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 - 2023
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 3.4.0 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 typedef unsigned char u8;
61 #define NULL ((void *) 0)
62
63 /* The entropy pool */
64 struct rand_data {
65 /* SHA3-256 is used as conditioner */
66 #define DATA_SIZE_BITS 256
67 /* all data values that are vital to maintain the security
68 * of the RNG are marked as SENSITIVE. A user must not
69 * access that information while the RNG executes its loops to
70 * calculate the next random value. */
71 struct sha3_ctx *hash_state; /* SENSITIVE hash state entropy pool */
72 __u64 prev_time; /* SENSITIVE Previous time stamp */
73 __u64 last_delta; /* SENSITIVE stuck test */
74 __s64 last_delta2; /* SENSITIVE stuck test */
75
76 unsigned int flags; /* Flags used to initialize */
77 unsigned int osr; /* Oversample rate */
78 #define JENT_MEMORY_ACCESSLOOPS 128
79 #define JENT_MEMORY_SIZE \
80 (CONFIG_CRYPTO_JITTERENTROPY_MEMORY_BLOCKS * \
81 CONFIG_CRYPTO_JITTERENTROPY_MEMORY_BLOCKSIZE)
82 unsigned char *mem; /* Memory access location with size of
83 * memblocks * memblocksize */
84 unsigned int memlocation; /* Pointer to byte in *mem */
85 unsigned int memblocks; /* Number of memory blocks in *mem */
86 unsigned int memblocksize; /* Size of one memory block in bytes */
87 unsigned int memaccessloops; /* Number of memory accesses per random
88 * bit generation */
89
90 /* Repetition Count Test */
91 unsigned int rct_count; /* Number of stuck values */
92
93 /* Adaptive Proportion Test cutoff values */
94 unsigned int apt_cutoff; /* Intermittent health test failure */
95 unsigned int apt_cutoff_permanent; /* Permanent health test failure */
96 #define JENT_APT_WINDOW_SIZE 512 /* Data window size */
97 /* LSB of time stamp to process */
98 #define JENT_APT_LSB 16
99 #define JENT_APT_WORD_MASK (JENT_APT_LSB - 1)
100 unsigned int apt_observations; /* Number of collected observations */
101 unsigned int apt_count; /* APT counter */
102 unsigned int apt_base; /* APT base reference */
103 unsigned int health_failure; /* Record health failure */
104
105 unsigned int apt_base_set:1; /* APT base reference set? */
106 };
107
108 /* Flags that can be used to initialize the RNG */
109 #define JENT_DISABLE_MEMORY_ACCESS (1<<2) /* Disable memory access for more
110 * entropy, saves MEMORY_SIZE RAM for
111 * entropy collector */
112
113 /* -- error codes for init function -- */
114 #define JENT_ENOTIME 1 /* Timer service not available */
115 #define JENT_ECOARSETIME 2 /* Timer too coarse for RNG */
116 #define JENT_ENOMONOTONIC 3 /* Timer is not monotonic increasing */
117 #define JENT_EVARVAR 5 /* Timer does not produce variations of
118 * variations (2nd derivation of time is
119 * zero). */
120 #define JENT_ESTUCK 8 /* Too many stuck results during init. */
121 #define JENT_EHEALTH 9 /* Health test failed during initialization */
122 #define JENT_ERCT 10 /* RCT failed during initialization */
123 #define JENT_EHASH 11 /* Hash self test failed */
124 #define JENT_EMEM 12 /* Can't allocate memory for initialization */
125
126 #define JENT_RCT_FAILURE 1 /* Failure in RCT health test. */
127 #define JENT_APT_FAILURE 2 /* Failure in APT health test. */
128 #define JENT_PERMANENT_FAILURE_SHIFT 16
129 #define JENT_PERMANENT_FAILURE(x) (x << JENT_PERMANENT_FAILURE_SHIFT)
130 #define JENT_RCT_FAILURE_PERMANENT JENT_PERMANENT_FAILURE(JENT_RCT_FAILURE)
131 #define JENT_APT_FAILURE_PERMANENT JENT_PERMANENT_FAILURE(JENT_APT_FAILURE)
132
133 /*
134 * The output n bits can receive more than n bits of min entropy, of course,
135 * but the fixed output of the conditioning function can only asymptotically
136 * approach the output size bits of min entropy, not attain that bound. Random
137 * maps will tend to have output collisions, which reduces the creditable
138 * output entropy (that is what SP 800-90B Section 3.1.5.1.2 attempts to bound).
