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bb5530e4 | 1 | /* |
dfc9fa91 SM |
2 | * Non-physical true random number generator based on timing jitter -- |
3 | * Jitter RNG standalone code. | |
bb5530e4 | 4 | * |
d9d67c87 | 5 | * Copyright Stephan Mueller <smueller@chronox.de>, 2015 - 2019 |
bb5530e4 SM |
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 | |
d9d67c87 | 50 | * version 2.1.2 provided at http://www.chronox.de/jent.html |
bb5530e4 SM |
51 | */ |
52 | ||
dfc9fa91 SM |
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) | |
bb5530e4 | 61 | |
bb5530e4 SM |
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 */ | |
bb5530e4 | 74 | unsigned int osr; /* Oversample rate */ |
bb5530e4 SM |
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 */ | |
bb5530e4 SM |
89 | #define JENT_DISABLE_MEMORY_ACCESS (1<<2) /* Disable memory access for more |
90 | * entropy, saves MEMORY_SIZE RAM for | |
91 | * entropy collector */ | |
92 | ||
bb5530e4 SM |
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 */ | |
bb5530e4 SM |
97 | #define JENT_EVARVAR 5 /* Timer does not produce variations of |
98 | * variations (2nd derivation of time is | |
99 | * zero). */ | |
d9d67c87 | 100 | #define JENT_ESTUCK 8 /* Too many stuck results during init. */ |
bb5530e4 SM |
101 | |
102 | /*************************************************************************** | |
103 | * Helper functions | |
104 | ***************************************************************************/ | |
105 | ||
965d7286 | 106 | #include "jitterentropy.h" |
bb5530e4 SM |
107 | |
108 | /** | |
109 | * Update of the loop count used for the next round of | |
110 | * an entropy collection. | |
111 | * | |
112 | * Input: | |
113 | * @ec entropy collector struct -- may be NULL | |
114 | * @bits is the number of low bits of the timer to consider | |
115 | * @min is the number of bits we shift the timer value to the right at | |
116 | * the end to make sure we have a guaranteed minimum value | |
117 | * | |
118 | * @return Newly calculated loop counter | |
119 | */ | |
120 | static __u64 jent_loop_shuffle(struct rand_data *ec, | |
121 | unsigned int bits, unsigned int min) | |
122 | { | |
123 | __u64 time = 0; | |
124 | __u64 shuffle = 0; | |
125 | unsigned int i = 0; | |
126 | unsigned int mask = (1<<bits) - 1; | |
127 | ||
128 | jent_get_nstime(&time); | |
129 | /* | |
d9d67c87 SM |
130 | * Mix the current state of the random number into the shuffle |
131 | * calculation to balance that shuffle a bit more. | |
bb5530e4 SM |
132 | */ |
133 | if (ec) | |
134 | time ^= ec->data; | |
135 | /* | |
d9d67c87 SM |
136 | * We fold the time value as much as possible to ensure that as many |
137 | * bits of the time stamp are included as possible. | |
bb5530e4 | 138 | */ |
d9d67c87 | 139 | for (i = 0; ((DATA_SIZE_BITS + bits - 1) / bits) > i; i++) { |
bb5530e4 SM |
140 | shuffle ^= time & mask; |
141 | time = time >> bits; | |
142 | } | |
143 | ||
144 | /* | |
145 | * We add a lower boundary value to ensure we have a minimum | |
146 | * RNG loop count. | |
147 | */ | |
148 | return (shuffle + (1<<min)); | |
149 | } | |
150 | ||
151 | /*************************************************************************** | |
152 | * Noise sources | |
153 | ***************************************************************************/ | |
154 | ||
155 | /** | |
156 | * CPU Jitter noise source -- this is the noise source based on the CPU | |
157 | * execution time jitter | |
158 | * | |
d9d67c87 SM |
159 | * This function injects the individual bits of the time value into the |
160 | * entropy pool using an LFSR. | |
bb5530e4 | 161 | * |
d9d67c87 SM |
162 | * The code is deliberately inefficient with respect to the bit shifting |
