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 - 2020 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 2.2.0 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 #define NULL ((void *) 0) 61 62 /* The entropy pool */ 63 struct rand_data { 64 /* all data values that are vital to maintain the security 65 * of the RNG are marked as SENSITIVE. A user must not 66 * access that information while the RNG executes its loops to 67 * calculate the next random value. */ 68 __u64 data; /* SENSITIVE Actual random number */ 69 __u64 old_data; /* SENSITIVE Previous random number */ 70 __u64 prev_time; /* SENSITIVE Previous time stamp */ 71 #define DATA_SIZE_BITS ((sizeof(__u64)) * 8) 72 __u64 last_delta; /* SENSITIVE stuck test */ 73 __s64 last_delta2; /* SENSITIVE stuck test */ 74 unsigned int osr; /* Oversample rate */ 75 #define JENT_MEMORY_BLOCKS 64 76 #define JENT_MEMORY_BLOCKSIZE 32 77 #define JENT_MEMORY_ACCESSLOOPS 128 78 #define JENT_MEMORY_SIZE (JENT_MEMORY_BLOCKS*JENT_MEMORY_BLOCKSIZE) 79 unsigned char *mem; /* Memory access location with size of 80 * memblocks * memblocksize */ 81 unsigned int memlocation; /* Pointer to byte in *mem */ 82 unsigned int memblocks; /* Number of memory blocks in *mem */ 83 unsigned int memblocksize; /* Size of one memory block in bytes */ 84 unsigned int memaccessloops; /* Number of memory accesses per random 85 * bit generation */ 86 87 /* Repetition Count Test */ 88 unsigned int rct_count; /* Number of stuck values */ 89 90 /* Intermittent health test failure threshold of 2^-30 */ 91 #define JENT_RCT_CUTOFF 30 /* Taken from SP800-90B sec 4.4.1 */ 92 #define JENT_APT_CUTOFF 325 /* Taken from SP800-90B sec 4.4.2 */ 93 /* Permanent health test failure threshold of 2^-60 */ 94 #define JENT_RCT_CUTOFF_PERMANENT 60 95 #define JENT_APT_CUTOFF_PERMANENT 355 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 apt_base_set:1; /* APT base reference set? */ 104 }; 105 106 /* Flags that can be used to initialize the RNG */ 107 #define JENT_DISABLE_MEMORY_ACCESS (1<<2) /* Disable memory access for more 108 * entropy, saves MEMORY_SIZE RAM for 109 * entropy collector */ 110 111 /* -- error codes for init function -- */ 112 #define JENT_ENOTIME 1 /* Timer service not available */ 113 #define JENT_ECOARSETIME 2 /* Timer too coarse for RNG */ 114 #define JENT_ENOMONOTONIC 3 /* Timer is not monotonic increasing */ 115 #define JENT_EVARVAR 5 /* Timer does not produce variations of 116 * variations (2nd derivation of time is 117 * zero). */ 118 #define JENT_ESTUCK 8 /* Too many stuck results during init. */ 119 #define JENT_EHEALTH 9 /* Health test failed during initialization */ 120 #define JENT_ERCT 10 /* RCT 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 * @ec entropy collector struct -- may be NULL 306 * @bits is the number of low bits of the timer to consider 307 * @min is the number of bits we shift the timer value to the right at 308 * the end to make sure we have a guaranteed minimum value 309 * 310 * @return Newly calculated loop counter 311 */ 312 static __u64 jent_loop_shuffle(struct rand_data *ec, 313 unsigned int bits, unsigned int min) 314 { 315 __u64 time = 0; 316 __u64 shuffle = 0; 317 unsigned int i = 0; 318 unsigned int mask = (1<<bits) - 1; 319 320 jent_get_nstime(&time); 321 /* 322 * Mix the current state of the random number into the shuffle 323 * calculation to balance that shuffle a bit more. 324 */ 325 if (ec) 326 time ^= ec->data; 327 /* 328 * We fold the time value as much as possible to ensure that as many 329 * bits of the time stamp are included as possible. 330 */ 331 for (i = 0; ((DATA_SIZE_BITS + bits - 1) / bits) > i; i++) { 332 shuffle ^= time & mask; 333 time = time >> bits; 334 } 335 336 /* 337 * We add a lower boundary value to ensure we have a minimum 338 * RNG loop count. 