Loading...
Note: File does not exist in v3.1.
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
57typedef unsigned long long __u64;
58typedef long long __s64;
59typedef unsigned int __u32;
60#define NULL ((void *) 0)
61
62/* The entropy pool */
63struct 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 */
149static 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 */
163static 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 */
207static 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 */
251static int jent_rct_failure(struct rand_data *ec)
252{
253 if (ec->rct_count < 0)
254 return 1;
255 return 0;
256}
257
258static 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 */
280static 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 */
315static 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 */
336static __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 */
392static 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 */
473static 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 */
527static 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 */
559static 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 */
606int 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
671struct 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
705void 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
712int 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}