163 | * and shall stay that way. This function is the root cause why the code | |
164 | * shall be compiled without optimization. This function not only acts as | |
165 | * folding operation, but this function's execution is used to measure | |
166 | * the CPU execution time jitter. Any change to the loop in this function | |
167 | * implies that careful retesting must be done. | |
bb5530e4 SM |
168 | * |
169 | * Input: | |
e1f653cb | 170 | * @ec entropy collector struct |
d9d67c87 | 171 | * @time time stamp to be injected |
bb5530e4 SM |
172 | * @loop_cnt if a value not equal to 0 is set, use the given value as number of |
173 | * loops to perform the folding | |
174 | * | |
175 | * Output: | |
d9d67c87 | 176 | * updated ec->data |
bb5530e4 SM |
177 | * |
178 | * @return Number of loops the folding operation is performed | |
179 | */ | |
d9d67c87 | 180 | static __u64 jent_lfsr_time(struct rand_data *ec, __u64 time, __u64 loop_cnt) |
bb5530e4 SM |
181 | { |
182 | unsigned int i; | |
183 | __u64 j = 0; | |
184 | __u64 new = 0; | |
185 | #define MAX_FOLD_LOOP_BIT 4 | |
186 | #define MIN_FOLD_LOOP_BIT 0 | |
187 | __u64 fold_loop_cnt = | |
188 | jent_loop_shuffle(ec, MAX_FOLD_LOOP_BIT, MIN_FOLD_LOOP_BIT); | |
189 | ||
190 | /* | |
191 | * testing purposes -- allow test app to set the counter, not | |
192 | * needed during runtime | |
193 | */ | |
194 | if (loop_cnt) | |
195 | fold_loop_cnt = loop_cnt; | |
196 | for (j = 0; j < fold_loop_cnt; j++) { | |
d9d67c87 | 197 | new = ec->data; |
bb5530e4 SM |
198 | for (i = 1; (DATA_SIZE_BITS) >= i; i++) { |
199 | __u64 tmp = time << (DATA_SIZE_BITS - i); | |
200 | ||
201 | tmp = tmp >> (DATA_SIZE_BITS - 1); | |
d9d67c87 SM |
202 | |
203 | /* | |
204 | * Fibonacci LSFR with polynomial of | |
205 | * x^64 + x^61 + x^56 + x^31 + x^28 + x^23 + 1 which is | |
206 | * primitive according to | |
207 | * http://poincare.matf.bg.ac.rs/~ezivkovm/publications/primpol1.pdf | |
208 | * (the shift values are the polynomial values minus one | |
209 | * due to counting bits from 0 to 63). As the current | |
210 | * position is always the LSB, the polynomial only needs | |
211 | * to shift data in from the left without wrap. | |
212 | */ | |
213 | tmp ^= ((new >> 63) & 1); | |
214 | tmp ^= ((new >> 60) & 1); | |
215 | tmp ^= ((new >> 55) & 1); | |
216 | tmp ^= ((new >> 30) & 1); | |
217 | tmp ^= ((new >> 27) & 1); | |
218 | tmp ^= ((new >> 22) & 1); | |
219 | new <<= 1; | |
bb5530e4 SM |
220 | new ^= tmp; |
221 | } | |
222 | } | |
d9d67c87 SM |
223 | ec->data = new; |
224 | ||
bb5530e4 SM |
225 | return fold_loop_cnt; |
226 | } | |
227 | ||
228 | /** | |
229 | * Memory Access noise source -- this is a noise source based on variations in | |
230 | * memory access times | |
231 | * | |
232 | * This function performs memory accesses which will add to the timing | |
233 | * variations due to an unknown amount of CPU wait states that need to be | |
234 | * added when accessing memory. The memory size should be larger than the L1 | |
235 | * caches as outlined in the documentation and the associated testing. | |
236 | * | |
237 | * The L1 cache has a very high bandwidth, albeit its access rate is usually | |
238 | * slower than accessing CPU registers. Therefore, L1 accesses only add minimal | |
239 | * variations as the CPU has hardly to wait. Starting with L2, significant | |
240 | * variations are added because L2 typically does not belong to the CPU any more | |
241 | * and therefore a wider range of CPU wait states is necessary for accesses. | |
242 | * L3 and real memory accesses have even a wider range of wait states. However, | |
243 | * to reliably access either L3 or memory, the ec->mem memory must be quite | |