339 */ 340 return (shuffle + (1<<min)); 341 } 342 343 /* 344 * CPU Jitter noise source -- this is the noise source based on the CPU 345 * execution time jitter 346 * 347 * This function injects the individual bits of the time value into the 348 * entropy pool using an LFSR. 349 * 350 * The code is deliberately inefficient with respect to the bit shifting 351 * and shall stay that way. This function is the root cause why the code 352 * shall be compiled without optimization. This function not only acts as 353 * folding operation, but this function's execution is used to measure 354 * the CPU execution time jitter. Any change to the loop in this function 355 * implies that careful retesting must be done. 356 * 357 * @ec [in] entropy collector struct 358 * @time [in] time stamp to be injected 359 * @loop_cnt [in] if a value not equal to 0 is set, use the given value as 360 * number of loops to perform the folding 361 * @stuck [in] Is the time stamp identified as stuck? 362 * 363 * Output: 364 * updated ec->data 365 * 366 * @return Number of loops the folding operation is performed 367 */ 368 static void jent_lfsr_time(struct rand_data *ec, __u64 time, __u64 loop_cnt, 369 int stuck) 370 { 371 unsigned int i; 372 __u64 j = 0; 373 __u64 new = 0; 374 #define MAX_FOLD_LOOP_BIT 4 375 #define MIN_FOLD_LOOP_BIT 0 376 __u64 fold_loop_cnt = 377 jent_loop_shuffle(ec, MAX_FOLD_LOOP_BIT, MIN_FOLD_LOOP_BIT); 378 379 /* 380 * testing purposes -- allow test app to set the counter, not 381 * needed during runtime 382 */ 383 if (loop_cnt) 384 fold_loop_cnt = loop_cnt; 385 for (j = 0; j < fold_loop_cnt; j++) { 386 new = ec->data; 387 for (i = 1; (DATA_SIZE_BITS) >= i; i++) { 388 __u64 tmp = time << (DATA_SIZE_BITS - i); 389 390 tmp = tmp >> (DATA_SIZE_BITS - 1); 391 392 /* 393 * Fibonacci LSFR with polynomial of 394 * x^64 + x^61 + x^56 + x^31 + x^28 + x^23 + 1 which is 395 * primitive according to 396 * http://poincare.matf.bg.ac.rs/~ezivkovm/publications/primpol1.pdf 397 * (the shift values are the polynomial values minus one 398 * due to counting bits from 0 to 63). As the current 399 * position is always the LSB, the polynomial only needs 400 * to shift data in from the left without wrap. 401 */ 402 tmp ^= ((new >> 63) & 1); 403 tmp ^= ((new >> 60) & 1); 404 tmp ^= ((new >> 55) & 1); 405 tmp ^= ((new >> 30) & 1); 406 tmp ^= ((new >> 27) & 1); 407 tmp ^= ((new >> 22) & 1); 408 new <<= 1; 409 new ^= tmp; 410 } 411 } 412 413 /* 414 * If the time stamp is stuck, do not finally insert the value into 415 * the entropy pool. Although this operation should not do any harm 416 * even when the time stamp has no entropy, SP800-90B requires that 417 * any conditioning operation (SP800-90B considers the LFSR to be a 418 * conditioning operation) to have an identical amount of input 419 * data according to section 3.1.5. 420 */ 421 if (!stuck) 422 ec->data = new; 423 } 424 425 /* 426 * Memory Access noise source -- this is a noise source based on variations in 427 * memory access times 428 * 429 * This function performs memory accesses which will add to the timing 430 * variations due to an unknown amount of CPU wait states that need to be 431 * added when accessing memory. The memory size should be larger than the L1 432 * caches as outlined in the documentation and the associated testing. 433 * 434 * The L1 cache has a very high bandwidth, albeit its access rate is usually 435 * slower than accessing CPU registers. Therefore, L1 accesses only add minimal 436 * variations as the CPU has hardly to wait. Starting with L2, significant 437 * variations are added because L2 typically does not belong to the CPU any more 438 * and therefore a wider range of CPU wait states is necessary for accesses. 439 * L3 and real memory accesses have even a wider range of wait states. However, 440 * to reliably access either L3 or memory, the ec->mem memory must be quite 441 * large which is usually not desirable. 