139 *
140 * The value "64" is justified in Appendix A.4 of the current 90C draft,
141 * and aligns with NIST's in "epsilon" definition in this document, which is
142 * that a string can be considered "full entropy" if you can bound the min
143 * entropy in each bit of output to at least 1-epsilon, where epsilon is
144 * required to be <= 2^(-32).
145 */
146 #define JENT_ENTROPY_SAFETY_FACTOR 64
147
148 #include <linux/array_size.h>
149 #include <linux/fips.h>
150 #include <linux/minmax.h>
151 #include "jitterentropy.h"
152
153 /***************************************************************************
154 * Adaptive Proportion Test
155 *
156 * This test complies with SP800-90B section 4.4.2.
157 ***************************************************************************/
158
159 /*
160 * See the SP 800-90B comment #10b for the corrected cutoff for the SP 800-90B
161 * APT.
162 * https://www.untruth.org/~josh/sp80090b/UL%20SP800-90B-final%20comments%20v1.9%2020191212.pdf
163 * In the syntax of R, this is C = 2 + qbinom(1 − 2^(−30), 511, 2^(-1/osr)).
164 * (The original formula wasn't correct because the first symbol must
165 * necessarily have been observed, so there is no chance of observing 0 of these
166 * symbols.)
167 *
168 * For the alpha < 2^-53, R cannot be used as it uses a float data type without
169 * arbitrary precision. A SageMath script is used to calculate those cutoff
170 * values.
171 *
172 * For any value above 14, this yields the maximal allowable value of 512
173 * (by FIPS 140-2 IG 7.19 Resolution # 16, we cannot choose a cutoff value that
174 * renders the test unable to fail).
175 */
176 static const unsigned int jent_apt_cutoff_lookup[15] = {
177 325, 422, 459, 477, 488, 494, 499, 502,
178 505, 507, 508, 509, 510, 511, 512 };
179 static const unsigned int jent_apt_cutoff_permanent_lookup[15] = {
180 355, 447, 479, 494, 502, 507, 510, 512,
181 512, 512, 512, 512, 512, 512, 512 };
182
jent_apt_init(struct rand_data * ec,unsigned int osr)183 static void jent_apt_init(struct rand_data *ec, unsigned int osr)
184 {
185 /*
186 * Establish the apt_cutoff based on the presumed entropy rate of
187 * 1/osr.
188 */
189 if (osr >= ARRAY_SIZE(jent_apt_cutoff_lookup)) {
190 ec->apt_cutoff = jent_apt_cutoff_lookup[
191 ARRAY_SIZE(jent_apt_cutoff_lookup) - 1];
192 ec->apt_cutoff_permanent = jent_apt_cutoff_permanent_lookup[
193 ARRAY_SIZE(jent_apt_cutoff_permanent_lookup) - 1];
194 } else {
195 ec->apt_cutoff = jent_apt_cutoff_lookup[osr - 1];
196 ec->apt_cutoff_permanent =
197 jent_apt_cutoff_permanent_lookup[osr - 1];
198 }
199 }
200 /*
201 * Reset the APT counter
202 *
203 * @ec [in] Reference to entropy collector
204 */
jent_apt_reset(struct rand_data * ec,unsigned int delta_masked)205 static void jent_apt_reset(struct rand_data *ec, unsigned int delta_masked)
206 {
207 /* Reset APT counter */
208 ec->apt_count = 0;
209 ec->apt_base = delta_masked;
210 ec->apt_observations = 0;
211 }
212
213 /*
214 * Insert a new entropy event into APT
215 *
216 * @ec [in] Reference to entropy collector
217 * @delta_masked [in] Masked time delta to process
218 */
jent_apt_insert(struct rand_data * ec,unsigned int delta_masked)219 static void jent_apt_insert(struct rand_data *ec, unsigned int delta_masked)
220 {
221 /* Initialize the base reference */
222 if (!ec->apt_base_set) {
223 ec->apt_base = delta_masked;
224 ec->apt_base_set = 1;
225 return;
226 }
227
228 if (delta_masked == ec->apt_base) {
229 ec->apt_count++;
230
231 /* Note, ec->apt_count starts with one. */
232 if (ec->apt_count >= ec->apt_cutoff_permanent)
233 ec->health_failure |= JENT_APT_FAILURE_PERMANENT;
234 else if (ec->apt_count >= ec->apt_cutoff)
235 ec->health_failure |= JENT_APT_FAILURE;
236 }
237
238 ec->apt_observations++;
239
240 if (ec->apt_observations >= JENT_APT_WINDOW_SIZE)
241 jent_apt_reset(ec, delta_masked);
242 }
243
244 /***************************************************************************
245 * Stuck Test and its use as Repetition Count Test
246 *
247 * The Jitter RNG uses an enhanced version of the Repetition Count Test
248 * (RCT) specified in SP800-90B section 4.4.1. Instead of counting identical
249 * back-to-back values, the input to the RCT is the counting of the stuck
250 * values during the generation of one Jitter RNG output block.
