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
   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 1.1.0 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 stuck:1;   /* Time measurement stuck */
  75         unsigned int osr;       /* Oversample rate */
  76         unsigned int stir:1;            /* Post-processing stirring */
  77         unsigned int disable_unbias:1;  /* Deactivate Von-Neuman unbias */
  78 #define JENT_MEMORY_BLOCKS 64
  79 #define JENT_MEMORY_BLOCKSIZE 32
  80 #define JENT_MEMORY_ACCESSLOOPS 128
  81 #define JENT_MEMORY_SIZE (JENT_MEMORY_BLOCKS*JENT_MEMORY_BLOCKSIZE)
  82         unsigned char *mem;     /* Memory access location with size of
  83                                  * memblocks * memblocksize */
  84         unsigned int memlocation; /* Pointer to byte in *mem */
  85         unsigned int memblocks; /* Number of memory blocks in *mem */
  86         unsigned int memblocksize; /* Size of one memory block in bytes */
  87         unsigned int memaccessloops; /* Number of memory accesses per random
  88                                       * bit generation */
  89 };
  90
  91 /* Flags that can be used to initialize the RNG */
  92 #define JENT_DISABLE_STIR (1<<0) /* Disable stirring the entropy pool */
  93 #define JENT_DISABLE_UNBIAS (1<<1) /* Disable the Von-Neuman Unbiaser */
  94 #define JENT_DISABLE_MEMORY_ACCESS (1<<2) /* Disable memory access for more
  95                                            * entropy, saves MEMORY_SIZE RAM for
  96                                            * entropy collector */
  97
  98 /* -- error codes for init function -- */
  99 #define JENT_ENOTIME            1 /* Timer service not available */
 100 #define JENT_ECOARSETIME        2 /* Timer too coarse for RNG */
 101 #define JENT_ENOMONOTONIC       3 /* Timer is not monotonic increasing */
 102 #define JENT_EMINVARIATION      4 /* Timer variations too small for RNG */
 103 #define JENT_EVARVAR            5 /* Timer does not produce variations of
 104                                    * variations (2nd derivation of time is
 105                                    * zero). */
 106 #define JENT_EMINVARVAR         6 /* Timer variations of variations is tooi
 107                                    * small. */
 108
 109 /***************************************************************************
 110  * Helper functions
 111  ***************************************************************************/
 112
 113 void jent_get_nstime(__u64 *out);
 114 __u64 jent_rol64(__u64 word, unsigned int shift);
 115 void *jent_zalloc(unsigned int len);
 116 void jent_zfree(void *ptr);
 117 int jent_fips_enabled(void);
 118 void jent_panic(char *s);
 119 void jent_memcpy(void *dest, const void *src, unsigned int n);
 120
 121 /**
 122  * Update of the loop count used for the next round of
 123  * an entropy collection.
 124  *
 125  * Input:
 126  * @ec entropy collector struct -- may be NULL
 127  * @bits is the number of low bits of the timer to consider
 128  * @min is the number of bits we shift the timer value to the right at
 129  *      the end to make sure we have a guaranteed minimum value
 130  *
 131  * @return Newly calculated loop counter
 132  */
 133 static __u64 jent_loop_shuffle(struct rand_data *ec,
 134                                unsigned int bits, unsigned int min)
 135 {
 136         __u64 time = 0;
 137         __u64 shuffle = 0;
 138         unsigned int i = 0;
 139         unsigned int mask = (1<<bits) - 1;
 140
 141         jent_get_nstime(&time);
 142         /*
 143          * mix the current state of the random number into the shuffle
 144          * calculation to balance that shuffle a bit more
 145          */
 146         if (ec)
 147                 time ^= ec->data;
 148         /*
 149          * we fold the time value as much as possible to ensure that as many
 150          * bits of the time stamp are included as possible
 151          */
 152         for (i = 0; (DATA_SIZE_BITS / bits) > i; i++) {
 153                 shuffle ^= time & mask;
 154                 time = time >> bits;
 155         }
 156
 157         /*
 158          * We add a lower boundary value to ensure we have a minimum
 159          * RNG loop count.
