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 unsigned int osr; /* Oversample rate */ 76 #define JENT_MEMORY_BLOCKS 64 77 #define JENT_MEMORY_BLOCKSIZE 32 78 #define JENT_MEMORY_ACCESSLOOPS 128 79 #define JENT_MEMORY_SIZE (JENT_MEMORY_BLOCKS*JENT_MEMORY_BLOCKSIZE) 80 unsigned char *mem; /* Memory access location with size of 81 * memblocks * memblocksize */ 82 unsigned int memlocation; /* Pointer to byte in *mem */ 83 unsigned int memblocks; /* Number of memory blocks in *mem */ 84 unsigned int memblocksize; /* Size of one memory block in bytes */ 85 unsigned int memaccessloops; /* Number of memory accesses per random 86 * bit generation */ 87 88 /* Repetition Count Test */ 89 unsigned int rct_count; /* Number of stuck values */ 90 91 /* Intermittent health test failure threshold of 2^-30 */ 92 #define JENT_RCT_CUTOFF 30 /* Taken from SP800-90B sec 4.4.1 */ 93 #define JENT_APT_CUTOFF 325 /* Taken from SP800-90B sec 4.4.2 */ 94 /* Permanent health test failure threshold of 2^-60 */ 95 #define JENT_RCT_CUTOFF_PERMANENT 60 96 #define JENT_APT_CUTOFF_PERMANENT 355 97 #define JENT_APT_WINDOW_SIZE 512 /* Data window size */ 98 /* LSB of time stamp to process */ 99 #define JENT_APT_LSB 16 100 #define JENT_APT_WORD_MASK (JENT_APT_LSB - 1) 101 unsigned int apt_observations; /* Number of collected observations */ 102 unsigned int apt_count; /* APT counter */ 103 unsigned int apt_base; /* APT base reference */ 104 unsigned int apt_base_set:1; /* APT base reference set? */ 105 }; 106 107 /* Flags that can be used to initialize the RNG */ 108 #define JENT_DISABLE_MEMORY_ACCESS (1<<2) /* Disable memory access for more 109 * entropy, saves MEMORY_SIZE RAM for 110 * entropy collector */ 111 112 /* -- error codes for init function -- */ 113 #define JENT_ENOTIME 1 /* Timer service not available */ 114 #define JENT_ECOARSETIME 2 /* Timer too coarse for RNG */ 115 #define JENT_ENOMONOTONIC 3 /* Timer is not monotonic increasing */ 116 #define JENT_EVARVAR 5 /* Timer does not produce variations of 117 * variations (2nd derivation of time is 118 * zero). */ 119 #define JENT_ESTUCK 8 /* Too many stuck results during init. */ 120 #define JENT_EHEALTH 9 /* Health test failed during initialization */ 121 122 /* 123 * The output n bits can receive more than n bits of min entropy, of course, 124 * but the fixed output of the conditioning function can only asymptotically 125 * approach the output size bits of min entropy, not attain that bound. Random 126 * maps will tend to have output collisions, which reduces the creditable 127 * output entropy (that is what SP 800-90B Section 3.1.5.1.2 attempts to bound). 128 * 129 * The value "64" is justified in Appendix A.4 of the current 90C draft, 130 * and aligns with NIST's in "epsilon" definition in this document, which is 131 * that a string can be considered "full entropy" if you can bound the min 132 * entropy in each bit of output to at least 1-epsilon, where epsilon is 133 * required to be <= 2^(-32). 134 */ 135 #define JENT_ENTROPY_SAFETY_FACTOR 64 136 137 #include <linux/fips.h> 138 #include "jitterentropy.h" 139 140 /*************************************************************************** 141 * Adaptive Proportion Test 142 * 143 * This test complies with SP800-90B section 4.4.2. 