251 *
252 * The RCT is applied with an alpha of 2^{-30} compliant to FIPS 140-2 IG 9.8.
253 *
254 * During the counting operation, the Jitter RNG always calculates the RCT
255 * cut-off value of C. If that value exceeds the allowed cut-off value,
256 * the Jitter RNG output block will be calculated completely but discarded at
257 * the end. The caller of the Jitter RNG is informed with an error code.
258 ***************************************************************************/
259
260 /*
261 * Repetition Count Test as defined in SP800-90B section 4.4.1
262 *
263 * @ec [in] Reference to entropy collector
264 * @stuck [in] Indicator whether the value is stuck
265 */
jent_rct_insert(struct rand_data * ec,int stuck)266 static void jent_rct_insert(struct rand_data *ec, int stuck)
267 {
268 if (stuck) {
269 ec->rct_count++;
270
271 /*
272 * The cutoff value is based on the following consideration:
273 * alpha = 2^-30 or 2^-60 as recommended in SP800-90B.
274 * In addition, we require an entropy value H of 1/osr as this
275 * is the minimum entropy required to provide full entropy.
276 * Note, we collect (DATA_SIZE_BITS + ENTROPY_SAFETY_FACTOR)*osr
277 * deltas for inserting them into the entropy pool which should
278 * then have (close to) DATA_SIZE_BITS bits of entropy in the
279 * conditioned output.
280 *
281 * Note, ec->rct_count (which equals to value B in the pseudo
282 * code of SP800-90B section 4.4.1) starts with zero. Hence
283 * we need to subtract one from the cutoff value as calculated
284 * following SP800-90B. Thus C = ceil(-log_2(alpha)/H) = 30*osr
285 * or 60*osr.
286 */
287 if ((unsigned int)ec->rct_count >= (60 * ec->osr)) {
288 ec->rct_count = -1;
289 ec->health_failure |= JENT_RCT_FAILURE_PERMANENT;
290 } else if ((unsigned int)ec->rct_count >= (30 * ec->osr)) {
291 ec->rct_count = -1;
292 ec->health_failure |= JENT_RCT_FAILURE;
293 }
294 } else {
295 /* Reset RCT */
296 ec->rct_count = 0;
297 }
298 }
299
jent_delta(__u64 prev,__u64 next)300 static inline __u64 jent_delta(__u64 prev, __u64 next)
301 {
302 #define JENT_UINT64_MAX (__u64)(~((__u64) 0))
303 return (prev < next) ? (next - prev) :
304 (JENT_UINT64_MAX - prev + 1 + next);
305 }
306
307 /*
308 * Stuck test by checking the:
309 * 1st derivative of the jitter measurement (time delta)
310 * 2nd derivative of the jitter measurement (delta of time deltas)
311 * 3rd derivative of the jitter measurement (delta of delta of time deltas)
312 *
313 * All values must always be non-zero.
314 *
315 * @ec [in] Reference to entropy collector
316 * @current_delta [in] Jitter time delta
317 *
318 * @return
319 * 0 jitter measurement not stuck (good bit)
320 * 1 jitter measurement stuck (reject bit)
321 */
jent_stuck(struct rand_data * ec,__u64 current_delta)322 static int jent_stuck(struct rand_data *ec, __u64 current_delta)
323 {
324 __u64 delta2 = jent_delta(ec->last_delta, current_delta);
325 __u64 delta3 = jent_delta(ec->last_delta2, delta2);
326
327 ec->last_delta = current_delta;
328 ec->last_delta2 = delta2;
329
330 /*
331 * Insert the result of the comparison of two back-to-back time
332 * deltas.