442 * 443 * @ec [in] Reference to the entropy collector with the memory access data -- if 444 * the reference to the memory block to be accessed is NULL, this noise 445 * source is disabled 446 * @loop_cnt [in] if a value not equal to 0 is set, use the given value 447 * number of loops to perform the LFSR 448 */ 449 static void jent_memaccess(struct rand_data *ec, __u64 loop_cnt) 450 { 451 unsigned int wrap = 0; 452 __u64 i = 0; 453 #define MAX_ACC_LOOP_BIT 7 454 #define MIN_ACC_LOOP_BIT 0 455 __u64 acc_loop_cnt = 456 jent_loop_shuffle(ec, MAX_ACC_LOOP_BIT, MIN_ACC_LOOP_BIT); 457 458 if (NULL == ec || NULL == ec->mem) 459 return; 460 wrap = ec->memblocksize * ec->memblocks; 461 462 /* 463 * testing purposes -- allow test app to set the counter, not 464 * needed during runtime 465 */ 466 if (loop_cnt) 467 acc_loop_cnt = loop_cnt; 468 469 for (i = 0; i < (ec->memaccessloops + acc_loop_cnt); i++) { 470 unsigned char *tmpval = ec->mem + ec->memlocation; 471 /* 472 * memory access: just add 1 to one byte, 473 * wrap at 255 -- memory access implies read 474 * from and write to memory location 475 */ 476 *tmpval = (*tmpval + 1) & 0xff; 477 /* 478 * Addition of memblocksize - 1 to pointer 479 * with wrap around logic to ensure that every 480 * memory location is hit evenly 481 */ 482 ec->memlocation = ec->memlocation + ec->memblocksize - 1; 483 ec->memlocation = ec->memlocation % wrap; 484 } 485 } 486 487 /*************************************************************************** 488 * Start of entropy processing logic 489 ***************************************************************************/ 490 /* 491 * This is the heart of the entropy generation: calculate time deltas and 492 * use the CPU jitter in the time deltas. The jitter is injected into the 493 * entropy pool. 494 * 495 * WARNING: ensure that ->prev_time is primed before using the output 496 * of this function! This can be done by calling this function 497 * and not using its result. 498 * 499 * @ec [in] Reference to entropy collector 500 * 501 * @return result of stuck test 502 */ 503 static int jent_measure_jitter(struct rand_data *ec) 504 { 505 __u64 time = 0; 506 __u64 current_delta = 0; 507 int stuck; 508 509 /* Invoke one noise source before time measurement to add variations */ 510 jent_memaccess(ec, 0); 511 512 /* 513 * Get time stamp and calculate time delta to previous 514 * invocation to measure the timing variations 515 */ 516 jent_get_nstime(&time); 517 current_delta = jent_delta(ec->prev_time, time); 518 ec->prev_time = time; 519 520 /* Check whether we have a stuck measurement. */ 521 stuck = jent_stuck(ec, current_delta); 522 523 /* Now call the next noise sources which also injects the data */ 524 jent_lfsr_time(ec, current_delta, 0, stuck); 525 526 return stuck; 527 } 528 529 /* 530 * Generator of one 64 bit random number 531 * Function fills rand_data->data 532 * 533 * @ec [in] Reference to entropy collector 534 */ 535 static void jent_gen_entropy(struct rand_data *ec) 536 { 537 unsigned int k = 0, safety_factor = 0; 538 539 if (fips_enabled) 540 safety_factor = JENT_ENTROPY_SAFETY_FACTOR; 541 542 /* priming of the ->prev_time value */ 543 jent_measure_jitter(ec); 544 545 while (!jent_health_failure(ec)) { 546 /* If a stuck measurement is received, repeat measurement */ 547 if (jent_measure_jitter(ec)) 548 continue; 549 550 /* 551 * We multiply the loop value with ->osr to obtain the 552 * oversampling rate requested by the caller 553 */ 554 if (++k >= ((DATA_SIZE_BITS + safety_factor) * ec->osr)) 555 break; 556 } 557 } 558 559 /* 560 * Entry function: Obtain entropy for the caller. 561 * 562 * This function invokes the entropy gathering logic as often to generate 563 * as many bytes as requested by the caller. The entropy gathering logic 564 * creates 64 bit per invocation. 