delta 316 * 317 * @return 318 * 0 jitter measurement not stuck (good bit) 319 * 1 jitter measurement stuck (reject bit) 320 */ 321static int jent_stuck(struct rand_data *ec, __u64 current_delta) 322{ 323 __u64 delta2 = jent_delta(ec->last_delta, current_delta); 324 __u64 delta3 = jent_delta(ec->last_delta2, delta2); 325 326 ec->last_delta = current_delta; 327 ec->last_delta2 = delta2; 328 329 /* 330 * Insert the result of the comparison of two back-to-back time 331 * deltas. 332 */ 333 jent_apt_insert(ec, current_delta); 334 335 if (!current_delta || !delta2 || !delta3) { 336 /* RCT with a stuck bit */ 337 jent_rct_insert(ec, 1); 338 return 1; 339 } 340 341 /* RCT with a non-stuck bit */ 342 jent_rct_insert(ec, 0); 343 344 return 0; 345} 346 347/* 348 * Report any health test failures 349 * 350 * @ec [in] Reference to entropy collector 351 * 352 * @return a bitmask indicating which tests failed 353 * 0 No health test failure 354 * 1 RCT failure 355 * 2 APT failure 356 * 1<<JENT_PERMANENT_FAILURE_SHIFT RCT permanent failure 357 * 2<<JENT_PERMANENT_FAILURE_SHIFT APT permanent failure 358 */ 359static unsigned int jent_health_failure(struct rand_data *ec) 360{ 361 /* Test is only enabled in FIPS mode */ 362 if (!fips_enabled) 363 return 0; 364 365 return ec->health_failure; 366} 367 368/*************************************************************************** 369 * Noise sources 370 ***************************************************************************/ 371 372/* 373 * Update of the loop count used for the next round of 374 * an entropy collection. 375 * 376 * Input: 377 * @bits is the number of low bits of the timer to consider 378 * @min is the number of bits we shift the timer value to the right at 379 * the end to make sure we have a guaranteed minimum value 380 * 381 * @return Newly calculated loop counter 382 */ 383static __u64 jent_loop_shuffle(unsigned int bits, unsigned int min) 384{ 385 __u64 time = 0; 386 __u64 shuffle = 0; 387 unsigned int i = 0; 388 unsigned int mask = (1<<bits) - 1; 389 390 jent_get_nstime(&time); 391 392 /* 393 * We fold the time value as much as possible to ensure that as many 394 * bits of the time stamp are included as possible. 395 */ 396 for (i = 0; ((DATA_SIZE_BITS + bits - 1) / bits) > i; i++) { 397 shuffle ^= time & mask; 398 time = time >> bits; 399 } 400 401 /* 402 * We add a lower boundary value to ensure we have a minimum 403 * RNG loop count. 404 */ 405 return (shuffle + (1<<min)); 406} 407 408/* 409 * CPU Jitter noise source -- this is the noise source based on the CPU 410 * execution time jitter 411 * 412 * This function injects the individual bits of the time value into the 413 * entropy pool using a hash. 414 * 415 * ec [in] entropy collector 416 * time [in] time stamp to be injected 417 * stuck [in] Is the time stamp identified as stuck? 418 * 419 * Output: 420 * updated hash context in the entropy collector or error code 421 */ 422static int jent_condition_data(struct rand_data *ec, __u64 time, int stuck) 423{ 424#define SHA3_HASH_LOOP (1<<3) 425 struct { 426 int rct_count; 427 unsigned int apt_observations; 428 unsigned int apt_count; 429 unsigned int apt_base; 430 } addtl = { 431 ec->rct_count, 432 ec->apt_observations, 433 ec->apt_count, 434 ec->apt_base 435 }; 436 437 return jent_hash_time(ec->hash_state, time, (u8 *)&addtl, sizeof(addtl), 438 SHA3_HASH_LOOP, stuck); 439} 440 441/* 442 * Memory Access noise source -- this is a noise source based on variations in 443 * memory access times 444 * 445 * This function performs memory accesses which will add to the timing 446 * variations due to an unknown amount of CPU wait states that need to be 447 * added when accessing memory. The memory size should be larger than the L1 448 * caches as outlined in the documentation and the associated testing. 