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 int rct_count; /* Number of stuck values */ 89 90 /* Adaptive Proportion Test for a significance level of 2^-30 */ 91 #define JENT_APT_CUTOFF 325 /* Taken from SP800-90B sec 4.4.2 */ 92 #define JENT_APT_WINDOW_SIZE 512 /* Data window size */ 93 /* LSB of time stamp to process */ 94 #define JENT_APT_LSB 16 95 #define JENT_APT_WORD_MASK (JENT_APT_LSB - 1) 96 unsigned int apt_observations; /* Number of collected observations */ 97 unsigned int apt_count; /* APT counter */ 98 unsigned int apt_base; /* APT base reference */ 99 unsigned int apt_base_set:1; /* APT base reference set? */ 100 101 unsigned int health_failure:1; /* Permanent health failure */ 102 }; 103 104 /* Flags that can be used to initialize the RNG */ 105 #define JENT_DISABLE_MEMORY_ACCESS (1<<2) /* Disable memory access for more 106 * entropy, saves MEMORY_SIZE RAM for 107 * entropy collector */ 108 109 /* -- error codes for init function -- */ 110 #define JENT_ENOTIME 1 /* Timer service not available */ 111 #define JENT_ECOARSETIME 2 /* Timer too coarse for RNG */ 112 #define JENT_ENOMONOTONIC 3 /* Timer is not monotonic increasing */ 113 #define JENT_EVARVAR 5 /* Timer does not produce variations of 114 * variations (2nd derivation of time is 115 * zero). */ 116 #define JENT_ESTUCK 8 /* Too many stuck results during init. */ 117 #define JENT_EHEALTH 9 /* Health test failed during initialization */ 118 #define JENT_ERCT 10 /* RCT failed during initialization */ 119 120 /* 121 * The output n bits can receive more than n bits of min entropy, of course, 122 * but the fixed output of the conditioning function can only asymptotically 123 * approach the output size bits of min entropy, not attain that bound. Random 124 * maps will tend to have output collisions, which reduces the creditable 125 * output entropy (that is what SP 800-90B Section 3.1.5.1.2 attempts to bound). 126 * 127 * The value "64" is justified in Appendix A.4 of the current 90C draft, 128 * and aligns with NIST's in "epsilon" definition in this document, which is 129 * that a string can be considered "full entropy" if you can bound the min 130 * entropy in each bit of output to at least 1-epsilon, where epsilon is 131 * required to be <= 2^(-32). 132 */ 133 #define JENT_ENTROPY_SAFETY_FACTOR 64 134 135 #include <linux/fips.h> 136 #include "jitterentropy.h" 137 138 /*************************************************************************** 139 * Adaptive Proportion Test 140 * 141 * This test complies with SP800-90B section 4.4.2. 142 ***************************************************************************/ 143 144 /* 145 * Reset the APT counter 146 * 147 * @ec [in] Reference to entropy collector 148 */ 149 static void jent_apt_reset(struct rand_data *ec, unsigned int delta_masked) 150 { 151 /* Reset APT counter */ 152 ec->apt_count = 0; 153 ec->apt_base = delta_masked; 154 ec->apt_observations = 0; 155 } 156 157 /* 158 * Insert a new entropy event into APT 159 * 160 * @ec [in] Reference to entropy collector 161 * @delta_masked [in] Masked time delta to process 162 */ 163 static void jent_apt_insert(struct rand_data *ec, unsigned int delta_masked) 164 { 165 /* Initialize the base reference */ 166 if (!ec->apt_base_set) { 167 ec->apt_base = delta_masked; 168 ec->apt_base_set = 1; 169 return; 170 } 171 172 if (delta_masked == ec->apt_base) { 173 ec->apt_count++; 174 175 if (ec->apt_count >= JENT_APT_CUTOFF) 176 ec->health_failure = 1; 177 } 178 179 ec->apt_observations++; 180 181 if (ec->apt_observations >= JENT_APT_WINDOW_SIZE) 182 jent_apt_reset(ec, delta_masked); 183 } 184 185 /*************************************************************************** 186 * Stuck Test and its use as Repetition Count Test 187 * 188 * The Jitter RNG uses an enhanced version of the Repetition Count Test 189 * (RCT) specified in SP800-90B section 4.4.1. Instead of counting identical 190 * back-to-back values, the input to the RCT is the counting of the stuck 191 * values during the generation of one Jitter RNG output block. 