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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 - 2019
6 *
7 * Design
8 * ======
9 *
10 * See http://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 2.1.2 provided at http://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
88/* Flags that can be used to initialize the RNG */
89#define JENT_DISABLE_MEMORY_ACCESS (1<<2) /* Disable memory access for more
90 * entropy, saves MEMORY_SIZE RAM for
91 * entropy collector */
92
93/* -- error codes for init function -- */
94#define JENT_ENOTIME 1 /* Timer service not available */
95#define JENT_ECOARSETIME 2 /* Timer too coarse for RNG */
96#define JENT_ENOMONOTONIC 3 /* Timer is not monotonic increasing */
97#define JENT_EVARVAR 5 /* Timer does not produce variations of
98 * variations (2nd derivation of time is
99 * zero). */
100#define JENT_ESTUCK 8 /* Too many stuck results during init. */
101
102/***************************************************************************
103 * Helper functions
104 ***************************************************************************/
105
106void jent_get_nstime(__u64 *out);
107void *jent_zalloc(unsigned int len);
108void jent_zfree(void *ptr);
109int jent_fips_enabled(void);
110void jent_panic(char *s);
111void jent_memcpy(void *dest, const void *src, unsigned int n);
112
113/**
114 * Update of the loop count used for the next round of
115 * an entropy collection.
116 *
117 * Input:
118 * @ec entropy collector struct -- may be NULL
119 * @bits is the number of low bits of the timer to consider
120 * @min is the number of bits we shift the timer value to the right at
121 * the end to make sure we have a guaranteed minimum value
122 *
123 * @return Newly calculated loop counter
124 */
125static __u64 jent_loop_shuffle(struct rand_data *ec,
126 unsigned int bits, unsigned int min)
127{
128 __u64 time = 0;
129 __u64 shuffle = 0;
130 unsigned int i = 0;
131 unsigned int mask = (1<<bits) - 1;
132
133 jent_get_nstime(&time);
134 /*
135 * Mix the current state of the random number into the shuffle
136 * calculation to balance that shuffle a bit more.
137 */
138 if (ec)
139 time ^= ec->data;
140 /*
141 * We fold the time value as much as possible to ensure that as many
142 * bits of the time stamp are included as possible.
143 */
144 for (i = 0; ((DATA_SIZE_BITS + bits - 1) / bits) > i; i++) {
145 shuffle ^= time & mask;
146 time = time >> bits;
147 }
148
149 /*
150 * We add a lower boundary value to ensure we have a minimum
151 * RNG loop count.
152 */
153 return (shuffle + (1<<min));
154}
155
156/***************************************************************************
157 * Noise sources
158 ***************************************************************************/
159
160/**
161 * CPU Jitter noise source -- this is the noise source based on the CPU
162 * execution time jitter
163 *
164 * This function injects the individual bits of the time value into the
165 * entropy pool using an LFSR.
166 *
167 * The code is deliberately inefficient with respect to the bit shifting
168 * and shall stay that way. This function is the root cause why the code
169 * shall be compiled without optimization. This function not only acts as
170 * folding operation, but this function's execution is used to measure
171 * the CPU execution time jitter. Any change to the loop in this function
172 * implies that careful retesting must be done.
173 *
174 * Input:
175 * @ec entropy collector struct -- may be NULL
176 * @time time stamp to be injected
177 * @loop_cnt if a value not equal to 0 is set, use the given value as number of
178 * loops to perform the folding
179 *
180 * Output:
181 * updated ec->data
182 *
183 * @return Number of loops the folding operation is performed
184 */
185static __u64 jent_lfsr_time(struct rand_data *ec, __u64 time, __u64 loop_cnt)
186{
187 unsigned int i;
188 __u64 j = 0;
189 __u64 new = 0;
190#define MAX_FOLD_LOOP_BIT 4
191#define MIN_FOLD_LOOP_BIT 0
192 __u64 fold_loop_cnt =
193 jent_loop_shuffle(ec, MAX_FOLD_LOOP_BIT, MIN_FOLD_LOOP_BIT);
194
195 /*
196 * testing purposes -- allow test app to set the counter, not
197 * needed during runtime
198 */
199 if (loop_cnt)
200 fold_loop_cnt = loop_cnt;
201 for (j = 0; j < fold_loop_cnt; j++) {
202 new = ec->data;
203 for (i = 1; (DATA_SIZE_BITS) >= i; i++) {
204 __u64 tmp = time << (DATA_SIZE_BITS - i);
205
206 tmp = tmp >> (DATA_SIZE_BITS - 1);
207
208 /*
209 * Fibonacci LSFR with polynomial of
210 * x^64 + x^61 + x^56 + x^31 + x^28 + x^23 + 1 which is
211 * primitive according to
212 * http://poincare.matf.bg.ac.rs/~ezivkovm/publications/primpol1.pdf
213 * (the shift values are the polynomial values minus one
214 * due to counting bits from 0 to 63). As the current
215 * position is always the LSB, the polynomial only needs
216 * to shift data in from the left without wrap.