333 */
334 jent_apt_insert(ec, current_delta);
335
336 if (!current_delta || !delta2 || !delta3) {
337 /* RCT with a stuck bit */
338 jent_rct_insert(ec, 1);
339 return 1;
340 }
341
342 /* RCT with a non-stuck bit */
343 jent_rct_insert(ec, 0);
344
345 return 0;
346 }
347
348 /*
349 * Report any health test failures
350 *
351 * @ec [in] Reference to entropy collector
352 *
353 * @return a bitmask indicating which tests failed
354 * 0 No health test failure
355 * 1 RCT failure
356 * 2 APT failure
357 * 1<<JENT_PERMANENT_FAILURE_SHIFT RCT permanent failure
358 * 2<<JENT_PERMANENT_FAILURE_SHIFT APT permanent failure
359 */
jent_health_failure(struct rand_data * ec)360 static unsigned int jent_health_failure(struct rand_data *ec)
361 {
362 /* Test is only enabled in FIPS mode */
363 if (!fips_enabled)
364 return 0;
365
366 return ec->health_failure;
367 }
368
369 /***************************************************************************
370 * Noise sources
371 ***************************************************************************/
372
373 /*
374 * Update of the loop count used for the next round of
375 * an entropy collection.
376 *
377 * Input:
378 * @bits is the number of low bits of the timer to consider
379 * @min is the number of bits we shift the timer value to the right at
380 * the end to make sure we have a guaranteed minimum value
381 *
382 * @return Newly calculated loop counter
383 */
jent_loop_shuffle(unsigned int bits,unsigned int min)384 static __u64 jent_loop_shuffle(unsigned int bits, unsigned int min)
385 {
386 __u64 time = 0;
387 __u64 shuffle = 0;
388 unsigned int i = 0;
389 unsigned int mask = (1<<bits) - 1;
390
391 jent_get_nstime(&time);
392
393 /*
394 * We fold the time value as much as possible to ensure that as many
395 * bits of the time stamp are included as possible.
396 */
397 for (i = 0; ((DATA_SIZE_BITS + bits - 1) / bits) > i; i++) {
398 shuffle ^= time & mask;
399 time = time >> bits;
400 }
401
402 /*
403 * We add a lower boundary value to ensure we have a minimum
404 * RNG loop count.
405 */
406 return (shuffle + (1<<min));
407 }
408
409 /*
410 * CPU Jitter noise source -- this is the noise source based on the CPU
411 * execution time jitter
412 *
413 * This function injects the individual bits of the time value into the
414 * entropy pool using a hash.
415 *
416 * ec [in] entropy collector
417 * time [in] time stamp to be injected
418 * stuck [in] Is the time stamp identified as stuck?
419 *
420 * Output: updated hash context in the entropy collector
421 */
jent_condition_data(struct rand_data * ec,__u64 time,int stuck)422 static void jent_condition_data(struct rand_data *ec, __u64 time, int stuck)
423 {
424 #define SHA3_HASH_LOOP (1<<3)
425 struct {
426 int rct_count;
427 unsigned int apt_observations;
428 unsigned int apt_count;
429 unsigned int apt_base;
430 } addtl = {
431 ec->rct_count,
432 ec->apt_observations,
433 ec->apt_count,
434 ec->apt_base
435 };
436
437 jent_hash_time(ec->hash_state, time, (u8 *)&addtl, sizeof(addtl),
438 SHA3_HASH_LOOP, stuck);
439 }
440
441 /*
442 * Memory Access noise source -- this is a noise source based on variations in
443 * memory access times
444 *
445 * This function performs memory accesses which will add to the timing
446 * variations due to an unknown amount of CPU wait states that need to be
447 * added when accessing memory. The memory size should be larger than the L1
448 * caches as outlined in the documentation and the associated testing.
449 *
450 * The L1 cache has a very high bandwidth, albeit its access rate is usually
451 * slower than accessing CPU registers. Therefore, L1 accesses only add minimal
452 * variations as the CPU has hardly to wait. Starting with L2, significant
453 * variations are added because L2 typically does not belong to the CPU any more
454 * and therefore a wider range of CPU wait states is necessary for accesses.
