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 */
jent_apt_reset(struct rand_data * ec,unsigned int delta_masked)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 */
jent_apt_insert(struct rand_data * ec,unsigned int delta_masked)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 */
jent_rct_insert(struct rand_data * ec,int stuck)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 */
jent_rct_failure(struct rand_data * ec)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
jent_delta(__u64 prev,__u64 next)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 */
jent_stuck(struct rand_data * ec,__u64 current_delta)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 */
jent_health_failure(struct rand_data * ec)315 static int jent_health_failure(struct rand_data *ec)
316 {
317 /* Test is only enabled in FIPS mode */
318 if (!jent_fips_enabled())
319 return 0;
320
321 return ec->health_failure;
322 }
323
324 /***************************************************************************
325 * Noise sources
326 ***************************************************************************/
327
328 /**
329 * Update of the loop count used for the next round of
330 * an entropy collection.
331 *
332 * Input:
333 * @ec entropy collector struct -- may be NULL
334 * @bits is the number of low bits of the timer to consider
335 * @min is the number of bits we shift the timer value to the right at
336 * the end to make sure we have a guaranteed minimum value
337 *
338 * @return Newly calculated loop counter
339 */
jent_loop_shuffle(struct rand_data * ec,unsigned int bits,unsigned int min)340 static __u64 jent_loop_shuffle(struct rand_data *ec,
341 unsigned int bits, unsigned int min)
342 {
343 __u64 time = 0;
344 __u64 shuffle = 0;
345 unsigned int i = 0;
346 unsigned int mask = (1<<bits) - 1;
347
348 jent_get_nstime(&time);
349 /*
350 * Mix the current state of the random number into the shuffle
351 * calculation to balance that shuffle a bit more.
352 */
353 if (ec)
354 time ^= ec->data;
355 /*
356 * We fold the time value as much as possible to ensure that as many
357 * bits of the time stamp are included as possible.
358 */
359 for (i = 0; ((DATA_SIZE_BITS + bits - 1) / bits) > i; i++) {
360 shuffle ^= time & mask;
361 time = time >> bits;
362 }
363
364 /*
365 * We add a lower boundary value to ensure we have a minimum
366 * RNG loop count.
367 */
368 return (shuffle + (1<<min));
369 }
370
371 /**
372 * CPU Jitter noise source -- this is the noise source based on the CPU
373 * execution time jitter
374 *
375 * This function injects the individual bits of the time value into the
376 * entropy pool using an LFSR.
377 *
378 * The code is deliberately inefficient with respect to the bit shifting
379 * and shall stay that way. This function is the root cause why the code
380 * shall be compiled without optimization. This function not only acts as
381 * folding operation, but this function's execution is used to measure
382 * the CPU execution time jitter. Any change to the loop in this function
383 * implies that careful retesting must be done.
384 *
385 * @ec [in] entropy collector struct
386 * @time [in] time stamp to be injected
387 * @loop_cnt [in] if a value not equal to 0 is set, use the given value as
388 * number of loops to perform the folding
389 * @stuck [in] Is the time stamp identified as stuck?
390 *
391 * Output:
392 * updated ec->data
393 *
394 * @return Number of loops the folding operation is performed
395 */
jent_lfsr_time(struct rand_data * ec,__u64 time,__u64 loop_cnt,int stuck)396 static void jent_lfsr_time(struct rand_data *ec, __u64 time, __u64 loop_cnt,
397 int stuck)
398 {
399 unsigned int i;
400 __u64 j = 0;
401 __u64 new = 0;
402 #define MAX_FOLD_LOOP_BIT 4
403 #define MIN_FOLD_LOOP_BIT 0
404 __u64 fold_loop_cnt =
405 jent_loop_shuffle(ec, MAX_FOLD_LOOP_BIT, MIN_FOLD_LOOP_BIT);
406
407 /*
408 * testing purposes -- allow test app to set the counter, not
409 * needed during runtime
410 */
411 if (loop_cnt)
412 fold_loop_cnt = loop_cnt;
413 for (j = 0; j < fold_loop_cnt; j++) {
414 new = ec->data;
415 for (i = 1; (DATA_SIZE_BITS) >= i; i++) {
416 __u64 tmp = time << (DATA_SIZE_BITS - i);
417
418 tmp = tmp >> (DATA_SIZE_BITS - 1);
419
420 /*
421 * Fibonacci LSFR with polynomial of
422 * x^64 + x^61 + x^56 + x^31 + x^28 + x^23 + 1 which is
423 * primitive according to
424 * http://poincare.matf.bg.ac.rs/~ezivkovm/publications/primpol1.pdf
425 * (the shift values are the polynomial values minus one
426 * due to counting bits from 0 to 63). As the current
427 * position is always the LSB, the polynomial only needs
428 * to shift data in from the left without wrap.