217 */
218 tmp ^= ((new >> 63) & 1);
219 tmp ^= ((new >> 60) & 1);
220 tmp ^= ((new >> 55) & 1);
221 tmp ^= ((new >> 30) & 1);
222 tmp ^= ((new >> 27) & 1);
223 tmp ^= ((new >> 22) & 1);
224 new <<= 1;
225 new ^= tmp;
226 }
227 }
228 ec->data = new;
229
230 return fold_loop_cnt;
231}
232
233/**
234 * Memory Access noise source -- this is a noise source based on variations in
235 * memory access times
236 *
237 * This function performs memory accesses which will add to the timing
238 * variations due to an unknown amount of CPU wait states that need to be
239 * added when accessing memory. The memory size should be larger than the L1
240 * caches as outlined in the documentation and the associated testing.
241 *
242 * The L1 cache has a very high bandwidth, albeit its access rate is usually
243 * slower than accessing CPU registers. Therefore, L1 accesses only add minimal
244 * variations as the CPU has hardly to wait. Starting with L2, significant
245 * variations are added because L2 typically does not belong to the CPU any more
246 * and therefore a wider range of CPU wait states is necessary for accesses.
247 * L3 and real memory accesses have even a wider range of wait states. However,
248 * to reliably access either L3 or memory, the ec->mem memory must be quite
249 * large which is usually not desirable.
250 *
251 * Input:
252 * @ec Reference to the entropy collector with the memory access data -- if
253 * the reference to the memory block to be accessed is NULL, this noise
254 * source is disabled
255 * @loop_cnt if a value not equal to 0 is set, use the given value as number of
256 * loops to perform the folding
257 *
258 * @return Number of memory access operations
259 */
260static unsigned int jent_memaccess(struct rand_data *ec, __u64 loop_cnt)
261{
262 unsigned int wrap = 0;
263 __u64 i = 0;
264#define MAX_ACC_LOOP_BIT 7
265#define MIN_ACC_LOOP_BIT 0
266 __u64 acc_loop_cnt =
267 jent_loop_shuffle(ec, MAX_ACC_LOOP_BIT, MIN_ACC_LOOP_BIT);
268
269 if (NULL == ec || NULL == ec->mem)
270 return 0;
271 wrap = ec->memblocksize * ec->memblocks;
272
273 /*
274 * testing purposes -- allow test app to set the counter, not
275 * needed during runtime
276 */
277 if (loop_cnt)
278 acc_loop_cnt = loop_cnt;
279
280 for (i = 0; i < (ec->memaccessloops + acc_loop_cnt); i++) {
281 unsigned char *tmpval = ec->mem + ec->memlocation;
282 /*
283 * memory access: just add 1 to one byte,
284 * wrap at 255 -- memory access implies read
285 * from and write to memory location
286 */
287 *tmpval = (*tmpval + 1) & 0xff;
288 /*
289 * Addition of memblocksize - 1 to pointer
290 * with wrap around logic to ensure that every
291 * memory location is hit evenly
292 */
293 ec->memlocation = ec->memlocation + ec->memblocksize - 1;
294 ec->memlocation = ec->memlocation % wrap;
295 }
296 return i;
297}
298
299/***************************************************************************
300 * Start of entropy processing logic
301 ***************************************************************************/
302
303/**
304 * Stuck test by checking the:
305 * 1st derivation of the jitter measurement (time delta)
306 * 2nd derivation of the jitter measurement (delta of time deltas)
307 * 3rd derivation of the jitter measurement (delta of delta of time deltas)
308 *
309 * All values must always be non-zero.
310 *
311 * Input:
312 * @ec Reference to entropy collector
313 * @current_delta Jitter time delta
314 *
315 * @return
316 * 0 jitter measurement not stuck (good bit)
317 * 1 jitter measurement stuck (reject bit)
318 */
319static int jent_stuck(struct rand_data *ec, __u64 current_delta)
320{
321 __s64 delta2 = ec->last_delta - current_delta;
322 __s64 delta3 = delta2 - ec->last_delta2;
323
324 ec->last_delta = current_delta;
325 ec->last_delta2 = delta2;
326
327 if (!current_delta || !delta2 || !delta3)
328 return 1;
329
330 return 0;
331}
332
333/**
334 * This is the heart of the entropy generation: calculate time deltas and
335 * use the CPU jitter in the time deltas. The jitter is injected into the
336 * entropy pool.
337 *
338 * WARNING: ensure that ->prev_time is primed before using the output
339 * of this function! This can be done by calling this function
340 * and not using its result.