192 * 193 * The RCT is applied with an alpha of 2^{-30} compliant to FIPS 140-2 IG 9.8. 194 * 195 * During the counting operation, the Jitter RNG always calculates the RCT 196 * cut-off value of C. If that value exceeds the allowed cut-off value, 197 * the Jitter RNG output block will be calculated completely but discarded at 198 * the end. The caller of the Jitter RNG is informed with an error code. 199 ***************************************************************************/ 200 201 /* 202 * Repetition Count Test as defined in SP800-90B section 4.4.1 203 * 204 * @ec [in] Reference to entropy collector 205 * @stuck [in] Indicator whether the value is stuck 206 */ 207 static void jent_rct_insert(struct rand_data *ec, int stuck) 208 { 209 /* 210 * If we have a count less than zero, a previous RCT round identified 211 * a failure. We will not overwrite it. 212 */ 213 if (ec->rct_count < 0) 214 return; 215 216 if (stuck) { 217 ec->rct_count++; 218 219 /* 220 * The cutoff value is based on the following consideration: 221 * alpha = 2^-30 as recommended in FIPS 140-2 IG 9.8. 222 * In addition, we require an entropy value H of 1/OSR as this 223 * is the minimum entropy required to provide full entropy. 224 * Note, we collect 64 * OSR deltas for inserting them into 225 * the entropy pool which should then have (close to) 64 bits 226 * of entropy. 227 * 228 * Note, ec->rct_count (which equals to value B in the pseudo 229 * code of SP800-90B section 4.4.1) starts with zero. Hence 230 * we need to subtract one from the cutoff value as calculated 231 * following SP800-90B. 232 */ 233 if ((unsigned int)ec->rct_count >= (31 * ec->osr)) { 234 ec->rct_count = -1; 235 ec->health_failure = 1; 236 } 237 } else { 238 ec->rct_count = 0; 239 } 240 } 241 242 /* 243 * Is there an RCT health test failure? 244 * 245 * @ec [in] Reference to entropy collector 246 * 247 * @return 248 * 0 No health test failure 249 * 1 Permanent health test failure 250 */ 251 static int jent_rct_failure(struct rand_data *ec) 252 { 253 if (ec->rct_count < 0) 254 return 1; 255 return 0; 256 } 257 258 static inline __u64 jent_delta(__u64 prev, __u64 next) 259 { 260 #define JENT_UINT64_MAX (__u64)(~((__u64) 0)) 261 return (prev < next) ? (next - prev) : 262 (JENT_UINT64_MAX - prev + 1 + next); 263 } 264 265 /* 266 * Stuck test by checking the: 267 * 1st derivative of the jitter measurement (time delta) 268 * 2nd derivative of the jitter measurement (delta of time deltas) 269 * 3rd derivative of the jitter measurement (delta of delta of time deltas) 270 * 271 * All values must always be non-zero. 272 * 273 * @ec [in] Reference to entropy collector 274 * @current_delta [in] Jitter time delta 275 * 276 * @return 277 * 0 jitter measurement not stuck (good bit) 278 * 1 jitter measurement stuck (reject bit) 279 */ 280 static int jent_stuck(struct rand_data *ec, __u64 current_delta) 281 { 282 __u64 delta2 = jent_delta(ec->last_delta, current_delta); 283 __u64 delta3 = jent_delta(ec->last_delta2, delta2); 284 285 ec->last_delta = current_delta; 286 ec->last_delta2 = delta2; 287 288 /* 289 * Insert the result of the comparison of two back-to-back time 290 * deltas. 