144 ***************************************************************************/ 145 146 /* 147 * Reset the APT counter 148 * 149 * @ec [in] Reference to entropy collector 150 */ 151 static void jent_apt_reset(struct rand_data *ec, unsigned int delta_masked) 152 { 153 /* Reset APT counter */ 154 ec->apt_count = 0; 155 ec->apt_base = delta_masked; 156 ec->apt_observations = 0; 157 } 158 159 /* 160 * Insert a new entropy event into APT 161 * 162 * @ec [in] Reference to entropy collector 163 * @delta_masked [in] Masked time delta to process 164 */ 165 static void jent_apt_insert(struct rand_data *ec, unsigned int delta_masked) 166 { 167 /* Initialize the base reference */ 168 if (!ec->apt_base_set) { 169 ec->apt_base = delta_masked; 170 ec->apt_base_set = 1; 171 return; 172 } 173 174 if (delta_masked == ec->apt_base) 175 ec->apt_count++; 176 177 ec->apt_observations++; 178 179 if (ec->apt_observations >= JENT_APT_WINDOW_SIZE) 180 jent_apt_reset(ec, delta_masked); 181 } 182 183 /* APT health test failure detection */ 184 static int jent_apt_permanent_failure(struct rand_data *ec) 185 { 186 return (ec->apt_count >= JENT_APT_CUTOFF_PERMANENT) ? 1 : 0; 187 } 188 189 static int jent_apt_failure(struct rand_data *ec) 190 { 191 return (ec->apt_count >= JENT_APT_CUTOFF) ? 1 : 0; 192 } 193 194 /*************************************************************************** 195 * Stuck Test and its use as Repetition Count Test 196 * 197 * The Jitter RNG uses an enhanced version of the Repetition Count Test 198 * (RCT) specified in SP800-90B section 4.4.1. Instead of counting identical 199 * back-to-back values, the input to the RCT is the counting of the stuck 200 * values during the generation of one Jitter RNG output block. 201 * 202 * The RCT is applied with an alpha of 2^{-30} compliant to FIPS 140-2 IG 9.8. 203 * 204 * During the counting operation, the Jitter RNG always calculates the RCT 205 * cut-off value of C. If that value exceeds the allowed cut-off value, 206 * the Jitter RNG output block will be calculated completely but discarded at 207 * the end. The caller of the Jitter RNG is informed with an error code. 208 ***************************************************************************/ 209 210 /* 211 * Repetition Count Test as defined in SP800-90B section 4.4.1 212 * 213 * @ec [in] Reference to entropy collector 214 * @stuck [in] Indicator whether the value is stuck 215 */ 216 static void jent_rct_insert(struct rand_data *ec, int stuck) 217 { 218 if (stuck) { 219 ec->rct_count++; 220 } else { 221 /* Reset RCT */ 222 ec->rct_count = 0; 223 } 224 } 225 226 static inline __u64 jent_delta(__u64 prev, __u64 next) 227 { 228 #define JENT_UINT64_MAX (__u64)(~((__u64) 0)) 229 return (prev < next) ? (next - prev) : 230 (JENT_UINT64_MAX - prev + 1 + next); 231 } 232 233 /* 234 * Stuck test by checking the: 235 * 1st derivative of the jitter measurement (time delta) 236 * 2nd derivative of the jitter measurement (delta of time deltas) 237 * 3rd derivative of the jitter measurement (delta of delta of time deltas) 238 * 239 * All values must always be non-zero. 240 * 241 * @ec [in] Reference to entropy collector 242 * @current_delta [in] Jitter time delta 243 * 244 * @return 245 * 0 jitter measurement not stuck (good bit) 246 * 1 jitter measurement stuck (reject bit) 247 */ 248 static int jent_stuck(struct rand_data *ec, __u64 current_delta) 249 { 250 __u64 delta2 = jent_delta(ec->last_delta, current_delta); 251 __u64 delta3 = jent_delta(ec->last_delta2, delta2); 252 253 ec->last_delta = current_delta; 254 ec->last_delta2 = delta2; 255 256 /* 257 * Insert the result of the comparison of two back-to-back time 258 * deltas. 259 */ 260 jent_apt_insert(ec, current_delta); 261 262 if (!current_delta || !delta2 || !delta3) { 263 /* RCT with a stuck bit */ 264 jent_rct_insert(ec, 1); 265 return 1; 266 } 267 268 /* RCT with a non-stuck bit */ 269 jent_rct_insert(ec, 0); 270 271 return 0; 272 } 273 274 /* RCT health test failure detection */ 275 static int jent_rct_permanent_failure(struct rand_data *ec) 276 { 277 return (ec->rct_count >= JENT_RCT_CUTOFF_PERMANENT) ? 1 : 0; 278 } 279 280 static int jent_rct_failure(struct rand_data *ec) 281 { 282 return (ec->rct_count >= JENT_RCT_CUTOFF) ? 