 160          */
 161         return (shuffle + (1<<min));
 162 }
 163
 164 /***************************************************************************
 165  * Noise sources
 166  ***************************************************************************/
 167
 168 /**
 169  * CPU Jitter noise source -- this is the noise source based on the CPU
 170  *                            execution time jitter
 171  *
 172  * This function folds the time into one bit units by iterating
 173  * through the DATA_SIZE_BITS bit time value as follows: assume our time value
 174  * is 0xabcd
 175  * 1st loop, 1st shift generates 0xd000
 176  * 1st loop, 2nd shift generates 0x000d
 177  * 2nd loop, 1st shift generates 0xcd00
 178  * 2nd loop, 2nd shift generates 0x000c
 179  * 3rd loop, 1st shift generates 0xbcd0
 180  * 3rd loop, 2nd shift generates 0x000b
 181  * 4th loop, 1st shift generates 0xabcd
 182  * 4th loop, 2nd shift generates 0x000a
 183  * Now, the values at the end of the 2nd shifts are XORed together.
 184  *
 185  * The code is deliberately inefficient and shall stay that way. This function
 186  * is the root cause why the code shall be compiled without optimization. This
 187  * function not only acts as folding operation, but this function's execution
 188  * is used to measure the CPU execution time jitter. Any change to the loop in
 189  * this function implies that careful retesting must be done.
 190  *
 191  * Input:
 192  * @ec entropy collector struct -- may be NULL
 193  * @time time stamp to be folded
 194  * @loop_cnt if a value not equal to 0 is set, use the given value as number of
 195  *           loops to perform the folding
 196  *
 197  * Output:
 198  * @folded result of folding operation
 199  *
 200  * @return Number of loops the folding operation is performed
 201  */
 202 static __u64 jent_fold_time(struct rand_data *ec, __u64 time,
 203                             __u64 *folded, __u64 loop_cnt)
 204 {
 205         unsigned int i;
 206         __u64 j = 0;
 207         __u64 new = 0;
 208 #define MAX_FOLD_LOOP_BIT 4
 209 #define MIN_FOLD_LOOP_BIT 0
 210         __u64 fold_loop_cnt =
 211                 jent_loop_shuffle(ec, MAX_FOLD_LOOP_BIT, MIN_FOLD_LOOP_BIT);
 212
 213         /*
 214          * testing purposes -- allow test app to set the counter, not
 215          * needed during runtime
 216          */
 217         if (loop_cnt)
 218                 fold_loop_cnt = loop_cnt;
 219         for (j = 0; j < fold_loop_cnt; j++) {
 220                 new = 0;
 221                 for (i = 1; (DATA_SIZE_BITS) >= i; i++) {
 222                         __u64 tmp = time << (DATA_SIZE_BITS - i);
 223
 224                         tmp = tmp >> (DATA_SIZE_BITS - 1);
 225                         new ^= tmp;
 226                 }
 227         }
 228         *folded = new;
 229         return fold_loop_cnt;
 230 }
 231
 232 /**
 233  * Memory Access noise source -- this is a noise source based on variations in
 234  *                               memory access times
 235  *
 236  * This function performs memory accesses which will add to the timing
 237  * variations due to an unknown amount of CPU wait states that need to be
 238  * added when accessing memory. The memory size should be larger than the L1
 239  * caches as outlined in the documentation and the associated testing.
 240  *
 241  * The L1 cache has a very high bandwidth, albeit its access rate is  usually
 242  * slower than accessing CPU registers. Therefore, L1 accesses only add minimal
 243  * variations as the CPU has hardly to wait. Starting with L2, significant
 244  * variations are added because L2 typically does not belong to the CPU any more
 245  * and therefore a wider range of CPU wait states is necessary for accesses.