341 *
342 * Input:
343 * @entropy_collector Reference to entropy collector
344 *
345 * @return result of stuck test
346 */
347static int jent_measure_jitter(struct rand_data *ec)
348{
349 __u64 time = 0;
350 __u64 current_delta = 0;
351
352 /* Invoke one noise source before time measurement to add variations */
353 jent_memaccess(ec, 0);
354
355 /*
356 * Get time stamp and calculate time delta to previous
357 * invocation to measure the timing variations
358 */
359 jent_get_nstime(&time);
360 current_delta = time - ec->prev_time;
361 ec->prev_time = time;
362
363 /* Now call the next noise sources which also injects the data */
364 jent_lfsr_time(ec, current_delta, 0);
365
366 /* Check whether we have a stuck measurement. */
367 return jent_stuck(ec, current_delta);
368}
369
370/**
371 * Generator of one 64 bit random number
372 * Function fills rand_data->data
373 *
374 * Input:
375 * @ec Reference to entropy collector
376 */
377static void jent_gen_entropy(struct rand_data *ec)
378{
379 unsigned int k = 0;
380
381 /* priming of the ->prev_time value */
382 jent_measure_jitter(ec);
383
384 while (1) {
385 /* If a stuck measurement is received, repeat measurement */
386 if (jent_measure_jitter(ec))
387 continue;
388
389 /*
390 * We multiply the loop value with ->osr to obtain the
391 * oversampling rate requested by the caller
392 */
393 if (++k >= (DATA_SIZE_BITS * ec->osr))
394 break;
395 }
396}
397
398/**
399 * The continuous test required by FIPS 140-2 -- the function automatically
400 * primes the test if needed.
401 *
402 * Return:
403 * 0 if FIPS test passed
404 * < 0 if FIPS test failed
405 */
406static void jent_fips_test(struct rand_data *ec)
407{
408 if (!jent_fips_enabled())
409 return;
410
411 /* prime the FIPS test */
412 if (!ec->old_data) {
413 ec->old_data = ec->data;
414 jent_gen_entropy(ec);
415 }
416
417 if (ec->data == ec->old_data)
418 jent_panic("jitterentropy: Duplicate output detected\n");
419
420 ec->old_data = ec->data;
421}
422
423/**
424 * Entry function: Obtain entropy for the caller.
425 *
426 * This function invokes the entropy gathering logic as often to generate
427 * as many bytes as requested by the caller. The entropy gathering logic
428 * creates 64 bit per invocation.
429 *
430 * This function truncates the last 64 bit entropy value output to the exact
431 * size specified by the caller.
432 *
433 * Input:
434 * @ec Reference to entropy collector
435 * @data pointer to buffer for storing random data -- buffer must already
436 * exist
437 * @len size of the buffer, specifying also the requested number of random
438 * in bytes
439 *
440 * @return 0 when request is fulfilled or an error
441 *
442 * The following error codes can occur:
443 * -1 entropy_collector is NULL
444 */
445int jent_read_entropy(struct rand_data *ec, unsigned char *data,
446 unsigned int len)
447{
448 unsigned char *p = data;
449
450 if (!ec)
451 return -1;
452
453 while (0 < len) {
454 unsigned int tocopy;
455
456 jent_gen_entropy(ec);
457 jent_fips_test(ec);
458 if ((DATA_SIZE_BITS / 8) < len)
459 tocopy = (DATA_SIZE_BITS / 8);
460 else
461 tocopy = len;
462 jent_memcpy(p, &ec->data, tocopy);
463
464 len -= tocopy;
465 p += tocopy;
466 }
467
468 return 0;
469}
470
471/***************************************************************************
472 * Initialization logic
473 ***************************************************************************/
474
475struct rand_data *jent_entropy_collector_alloc(unsigned int osr,
476 unsigned int flags)
477{
478 struct rand_data *entropy_collector;
479
480 entropy_collector = jent_zalloc(sizeof(struct rand_data));
481 if (!entropy_collector)
482 return NULL;
483
484 if (!(flags & JENT_DISABLE_MEMORY_ACCESS)) {
485 /* Allocate memory for adding variations based on memory
486 * access
487 */
488 entropy_collector->mem = jent_zalloc(JENT_MEMORY_SIZE);
489 if (!entropy_collector->mem) {
490 jent_zfree(entropy_collector);
491 return NULL;
492 }
493 entropy_collector->memblocksize = JENT_MEMORY_BLOCKSIZE;
494 entropy_collector->memblocks = JENT_MEMORY_BLOCKS;
495 entropy_collector->memaccessloops = JENT_MEMORY_ACCESSLOOPS;
496 }
497
498 /* verify and set the oversampling rate */
499 if (0 == osr)
500 osr = 1; /* minimum sampling rate is 1 */
501 entropy_collector->osr = osr;
502
503 /* fill the data pad with non-zero values */
504 jent_gen_entropy(entropy_collector);
505
506 return entropy_collector;
507}
508
509void jent_entropy_collector_free(struct rand_data *entropy_collector)
510{
511 jent_zfree(entropy_collector->mem);
512 entropy_collector->mem = NULL;
513 jent_zfree(entropy_collector);
514}
515
516int jent_entropy_init(void)
517{
518 int i;
519 __u64 delta_sum = 0;
520 __u64 old_delta = 0;
521 int time_backwards = 0;
522 int count_mod = 0;
523 int count_stuck = 0;
524 struct rand_data ec = { 0 };
525
526 /* We could perform statistical tests here, but the problem is
527 * that we only have a few loop counts to do testing. These
528 * loop counts may show some slight skew and we produce
529 * false positives.