244 | * large which is usually not desirable. | |
245 | * | |
246 | * Input: | |
247 | * @ec Reference to the entropy collector with the memory access data -- if | |
248 | * the reference to the memory block to be accessed is NULL, this noise | |
249 | * source is disabled | |
250 | * @loop_cnt if a value not equal to 0 is set, use the given value as number of | |
251 | * loops to perform the folding | |
252 | * | |
253 | * @return Number of memory access operations | |
254 | */ | |
255 | static unsigned int jent_memaccess(struct rand_data *ec, __u64 loop_cnt) | |
256 | { | |
bb5530e4 SM |
257 | unsigned int wrap = 0; |
258 | __u64 i = 0; | |
259 | #define MAX_ACC_LOOP_BIT 7 | |
260 | #define MIN_ACC_LOOP_BIT 0 | |
261 | __u64 acc_loop_cnt = | |
262 | jent_loop_shuffle(ec, MAX_ACC_LOOP_BIT, MIN_ACC_LOOP_BIT); | |
263 | ||
264 | if (NULL == ec || NULL == ec->mem) | |
265 | return 0; | |
266 | wrap = ec->memblocksize * ec->memblocks; | |
267 | ||
268 | /* | |
269 | * testing purposes -- allow test app to set the counter, not | |
270 | * needed during runtime | |
271 | */ | |
272 | if (loop_cnt) | |
273 | acc_loop_cnt = loop_cnt; | |
274 | ||
275 | for (i = 0; i < (ec->memaccessloops + acc_loop_cnt); i++) { | |
d9d67c87 | 276 | unsigned char *tmpval = ec->mem + ec->memlocation; |
bb5530e4 SM |
277 | /* |
278 | * memory access: just add 1 to one byte, | |
279 | * wrap at 255 -- memory access implies read | |
280 | * from and write to memory location | |
281 | */ | |
282 | *tmpval = (*tmpval + 1) & 0xff; | |
283 | /* | |
284 | * Addition of memblocksize - 1 to pointer | |
285 | * with wrap around logic to ensure that every | |
286 | * memory location is hit evenly | |
287 | */ | |
288 | ec->memlocation = ec->memlocation + ec->memblocksize - 1; | |
289 | ec->memlocation = ec->memlocation % wrap; | |
290 | } | |
291 | return i; | |
292 | } | |
293 | ||
294 | /*************************************************************************** | |
295 | * Start of entropy processing logic | |
296 | ***************************************************************************/ | |
297 | ||
298 | /** | |
299 | * Stuck test by checking the: | |
300 | * 1st derivation of the jitter measurement (time delta) | |
301 | * 2nd derivation of the jitter measurement (delta of time deltas) | |
302 | * 3rd derivation of the jitter measurement (delta of delta of time deltas) | |
303 | * | |
304 | * All values must always be non-zero. | |
305 | * | |
306 | * Input: | |
307 | * @ec Reference to entropy collector | |
308 | * @current_delta Jitter time delta | |
309 | * | |
310 | * @return | |
311 | * 0 jitter measurement not stuck (good bit) | |
312 | * 1 jitter measurement stuck (reject bit) | |
313 | */ | |
d9d67c87 | 314 | static int jent_stuck(struct rand_data *ec, __u64 current_delta) |
bb5530e4 SM |
315 | { |
316 | __s64 delta2 = ec->last_delta - current_delta; | |
317 | __s64 delta3 = delta2 - ec->last_delta2; | |
318 | ||
319 | ec->last_delta = current_delta; | |
320 | ec->last_delta2 = delta2; | |
321 | ||
322 | if (!current_delta || !delta2 || !delta3) | |
d9d67c87 SM |
323 | return 1; |
324 | ||
325 | return 0; | |
bb5530e4 SM |
326 | } |
327 | ||
328 | /** | |
329 | * This is the heart of the entropy generation: calculate time deltas and | |
d9d67c87 SM |
330 | * use the CPU jitter in the time deltas. The jitter is injected into the |
331 | * entropy pool. | |
bb5530e4 SM |
332 | * |
333 | * WARNING: ensure that ->prev_time is primed before using the output | |
334 | * of this function! This can be done by calling this function | |
335 | * and not using its result. | |
336 | * | |
337 | * Input: | |
338 | * @entropy_collector Reference to entropy collector | |
