crypto/jitterentropy.c

   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 #include "jitterentropy.h"
 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         /*
 130          * Mix the current state of the random number into the shuffle
 131          * calculation to balance that shuffle a bit more.
 132          */
 133         if (ec)
 134                 time ^= ec->data;
 135         /*
 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.
 138          */
 139         for (i = 0; ((DATA_SIZE_BITS + bits - 1) / bits) > i; i++) {
 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  *
 159  * This function injects the individual bits of the time value into the
 160  * entropy pool using an LFSR.
 161  *
 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.
 168  *
 169  * Input:
 170  * @ec entropy collector struct
 171  * @time time stamp to be injected
 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:
 176  * updated ec->data
 177  *
 178  * @return Number of loops the folding operation is performed
 179  */
 180 static __u64 jent_lfsr_time(struct rand_data *ec, __u64 time, __u64 loop_cnt)
 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++) {
 197                 new = ec->data;
 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);
 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;
 220                         new ^= tmp;
 221                 }
 222         }
 223         ec->data = new;
 224
 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 {
 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++) {
 276                 unsigned char *tmpval = ec->mem + ec->memlocation;
 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  */
 314 static int jent_stuck(struct rand_data *ec, __u64 current_delta)
 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)
 323                 return 1;
 324
 325         return 0;
 326 }
 327
 328 /**
 329  * This is the heart of the entropy generation: calculate time deltas and
 330  * use the CPU jitter in the time deltas. The jitter is injected into the
 331  * entropy pool.
 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  *
 340  * @return result of stuck test
 341  */
 342 static int jent_measure_jitter(struct rand_data *ec)
 343 {
 344         __u64 time = 0;
 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
 358         /* Now call the next noise sources which also injects the data */
 359         jent_lfsr_time(ec, current_delta, 0);
 360
 361         /* Check whether we have a stuck measurement. */
 362         return jent_stuck(ec, current_delta);
 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) {
 380                 /* If a stuck measurement is received, repeat measurement */
 381                 if (jent_measure_jitter(ec))
 382                         continue;
 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         }
 391 }
 392
 393 /**
 394  * The continuous test required by FIPS 140-2 -- the function automatically
 395  * primes the test if needed.
 396  *
 397  * Return:
 398  * returns normally if FIPS test passed
 399  * panics the kernel if FIPS test failed
 400  */
 401 static void jent_fips_test(struct rand_data *ec)
 402 {
 403         if (!jent_fips_enabled())
 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)
 413                 jent_panic("jitterentropy: Duplicate output detected\n");
 414
 415         ec->old_data = ec->data;
 416 }
 417
 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  */
 440 int jent_read_entropy(struct rand_data *ec, unsigned char *data,
 441                       unsigned int len)
 442 {
 443         unsigned char *p = data;
 444
 445         if (!ec)
 446                 return -1;
 447
 448         while (0 < len) {
 449                 unsigned int tocopy;
 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;
 457                 jent_memcpy(p, &ec->data, tocopy);
 458
 459                 len -= tocopy;
 460                 p += tocopy;
 461         }
 462
 463         return 0;
 464 }
 465
 466 /***************************************************************************
 467  * Initialization logic
 468  ***************************************************************************/
 469
 470 struct rand_data *jent_entropy_collector_alloc(unsigned int osr,
 471                                                unsigned int flags)
 472 {
 473         struct rand_data *entropy_collector;
 474
 475         entropy_collector = jent_zalloc(sizeof(struct rand_data));
 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                  */
 483                 entropy_collector->mem = jent_zalloc(JENT_MEMORY_SIZE);
 484                 if (!entropy_collector->mem) {
 485                         jent_zfree(entropy_collector);
 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
 498         /* fill the data pad with non-zero values */
 499         jent_gen_entropy(entropy_collector);
 500
 501         return entropy_collector;
 502 }
 503
 504 void jent_entropy_collector_free(struct rand_data *entropy_collector)
 505 {
 506         jent_zfree(entropy_collector->mem);
 507         entropy_collector->mem = NULL;
 508         jent_zfree(entropy_collector);
 509 }
 510
 511 int jent_entropy_init(void)
 512 {
 513         int i;
 514         __u64 delta_sum = 0;
 515         __u64 old_delta = 0;
 516         int time_backwards = 0;
 517         int count_mod = 0;
 518         int count_stuck = 0;
 519         struct rand_data ec = { 0 };
 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;
 548                 __u64 delta = 0;
 549                 unsigned int lowdelta = 0;
 550                 int stuck;
 551
 552                 /* Invoke core entropy collection logic */
 553                 jent_get_nstime(&time);
 554                 ec.prev_time = time;
 555                 jent_lfsr_time(&ec, time, 0);
 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
 570                 stuck = jent_stuck(&ec, delta);
 571
 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
 582                 if (stuck)
 583                         count_stuck++;
 584
 585                 /* test whether we have an increasing timer */
 586                 if (!(time2 > time))
 587                         time_backwards++;
 588
 589                 /* use 32 bit value to ensure compilation on 32 bit arches */
 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                  */
 600                 if (delta > old_delta)
 601                         delta_sum += (delta - old_delta);
 602                 else
 603                         delta_sum += (old_delta - delta);
 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;
 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          */
 622         if ((delta_sum) <= 1)
 623                 return JENT_EVARVAR;
 624
 625         /*
 626          * Ensure that we have variations in the time stamp below 10 for at
 627          * least 10% of all checks -- on some platforms, the counter increments
 628          * in multiples of 100, but not always
 629          */
 630         if ((TESTLOOPCOUNT/10 * 9) < count_mod)
 631                 return JENT_ECOARSETIME;
 632
 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
 640         return 0;
 641 }