429 */
430 tmp ^= ((new >> 63) & 1);
431 tmp ^= ((new >> 60) & 1);
432 tmp ^= ((new >> 55) & 1);
433 tmp ^= ((new >> 30) & 1);
434 tmp ^= ((new >> 27) & 1);
435 tmp ^= ((new >> 22) & 1);
436 new <<= 1;
437 new ^= tmp;
438 }
439 }
440
441 /*
442 * If the time stamp is stuck, do not finally insert the value into
443 * the entropy pool. Although this operation should not do any harm
444 * even when the time stamp has no entropy, SP800-90B requires that
445 * any conditioning operation (SP800-90B considers the LFSR to be a
446 * conditioning operation) to have an identical amount of input
447 * data according to section 3.1.5.
448 */
449 if (!stuck)
450 ec->data = new;
451 }
452
453 /**
454 * Memory Access noise source -- this is a noise source based on variations in
455 * memory access times
456 *
457 * This function performs memory accesses which will add to the timing
458 * variations due to an unknown amount of CPU wait states that need to be
459 * added when accessing memory. The memory size should be larger than the L1
460 * caches as outlined in the documentation and the associated testing.
461 *
462 * The L1 cache has a very high bandwidth, albeit its access rate is usually
463 * slower than accessing CPU registers. Therefore, L1 accesses only add minimal
464 * variations as the CPU has hardly to wait. Starting with L2, significant
465 * variations are added because L2 typically does not belong to the CPU any more
466 * and therefore a wider range of CPU wait states is necessary for accesses.
467 * L3 and real memory accesses have even a wider range of wait states. However,
468 * to reliably access either L3 or memory, the ec->mem memory must be quite
469 * large which is usually not desirable.
470 *
471 * @ec [in] Reference to the entropy collector with the memory access data -- if
472 * the reference to the memory block to be accessed is NULL, this noise
473 * source is disabled
474 * @loop_cnt [in] if a value not equal to 0 is set, use the given value
475 * number of loops to perform the LFSR
476 */
jent_memaccess(struct rand_data * ec,__u64 loop_cnt)477 static void jent_memaccess(struct rand_data *ec, __u64 loop_cnt)
478 {
479 unsigned int wrap = 0;
480 __u64 i = 0;
481 #define MAX_ACC_LOOP_BIT 7
482 #define MIN_ACC_LOOP_BIT 0
483 __u64 acc_loop_cnt =
484 jent_loop_shuffle(ec, MAX_ACC_LOOP_BIT, MIN_ACC_LOOP_BIT);
485
486 if (NULL == ec || NULL == ec->mem)
487 return;
488 wrap = ec->memblocksize * ec->memblocks;
489
490 /*
491 * testing purposes -- allow test app to set the counter, not
492 * needed during runtime
493 */
494 if (loop_cnt)
495 acc_loop_cnt = loop_cnt;
496
497 for (i = 0; i < (ec->memaccessloops + acc_loop_cnt); i++) {
498 unsigned char *tmpval = ec->mem + ec->memlocation;
499 /*
500 * memory access: just add 1 to one byte,
501 * wrap at 255 -- memory access implies read
502 * from and write to memory location
503 */
504 *tmpval = (*tmpval + 1) & 0xff;
505 /*
506 * Addition of memblocksize - 1 to pointer
507 * with wrap around logic to ensure that every
508 * memory location is hit evenly
509 */
510 ec->memlocation = ec->memlocation + ec->memblocksize - 1;
511 ec->memlocation = ec->memlocation % wrap;
512 }
513 }
514
515 /***************************************************************************
516 * Start of entropy processing logic
517 ***************************************************************************/
518 /**
519 * This is the heart of the entropy generation: calculate time deltas and
520 * use the CPU jitter in the time deltas. The jitter is injected into the
521 * entropy pool.