455 * L3 and real memory accesses have even a wider range of wait states. However,
456 * to reliably access either L3 or memory, the ec->mem memory must be quite
457 * large which is usually not desirable.
458 *
459 * @ec [in] Reference to the entropy collector with the memory access data -- if
460 * the reference to the memory block to be accessed is NULL, this noise
461 * source is disabled
462 * @loop_cnt [in] if a value not equal to 0 is set, use the given value
463 * number of loops to perform the LFSR
464 */
jent_memaccess(struct rand_data * ec,__u64 loop_cnt)465 static void jent_memaccess(struct rand_data *ec, __u64 loop_cnt)
466 {
467 unsigned int wrap = 0;
468 __u64 i = 0;
469 #define MAX_ACC_LOOP_BIT 7
470 #define MIN_ACC_LOOP_BIT 0
471 __u64 acc_loop_cnt =
472 jent_loop_shuffle(MAX_ACC_LOOP_BIT, MIN_ACC_LOOP_BIT);
473
474 if (NULL == ec || NULL == ec->mem)
475 return;
476 wrap = ec->memblocksize * ec->memblocks;
477
478 /*
479 * testing purposes -- allow test app to set the counter, not
480 * needed during runtime
481 */
482 if (loop_cnt)
483 acc_loop_cnt = loop_cnt;
484
485 for (i = 0; i < (ec->memaccessloops + acc_loop_cnt); i++) {
486 unsigned char *tmpval = ec->mem + ec->memlocation;
487 /*
488 * memory access: just add 1 to one byte,
489 * wrap at 255 -- memory access implies read
490 * from and write to memory location
491 */
492 *tmpval = (*tmpval + 1) & 0xff;
493 /*
494 * Addition of memblocksize - 1 to pointer
495 * with wrap around logic to ensure that every
496 * memory location is hit evenly
497 */
498 ec->memlocation = ec->memlocation + ec->memblocksize - 1;
499 ec->memlocation = ec->memlocation % wrap;
500 }
501 }
502
503 /***************************************************************************
504 * Start of entropy processing logic
505 ***************************************************************************/
506 /*
507 * This is the heart of the entropy generation: calculate time deltas and
508 * use the CPU jitter in the time deltas. The jitter is injected into the
509 * entropy pool.
510 *
511 * WARNING: ensure that ->prev_time is primed before using the output
512 * of this function! This can be done by calling this function
513 * and not using its result.
514 *
515 * @ec [in] Reference to entropy collector
516 *
517 * @return result of stuck test
518 */
jent_measure_jitter(struct rand_data * ec,__u64 * ret_current_delta)519 static int jent_measure_jitter(struct rand_data *ec, __u64 *ret_current_delta)
520 {
521 __u64 time = 0;
522 __u64 current_delta = 0;
523 int stuck;
524
525 /* Invoke one noise source before time measurement to add variations */
526 jent_memaccess(ec, 0);
527
528 /*
529 * Get time stamp and calculate time delta to previous
530 * invocation to measure the timing variations
531 */
532 jent_get_nstime(&time);
533 current_delta = jent_delta(ec->prev_time, time);
534 ec->prev_time = time;
535
536 /* Check whether we have a stuck measurement. */
537 stuck = jent_stuck(ec, current_delta);
538
539 /* Now call the next noise sources which also injects the data */
540 jent_condition_data(ec, current_delta, stuck);
541
542 /* return the raw entropy value */
543 if (ret_current_delta)
544 *ret_current_delta = current_delta;
545
546 return stuck;
547 }
548
549 /*
550 * Generator of one 64 bit random number
551 * Function fills rand_data->hash_state
552 *
553 * @ec [in] Reference to entropy collector
554 */
jent_gen_entropy(struct rand_data * ec)555 static void jent_gen_entropy(struct rand_data *ec)
556 {
557 unsigned int k = 0, safety_factor = 0;
558
559 if (fips_enabled)
560 safety_factor = JENT_ENTROPY_SAFETY_FACTOR;
561
562 /* priming of the ->prev_time value */
563 jent_measure_jitter(ec, NULL);
564
565 while (!jent_health_failure(ec)) {
566 /* If a stuck measurement is received, repeat measurement */
567 if (jent_measure_jitter(ec, NULL))
568 continue;
569
570 /*
571 * We multiply the loop value with ->osr to obtain the
572 * oversampling rate requested by the caller
573 */
574 if (++k >= ((DATA_SIZE_BITS + safety_factor) * ec->osr))
575 break;
576 }
577 }
578
579 /*
580 * Entry function: Obtain entropy for the caller.
