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}