449 * 450 * The L1 cache has a very high bandwidth, albeit its access rate is usually 451 * slower than accessing CPU registers. Therefore, L1 accesses only add minimal 452 * variations as the CPU has hardly to wait. Starting with L2, significant 453 * variations are added because L2 typically does not belong to the CPU any more 454 * and therefore a wider range of CPU wait states is necessary for accesses. 455 * L3 and real memory accesses have even a wider range of wait states. However, 456 * to reliably access either L3 or memory, the ec->mem memory must be quite 457 * large which is usually not desirable. 458 * 459 * @ec [in] Reference to the entropy collector with the memory access data -- if 460 * the reference to the memory block to be accessed is NULL, this noise 461 * source is disabled 462 * @loop_cnt [in] if a value not equal to 0 is set, use the given value 463 * number of loops to perform the LFSR 464 */ 465static void jent_memaccess(struct rand_data *ec, __u64 loop_cnt) 466{ 467 unsigned int wrap = 0; 468 __u64 i = 0; 469#define MAX_ACC_LOOP_BIT 7 470#define MIN_ACC_LOOP_BIT 0 471 __u64 acc_loop_cnt = 472 jent_loop_shuffle(MAX_ACC_LOOP_BIT, MIN_ACC_LOOP_BIT); 473 474 if (NULL == ec || NULL == ec->mem) 475 return; 476 wrap = ec->memblocksize * ec->memblocks; 477 478 /* 479 * testing purposes -- allow test app to set the counter, not 480 * needed during runtime 481 */ 482 if (loop_cnt) 483 acc_loop_cnt = loop_cnt; 484 485 for (i = 0; i < (ec->memaccessloops + acc_loop_cnt); i++) { 486 unsigned char *tmpval = ec->mem + ec->memlocation; 487 /* 488 * memory access: just add 1 to one byte, 489 * wrap at 255 -- memory access implies read 490 * from and write to memory location 491 */ 492 *tmpval = (*tmpval + 1) & 0xff; 493 /* 494 * Addition of memblocksize - 1 to pointer 495 * with wrap around logic to ensure that every 496 * memory location is hit evenly 497 */ 498 ec->memlocation = ec->memlocation + ec->memblocksize - 1; 499 ec->memlocation = ec->memlocation % wrap; 500 } 501} 502 503/*************************************************************************** 504 * Start of entropy processing logic 505 ***************************************************************************/ 506/* 507 * This is the heart of the entropy generation: calculate time deltas and 508 * use the CPU jitter in the time deltas. The jitter is injected into the 509 * entropy pool. 510 * 511 * WARNING: ensure that ->prev_time is primed before using the output 512 * of this function! This can be done by calling this function 513 * and not using its result. 514 * 515 * @ec [in] Reference to entropy collector 516 * 517 * @return result of stuck test 518 */ 519static int jent_measure_jitter(struct rand_data *ec, __u64 *ret_current_delta) 520{ 521 __u64 time = 0; 522 __u64 current_delta = 0; 523 int stuck; 524 525 /* Invoke one noise source before time measurement to add variations */ 526 jent_memaccess(ec, 0); 527 528 /* 529 * Get time stamp and calculate time delta to previous 530 * invocation to measure the timing variations 531 */ 532 jent_get_nstime(&time); 533 current_delta = jent_delta(ec->prev_time, time); 534 ec->prev_time = time; 535 536 /* Check whether we have a stuck measurement. */ 537 stuck = jent_stuck(ec, current_delta); 538 539 /* Now call the next noise sources which also injects the data */ 540 if (jent_condition_data(ec, current_delta, stuck)) 541 stuck = 1; 542 543 /* return the raw entropy value */ 544 if (ret_current_delta) 545 *ret_current_delta = current_delta; 546 547 return stuck; 548} 549 550/* 551 * Generator of one 64 bit random number 552 * Function fills rand_data->hash_state 553 * 554 * @ec [in] Reference to entropy collector 555 */ 556static void jent_gen_entropy(struct rand_data *ec) 557{ 558 unsigned int k = 0, safety_factor = 0; 559 560 if (fips_enabled) 561 safety_factor = JENT_ENTROPY_SAFETY_FACTOR; 562 563 /* priming of the ->prev_time value */ 564 jent_measure_jitter(ec, NULL); 565 566 while (!jent_health_failure(ec)) { 567 /* If a stuck measurement is received, repeat measurement */ 568 if (jent_measure_jitter(ec, NULL)) 569 continue; 570 571 /* 572 * We multiply the loop value with ->osr to obtain the 573 * oversampling rate requested by the caller 574 */ 575 if (++k >= ((DATA_SIZE_BITS + safety_factor) * ec->osr)) 576 break; 577 } 578} 579 580/* 581 * Entry function: Obtain entropy for the caller. 