581 *
582 * This function invokes the entropy gathering logic as often to generate
583 * as many bytes as requested by the caller. The entropy gathering logic
584 * creates 64 bit per invocation.
585 *
586 * This function truncates the last 64 bit entropy value output to the exact
587 * size specified by the caller.
588 *
589 * @ec [in] Reference to entropy collector
590 * @data [in] pointer to buffer for storing random data -- buffer must already
591 * exist
592 * @len [in] size of the buffer, specifying also the requested number of random
593 * in bytes
594 *
595 * @return 0 when request is fulfilled or an error
596 *
597 * The following error codes can occur:
598 * -1 entropy_collector is NULL
599 * -2 Intermittent health failure
600 * -3 Permanent health failure
601 */
jent_read_entropy(struct rand_data * ec,unsigned char * data,unsigned int len)602 int jent_read_entropy(struct rand_data *ec, unsigned char *data,
603 unsigned int len)
604 {
605 unsigned char *p = data;
606
607 if (!ec)
608 return -1;
609
610 while (len > 0) {
611 unsigned int tocopy, health_test_result;
612
613 jent_gen_entropy(ec);
614
615 health_test_result = jent_health_failure(ec);
616 if (health_test_result > JENT_PERMANENT_FAILURE_SHIFT) {
617 /*
618 * At this point, the Jitter RNG instance is considered
619 * as a failed instance. There is no rerun of the
620 * startup test any more, because the caller
621 * is assumed to not further use this instance.
622 */
623 return -3;
624 } else if (health_test_result) {
625 /*
626 * Perform startup health tests and return permanent
627 * error if it fails.
628 */
629 if (jent_entropy_init(0, 0, NULL, ec)) {
630 /* Mark the permanent error */
631 ec->health_failure &=
632 JENT_RCT_FAILURE_PERMANENT |
633 JENT_APT_FAILURE_PERMANENT;
634 return -3;
635 }
636
637 return -2;
638 }
639
640 tocopy = min(DATA_SIZE_BITS / 8, len);
641 jent_read_random_block(ec->hash_state, p, tocopy);
642
643 len -= tocopy;
644 p += tocopy;
645 }
646
647 return 0;
648 }
649
650 /***************************************************************************
651 * Initialization logic
652 ***************************************************************************/
653
jent_entropy_collector_alloc(unsigned int osr,unsigned int flags,struct sha3_ctx * hash_state)654 struct rand_data *jent_entropy_collector_alloc(unsigned int osr,
655 unsigned int flags,
656 struct sha3_ctx *hash_state)
657 {
658 struct rand_data *entropy_collector;
659
660 entropy_collector = jent_zalloc(sizeof(struct rand_data));
661 if (!entropy_collector)
662 return NULL;
663
664 if (!(flags & JENT_DISABLE_MEMORY_ACCESS)) {
665 /* Allocate memory for adding variations based on memory
666 * access
667 */
668 entropy_collector->mem = jent_kvzalloc(JENT_MEMORY_SIZE);
669 if (!entropy_collector->mem) {
670 jent_zfree(entropy_collector);
671 return NULL;
672 }
673 entropy_collector->memblocksize =
674 CONFIG_CRYPTO_JITTERENTROPY_MEMORY_BLOCKSIZE;
675 entropy_collector->memblocks =
676 CONFIG_CRYPTO_JITTERENTROPY_MEMORY_BLOCKS;
677 entropy_collector->memaccessloops = JENT_MEMORY_ACCESSLOOPS;
678 }
679
680 /* verify and set the oversampling rate */
681 if (osr == 0)
682 osr = 1; /* H_submitter = 1 / osr */
683 entropy_collector->osr = osr;
684 entropy_collector->flags = flags;
685
686 entropy_collector->hash_state = hash_state;
687
688 /* Initialize the APT */
689 jent_apt_init(entropy_collector, osr);
690
691 /* fill the data pad with non-zero values */
692 jent_gen_entropy(entropy_collector);
693
694 return entropy_collector;
695 }
696
jent_entropy_collector_free(struct rand_data * entropy_collector)697 void jent_entropy_collector_free(struct rand_data *entropy_collector)
698 {
699 jent_kvzfree(entropy_collector->mem, JENT_MEMORY_SIZE);
700 entropy_collector->mem = NULL;
701 jent_zfree(entropy_collector);
702 }
703
jent_entropy_init(unsigned int osr,unsigned int flags,struct sha3_ctx * hash_state,struct rand_data * p_ec)704 int jent_entropy_init(unsigned int osr, unsigned int flags,
705 struct sha3_ctx *hash_state, struct rand_data *p_ec)
706 {
707 /*
708 * If caller provides an allocated ec, reuse it which implies that the
709 * health test entropy data is used to further still the available
710 * entropy pool.
