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
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
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
106 void jent_get_nstime(__u64 *out);
107 void *jent_zalloc(unsigned int len);
108 void jent_zfree(void *ptr);
109 int jent_fips_enabled(void);
110 void jent_panic(char *s);
111 void 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 */
125 static __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 */
185 static __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 */
260 static 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 */
319 static 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 */
347 static 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 */
377 static 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 */
406 static 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 */
445 int 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
475 struct 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
509 void 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
516 int 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 }