 246  * L3 and real memory accesses have even a wider range of wait states. However,
 247  * to reliably access either L3 or memory, the ec->mem memory must be quite
 248  * large which is usually not desirable.
 249  *
 250  * Input:
 251  * @ec Reference to the entropy collector with the memory access data -- if
 252  *     the reference to the memory block to be accessed is NULL, this noise
 253  *     source is disabled
 254  * @loop_cnt if a value not equal to 0 is set, use the given value as number of
 255  *           loops to perform the folding
 256  *
 257  * @return Number of memory access operations
 258  */
 259 static unsigned int jent_memaccess(struct rand_data *ec, __u64 loop_cnt)
 260 {
 261         unsigned char *tmpval = NULL;
 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                 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 void 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                 ec->stuck = 1;
 329 }
 330
 331 /**
 332  * This is the heart of the entropy generation: calculate time deltas and
 333  * use the CPU jitter in the time deltas. The jitter is folded into one
 334  * bit. You can call this function the "random bit generator" as it
 335  * produces one random bit per invocation.
 336  *
 337  * WARNING: ensure that ->prev_time is primed before using the output
 338  *          of this function! This can be done by calling this function
 339  *          and not using its result.
 340  *
 341  * Input:
 342  * @entropy_collector Reference to entropy collector
 343  *
 344  * @return One random bit
 345  */
 346 static __u64 jent_measure_jitter(struct rand_data *ec)
 347 {
 348         __u64 time = 0;
 349         __u64 data = 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 folds the data */
 364         jent_fold_time(ec, current_delta, &data, 0);
 365
 366         /*
 367          * Check whether we have a stuck measurement. The enforcement
 368          * is performed after the stuck value has been mixed into the
 369          * entropy pool.
 370          */
 371         jent_stuck(ec, current_delta);
 372
 373         return data;
 374 }
 375
 376 /**
 377  * Von Neuman unbias as explained in RFC 4086 section 4.2. As shown in the
 378  * documentation of that RNG, the bits from jent_measure_jitter are considered
 379  * independent which implies that the Von Neuman unbias operation is applicable.
 380  * A proof of the Von-Neumann unbias operation to remove skews is given in the
 381  * document "A proposal for: Functionality classes for random number
 382  * generators", version 2.0 by Werner Schindler, section 5.4.1.
 383  *
 384  * Input:
 385  * @entropy_collector Reference to entropy collector
 386  *
 387  * @return One random bit
 388  */
 389 static __u64 jent_unbiased_bit(struct rand_data *entropy_collector)
 390 {
 391         do {
 392                 __u64 a = jent_measure_jitter(entropy_collector);
 393                 __u64 b = jent_measure_jitter(entropy_collector);
 394
 395                 if (a == b)
 396                         continue;
 397                 if (1 == a)
 398                         return 1;
 399                 else
 400                         return 0;
 401         } while (1);
 402 }
 403
 404 /**
 405  * Shuffle the pool a bit by mixing some value with a bijective function (XOR)
 406  * into the pool.
 407  *
 408  * The function generates a mixer value that depends on the bits set and the
 409  * location of the set bits in the random number generated by the entropy
 410  * source. Therefore, based on the generated random number, this mixer value
 411  * can have 2**64 different values. That mixer value is initialized with the
 412  * first two SHA-1 constants. After obtaining the mixer value, it is XORed into
 413  * the random number.
 414  *
 415  * The mixer value is not assumed to contain any entropy. But due to the XOR
 416  * operation, it can also not destroy any entropy present in the entropy pool.
