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