339 | * | |
d9d67c87 | 340 | * @return result of stuck test |
bb5530e4 | 341 | */ |
d9d67c87 | 342 | static int jent_measure_jitter(struct rand_data *ec) |
bb5530e4 SM |
343 | { |
344 | __u64 time = 0; | |
bb5530e4 SM |
345 | __u64 current_delta = 0; |
346 | ||
347 | /* Invoke one noise source before time measurement to add variations */ | |
348 | jent_memaccess(ec, 0); | |
349 | ||
350 | /* | |
351 | * Get time stamp and calculate time delta to previous | |
352 | * invocation to measure the timing variations | |
353 | */ | |
354 | jent_get_nstime(&time); | |
355 | current_delta = time - ec->prev_time; | |
356 | ec->prev_time = time; | |
357 | ||
d9d67c87 SM |
358 | /* Now call the next noise sources which also injects the data */ |
359 | jent_lfsr_time(ec, current_delta, 0); | |
bb5530e4 | 360 | |
d9d67c87 SM |
361 | /* Check whether we have a stuck measurement. */ |
362 | return jent_stuck(ec, current_delta); | |
bb5530e4 SM |
363 | } |
364 | ||
365 | /** | |
366 | * Generator of one 64 bit random number | |
367 | * Function fills rand_data->data | |
368 | * | |
369 | * Input: | |
370 | * @ec Reference to entropy collector | |
371 | */ | |
372 | static void jent_gen_entropy(struct rand_data *ec) | |
373 | { | |
374 | unsigned int k = 0; | |
375 | ||
376 | /* priming of the ->prev_time value */ | |
377 | jent_measure_jitter(ec); | |
378 | ||
379 | while (1) { | |
d9d67c87 SM |
380 | /* If a stuck measurement is received, repeat measurement */ |
381 | if (jent_measure_jitter(ec)) | |
bb5530e4 | 382 | continue; |
bb5530e4 SM |
383 | |
384 | /* | |
385 | * We multiply the loop value with ->osr to obtain the | |
386 | * oversampling rate requested by the caller | |
387 | */ | |
388 | if (++k >= (DATA_SIZE_BITS * ec->osr)) | |
389 | break; | |
390 | } | |
bb5530e4 SM |
391 | } |
392 | ||
393 | /** | |
394 | * The continuous test required by FIPS 140-2 -- the function automatically | |
395 | * primes the test if needed. | |
396 | * | |
397 | * Return: | |
e1f653cb AP |
398 | * returns normally if FIPS test passed |
399 | * panics the kernel if FIPS test failed | |
bb5530e4 SM |
400 | */ |
401 | static void jent_fips_test(struct rand_data *ec) | |
402 | { | |
dfc9fa91 | 403 | if (!jent_fips_enabled()) |
bb5530e4 SM |
404 | return; |
405 | ||
406 | /* prime the FIPS test */ | |
407 | if (!ec->old_data) { | |
408 | ec->old_data = ec->data; | |
409 | jent_gen_entropy(ec); | |
410 | } | |
411 | ||
412 | if (ec->data == ec->old_data) | |
dfc9fa91 | 413 | jent_panic("jitterentropy: Duplicate output detected\n"); |
bb5530e4 SM |
414 | |
415 | ec->old_data = ec->data; | |
416 | } | |
417 | ||
bb5530e4 SM |
418 | /** |
419 | * Entry function: Obtain entropy for the caller. | |
420 | * | |
421 | * This function invokes the entropy gathering logic as often to generate | |
422 | * as many bytes as requested by the caller. The entropy gathering logic | |
423 | * creates 64 bit per invocation. | |
424 | * | |
425 | * This function truncates the last 64 bit entropy value output to the exact | |
426 | * size specified by the caller. | |
427 | * | |
428 | * Input: | |
429 | * @ec Reference to entropy collector | |
430 | * @data pointer to buffer for storing random data -- buffer must already | |
431 | * exist | |
432 | * @len size of the buffer, specifying also the requested number of random | |
433 | * in bytes | |
434 | * | |
435 | * @return 0 when request is fulfilled or an error | |
436 | * | |
437 | * The following error codes can occur: | |
438 | * -1 entropy_collector is NULL | |
439 | */ | |
dfc9fa91 SM |
440 | int jent_read_entropy(struct rand_data *ec, unsigned char *data, |
441 | unsigned int len) | |
bb5530e4 | 442 | { |