530 *
531 * Moreover, only old systems show potentially problematic
532 * jitter entropy that could potentially be caught here. But
533 * the RNG is intended for hardware that is available or widely
534 * used, but not old systems that are long out of favor. Thus,
535 * no statistical tests.
536 */
537
538 /*
539 * We could add a check for system capabilities such as clock_getres or
540 * check for CONFIG_X86_TSC, but it does not make much sense as the
541 * following sanity checks verify that we have a high-resolution
542 * timer.
543 */
544 /*
545 * TESTLOOPCOUNT needs some loops to identify edge systems. 100 is
546 * definitely too little.
547 */
548#define TESTLOOPCOUNT 300
549#define CLEARCACHE 100
550 for (i = 0; (TESTLOOPCOUNT + CLEARCACHE) > i; i++) {
551 __u64 time = 0;
552 __u64 time2 = 0;
553 __u64 delta = 0;
554 unsigned int lowdelta = 0;
555 int stuck;
556
557 /* Invoke core entropy collection logic */
558 jent_get_nstime(&time);
559 ec.prev_time = time;
560 jent_lfsr_time(&ec, time, 0);
561 jent_get_nstime(&time2);
562
563 /* test whether timer works */
564 if (!time || !time2)
565 return JENT_ENOTIME;
566 delta = time2 - time;
567 /*
568 * test whether timer is fine grained enough to provide
569 * delta even when called shortly after each other -- this
570 * implies that we also have a high resolution timer
571 */
572 if (!delta)
573 return JENT_ECOARSETIME;
574
575 stuck = jent_stuck(&ec, delta);
576
577 /*
578 * up to here we did not modify any variable that will be
579 * evaluated later, but we already performed some work. Thus we
580 * already have had an impact on the caches, branch prediction,
581 * etc. with the goal to clear it to get the worst case
582 * measurements.
583 */
584 if (CLEARCACHE > i)
585 continue;
586
587 if (stuck)
588 count_stuck++;
589
590 /* test whether we have an increasing timer */
591 if (!(time2 > time))
592 time_backwards++;
593
594 /* use 32 bit value to ensure compilation on 32 bit arches */
595 lowdelta = time2 - time;
596 if (!(lowdelta % 100))
597 count_mod++;
598
599 /*
600 * ensure that we have a varying delta timer which is necessary
601 * for the calculation of entropy -- perform this check
602 * only after the first loop is executed as we need to prime
603 * the old_data value
604 */
605 if (delta > old_delta)
606 delta_sum += (delta - old_delta);
607 else
608 delta_sum += (old_delta - delta);
609 old_delta = delta;
610 }
611
612 /*
613 * we allow up to three times the time running backwards.
614 * CLOCK_REALTIME is affected by adjtime and NTP operations. Thus,
615 * if such an operation just happens to interfere with our test, it
616 * should not fail. The value of 3 should cover the NTP case being
617 * performed during our test run.
618 */
619 if (3 < time_backwards)
620 return JENT_ENOMONOTONIC;
621
622 /*
623 * Variations of deltas of time must on average be larger
624 * than 1 to ensure the entropy estimation
625 * implied with 1 is preserved
626 */
627 if ((delta_sum) <= 1)
628 return JENT_EVARVAR;
629
630 /*
631 * Ensure that we have variations in the time stamp below 10 for at
632 * least 10% of all checks -- on some platforms, the counter increments
633 * in multiples of 100, but not always
634 */
635 if ((TESTLOOPCOUNT/10 * 9) < count_mod)
636 return JENT_ECOARSETIME;
637
638 /*
639 * If we have more than 90% stuck results, then this Jitter RNG is
640 * likely to not work well.
641 */
642 if ((TESTLOOPCOUNT/10 * 9) < count_stuck)
643 return JENT_ESTUCK;
644
645 return 0;
646}
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
57typedef unsigned long long __u64;
58typedef long long __s64;
59typedef unsigned int __u32;
60typedef unsigned char u8;
61#define NULL ((void *) 0)
62
63/* The entropy pool */
64struct 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 void *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/fips.h>
149#include "jitterentropy.h"
150
151/***************************************************************************
152 * Adaptive Proportion Test
153 *
154 * This test complies with SP800-90B section 4.4.2.
155 ***************************************************************************/
156
157/*
158 * See the SP 800-90B comment #10b for the corrected cutoff for the SP 800-90B
159 * APT.