291 */ 292 jent_apt_insert(ec, current_delta); 293 294 if (!current_delta || !delta2 || !delta3) { 295 /* RCT with a stuck bit */ 296 jent_rct_insert(ec, 1); 297 return 1; 298 } 299 300 /* RCT with a non-stuck bit */ 301 jent_rct_insert(ec, 0); 302 303 return 0; 304 } 305 306 /* 307 * Report any health test failures 308 * 309 * @ec [in] Reference to entropy collector 310 * 311 * @return 312 * 0 No health test failure 313 * 1 Permanent health test failure 314 */ 315 static int jent_health_failure(struct rand_data *ec) 316 { 317 return ec->health_failure; 318 } 319 320 /*************************************************************************** 321 * Noise sources 322 ***************************************************************************/ 323 324 /* 325 * Update of the loop count used for the next round of 326 * an entropy collection. 327 * 328 * Input: 329 * @ec entropy collector struct -- may be NULL 330 * @bits is the number of low bits of the timer to consider 331 * @min is the number of bits we shift the timer value to the right at 332 * the end to make sure we have a guaranteed minimum value 333 * 334 * @return Newly calculated loop counter 335 */ 336 static __u64 jent_loop_shuffle(struct rand_data *ec, 337 unsigned int bits, unsigned int min) 338 { 339 __u64 time = 0; 340 __u64 shuffle = 0; 341 unsigned int i = 0; 342 unsigned int mask = (1<<bits) - 1; 343 344 jent_get_nstime(&time); 345 /* 346 * Mix the current state of the random number into the shuffle 347 * calculation to balance that shuffle a bit more. 348 */ 349 if (ec) 350 time ^= ec->data; 351 /* 352 * We fold the time value as much as possible to ensure that as many 353 * bits of the time stamp are included as possible. 354 */ 355 for (i = 0; ((DATA_SIZE_BITS + bits - 1) / bits) > i; i++) { 356 shuffle ^= time & mask; 357 time = time >> bits; 358 } 359 360 /* 361 * We add a lower boundary value to ensure we have a minimum 362 * RNG loop count. 363 */ 364 return (shuffle + (1<<min)); 365 } 366 367 /* 368 * CPU Jitter noise source -- this is the noise source based on the CPU 369 * execution time jitter 370 * 371 * This function injects the individual bits of the time value into the 372 * entropy pool using an LFSR. 373 * 374 * The code is deliberately inefficient with respect to the bit shifting 375 * and shall stay that way. This function is the root cause why the code 376 * shall be compiled without optimization. This function not only acts as 377 * folding operation, but this function's execution is used to measure 378 * the CPU execution time jitter. Any change to the loop in this function 379 * implies that careful retesting must be done. 380 * 381 * @ec [in] entropy collector struct 382 * @time [in] time stamp to be injected 383 * @loop_cnt [in] if a value not equal to 0 is set, use the given value as 384 * number of loops to perform the folding 385 * @stuck [in] Is the time stamp identified as stuck? 