1 : 0; 283 } 284 285 /* Report of health test failures */ 286 static int jent_health_failure(struct rand_data *ec) 287 { 288 return jent_rct_failure(ec) | jent_apt_failure(ec); 289 } 290 291 static int jent_permanent_health_failure(struct rand_data *ec) 292 { 293 return jent_rct_permanent_failure(ec) | jent_apt_permanent_failure(ec); 294 } 295 296 /*************************************************************************** 297 * Noise sources 298 ***************************************************************************/ 299 300 /* 301 * Update of the loop count used for the next round of 302 * an entropy collection. 303 * 304 * Input: 305 * @bits is the number of low bits of the timer to consider 306 * @min is the number of bits we shift the timer value to the right at 307 * the end to make sure we have a guaranteed minimum value 308 * 309 * @return Newly calculated loop counter 310 */ 311 static __u64 jent_loop_shuffle(unsigned int bits, unsigned int min) 312 { 313 __u64 time = 0; 314 __u64 shuffle = 0; 315 unsigned int i = 0; 316 unsigned int mask = (1<<bits) - 1; 317 318 jent_get_nstime(&time); 319 320 /* 321 * We fold the time value as much as possible to ensure that as many 322 * bits of the time stamp are included as possible. 323 */ 324 for (i = 0; ((DATA_SIZE_BITS + bits - 1) / bits) > i; i++) { 325 shuffle ^= time & mask; 326 time = time >> bits; 327 } 328 329 /* 330 * We add a lower boundary value to ensure we have a minimum 331 * RNG loop count. 332 */ 333 return (shuffle + (1<<min)); 334 } 335 336 /* 337 * CPU Jitter noise source -- this is the noise source based on the CPU 338 * execution time jitter 339 * 340 * This function injects the individual bits of the time value into the 341 * entropy pool using a hash. 342 * 343 * ec [in] entropy collector 344 * time [in] time stamp to be injected 345 * stuck [in] Is the time stamp identified as stuck? 346 * 347 * Output: 348 * updated hash context in the entropy collector or error code 349 */ 350 static int jent_condition_data(struct rand_data *ec, __u64 time, int stuck) 351 { 352 #define SHA3_HASH_LOOP (1<<3) 353 struct { 354 int rct_count; 355 unsigned int apt_observations; 356 unsigned int apt_count; 357 unsigned int apt_base; 358 } addtl = { 359 ec->rct_count, 360 ec->apt_observations, 361 ec->apt_count, 362 ec->apt_base 363 }; 364 365 return jent_hash_time(ec->hash_state, time, (u8 *)&addtl, sizeof(addtl), 366 SHA3_HASH_LOOP, stuck); 367 } 368 369 /* 370 * Memory Access noise source -- this is a noise source based on variations in 371 * memory access times 372 * 373 * This function performs memory accesses which will add to the timing 374 * variations due to an unknown amount of CPU wait states that need to be 375 * added when accessing memory. The memory size should be larger than the L1 376 * caches as outlined in the documentation and the associated testing. 377 * 378 * The L1 cache has a very high bandwidth, albeit its access rate is usually 379 * slower than accessing CPU registers. Therefore, L1 accesses only add minimal 380 * variations as the CPU has hardly to wait. Starting with L2, significant 381 * variations are added because L2 typically does not belong to the CPU any more 382 * and therefore a wider range of CPU wait states is necessary for accesses. 383 * L3 and real memory accesses have even a wider range of wait states. However, 384 * to reliably access either L3 or memory, the ec->mem memory must be quite 385 * large which is usually not desirable. 