522 *
523 * WARNING: ensure that ->prev_time is primed before using the output
524 * of this function! This can be done by calling this function
525 * and not using its result.
526 *
527 * @ec [in] Reference to entropy collector
528 *
529 * @return result of stuck test
530 */
jent_measure_jitter(struct rand_data * ec)531 static int jent_measure_jitter(struct rand_data *ec)
532 {
533 __u64 time = 0;
534 __u64 current_delta = 0;
535 int stuck;
536
537 /* Invoke one noise source before time measurement to add variations */
538 jent_memaccess(ec, 0);
539
540 /*
541 * Get time stamp and calculate time delta to previous
542 * invocation to measure the timing variations
543 */
544 jent_get_nstime(&time);
545 current_delta = jent_delta(ec->prev_time, time);
546 ec->prev_time = time;
547
548 /* Check whether we have a stuck measurement. */
549 stuck = jent_stuck(ec, current_delta);
550
551 /* Now call the next noise sources which also injects the data */
552 jent_lfsr_time(ec, current_delta, 0, stuck);
553
554 return stuck;
555 }
556
557 /**
558 * Generator of one 64 bit random number
559 * Function fills rand_data->data
560 *
561 * @ec [in] Reference to entropy collector
562 */
jent_gen_entropy(struct rand_data * ec)563 static void jent_gen_entropy(struct rand_data *ec)
564 {
565 unsigned int k = 0, safety_factor = 0;
566
567 if (fips_enabled)
568 safety_factor = JENT_ENTROPY_SAFETY_FACTOR;
569
570 /* priming of the ->prev_time value */
571 jent_measure_jitter(ec);
572
573 while (1) {
574 /* If a stuck measurement is received, repeat measurement */
575 if (jent_measure_jitter(ec))
576 continue;
577
578 /*
579 * We multiply the loop value with ->osr to obtain the
580 * oversampling rate requested by the caller
581 */
582 if (++k >= ((DATA_SIZE_BITS + safety_factor) * ec->osr))
583 break;
584 }
585 }
586
587 /**
588 * Entry function: Obtain entropy for the caller.
589 *
590 * This function invokes the entropy gathering logic as often to generate
591 * as many bytes as requested by the caller. The entropy gathering logic
592 * creates 64 bit per invocation.
593 *
594 * This function truncates the last 64 bit entropy value output to the exact
595 * size specified by the caller.
596 *
597 * @ec [in] Reference to entropy collector
598 * @data [in] pointer to buffer for storing random data -- buffer must already
599 * exist
600 * @len [in] size of the buffer, specifying also the requested number of random
601 * in bytes
602 *
603 * @return 0 when request is fulfilled or an error
604 *
605 * The following error codes can occur:
606 * -1 entropy_collector is NULL
607 * -2 RCT failed
608 * -3 APT test failed
609 */
jent_read_entropy(struct rand_data * ec,unsigned char * data,unsigned int len)610 int jent_read_entropy(struct rand_data *ec, unsigned char *data,
611 unsigned int len)
612 {
613 unsigned char *p = data;
614
615 if (!ec)
616 return -1;
617
618 while (len > 0) {
619 unsigned int tocopy;
620
621 jent_gen_entropy(ec);
622
623 if (jent_health_failure(ec)) {
624 int ret;
625
626 if (jent_rct_failure(ec))
627 ret = -2;
628 else
629 ret = -3;
630
631 /*
632 * Re-initialize the noise source
633 *
634 * If the health test fails, the Jitter RNG remains
635 * in failure state and will return a health failure
636 * during next invocation.