dfc9fa91 | 443 | unsigned char *p = data; |
bb5530e4 SM |
444 | |
445 | if (!ec) | |
dfc9fa91 | 446 | return -1; |
bb5530e4 SM |
447 | |
448 | while (0 < len) { | |
dfc9fa91 | 449 | unsigned int tocopy; |
bb5530e4 SM |
450 | |
451 | jent_gen_entropy(ec); | |
452 | jent_fips_test(ec); | |
453 | if ((DATA_SIZE_BITS / 8) < len) | |
454 | tocopy = (DATA_SIZE_BITS / 8); | |
455 | else | |
456 | tocopy = len; | |
dfc9fa91 | 457 | jent_memcpy(p, &ec->data, tocopy); |
bb5530e4 SM |
458 | |
459 | len -= tocopy; | |
460 | p += tocopy; | |
461 | } | |
462 | ||
463 | return 0; | |
464 | } | |
465 | ||
466 | /*************************************************************************** | |
467 | * Initialization logic | |
468 | ***************************************************************************/ | |
469 | ||
dfc9fa91 SM |
470 | struct rand_data *jent_entropy_collector_alloc(unsigned int osr, |
471 | unsigned int flags) | |
bb5530e4 SM |
472 | { |
473 | struct rand_data *entropy_collector; | |
474 | ||
dfc9fa91 | 475 | entropy_collector = jent_zalloc(sizeof(struct rand_data)); |
bb5530e4 SM |
476 | if (!entropy_collector) |
477 | return NULL; | |
478 | ||
479 | if (!(flags & JENT_DISABLE_MEMORY_ACCESS)) { | |
480 | /* Allocate memory for adding variations based on memory | |
481 | * access | |
482 | */ | |
dfc9fa91 | 483 | entropy_collector->mem = jent_zalloc(JENT_MEMORY_SIZE); |
bb5530e4 | 484 | if (!entropy_collector->mem) { |
dfc9fa91 | 485 | jent_zfree(entropy_collector); |
bb5530e4 SM |
486 | return NULL; |
487 | } | |
488 | entropy_collector->memblocksize = JENT_MEMORY_BLOCKSIZE; | |
489 | entropy_collector->memblocks = JENT_MEMORY_BLOCKS; | |
490 | entropy_collector->memaccessloops = JENT_MEMORY_ACCESSLOOPS; | |
491 | } | |
492 | ||
493 | /* verify and set the oversampling rate */ | |
494 | if (0 == osr) | |
495 | osr = 1; /* minimum sampling rate is 1 */ | |
496 | entropy_collector->osr = osr; | |
497 | ||
bb5530e4 SM |
498 | /* fill the data pad with non-zero values */ |
499 | jent_gen_entropy(entropy_collector); | |
500 | ||
501 | return entropy_collector; | |
502 | } | |
503 | ||
dfc9fa91 | 504 | void jent_entropy_collector_free(struct rand_data *entropy_collector) |
bb5530e4 | 505 | { |
cea0a3c3 | 506 | jent_zfree(entropy_collector->mem); |
bb5530e4 | 507 | entropy_collector->mem = NULL; |
cea0a3c3 | 508 | jent_zfree(entropy_collector); |
bb5530e4 SM |
509 | } |
510 | ||
dfc9fa91 | 511 | int jent_entropy_init(void) |
bb5530e4 SM |
512 | { |
513 | int i; | |
514 | __u64 delta_sum = 0; | |
515 | __u64 old_delta = 0; | |
516 | int time_backwards = 0; | |
bb5530e4 | 517 | int count_mod = 0; |
d9d67c87 SM |
518 | int count_stuck = 0; |
519 | struct rand_data ec = { 0 }; | |
bb5530e4 SM |
520 | |
521 | /* We could perform statistical tests here, but the problem is | |
522 | * that we only have a few loop counts to do testing. These | |
523 | * loop counts may show some slight skew and we produce | |
524 | * false positives. | |
525 | * | |
526 | * Moreover, only old systems show potentially problematic | |
527 | * jitter entropy that could potentially be caught here. But | |
528 | * the RNG is intended for hardware that is available or widely | |
529 | * used, but not old systems that are long out of favor. Thus, | |
530 | * no statistical tests. | |
531 | */ | |
532 | ||
533 | /* | |
534 | * We could add a check for system capabilities such as clock_getres or | |
535 | * check for CONFIG_X86_TSC, but it does not make much sense as the | |
536 | * following sanity checks verify that we have a high-resolution | |
537 | * timer. | |
538 | */ | |
539 | /* | |
540 | * TESTLOOPCOUNT needs some loops to identify edge systems. 100 is | |
541 | * definitely too little. | |