160 * http://www.untruth.org/~josh/sp80090b/UL%20SP800-90B-final%20comments%20v1.9%2020191212.pdf
161 * In in the syntax of R, this is C = 2 + qbinom(1 − 2^(−30), 511, 2^(-1/osr)).
162 * (The original formula wasn't correct because the first symbol must
163 * necessarily have been observed, so there is no chance of observing 0 of these
164 * symbols.)
165 *
166 * For the alpha < 2^-53, R cannot be used as it uses a float data type without
167 * arbitrary precision. A SageMath script is used to calculate those cutoff
168 * values.
169 *
170 * For any value above 14, this yields the maximal allowable value of 512
171 * (by FIPS 140-2 IG 7.19 Resolution # 16, we cannot choose a cutoff value that
172 * renders the test unable to fail).
173 */
174static const unsigned int jent_apt_cutoff_lookup[15] = {
175 325, 422, 459, 477, 488, 494, 499, 502,
176 505, 507, 508, 509, 510, 511, 512 };
177static const unsigned int jent_apt_cutoff_permanent_lookup[15] = {
178 355, 447, 479, 494, 502, 507, 510, 512,
179 512, 512, 512, 512, 512, 512, 512 };
180#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
181
182static void jent_apt_init(struct rand_data *ec, unsigned int osr)
183{
184 /*
185 * Establish the apt_cutoff based on the presumed entropy rate of
186 * 1/osr.
187 */
188 if (osr >= ARRAY_SIZE(jent_apt_cutoff_lookup)) {
189 ec->apt_cutoff = jent_apt_cutoff_lookup[
190 ARRAY_SIZE(jent_apt_cutoff_lookup) - 1];
191 ec->apt_cutoff_permanent = jent_apt_cutoff_permanent_lookup[
192 ARRAY_SIZE(jent_apt_cutoff_permanent_lookup) - 1];
193 } else {
194 ec->apt_cutoff = jent_apt_cutoff_lookup[osr - 1];
195 ec->apt_cutoff_permanent =
196 jent_apt_cutoff_permanent_lookup[osr - 1];
197 }
198}
199/*
200 * Reset the APT counter
201 *
202 * @ec [in] Reference to entropy collector
203 */
204static void jent_apt_reset(struct rand_data *ec, unsigned int delta_masked)
205{
206 /* Reset APT counter */
207 ec->apt_count = 0;
208 ec->apt_base = delta_masked;
209 ec->apt_observations = 0;
210}
211
212/*
213 * Insert a new entropy event into APT
214 *
215 * @ec [in] Reference to entropy collector
216 * @delta_masked [in] Masked time delta to process
217 */
218static void jent_apt_insert(struct rand_data *ec, unsigned int delta_masked)
219{
220 /* Initialize the base reference */
221 if (!ec->apt_base_set) {
222 ec->apt_base = delta_masked;
223 ec->apt_base_set = 1;
224 return;
225 }
226
227 if (delta_masked == ec->apt_base) {
228 ec->apt_count++;
229
230 /* Note, ec->apt_count starts with one. */
231 if (ec->apt_count >= ec->apt_cutoff_permanent)
232 ec->health_failure |= JENT_APT_FAILURE_PERMANENT;
233 else if (ec->apt_count >= ec->apt_cutoff)
234 ec->health_failure |= JENT_APT_FAILURE;
235 }
236
237 ec->apt_observations++;
238
239 if (ec->apt_observations >= JENT_APT_WINDOW_SIZE)
240 jent_apt_reset(ec, delta_masked);
241}
242
243/***************************************************************************
244 * Stuck Test and its use as Repetition Count Test
245 *
246 * The Jitter RNG uses an enhanced version of the Repetition Count Test
247 * (RCT) specified in SP800-90B section 4.4.1. Instead of counting identical
248 * back-to-back values, the input to the RCT is the counting of the stuck
249 * values during the generation of one Jitter RNG output block.
250 *
251 * The RCT is applied with an alpha of 2^{-30} compliant to FIPS 140-2 IG 9.8.
252 *
253 * During the counting operation, the Jitter RNG always calculates the RCT
254 * cut-off value of C. If that value exceeds the allowed cut-off value,
255 * the Jitter RNG output block will be calculated completely but discarded at
256 * the end. The caller of the Jitter RNG is informed with an error code.
257 ***************************************************************************/
258
259/*
260 * Repetition Count Test as defined in SP800-90B section 4.4.1
261 *
262 * @ec [in] Reference to entropy collector
263 * @stuck [in] Indicator whether the value is stuck
264 */
265static void jent_rct_insert(struct rand_data *ec, int stuck)
266{
267 if (stuck) {
268 ec->rct_count++;
269
270 /*
271 * The cutoff value is based on the following consideration:
272 * alpha = 2^-30 or 2^-60 as recommended in SP800-90B.