637 */
638 if (jent_entropy_init())
639 return ret;
640
641 /* Set APT to initial state */
642 jent_apt_reset(ec, 0);
643 ec->apt_base_set = 0;
644
645 /* Set RCT to initial state */
646 ec->rct_count = 0;
647
648 /* Re-enable Jitter RNG */
649 ec->health_failure = 0;
650
651 /*
652 * Return the health test failure status to the
653 * caller as the generated value is not appropriate.
654 */
655 return ret;
656 }
657
658 if ((DATA_SIZE_BITS / 8) < len)
659 tocopy = (DATA_SIZE_BITS / 8);
660 else
661 tocopy = len;
662 jent_memcpy(p, &ec->data, tocopy);
663
664 len -= tocopy;
665 p += tocopy;
666 }
667
668 return 0;
669 }
670
671 /***************************************************************************
672 * Initialization logic
673 ***************************************************************************/
674
jent_entropy_collector_alloc(unsigned int osr,unsigned int flags)675 struct rand_data *jent_entropy_collector_alloc(unsigned int osr,
676 unsigned int flags)
677 {
678 struct rand_data *entropy_collector;
679
680 entropy_collector = jent_zalloc(sizeof(struct rand_data));
681 if (!entropy_collector)
682 return NULL;
683
684 if (!(flags & JENT_DISABLE_MEMORY_ACCESS)) {
685 /* Allocate memory for adding variations based on memory
686 * access
687 */
688 entropy_collector->mem = jent_zalloc(JENT_MEMORY_SIZE);
689 if (!entropy_collector->mem) {
690 jent_zfree(entropy_collector);
691 return NULL;
692 }
693 entropy_collector->memblocksize = JENT_MEMORY_BLOCKSIZE;
694 entropy_collector->memblocks = JENT_MEMORY_BLOCKS;
695 entropy_collector->memaccessloops = JENT_MEMORY_ACCESSLOOPS;
696 }
697
698 /* verify and set the oversampling rate */
699 if (osr == 0)
700 osr = 1; /* minimum sampling rate is 1 */
701 entropy_collector->osr = osr;
702
703 /* fill the data pad with non-zero values */
704 jent_gen_entropy(entropy_collector);
705
706 return entropy_collector;
707 }
708
jent_entropy_collector_free(struct rand_data * entropy_collector)709 void jent_entropy_collector_free(struct rand_data *entropy_collector)
710 {
711 jent_zfree(entropy_collector->mem);
712 entropy_collector->mem = NULL;
713 jent_zfree(entropy_collector);
714 }
715
jent_entropy_init(void)716 int jent_entropy_init(void)
717 {
718 int i;
719 __u64 delta_sum = 0;
720 __u64 old_delta = 0;
721 unsigned int nonstuck = 0;
722 int time_backwards = 0;
723 int count_mod = 0;
724 int count_stuck = 0;
725 struct rand_data ec = { 0 };
726
727 /* Required for RCT */
728 ec.osr = 1;
729
730 /* We could perform statistical tests here, but the problem is
731 * that we only have a few loop counts to do testing. These
732 * loop counts may show some slight skew and we produce
733 * false positives.
734 *
735 * Moreover, only old systems show potentially problematic
736 * jitter entropy that could potentially be caught here. But
737 * the RNG is intended for hardware that is available or widely
738 * used, but not old systems that are long out of favor. Thus,
739 * no statistical tests.
740 */
741
742 /*
743 * We could add a check for system capabilities such as clock_getres or
744 * check for CONFIG_X86_TSC, but it does not make much sense as the
745 * following sanity checks verify that we have a high-resolution
746 * timer.
747 */
748 /*
749 * TESTLOOPCOUNT needs some loops to identify edge systems. 100 is
750 * definitely too little.
751 *
752 * SP800-90B requires at least 1024 initial test cycles.
