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