542 | */ | |
543 | #define TESTLOOPCOUNT 300 | |
544 | #define CLEARCACHE 100 | |
545 | for (i = 0; (TESTLOOPCOUNT + CLEARCACHE) > i; i++) { | |
546 | __u64 time = 0; | |
547 | __u64 time2 = 0; | |
bb5530e4 SM |
548 | __u64 delta = 0; |
549 | unsigned int lowdelta = 0; | |
d9d67c87 | 550 | int stuck; |
bb5530e4 | 551 | |
d9d67c87 | 552 | /* Invoke core entropy collection logic */ |
bb5530e4 | 553 | jent_get_nstime(&time); |
d9d67c87 SM |
554 | ec.prev_time = time; |
555 | jent_lfsr_time(&ec, time, 0); | |
bb5530e4 SM |
556 | jent_get_nstime(&time2); |
557 | ||
558 | /* test whether timer works */ | |
559 | if (!time || !time2) | |
560 | return JENT_ENOTIME; | |
561 | delta = time2 - time; | |
562 | /* | |
563 | * test whether timer is fine grained enough to provide | |
564 | * delta even when called shortly after each other -- this | |
565 | * implies that we also have a high resolution timer | |
566 | */ | |
567 | if (!delta) | |
568 | return JENT_ECOARSETIME; | |
569 | ||
d9d67c87 SM |
570 | stuck = jent_stuck(&ec, delta); |
571 | ||
bb5530e4 SM |
572 | /* |
573 | * up to here we did not modify any variable that will be | |
574 | * evaluated later, but we already performed some work. Thus we | |
575 | * already have had an impact on the caches, branch prediction, | |
576 | * etc. with the goal to clear it to get the worst case | |
577 | * measurements. | |
578 | */ | |
579 | if (CLEARCACHE > i) | |
580 | continue; | |
581 | ||
d9d67c87 SM |
582 | if (stuck) |
583 | count_stuck++; | |
584 | ||
bb5530e4 SM |
585 | /* test whether we have an increasing timer */ |
586 | if (!(time2 > time)) | |
587 | time_backwards++; | |
588 | ||
d9d67c87 | 589 | /* use 32 bit value to ensure compilation on 32 bit arches */ |
bb5530e4 SM |
590 | lowdelta = time2 - time; |
591 | if (!(lowdelta % 100)) | |
592 | count_mod++; | |
593 | ||
594 | /* | |
595 | * ensure that we have a varying delta timer which is necessary | |
596 | * for the calculation of entropy -- perform this check | |
597 | * only after the first loop is executed as we need to prime | |
598 | * the old_data value | |
599 | */ | |
d9d67c87 SM |
600 | if (delta > old_delta) |
601 | delta_sum += (delta - old_delta); | |
602 | else | |
603 | delta_sum += (old_delta - delta); | |
bb5530e4 SM |
604 | old_delta = delta; |
605 | } | |
606 | ||
607 | /* | |
608 | * we allow up to three times the time running backwards. | |
609 | * CLOCK_REALTIME is affected by adjtime and NTP operations. Thus, | |
610 | * if such an operation just happens to interfere with our test, it | |
611 | * should not fail. The value of 3 should cover the NTP case being | |
612 | * performed during our test run. | |
613 | */ | |
614 | if (3 < time_backwards) | |
615 | return JENT_ENOMONOTONIC; | |
bb5530e4 SM |
616 | |
617 | /* | |
618 | * Variations of deltas of time must on average be larger | |
619 | * than 1 to ensure the entropy estimation | |
620 | * implied with 1 is preserved | |
621 | */ | |
d9d67c87 SM |
622 | if ((delta_sum) <= 1) |
623 | return JENT_EVARVAR; | |
bb5530e4 SM |
624 | |
625 | /* | |
626 | * Ensure that we have variations in the time stamp below 10 for at | |
d9d67c87 SM |
627 | * least 10% of all checks -- on some platforms, the counter increments |
628 | * in multiples of 100, but not always | |
bb5530e4 SM |
629 | */ |
630 | if ((TESTLOOPCOUNT/10 * 9) < count_mod) | |
631 | return JENT_ECOARSETIME; | |
632 | ||
d9d67c87 SM |
633 | /* |
634 | * If we have more than 90% stuck results, then this Jitter RNG is | |
635 | * likely to not work well. | |
636 | */ | |
637 | if ((TESTLOOPCOUNT/10 * 9) < count_stuck) | |
638 | return JENT_ESTUCK; | |
639 | ||
bb5530e4 SM |
640 | return 0; |
641 | } |