582 * 583 * This function invokes the entropy gathering logic as often to generate 584 * as many bytes as requested by the caller. The entropy gathering logic 585 * creates 64 bit per invocation. 586 * 587 * This function truncates the last 64 bit entropy value output to the exact 588 * size specified by the caller. 589 * 590 * @ec [in] Reference to entropy collector 591 * @data [in] pointer to buffer for storing random data -- buffer must already 592 * exist 593 * @len [in] size of the buffer, specifying also the requested number of random 594 * in bytes 595 * 596 * @return 0 when request is fulfilled or an error 597 * 598 * The following error codes can occur: 599 * -1 entropy_collector is NULL or the generation failed 600 * -2 Intermittent health failure 601 * -3 Permanent health failure 602 */ 603int jent_read_entropy(struct rand_data *ec, unsigned char *data, 604 unsigned int len) 605{ 606 unsigned char *p = data; 607 608 if (!ec) 609 return -1; 610 611 while (len > 0) { 612 unsigned int tocopy, health_test_result; 613 614 jent_gen_entropy(ec); 615 616 health_test_result = jent_health_failure(ec); 617 if (health_test_result > JENT_PERMANENT_FAILURE_SHIFT) { 618 /* 619 * At this point, the Jitter RNG instance is considered 620 * as a failed instance. There is no rerun of the 621 * startup test any more, because the caller 622 * is assumed to not further use this instance. 623 */ 624 return -3; 625 } else if (health_test_result) { 626 /* 627 * Perform startup health tests and return permanent 628 * error if it fails. 629 */ 630 if (jent_entropy_init(0, 0, NULL, ec)) { 631 /* Mark the permanent error */ 632 ec->health_failure &= 633 JENT_RCT_FAILURE_PERMANENT | 634 JENT_APT_FAILURE_PERMANENT; 635 return -3; 636 } 637 638 return -2; 639 } 640 641 if ((DATA_SIZE_BITS / 8) < len) 642 tocopy = (DATA_SIZE_BITS / 8); 643 else 644 tocopy = len; 645 if (jent_read_random_block(ec->hash_state, p, tocopy)) 646 return -1; 647 648 len -= tocopy; 649 p += tocopy; 650 } 651 652 return 0; 653} 654 655/*************************************************************************** 656 * Initialization logic 657 ***************************************************************************/ 658 659struct rand_data *jent_entropy_collector_alloc(unsigned int osr, 660 unsigned int flags, 661 void *hash_state) 662{ 663 struct rand_data *entropy_collector; 664 665 entropy_collector = jent_zalloc(sizeof(struct rand_data)); 666 if (!entropy_collector) 667 return NULL; 668 669 if (!(flags & JENT_DISABLE_MEMORY_ACCESS)) { 670 /* Allocate memory for adding variations based on memory 671 * access 672 */ 673 entropy_collector->mem = jent_kvzalloc(JENT_MEMORY_SIZE); 674 if (!entropy_collector->mem) { 675 jent_zfree(entropy_collector); 676 return NULL; 677 } 678 entropy_collector->memblocksize = 679 CONFIG_CRYPTO_JITTERENTROPY_MEMORY_BLOCKSIZE; 680 entropy_collector->memblocks = 681 CONFIG_CRYPTO_JITTERENTROPY_MEMORY_BLOCKS; 682 entropy_collector->memaccessloops = JENT_MEMORY_ACCESSLOOPS; 683 } 684 685 /* verify and set the oversampling rate */ 686 if (osr == 0) 687 osr = 1; /* H_submitter = 1 / osr */ 688 entropy_collector->osr = osr; 689 entropy_collector->flags = flags; 690 691 entropy_collector->hash_state = hash_state; 692 693 /* Initialize the APT */ 694 jent_apt_init(entropy_collector, osr); 695 696 /* fill the data pad with non-zero values */ 697 jent_gen_entropy(entropy_collector); 698 699 return entropy_collector; 700} 701 702void jent_entropy_collector_free(struct rand_data *entropy_collector) 703{ 704 jent_kvzfree(entropy_collector->mem, JENT_MEMORY_SIZE); 705 entropy_collector->mem = NULL; 706 jent_zfree(entropy_collector); 707} 708 709int jent_entropy_init(unsigned int osr, unsigned int flags, void *hash_state, 710 struct rand_data *p_ec) 711{ 712 /* 713 * If caller provides an allocated ec, reuse it which implies that the 714 * health test entropy data is used to further still the available 715 * entropy pool. 716 */ 717 struct rand_data *ec = p_ec; 718 int i, time_backwards = 0, ret = 0, ec_free = 0; 719 unsigned int health_test_result; 720 721 if (!ec) { 722 ec = jent_entropy_collector_alloc(osr, flags, hash_state); 723 if (!ec) 724 return JENT_EMEM; 725 ec_free = 1; 726 } else { 727 /* Reset the APT */ 728 jent_apt_reset(ec, 0); 729 /* Ensure that a new APT base is obtained */ 730 ec->apt_base_set = 0; 731 /* Reset the RCT */ 732 ec->rct_count = 0; 733 /* Reset intermittent, leave permanent health test result */ 734 ec->health_failure &= (~JENT_RCT_FAILURE); 735 ec->health_failure &= (~JENT_APT_FAILURE); 736 } 737 738 /* We could perform statistical tests here, but the problem is 739 * that we only have a few loop counts to do testing. These 740 * loop counts may show some slight skew and we produce 741 * false positives. 742 * 743 * Moreover, only old systems show potentially problematic 744 * jitter entropy that could potentially be caught here. But 745 * the RNG is intended for hardware that is available or widely 746 * used, but not old systems that are long out of favor. Thus, 747 * no statistical tests. 748 */ 749 750 /* 751 * We could add a check for system capabilities such as clock_getres or 752 * check for CONFIG_X86_TSC, but it does not make much sense as the 753 * following sanity checks verify that we have a high-resolution 754 * timer. 755 */ 756 /* 757 * TESTLOOPCOUNT needs some loops to identify edge systems. 100 is 758 * definitely too little. 759 * 760 * SP800-90B requires at least 1024 initial test cycles. 761 */ 762#define TESTLOOPCOUNT 1024 763#define CLEARCACHE 100 764 for (i = 0; (TESTLOOPCOUNT + CLEARCACHE) > i; i++) { 765 __u64 start_time = 0, end_time = 0, delta = 0; 766 767 /* Invoke core entropy collection logic */ 768 jent_measure_jitter(ec, &delta); 769 end_time = ec->prev_time; 770 start_time = ec->prev_time - delta; 771 772 /* test whether timer works */ 773 if (!start_time || !end_time) { 774 ret = JENT_ENOTIME; 775 goto out; 776 } 777 778 /* 779 * test whether timer is fine grained enough to provide 780 * delta even when called shortly after each other -- this 781 * implies that we also have a high resolution timer 782 */ 783 if (!delta || (end_time == start_time)) { 784 ret = JENT_ECOARSETIME; 785 goto out; 786 } 787 788 /* 789 * up to here we did not modify any variable that will be 790 * evaluated later, but we already performed some work. Thus we 791 * already have had an impact on the caches, branch prediction, 792 * etc. with the goal to clear it to get the worst case 793 * measurements. 794 */ 795 if (i < CLEARCACHE) 796 continue; 797 798 /* test whether we have an increasing timer */ 799 if (!(end_time > start_time)) 800 time_backwards++; 801 } 802 803 /* 804 * we allow up to three times the time running backwards. 805 * CLOCK_REALTIME is affected by adjtime and NTP operations. Thus, 806 * if such an operation just happens to interfere with our test, it 807 * should not fail. The value of 3 should cover the NTP case being 808 * performed during our test run. 809 */ 810 if (time_backwards > 3) { 811 ret = JENT_ENOMONOTONIC; 812 goto out; 813 } 814 815 /* Did we encounter a health test failure? */ 816 health_test_result = jent_health_failure(ec); 817 if (health_test_result) { 818 ret = (health_test_result & JENT_RCT_FAILURE) ? JENT_ERCT : 819 JENT_EHEALTH; 820 goto out; 821 } 822 823out: 824 if (ec_free) 825 jent_entropy_collector_free(ec); 826 827 return ret; 828} 829