565 * 566 * This function truncates the last 64 bit entropy value output to the exact 567 * size specified by the caller. 568 * 569 * @ec [in] Reference to entropy collector 570 * @data [in] pointer to buffer for storing random data -- buffer must already 571 * exist 572 * @len [in] size of the buffer, specifying also the requested number of random 573 * in bytes 574 * 575 * @return 0 when request is fulfilled or an error 576 * 577 * The following error codes can occur: 578 * -1 entropy_collector is NULL 579 * -2 Intermittent health failure 580 * -3 Permanent health failure 581 */ 582 int jent_read_entropy(struct rand_data *ec, unsigned char *data, 583 unsigned int len) 584 { 585 unsigned char *p = data; 586 587 if (!ec) 588 return -1; 589 590 while (len > 0) { 591 unsigned int tocopy; 592 593 jent_gen_entropy(ec); 594 595 if (jent_permanent_health_failure(ec)) { 596 /* 597 * At this point, the Jitter RNG instance is considered 598 * as a failed instance. There is no rerun of the 599 * startup test any more, because the caller 600 * is assumed to not further use this instance. 601 */ 602 return -3; 603 } else if (jent_health_failure(ec)) { 604 /* 605 * Perform startup health tests and return permanent 606 * error if it fails. 607 */ 608 if (jent_entropy_init()) 609 return -3; 610 611 return -2; 612 } 613 614 if ((DATA_SIZE_BITS / 8) < len) 615 tocopy = (DATA_SIZE_BITS / 8); 616 else 617 tocopy = len; 618 jent_memcpy(p, &ec->data, tocopy); 619 620 len -= tocopy; 621 p += tocopy; 622 } 623 624 return 0; 625 } 626 627 /*************************************************************************** 628 * Initialization logic 629 ***************************************************************************/ 630 631 struct rand_data *jent_entropy_collector_alloc(unsigned int osr, 632 unsigned int flags) 633 { 634 struct rand_data *entropy_collector; 635 636 entropy_collector = jent_zalloc(sizeof(struct rand_data)); 637 if (!entropy_collector) 638 return NULL; 639 640 if (!(flags & JENT_DISABLE_MEMORY_ACCESS)) { 641 /* Allocate memory for adding variations based on memory 642 * access 643 */ 644 entropy_collector->mem = jent_zalloc(JENT_MEMORY_SIZE); 645 if (!entropy_collector->mem) { 646 jent_zfree(entropy_collector); 647 return NULL; 648 } 649 entropy_collector->memblocksize = JENT_MEMORY_BLOCKSIZE; 650 entropy_collector->memblocks = JENT_MEMORY_BLOCKS; 651 entropy_collector->memaccessloops = JENT_MEMORY_ACCESSLOOPS; 652 } 653 654 /* verify and set the oversampling rate */ 655 if (osr == 0) 656 osr = 1; /* minimum sampling rate is 1 */ 657 entropy_collector->osr = osr; 658 659 /* fill the data pad with non-zero values */ 660 jent_gen_entropy(entropy_collector); 661 662 return entropy_collector; 663 } 664 665 void jent_entropy_collector_free(struct rand_data *entropy_collector) 666 { 667 jent_zfree(entropy_collector->mem); 668 entropy_collector->mem = NULL; 669 jent_zfree(entropy_collector); 670 } 671 672 int jent_entropy_init(void) 673 { 674 int i; 675 __u64 delta_sum = 0; 676 __u64 old_delta = 0; 677 unsigned int nonstuck = 0; 678 int time_backwards = 0; 679 int count_mod = 0; 680 int count_stuck = 0; 681 struct rand_data ec = { 0 }; 682 683 /* Required for RCT */ 684 ec.osr = 1; 685 686 /* We could perform statistical tests here, but the problem is 687 * that we only have a few loop counts to do testing. These 688 * loop counts may show some slight skew and we produce 689 * false positives. 690 * 691 * Moreover, only old systems show potentially problematic 692 * jitter entropy that could potentially be caught here. But 693 * the RNG is intended for hardware that is available or widely 694 * used, but not old systems that are long out of favor. Thus, 695 * no statistical tests. 