386 * 387 * @ec [in] Reference to the entropy collector with the memory access data -- if 388 * the reference to the memory block to be accessed is NULL, this noise 389 * source is disabled 390 * @loop_cnt [in] if a value not equal to 0 is set, use the given value 391 * number of loops to perform the LFSR 392 */ 393 static void jent_memaccess(struct rand_data *ec, __u64 loop_cnt) 394 { 395 unsigned int wrap = 0; 396 __u64 i = 0; 397 #define MAX_ACC_LOOP_BIT 7 398 #define MIN_ACC_LOOP_BIT 0 399 __u64 acc_loop_cnt = 400 jent_loop_shuffle(MAX_ACC_LOOP_BIT, MIN_ACC_LOOP_BIT); 401 402 if (NULL == ec || NULL == ec->mem) 403 return; 404 wrap = ec->memblocksize * ec->memblocks; 405 406 /* 407 * testing purposes -- allow test app to set the counter, not 408 * needed during runtime 409 */ 410 if (loop_cnt) 411 acc_loop_cnt = loop_cnt; 412 413 for (i = 0; i < (ec->memaccessloops + acc_loop_cnt); i++) { 414 unsigned char *tmpval = ec->mem + ec->memlocation; 415 /* 416 * memory access: just add 1 to one byte, 417 * wrap at 255 -- memory access implies read 418 * from and write to memory location 419 */ 420 *tmpval = (*tmpval + 1) & 0xff; 421 /* 422 * Addition of memblocksize - 1 to pointer 423 * with wrap around logic to ensure that every 424 * memory location is hit evenly 425 */ 426 ec->memlocation = ec->memlocation + ec->memblocksize - 1; 427 ec->memlocation = ec->memlocation % wrap; 428 } 429 } 430 431 /*************************************************************************** 432 * Start of entropy processing logic 433 ***************************************************************************/ 434 /* 435 * This is the heart of the entropy generation: calculate time deltas and 436 * use the CPU jitter in the time deltas. The jitter is injected into the 437 * entropy pool. 438 * 439 * WARNING: ensure that ->prev_time is primed before using the output 440 * of this function! This can be done by calling this function 441 * and not using its result. 442 * 443 * @ec [in] Reference to entropy collector 444 * 445 * @return result of stuck test 446 */ 447 static int jent_measure_jitter(struct rand_data *ec) 448 { 449 __u64 time = 0; 450 __u64 current_delta = 0; 451 int stuck; 452 453 /* Invoke one noise source before time measurement to add variations */ 454 jent_memaccess(ec, 0); 455 456 /* 457 * Get time stamp and calculate time delta to previous 458 * invocation to measure the timing variations 459 */ 460 jent_get_nstime(&time); 461 current_delta = jent_delta(ec->prev_time, time); 462 ec->prev_time = time; 463 464 /* Check whether we have a stuck measurement. */ 465 stuck = jent_stuck(ec, current_delta); 466 467 /* Now call the next noise sources which also injects the data */ 468 if (jent_condition_data(ec, current_delta, stuck)) 469 stuck = 1; 470 471 return stuck; 472 } 473 474 /* 475 * Generator of one 64 bit random number 476 * Function fills rand_data->hash_state 477 * 478 * @ec [in] Reference to entropy collector 479 */ 480 static void jent_gen_entropy(struct rand_data *ec) 481 { 482 unsigned int k = 0, safety_factor = 0; 483 484 if (fips_enabled) 485 safety_factor = JENT_ENTROPY_SAFETY_FACTOR; 486 487 /* priming of the ->prev_time value */ 488 jent_measure_jitter(ec); 489 490 while (!jent_health_failure(ec)) { 491 /* If a stuck measurement is received, repeat measurement */ 492 if (jent_measure_jitter(ec)) 493 continue; 494 495 /* 496 * We multiply the loop value with ->osr to obtain the 497 * oversampling rate requested by the caller 498 */ 499 if (++k >= ((DATA_SIZE_BITS + safety_factor) * ec->osr)) 500 break; 501 } 502 } 503 504 /* 505 * Entry function: Obtain entropy for the caller. 506 * 507 * This function invokes the entropy gathering logic as often to generate 508 * as many bytes as requested by the caller. The entropy gathering logic 509 * creates 64 bit per invocation. 510 * 511 * This function truncates the last 64 bit entropy value output to the exact 512 * size specified by the caller. 