386 * 387 * Output: 388 * updated ec->data 389 * 390 * @return Number of loops the folding operation is performed 391 */ 392 static void jent_lfsr_time(struct rand_data *ec, __u64 time, __u64 loop_cnt, 393 int stuck) 394 { 395 unsigned int i; 396 __u64 j = 0; 397 __u64 new = 0; 398 #define MAX_FOLD_LOOP_BIT 4 399 #define MIN_FOLD_LOOP_BIT 0 400 __u64 fold_loop_cnt = 401 jent_loop_shuffle(ec, MAX_FOLD_LOOP_BIT, MIN_FOLD_LOOP_BIT); 402 403 /* 404 * testing purposes -- allow test app to set the counter, not 405 * needed during runtime 406 */ 407 if (loop_cnt) 408 fold_loop_cnt = loop_cnt; 409 for (j = 0; j < fold_loop_cnt; j++) { 410 new = ec->data; 411 for (i = 1; (DATA_SIZE_BITS) >= i; i++) { 412 __u64 tmp = time << (DATA_SIZE_BITS - i); 413 414 tmp = tmp >> (DATA_SIZE_BITS - 1); 415 416 /* 417 * Fibonacci LSFR with polynomial of 418 * x^64 + x^61 + x^56 + x^31 + x^28 + x^23 + 1 which is 419 * primitive according to 420 * http://poincare.matf.bg.ac.rs/~ezivkovm/publications/primpol1.pdf 421 * (the shift values are the polynomial values minus one 422 * due to counting bits from 0 to 63). As the current 423 * position is always the LSB, the polynomial only needs 424 * to shift data in from the left without wrap. 425 */ 426 tmp ^= ((new >> 63) & 1); 427 tmp ^= ((new >> 60) & 1); 428 tmp ^= ((new >> 55) & 1); 429 tmp ^= ((new >> 30) & 1); 430 tmp ^= ((new >> 27) & 1); 431 tmp ^= ((new >> 22) & 1); 432 new <<= 1; 433 new ^= tmp; 434 } 435 } 436 437 /* 438 * If the time stamp is stuck, do not finally insert the value into 439 * the entropy pool. Although this operation should not do any harm 440 * even when the time stamp has no entropy, SP800-90B requires that 441 * any conditioning operation (SP800-90B considers the LFSR to be a 442 * conditioning operation) to have an identical amount of input 443 * data according to section 3.1.5. 444 */ 445 if (!stuck) 446 ec->data = new; 447 } 448 449 /* 450 * Memory Access noise source -- this is a noise source based on variations in 451 * memory access times 452 * 453 * This function performs memory accesses which will add to the timing 454 * variations due to an unknown amount of CPU wait states that need to be 455 * added when accessing memory. The memory size should be larger than the L1 456 * caches as outlined in the documentation and the associated testing. 457 * 458 * The L1 cache has a very high bandwidth, albeit its access rate is usually 459 * slower than accessing CPU registers. Therefore, L1 accesses only add minimal 460 * variations as the CPU has hardly to wait. Starting with L2, significant 461 * variations are added because L2 typically does not belong to the CPU any more 462 * and therefore a wider range of CPU wait states is necessary for accesses. 463 * L3 and real memory accesses have even a wider range of wait states. However, 464 * to reliably access either L3 or memory, the ec->mem memory must be quite 465 * large which is usually not desirable. 466 * 467 * @ec [in] Reference to the entropy collector with the memory access data -- if 468 * the reference to the memory block to be accessed is NULL, this noise 469 * source is disabled 470 * @loop_cnt [in] if a value not equal to 0 is set, use the given value 471 * number of loops to perform the LFSR 472 */ 473 static void jent_memaccess(struct rand_data *ec, __u64 loop_cnt) 474 { 475 unsigned int wrap = 0; 476 __u64 i = 0; 477 #define MAX_ACC_LOOP_BIT 7 478 #define MIN_ACC_LOOP_BIT 0 479 __u64 acc_loop_cnt = 480 jent_loop_shuffle(ec, MAX_ACC_LOOP_BIT, MIN_ACC_LOOP_BIT); 481 482 if (NULL == ec || NULL == ec->mem) 483 return; 484 wrap = ec->memblocksize * ec->memblocks; 485 486 /* 487 * testing purposes -- allow test app to set the counter, not 488 * needed during runtime 489 */ 490 if (loop_cnt) 491 acc_loop_cnt = loop_cnt; 492 493 for (i = 0; i < (ec->memaccessloops + acc_loop_cnt); i++) { 494 unsigned char *tmpval = ec->mem + ec->memlocation; 495 /* 496 * memory access: just add 1 to one byte, 497 * wrap at 255 -- memory access implies read 498 * from and write to memory location 499 */ 500 *tmpval = (*tmpval + 1) & 0xff; 501 /* 502 * Addition of memblocksize - 1 to pointer 503 * with wrap around logic to ensure that every 504 * memory location is hit evenly 505 */ 506 ec->memlocation = ec->memlocation + ec->memblocksize - 1; 507 ec->memlocation = ec->memlocation % wrap; 508 } 509 } 510 511 /*************************************************************************** 512 * Start of entropy processing logic 513 ***************************************************************************/ 514 /* 515 * This is the heart of the entropy generation: calculate time deltas and 516 * use the CPU jitter in the time deltas. The jitter is injected into the 517 * entropy pool. 518 * 519 * WARNING: ensure that ->prev_time is primed before using the output 520 * of this function! This can be done by calling this function 521 * and not using its result. 522 * 523 * @ec [in] Reference to entropy collector 524 * 525 * @return result of stuck test 526 */ 527 static int jent_measure_jitter(struct rand_data *ec) 528 { 529 __u64 time = 0; 530 __u64 current_delta = 0; 531 int stuck; 532 533 /* Invoke one noise source before time measurement to add variations */ 534 jent_memaccess(ec, 0); 535 536 /* 537 * Get time stamp and calculate time delta to previous 538 * invocation to measure the timing variations 539 */ 540 jent_get_nstime(&time); 541 current_delta = jent_delta(ec->prev_time, time); 542 ec->prev_time = time; 543 544 /* Check whether we have a stuck measurement. */ 545 stuck = jent_stuck(ec, current_delta); 546 547 /* Now call the next noise sources which also injects the data */ 548 jent_lfsr_time(ec, current_delta, 0, stuck); 549 550 return stuck; 551 } 552 553 /* 554 * Generator of one 64 bit random number 555 * Function fills rand_data->data 556 * 557 * @ec [in] Reference to entropy collector 558 */ 559 static void jent_gen_entropy(struct rand_data *ec) 560 { 561 unsigned int k = 0, safety_factor = 0; 562 563 if (fips_enabled) 564 safety_factor = JENT_ENTROPY_SAFETY_FACTOR; 565 566 /* priming of the ->prev_time value */ 567 jent_measure_jitter(ec); 568 569 while (!jent_health_failure(ec)) { 570 /* If a stuck measurement is received, repeat measurement */ 571 if (jent_measure_jitter(ec)) 572 continue; 573 574 /* 575 * We multiply the loop value with ->osr to obtain the 576 * oversampling rate requested by the caller 577 */ 578 if (++k >= ((DATA_SIZE_BITS + safety_factor) * ec->osr)) 579 break; 580 } 581 } 582 583 /* 584 * Entry function: Obtain entropy for the caller. 585 * 586 * This function invokes the entropy gathering logic as often to generate 587 * as many bytes as requested by the caller. The entropy gathering logic 588 * creates 64 bit per invocation. 589 * 590 * This function truncates the last 64 bit entropy value output to the exact 591 * size specified by the caller. 592 * 593 * @ec [in] Reference to entropy collector 594 * @data [in] pointer to buffer for storing random data -- buffer must already 595 * exist 596 * @len [in] size of the buffer, specifying also the requested number of random 597 * in bytes 598 * 599 * @return 0 when request is fulfilled or an error 600 * 601 * The following error codes can occur: 602 * -1 entropy_collector is NULL 603 * -2 RCT failed 604 * -3 APT test failed 605 */ 606 int jent_read_entropy(struct rand_data *ec, unsigned char *data, 607 unsigned int len) 608 { 609 unsigned char *p = data; 610 611 if (!ec) 612 return -1; 613 614 while (len > 0) { 615 unsigned int tocopy; 616 617 jent_gen_entropy(ec); 618 619 if (jent_health_failure(ec)) { 620 int ret; 621 622 if (jent_rct_failure(ec)) 623 ret = -2; 624 else 625 ret = -3; 626 627 /* 628 * Re-initialize the noise source 629 * 630 * If the health test fails, the Jitter RNG remains 631 * in failure state and will return a health failure 632 * during next invocation. 