711 */
712 struct rand_data *ec = p_ec;
713 int i, time_backwards = 0, ret = 0, ec_free = 0;
714 unsigned int health_test_result;
715
716 if (!ec) {
717 ec = jent_entropy_collector_alloc(osr, flags, hash_state);
718 if (!ec)
719 return JENT_EMEM;
720 ec_free = 1;
721 } else {
722 /* Reset the APT */
723 jent_apt_reset(ec, 0);
724 /* Ensure that a new APT base is obtained */
725 ec->apt_base_set = 0;
726 /* Reset the RCT */
727 ec->rct_count = 0;
728 /* Reset intermittent, leave permanent health test result */
729 ec->health_failure &= (~JENT_RCT_FAILURE);
730 ec->health_failure &= (~JENT_APT_FAILURE);
731 }
732
733 /* We could perform statistical tests here, but the problem is
734 * that we only have a few loop counts to do testing. These
735 * loop counts may show some slight skew and we produce
736 * false positives.
737 *
738 * Moreover, only old systems show potentially problematic
739 * jitter entropy that could potentially be caught here. But
740 * the RNG is intended for hardware that is available or widely
741 * used, but not old systems that are long out of favor. Thus,
742 * no statistical tests.
743 */
744
745 /*
746 * We could add a check for system capabilities such as clock_getres or
747 * check for CONFIG_X86_TSC, but it does not make much sense as the
748 * following sanity checks verify that we have a high-resolution
749 * timer.
750 */
751 /*
752 * TESTLOOPCOUNT needs some loops to identify edge systems. 100 is
753 * definitely too little.
754 *
755 * SP800-90B requires at least 1024 initial test cycles.
756 */
757 #define TESTLOOPCOUNT 1024
758 #define CLEARCACHE 100
759 for (i = 0; (TESTLOOPCOUNT + CLEARCACHE) > i; i++) {
760 __u64 start_time = 0, end_time = 0, delta = 0;
761
762 /* Invoke core entropy collection logic */
763 jent_measure_jitter(ec, &delta);
764 end_time = ec->prev_time;
765 start_time = ec->prev_time - delta;
766
767 /* test whether timer works */
768 if (!start_time || !end_time) {
769 ret = JENT_ENOTIME;
770 goto out;
771 }
772
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 || (end_time == start_time)) {
779 ret = JENT_ECOARSETIME;
780 goto out;
781 }
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 /* test whether we have an increasing timer */
794 if (!(end_time > start_time))
795 time_backwards++;
796 }
797
798 /*
799 * we allow up to three times the time running backwards.
800 * CLOCK_REALTIME is affected by adjtime and NTP operations. Thus,
801 * if such an operation just happens to interfere with our test, it
802 * should not fail. The value of 3 should cover the NTP case being
803 * performed during our test run.
804 */
805 if (time_backwards > 3) {
806 ret = JENT_ENOMONOTONIC;
807 goto out;
808 }
809
810 /* Did we encounter a health test failure? */
811 health_test_result = jent_health_failure(ec);
812 if (health_test_result) {
813 ret = (health_test_result & JENT_RCT_FAILURE) ? JENT_ERCT :
814 JENT_EHEALTH;
815 goto out;
816 }
817
818 out:
819 if (ec_free)
820 jent_entropy_collector_free(ec);
821
822 return ret;
823 }
824