273 * In addition, we require an entropy value H of 1/osr as this
274 * is the minimum entropy required to provide full entropy.
275 * Note, we collect (DATA_SIZE_BITS + ENTROPY_SAFETY_FACTOR)*osr
276 * deltas for inserting them into the entropy pool which should
277 * then have (close to) DATA_SIZE_BITS bits of entropy in the
278 * conditioned output.
279 *
280 * Note, ec->rct_count (which equals to value B in the pseudo
281 * code of SP800-90B section 4.4.1) starts with zero. Hence
282 * we need to subtract one from the cutoff value as calculated
283 * following SP800-90B. Thus C = ceil(-log_2(alpha)/H) = 30*osr
284 * or 60*osr.
285 */
286 if ((unsigned int)ec->rct_count >= (60 * ec->osr)) {
287 ec->rct_count = -1;
288 ec->health_failure |= JENT_RCT_FAILURE_PERMANENT;
289 } else if ((unsigned int)ec->rct_count >= (30 * ec->osr)) {
290 ec->rct_count = -1;
291 ec->health_failure |= JENT_RCT_FAILURE;
292 }
293 } else {
294 /* Reset RCT */
295 ec->rct_count = 0;
296 }
297}
298
299static inline __u64 jent_delta(__u64 prev, __u64 next)
300{
301#define JENT_UINT64_MAX (__u64)(~((__u64) 0))
302 return (prev < next) ? (next - prev) :
303 (JENT_UINT64_MAX - prev + 1 + next);
304}
305
306/*
307 * Stuck test by checking the:
308 * 1st derivative of the jitter measurement (time delta)
309 * 2nd derivative of the jitter measurement (delta of time deltas)
310 * 3rd derivative of the jitter measurement (delta of delta of time deltas)
311 *
312 * All values must always be non-zero.
313 *
314 * @ec [in] Reference to entropy collector
315 * @current_delta [in] Jitter time delta
316 *
317 * @return
318 * 0 jitter measurement not stuck (good bit)
319 * 1 jitter measurement stuck (reject bit)
320 */
321static int jent_stuck(struct rand_data *ec, __u64 current_delta)
322{
323 __u64 delta2 = jent_delta(ec->last_delta, current_delta);
324 __u64 delta3 = jent_delta(ec->last_delta2, delta2);
325
326 ec->last_delta = current_delta;
327 ec->last_delta2 = delta2;
328
329 /*
330 * Insert the result of the comparison of two back-to-back time
331 * deltas.
332 */
333 jent_apt_insert(ec, current_delta);
334
335 if (!current_delta || !delta2 || !delta3) {
336 /* RCT with a stuck bit */
337 jent_rct_insert(ec, 1);
338 return 1;
339 }
340
341 /* RCT with a non-stuck bit */
342 jent_rct_insert(ec, 0);
343
344 return 0;
345}
346
347/*
348 * Report any health test failures
349 *
350 * @ec [in] Reference to entropy collector
351 *
352 * @return a bitmask indicating which tests failed
353 * 0 No health test failure
354 * 1 RCT failure
355 * 2 APT failure
356 * 1<<JENT_PERMANENT_FAILURE_SHIFT RCT permanent failure
357 * 2<<JENT_PERMANENT_FAILURE_SHIFT APT permanent failure
358 */
359static unsigned int jent_health_failure(struct rand_data *ec)
360{
361 /* Test is only enabled in FIPS mode */
362 if (!fips_enabled)
363 return 0;
364
365 return ec->health_failure;
366}
367
368/***************************************************************************
369 * Noise sources
370 ***************************************************************************/
371
372/*
373 * Update of the loop count used for the next round of
374 * an entropy collection.
375 *
376 * Input:
377 * @bits is the number of low bits of the timer to consider
378 * @min is the number of bits we shift the timer value to the right at
379 * the end to make sure we have a guaranteed minimum value
380 *
381 * @return Newly calculated loop counter
382 */
383static __u64 jent_loop_shuffle(unsigned int bits, unsigned int min)
384{
385 __u64 time = 0;
386 __u64 shuffle = 0;
387 unsigned int i = 0;
388 unsigned int mask = (1<<bits) - 1;
389
390 jent_get_nstime(&time);
391
392 /*
393 * We fold the time value as much as possible to ensure that as many
394 * bits of the time stamp are included as possible.
395 */
396 for (i = 0; ((DATA_SIZE_BITS + bits - 1) / bits) > i; i++) {
397 shuffle ^= time & mask;
398 time = time >> bits;
399 }
400
401 /*
402 * We add a lower boundary value to ensure we have a minimum
403 * RNG loop count.
404 */
405 return (shuffle + (1<<min));
406}
407
408/*
409 * CPU Jitter noise source -- this is the noise source based on the CPU
410 * execution time jitter
411 *
412 * This function injects the individual bits of the time value into the
413 * entropy pool using a hash.