633 */ 634 if (jent_entropy_init()) 635 return ret; 636 637 /* Set APT to initial state */ 638 jent_apt_reset(ec, 0); 639 ec->apt_base_set = 0; 640 641 /* Set RCT to initial state */ 642 ec->rct_count = 0; 643 644 /* Re-enable Jitter RNG */ 645 ec->health_failure = 0; 646 647 /* 648 * Return the health test failure status to the 649 * caller as the generated value is not appropriate. 650 */ 651 return ret; 652 } 653 654 if ((DATA_SIZE_BITS / 8) < len) 655 tocopy = (DATA_SIZE_BITS / 8); 656 else 657 tocopy = len; 658 jent_memcpy(p, &ec->data, tocopy); 659 660 len -= tocopy; 661 p += tocopy; 662 } 663 664 return 0; 665 } 666 667 /*************************************************************************** 668 * Initialization logic 669 ***************************************************************************/ 670 671 struct rand_data *jent_entropy_collector_alloc(unsigned int osr, 672 unsigned int flags) 673 { 674 struct rand_data *entropy_collector; 675 676 entropy_collector = jent_zalloc(sizeof(struct rand_data)); 677 if (!entropy_collector) 678 return NULL; 679 680 if (!(flags & JENT_DISABLE_MEMORY_ACCESS)) { 681 /* Allocate memory for adding variations based on memory 682 * access 683 */ 684 entropy_collector->mem = jent_zalloc(JENT_MEMORY_SIZE); 685 if (!entropy_collector->mem) { 686 jent_zfree(entropy_collector); 687 return NULL; 688 } 689 entropy_collector->memblocksize = JENT_MEMORY_BLOCKSIZE; 690 entropy_collector->memblocks = JENT_MEMORY_BLOCKS; 691 entropy_collector->memaccessloops = JENT_MEMORY_ACCESSLOOPS; 692 } 693 694 /* verify and set the oversampling rate */ 695 if (osr == 0) 696 osr = 1; /* minimum sampling rate is 1 */ 697 entropy_collector->osr = osr; 698 699 /* fill the data pad with non-zero values */ 700 jent_gen_entropy(entropy_collector); 701 702 return entropy_collector; 703 } 704 705 void jent_entropy_collector_free(struct rand_data *entropy_collector) 706 { 707 jent_zfree(entropy_collector->mem); 708 entropy_collector->mem = NULL; 709 jent_zfree(entropy_collector); 710 } 711 712 int jent_entropy_init(void) 713 { 714 int i; 715 __u64 delta_sum = 0; 716 __u64 old_delta = 0; 717 unsigned int nonstuck = 0; 718 int time_backwards = 0; 719 int count_mod = 0; 720 int count_stuck = 0; 721 struct rand_data ec = { 0 }; 722 723 /* Required for RCT */ 724 ec.osr = 1; 725 726 /* We could perform statistical tests here, but the problem is 727 * that we only have a few loop counts to do testing. These 728 * loop counts may show some slight skew and we produce 729 * false positives. 730 * 731 * Moreover, only old systems show potentially problematic 732 * jitter entropy that could potentially be caught here. But 733 * the RNG is intended for hardware that is available or widely 734 * used, but not old systems that are long out of favor. Thus, 735 * no statistical tests. 736 */ 737 738 /* 739 * We could add a check for system capabilities such as clock_getres or 740 * check for CONFIG_X86_TSC, but it does not make much sense as the 741 * following sanity checks verify that we have a high-resolution 742 * timer. 743 */ 744 /* 745 * TESTLOOPCOUNT needs some loops to identify edge systems. 