753 */
754 #define TESTLOOPCOUNT 1024
755 #define CLEARCACHE 100
756 for (i = 0; (TESTLOOPCOUNT + CLEARCACHE) > i; i++) {
757 __u64 time = 0;
758 __u64 time2 = 0;
759 __u64 delta = 0;
760 unsigned int lowdelta = 0;
761 int stuck;
762
763 /* Invoke core entropy collection logic */
764 jent_get_nstime(&time);
765 ec.prev_time = time;
766 jent_lfsr_time(&ec, time, 0, 0);
767 jent_get_nstime(&time2);
768
769 /* test whether timer works */
770 if (!time || !time2)
771 return JENT_ENOTIME;
772 delta = jent_delta(time, time2);
773 /*
774 * test whether timer is fine grained enough to provide
775 * delta even when called shortly after each other -- this
776 * implies that we also have a high resolution timer
777 */
778 if (!delta)
779 return JENT_ECOARSETIME;
780
781 stuck = jent_stuck(&ec, delta);
782
783 /*
784 * up to here we did not modify any variable that will be
785 * evaluated later, but we already performed some work. Thus we
786 * already have had an impact on the caches, branch prediction,
787 * etc. with the goal to clear it to get the worst case
788 * measurements.
789 */
790 if (i < CLEARCACHE)
791 continue;
792
793 if (stuck)
794 count_stuck++;
795 else {
796 nonstuck++;
797
798 /*
799 * Ensure that the APT succeeded.
800 *
801 * With the check below that count_stuck must be less
802 * than 10% of the overall generated raw entropy values
803 * it is guaranteed that the APT is invoked at
804 * floor((TESTLOOPCOUNT * 0.9) / 64) == 14 times.
805 */
806 if ((nonstuck % JENT_APT_WINDOW_SIZE) == 0) {
807 jent_apt_reset(&ec,
808 delta & JENT_APT_WORD_MASK);
809 if (jent_health_failure(&ec))
810 return JENT_EHEALTH;
811 }
812 }
813
814 /* Validate RCT */
815 if (jent_rct_failure(&ec))
816 return JENT_ERCT;
817
818 /* test whether we have an increasing timer */
819 if (!(time2 > time))
820 time_backwards++;
821
822 /* use 32 bit value to ensure compilation on 32 bit arches */
823 lowdelta = time2 - time;
824 if (!(lowdelta % 100))
825 count_mod++;
826
827 /*
828 * ensure that we have a varying delta timer which is necessary
829 * for the calculation of entropy -- perform this check
830 * only after the first loop is executed as we need to prime
831 * the old_data value
832 */
833 if (delta > old_delta)
834 delta_sum += (delta - old_delta);
835 else
836 delta_sum += (old_delta - delta);
837 old_delta = delta;
838 }
839
840 /*
841 * we allow up to three times the time running backwards.
842 * CLOCK_REALTIME is affected by adjtime and NTP operations. Thus,
843 * if such an operation just happens to interfere with our test, it
844 * should not fail. The value of 3 should cover the NTP case being
845 * performed during our test run.
846 */
847 if (time_backwards > 3)
848 return JENT_ENOMONOTONIC;
849
850 /*
851 * Variations of deltas of time must on average be larger
852 * than 1 to ensure the entropy estimation
853 * implied with 1 is preserved
854 */
855 if ((delta_sum) <= 1)
856 return JENT_EVARVAR;
857
858 /*
859 * Ensure that we have variations in the time stamp below 10 for at
860 * least 10% of all checks -- on some platforms, the counter increments
861 * in multiples of 100, but not always
862 */
863 if ((TESTLOOPCOUNT/10 * 9) < count_mod)
864 return JENT_ECOARSETIME;
865
866 /*
867 * If we have more than 90% stuck results, then this Jitter RNG is
868 * likely to not work well.
869 */
870 if ((TESTLOOPCOUNT/10 * 9) < count_stuck)
871 return JENT_ESTUCK;
872
873 return 0;
874 }
875