414 *
415 * ec [in] entropy collector
416 * time [in] time stamp to be injected
417 * stuck [in] Is the time stamp identified as stuck?
418 *
419 * Output:
420 * updated hash context in the entropy collector or error code
421 */
422static int 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 return 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 */
465static 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 */
519static 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 if (jent_condition_data(ec, current_delta, stuck))
541 stuck = 1;
542
543 /* return the raw entropy value */
544 if (ret_current_delta)
545 *ret_current_delta = current_delta;
546
547 return stuck;
548}
549
550/*
551 * Generator of one 64 bit random number
552 * Function fills rand_data->hash_state
553 *
554 * @ec [in] Reference to entropy collector
555 */
556static void jent_gen_entropy(struct rand_data *ec)
557{
558 unsigned int k = 0, safety_factor = 0;
559
560 if (fips_enabled)
561 safety_factor = JENT_ENTROPY_SAFETY_FACTOR;
562
563 /* priming of the ->prev_time value */
564 jent_measure_jitter(ec, NULL);
565
566 while (!jent_health_failure(ec)) {
567 /* If a stuck measurement is received, repeat measurement */
568 if (jent_measure_jitter(ec, NULL))
569 continue;
570
571 /*
572 * We multiply the loop value with ->osr to obtain the
573 * oversampling rate requested by the caller
574 */
575 if (++k >= ((DATA_SIZE_BITS + safety_factor) * ec->osr))
576 break;
577 }
578}
579
580/*
581 * Entry function: Obtain entropy for the caller.
582 *
583 * This function invokes the entropy gathering logic as often to generate
584 * as many bytes as requested by the caller. The entropy gathering logic
585 * creates 64 bit per invocation.
586 *
587 * This function truncates the last 64 bit entropy value output to the exact
588 * size specified by the caller.
589 *
590 * @ec [in] Reference to entropy collector
591 * @data [in] pointer to buffer for storing random data -- buffer must already
592 * exist
593 * @len [in] size of the buffer, specifying also the requested number of random
594 * in bytes
595 *
596 * @return 0 when request is fulfilled or an error
597 *
598 * The following error codes can occur:
599 * -1 entropy_collector is NULL or the generation failed
600 * -2 Intermittent health failure
601 * -3 Permanent health failure
602 */
603int jent_read_entropy(struct rand_data *ec, unsigned char *data,
604 unsigned int len)
605{
606 unsigned char *p = data;
607
608 if (!ec)
609 return -1;
610
611 while (len > 0) {
612 unsigned int tocopy, health_test_result;
613
614 jent_gen_entropy(ec);
615
616 health_test_result = jent_health_failure(ec);
617 if (health_test_result > JENT_PERMANENT_FAILURE_SHIFT) {
618 /*
619 * At this point, the Jitter RNG instance is considered
620 * as a failed instance. There is no rerun of the
621 * startup test any more, because the caller
622 * is assumed to not further use this instance.
623 */
624 return -3;
625 } else if (health_test_result) {
626 /*
627 * Perform startup health tests and return permanent
628 * error if it fails.
629 */
630 if (jent_entropy_init(0, 0, NULL, ec)) {
631 /* Mark the permanent error */
632 ec->health_failure &=
633 JENT_RCT_FAILURE_PERMANENT |
634 JENT_APT_FAILURE_PERMANENT;
635 return -3;
636 }
637
638 return -2;
639 }
640
641 if ((DATA_SIZE_BITS / 8) < len)
642 tocopy = (DATA_SIZE_BITS / 8);
643 else
644 tocopy = len;
645 if (jent_read_random_block(ec->hash_state, p, tocopy))
646 return -1;
647
648 len -= tocopy;
649 p += tocopy;
650 }
651
652 return 0;
653}
654
655/***************************************************************************
656 * Initialization logic
657 ***************************************************************************/
658
659struct rand_data *jent_entropy_collector_alloc(unsigned int osr,
660 unsigned int flags,
661 void *hash_state)
662{
663 struct rand_data *entropy_collector;
664
665 entropy_collector = jent_zalloc(sizeof(struct rand_data));
666 if (!entropy_collector)
667 return NULL;
668
669 if (!(flags & JENT_DISABLE_MEMORY_ACCESS)) {
670 /* Allocate memory for adding variations based on memory
671 * access
672 */
673 entropy_collector->mem = jent_kvzalloc(JENT_MEMORY_SIZE);
674 if (!entropy_collector->mem) {
675 jent_zfree(entropy_collector);
676 return NULL;
677 }
678 entropy_collector->memblocksize =
679 CONFIG_CRYPTO_JITTERENTROPY_MEMORY_BLOCKSIZE;
680 entropy_collector->memblocks =
681 CONFIG_CRYPTO_JITTERENTROPY_MEMORY_BLOCKS;
682 entropy_collector->memaccessloops = JENT_MEMORY_ACCESSLOOPS;
683 }
684
685 /* verify and set the oversampling rate */
686 if (osr == 0)
687 osr = 1; /* H_submitter = 1 / osr */
688 entropy_collector->osr = osr;
689 entropy_collector->flags = flags;
690
691 entropy_collector->hash_state = hash_state;
692
693 /* Initialize the APT */
694 jent_apt_init(entropy_collector, osr);
695
696 /* fill the data pad with non-zero values */
697 jent_gen_entropy(entropy_collector);
698
699 return entropy_collector;
700}
701
702void jent_entropy_collector_free(struct rand_data *entropy_collector)
703{
704 jent_kvzfree(entropy_collector->mem, JENT_MEMORY_SIZE);
705 entropy_collector->mem = NULL;
706 jent_zfree(entropy_collector);
707}
708
709int jent_entropy_init(unsigned int osr, unsigned int flags, void *hash_state,
710 struct rand_data *p_ec)
711{
712 /*
713 * If caller provides an allocated ec, reuse it which implies that the
714 * health test entropy data is used to further still the available
715 * entropy pool.