513 * 514 * @ec [in] Reference to entropy collector 515 * @data [in] pointer to buffer for storing random data -- buffer must already 516 * exist 517 * @len [in] size of the buffer, specifying also the requested number of random 518 * in bytes 519 * 520 * @return 0 when request is fulfilled or an error 521 * 522 * The following error codes can occur: 523 * -1 entropy_collector is NULL or the generation failed 524 * -2 Intermittent health failure 525 * -3 Permanent health failure 526 */ 527 int jent_read_entropy(struct rand_data *ec, unsigned char *data, 528 unsigned int len) 529 { 530 unsigned char *p = data; 531 532 if (!ec) 533 return -1; 534 535 while (len > 0) { 536 unsigned int tocopy; 537 538 jent_gen_entropy(ec); 539 540 if (jent_permanent_health_failure(ec)) { 541 /* 542 * At this point, the Jitter RNG instance is considered 543 * as a failed instance. There is no rerun of the 544 * startup test any more, because the caller 545 * is assumed to not further use this instance. 546 */ 547 return -3; 548 } else if (jent_health_failure(ec)) { 549 /* 550 * Perform startup health tests and return permanent 551 * error if it fails. 552 */ 553 if (jent_entropy_init(ec->hash_state)) 554 return -3; 555 556 return -2; 557 } 558 559 if ((DATA_SIZE_BITS / 8) < len) 560 tocopy = (DATA_SIZE_BITS / 8); 561 else 562 tocopy = len; 563 if (jent_read_random_block(ec->hash_state, p, tocopy)) 564 return -1; 565 566 len -= tocopy; 567 p += tocopy; 568 } 569 570 return 0; 571 } 572 573 /*************************************************************************** 574 * Initialization logic 575 ***************************************************************************/ 576 577 struct rand_data *jent_entropy_collector_alloc(unsigned int osr, 578 unsigned int flags, 579 void *hash_state) 580 { 581 struct rand_data *entropy_collector; 582 583 entropy_collector = jent_zalloc(sizeof(struct rand_data)); 584 if (!entropy_collector) 585 return NULL; 586 587 if (!(flags & JENT_DISABLE_MEMORY_ACCESS)) { 588 /* Allocate memory for adding variations based on memory 589 * access 590 */ 591 entropy_collector->mem = jent_zalloc(JENT_MEMORY_SIZE); 592 if (!entropy_collector->mem) { 593 jent_zfree(entropy_collector); 594 return NULL; 595 } 596 entropy_collector->memblocksize = JENT_MEMORY_BLOCKSIZE; 597 entropy_collector->memblocks = JENT_MEMORY_BLOCKS; 598 entropy_collector->memaccessloops = JENT_MEMORY_ACCESSLOOPS; 599 } 600 601 /* verify and set the oversampling rate */ 602 if (osr == 0) 603 osr = 1; /* minimum sampling rate is 1 */ 604 entropy_collector->osr = osr; 605 606 entropy_collector->hash_state = hash_state; 607 608 /* fill the data pad with non-zero values */ 609 jent_gen_entropy(entropy_collector); 610 611 return entropy_collector; 612 } 613 614 void jent_entropy_collector_free(struct rand_data *entropy_collector) 615 { 616 jent_zfree(entropy_collector->mem); 617 entropy_collector->mem = NULL; 618 jent_zfree(entropy_collector); 619 } 620 621 int jent_entropy_init(void *hash_state) 622 { 623 int i; 624 __u64 delta_sum = 0; 625 __u64 old_delta = 0; 626 unsigned int nonstuck = 0; 627 int time_backwards = 0; 628 int count_mod = 0; 629 int count_stuck = 0; 630 struct rand_data ec = { 0 }; 631 632 /* Required for RCT */ 633 ec.osr = 1; 634 ec.hash_state = hash_state; 635 636 /* We could perform statistical tests here, but the problem is 637 * that we only have a few loop counts to do testing. These 638 * loop counts may show some slight skew and we produce 639 * false positives. 640 * 641 * Moreover, only old systems show potentially problematic 642 * jitter entropy that could potentially be caught here. But 643 * the RNG is intended for hardware that is available or widely 644 * used, but not old systems that are long out of favor. Thus, 645 * no statistical tests. 