100 is 746 * definitely too little. 747 * 748 * SP800-90B requires at least 1024 initial test cycles. 749 */ 750 #define TESTLOOPCOUNT 1024 751 #define CLEARCACHE 100 752 for (i = 0; (TESTLOOPCOUNT + CLEARCACHE) > i; i++) { 753 __u64 time = 0; 754 __u64 time2 = 0; 755 __u64 delta = 0; 756 unsigned int lowdelta = 0; 757 int stuck; 758 759 /* Invoke core entropy collection logic */ 760 jent_get_nstime(&time); 761 ec.prev_time = time; 762 jent_lfsr_time(&ec, time, 0, 0); 763 jent_get_nstime(&time2); 764 765 /* test whether timer works */ 766 if (!time || !time2) 767 return JENT_ENOTIME; 768 delta = jent_delta(time, time2); 769 /* 770 * test whether timer is fine grained enough to provide 771 * delta even when called shortly after each other -- this 772 * implies that we also have a high resolution timer 773 */ 774 if (!delta) 775 return JENT_ECOARSETIME; 776 777 stuck = jent_stuck(&ec, delta); 778 779 /* 780 * up to here we did not modify any variable that will be 781 * evaluated later, but we already performed some work. Thus we 782 * already have had an impact on the caches, branch prediction, 783 * etc. with the goal to clear it to get the worst case 784 * measurements. 785 */ 786 if (i < CLEARCACHE) 787 continue; 788 789 if (stuck) 790 count_stuck++; 791 else { 792 nonstuck++; 793 794 /* 795 * Ensure that the APT succeeded. 796 * 797 * With the check below that count_stuck must be less 798 * than 10% of the overall generated raw entropy values 799 * it is guaranteed that the APT is invoked at 800 * floor((TESTLOOPCOUNT * 0.9) / 64) == 14 times. 801 */ 802 if ((nonstuck % JENT_APT_WINDOW_SIZE) == 0) { 803 jent_apt_reset(&ec, 804 delta & JENT_APT_WORD_MASK); 805 if (jent_health_failure(&ec)) 806 return JENT_EHEALTH; 807 } 808 } 809 810 /* Validate RCT */ 811 if (jent_rct_failure(&ec)) 812 return JENT_ERCT; 813 814 /* test whether we have an increasing timer */ 815 if (!(time2 > time)) 816 time_backwards++; 817 818 /* use 32 bit value to ensure compilation on 32 bit arches */ 819 lowdelta = time2 - time; 820 if (!(lowdelta % 100)) 821 count_mod++; 822 823 /* 824 * ensure that we have a varying delta timer which is necessary 825 * for the calculation of entropy -- perform this check 826 * only after the first loop is executed as we need to prime 827 * the old_data value 828 */ 829 if (delta > old_delta) 830 delta_sum += (delta - old_delta); 831 else 832 delta_sum += (old_delta - delta); 833 old_delta = delta; 834 } 835 836 /* 837 * we allow up to three times the time running backwards. 838 * CLOCK_REALTIME is affected by adjtime and NTP operations. Thus, 839 * if such an operation just happens to interfere with our test, it 840 * should not fail. The value of 3 should cover the NTP case being 841 * performed during our test run. 842 */ 843 if (time_backwards > 3) 844 return JENT_ENOMONOTONIC; 845 846 /* 847 * Variations of deltas of time must on average be larger 848 * than 1 to ensure the entropy estimation 849 * implied with 1 is preserved 850 */ 851 if ((delta_sum) <= 1) 852 return JENT_EVARVAR; 853 854 /* 855 * Ensure that we have variations in the time stamp below 10 for at 856 * least 10% of all checks -- on some platforms, the counter increments 857 * in multiples of 100, but not always 858 */ 859 if ((TESTLOOPCOUNT/10 * 9) < count_mod) 860 return JENT_ECOARSETIME; 861 862 /* 863 * If we have more than 90% stuck results, then this Jitter RNG is 864 * likely to not work well. 865 */ 866 if ((TESTLOOPCOUNT/10 * 9) < count_stuck) 867 return JENT_ESTUCK; 868 869 return 0; 870 } 871