716 */
717 struct rand_data *ec = p_ec;
718 int i, time_backwards = 0, ret = 0, ec_free = 0;
719 unsigned int health_test_result;
720
721 if (!ec) {
722 ec = jent_entropy_collector_alloc(osr, flags, hash_state);
723 if (!ec)
724 return JENT_EMEM;
725 ec_free = 1;
726 } else {
727 /* Reset the APT */
728 jent_apt_reset(ec, 0);
729 /* Ensure that a new APT base is obtained */
730 ec->apt_base_set = 0;
731 /* Reset the RCT */
732 ec->rct_count = 0;
733 /* Reset intermittent, leave permanent health test result */
734 ec->health_failure &= (~JENT_RCT_FAILURE);
735 ec->health_failure &= (~JENT_APT_FAILURE);
736 }
737
738 /* We could perform statistical tests here, but the problem is
739 * that we only have a few loop counts to do testing. These
740 * loop counts may show some slight skew and we produce
741 * false positives.
742 *
743 * Moreover, only old systems show potentially problematic
744 * jitter entropy that could potentially be caught here. But
745 * the RNG is intended for hardware that is available or widely
746 * used, but not old systems that are long out of favor. Thus,
747 * no statistical tests.
748 */
749
750 /*
751 * We could add a check for system capabilities such as clock_getres or
752 * check for CONFIG_X86_TSC, but it does not make much sense as the
753 * following sanity checks verify that we have a high-resolution
754 * timer.
755 */
756 /*
757 * TESTLOOPCOUNT needs some loops to identify edge systems. 100 is
758 * definitely too little.
759 *
760 * SP800-90B requires at least 1024 initial test cycles.
761 */
762#define TESTLOOPCOUNT 1024
763#define CLEARCACHE 100
764 for (i = 0; (TESTLOOPCOUNT + CLEARCACHE) > i; i++) {
765 __u64 start_time = 0, end_time = 0, delta = 0;
766
767 /* Invoke core entropy collection logic */
768 jent_measure_jitter(ec, &delta);
769 end_time = ec->prev_time;
770 start_time = ec->prev_time - delta;
771
772 /* test whether timer works */
773 if (!start_time || !end_time) {
774 ret = JENT_ENOTIME;
775 goto out;
776 }
777
778 /*
779 * test whether timer is fine grained enough to provide
780 * delta even when called shortly after each other -- this
781 * implies that we also have a high resolution timer
782 */
783 if (!delta || (end_time == start_time)) {
784 ret = JENT_ECOARSETIME;
785 goto out;
786 }
787
788 /*
789 * up to here we did not modify any variable that will be
790 * evaluated later, but we already performed some work. Thus we
791 * already have had an impact on the caches, branch prediction,
792 * etc. with the goal to clear it to get the worst case
793 * measurements.
794 */
795 if (i < CLEARCACHE)
796 continue;
797
798 /* test whether we have an increasing timer */
799 if (!(end_time > start_time))
800 time_backwards++;
801 }
802
803 /*
804 * we allow up to three times the time running backwards.
805 * CLOCK_REALTIME is affected by adjtime and NTP operations. Thus,
806 * if such an operation just happens to interfere with our test, it
807 * should not fail. The value of 3 should cover the NTP case being
808 * performed during our test run.
809 */
810 if (time_backwards > 3) {
811 ret = JENT_ENOMONOTONIC;
812 goto out;
813 }
814
815 /* Did we encounter a health test failure? */
816 health_test_result = jent_health_failure(ec);
817 if (health_test_result) {
818 ret = (health_test_result & JENT_RCT_FAILURE) ? JENT_ERCT :
819 JENT_EHEALTH;
820 goto out;
821 }
822
823out:
824 if (ec_free)
825 jent_entropy_collector_free(ec);
826
827 return ret;
828}