646 */ 647 648 /* 649 * We could add a check for system capabilities such as clock_getres or 650 * check for CONFIG_X86_TSC, but it does not make much sense as the 651 * following sanity checks verify that we have a high-resolution 652 * timer. 653 */ 654 /* 655 * TESTLOOPCOUNT needs some loops to identify edge systems. 100 is 656 * definitely too little. 657 * 658 * SP800-90B requires at least 1024 initial test cycles. 659 */ 660 #define TESTLOOPCOUNT 1024 661 #define CLEARCACHE 100 662 for (i = 0; (TESTLOOPCOUNT + CLEARCACHE) > i; i++) { 663 __u64 time = 0; 664 __u64 time2 = 0; 665 __u64 delta = 0; 666 unsigned int lowdelta = 0; 667 int stuck; 668 669 /* Invoke core entropy collection logic */ 670 jent_get_nstime(&time); 671 ec.prev_time = time; 672 jent_condition_data(&ec, time, 0); 673 jent_get_nstime(&time2); 674 675 /* test whether timer works */ 676 if (!time || !time2) 677 return JENT_ENOTIME; 678 delta = jent_delta(time, time2); 679 /* 680 * test whether timer is fine grained enough to provide 681 * delta even when called shortly after each other -- this 682 * implies that we also have a high resolution timer 683 */ 684 if (!delta) 685 return JENT_ECOARSETIME; 686 687 stuck = jent_stuck(&ec, delta); 688 689 /* 690 * up to here we did not modify any variable that will be 691 * evaluated later, but we already performed some work. Thus we 692 * already have had an impact on the caches, branch prediction, 693 * etc. with the goal to clear it to get the worst case 694 * measurements. 695 */ 696 if (i < CLEARCACHE) 697 continue; 698 699 if (stuck) 700 count_stuck++; 701 else { 702 nonstuck++; 703 704 /* 705 * Ensure that the APT succeeded. 706 * 707 * With the check below that count_stuck must be less 708 * than 10% of the overall generated raw entropy values 709 * it is guaranteed that the APT is invoked at 710 * floor((TESTLOOPCOUNT * 0.9) / 64) == 14 times. 711 */ 712 if ((nonstuck % JENT_APT_WINDOW_SIZE) == 0) { 713 jent_apt_reset(&ec, 714 delta & JENT_APT_WORD_MASK); 715 } 716 } 717 718 /* Validate health test result */ 719 if (jent_health_failure(&ec)) 720 return JENT_EHEALTH; 721 722 /* test whether we have an increasing timer */ 723 if (!(time2 > time)) 724 time_backwards++; 725 726 /* use 32 bit value to ensure compilation on 32 bit arches */ 727 lowdelta = time2 - time; 728 if (!(lowdelta % 100)) 729 count_mod++; 730 731 /* 732 * ensure that we have a varying delta timer which is necessary 733 * for the calculation of entropy -- perform this check 734 * only after the first loop is executed as we need to prime 735 * the old_data value 736 */ 737 if (delta > old_delta) 738 delta_sum += (delta - old_delta); 739 else 740 delta_sum += (old_delta - delta); 741 old_delta = delta; 742 } 743 744 /* 745 * we allow up to three times the time running backwards. 746 * CLOCK_REALTIME is affected by adjtime and NTP operations. Thus, 747 * if such an operation just happens to interfere with our test, it 748 * should not fail. The value of 3 should cover the NTP case being 749 * performed during our test run. 750 */ 751 if (time_backwards > 3) 752 return JENT_ENOMONOTONIC; 753 754 /* 755 * Variations of deltas of time must on average be larger 756 * than 1 to ensure the entropy estimation 757 * implied with 1 is preserved 758 */ 759 if ((delta_sum) <= 1) 760 return JENT_EVARVAR; 761 762 /* 763 * Ensure that we have variations in the time stamp below 10 for at 764 * least 10% of all checks -- on some platforms, the counter increments 765 * in multiples of 100, but not always 766 */ 767 if ((TESTLOOPCOUNT/10 * 9) < count_mod) 768 return JENT_ECOARSETIME; 769 770 /* 771 * If we have more than 90% stuck results, then this Jitter RNG is 772 * likely to not work well. 773 */ 774 if ((TESTLOOPCOUNT/10 * 9) < count_stuck) 775 return JENT_ESTUCK; 776 777 return 0; 778 } 779