696 */ 697 698 /* 699 * We could add a check for system capabilities such as clock_getres or 700 * check for CONFIG_X86_TSC, but it does not make much sense as the 701 * following sanity checks verify that we have a high-resolution 702 * timer. 703 */ 704 /* 705 * TESTLOOPCOUNT needs some loops to identify edge systems. 100 is 706 * definitely too little. 707 * 708 * SP800-90B requires at least 1024 initial test cycles. 709 */ 710 #define TESTLOOPCOUNT 1024 711 #define CLEARCACHE 100 712 for (i = 0; (TESTLOOPCOUNT + CLEARCACHE) > i; i++) { 713 __u64 time = 0; 714 __u64 time2 = 0; 715 __u64 delta = 0; 716 unsigned int lowdelta = 0; 717 int stuck; 718 719 /* Invoke core entropy collection logic */ 720 jent_get_nstime(&time); 721 ec.prev_time = time; 722 jent_lfsr_time(&ec, time, 0, 0); 723 jent_get_nstime(&time2); 724 725 /* test whether timer works */ 726 if (!time || !time2) 727 return JENT_ENOTIME; 728 delta = jent_delta(time, time2); 729 /* 730 * test whether timer is fine grained enough to provide 731 * delta even when called shortly after each other -- this 732 * implies that we also have a high resolution timer 733 */ 734 if (!delta) 735 return JENT_ECOARSETIME; 736 737 stuck = jent_stuck(&ec, delta); 738 739 /* 740 * up to here we did not modify any variable that will be 741 * evaluated later, but we already performed some work. Thus we 742 * already have had an impact on the caches, branch prediction, 743 * etc. with the goal to clear it to get the worst case 744 * measurements. 745 */ 746 if (i < CLEARCACHE) 747 continue; 748 749 if (stuck) 750 count_stuck++; 751 else { 752 nonstuck++; 753 754 /* 755 * Ensure that the APT succeeded. 756 * 757 * With the check below that count_stuck must be less 758 * than 10% of the overall generated raw entropy values 759 * it is guaranteed that the APT is invoked at 760 * floor((TESTLOOPCOUNT * 0.9) / 64) == 14 times. 761 */ 762 if ((nonstuck % JENT_APT_WINDOW_SIZE) == 0) { 763 jent_apt_reset(&ec, 764 delta & JENT_APT_WORD_MASK); 765 if (jent_health_failure(&ec)) 766 return JENT_EHEALTH; 767 } 768 } 769 770 /* Validate RCT */ 771 if (jent_rct_failure(&ec)) 772 return JENT_ERCT; 773 774 /* test whether we have an increasing timer */ 775 if (!(time2 > time)) 776 time_backwards++; 777 778 /* use 32 bit value to ensure compilation on 32 bit arches */ 779 lowdelta = time2 - time; 780 if (!(lowdelta % 100)) 781 count_mod++; 782 783 /* 784 * ensure that we have a varying delta timer which is necessary 785 * for the calculation of entropy -- perform this check 786 * only after the first loop is executed as we need to prime 787 * the old_data value 788 */ 789 if (delta > old_delta) 790 delta_sum += (delta - old_delta); 791 else 792 delta_sum += (old_delta - delta); 793 old_delta = delta; 794 } 795 796 /* 797 * we allow up to three times the time running backwards. 798 * CLOCK_REALTIME is affected by adjtime and NTP operations. Thus, 799 * if such an operation just happens to interfere with our test, it 800 * should not fail. The value of 3 should cover the NTP case being 801 * performed during our test run. 802 */ 803 if (time_backwards > 3) 804 return JENT_ENOMONOTONIC; 805 806 /* 807 * Variations of deltas of time must on average be larger 808 * than 1 to ensure the entropy estimation 809 * implied with 1 is preserved 810 */ 811 if ((delta_sum) <= 1) 812 return JENT_EVARVAR; 813 814 /* 815 * Ensure that we have variations in the time stamp below 10 for at 816 * least 10% of all checks -- on some platforms, the counter increments 817 * in multiples of 100, but not always 818 */ 819 if ((TESTLOOPCOUNT/10 * 9) < count_mod) 820 return JENT_ECOARSETIME; 821 822 /* 823 * If we have more than 90% stuck results, then this Jitter RNG is 824 * likely to not work well. 825 */ 826 if ((TESTLOOPCOUNT/10 * 9) < count_stuck) 827 return JENT_ESTUCK; 828 829 return 0; 830 } 831