 417  *
 418  * Input:
 419  * @entropy_collector Reference to entropy collector
 420  */
 421 static void jent_stir_pool(struct rand_data *entropy_collector)
 422 {
 423         /*
 424          * to shut up GCC on 32 bit, we have to initialize the 64 variable
 425          * with two 32 bit variables
 426          */
 427         union c {
 428                 __u64 u64;
 429                 __u32 u32[2];
 430         };
 431         /*
 432          * This constant is derived from the first two 32 bit initialization
 433          * vectors of SHA-1 as defined in FIPS 180-4 section 5.3.1
 434          */
 435         union c constant;
 436         /*
 437          * The start value of the mixer variable is derived from the third
 438          * and fourth 32 bit initialization vector of SHA-1 as defined in
 439          * FIPS 180-4 section 5.3.1
 440          */
 441         union c mixer;
 442         unsigned int i = 0;
 443
 444         /*
 445          * Store the SHA-1 constants in reverse order to make up the 64 bit
 446          * value -- this applies to a little endian system, on a big endian
 447          * system, it reverses as expected. But this really does not matter
 448          * as we do not rely on the specific numbers. We just pick the SHA-1
 449          * constants as they have a good mix of bit set and unset.
 450          */
 451         constant.u32[1] = 0x67452301;
 452         constant.u32[0] = 0xefcdab89;
 453         mixer.u32[1] = 0x98badcfe;
 454         mixer.u32[0] = 0x10325476;
 455
 456         for (i = 0; i < DATA_SIZE_BITS; i++) {
 457                 /*
 458                  * get the i-th bit of the input random number and only XOR
 459                  * the constant into the mixer value when that bit is set
 460                  */
 461                 if ((entropy_collector->data >> i) & 1)
 462                         mixer.u64 ^= constant.u64;
 463                 mixer.u64 = jent_rol64(mixer.u64, 1);
 464         }
 465         entropy_collector->data ^= mixer.u64;
 466 }
 467
 468 /**
 469  * Generator of one 64 bit random number
 470  * Function fills rand_data->data
 471  *
 472  * Input:
 473  * @ec Reference to entropy collector
 474  */
 475 static void jent_gen_entropy(struct rand_data *ec)
 476 {
 477         unsigned int k = 0;
 478
 479         /* priming of the ->prev_time value */
 480         jent_measure_jitter(ec);
 481
 482         while (1) {
 483                 __u64 data = 0;
 484
 485                 if (ec->disable_unbias == 1)
 486                         data = jent_measure_jitter(ec);
 487                 else
 488                         data = jent_unbiased_bit(ec);
 489
 490                 /* enforcement of the jent_stuck test */
 491                 if (ec->stuck) {
 492                         /*
 493                          * We only mix in the bit considered not appropriate
 494                          * without the LSFR. The reason is that if we apply
 495                          * the LSFR and we do not rotate, the 2nd bit with LSFR
 496                          * will cancel out the first LSFR application on the
 497                          * bad bit.
 498                          *
 499                          * And we do not rotate as we apply the next bit to the
 500                          * current bit location again.
 501                          */
 502                         ec->data ^= data;
 503                         ec->stuck = 0;
 504                         continue;
 505                 }
 506
 507                 /*
 508                  * Fibonacci LSFR with polynom of
 509                  *  x^64 + x^61 + x^56 + x^31 + x^28 + x^23 + 1 which is
 510                  *  primitive according to
 511                  *   http://poincare.matf.bg.ac.rs/~ezivkovm/publications/primpol1.pdf
 512                  * (the shift values are the polynom values minus one
 513                  * due to counting bits from 0 to 63). As the current
 514                  * position is always the LSB, the polynom only needs
 515                  * to shift data in from the left without wrap.
 516                  */
 517                 ec->data ^= data;
 518                 ec->data ^= ((ec->data >> 63) & 1);
 519                 ec->data ^= ((ec->data >> 60) & 1);
 520                 ec->data ^= ((ec->data >> 55) & 1);
 521                 ec->data ^= ((ec->data >> 30) & 1);
 522                 ec->data ^= ((ec->data >> 27) & 1);
 523                 ec->data ^= ((ec->data >> 22) & 1);
 524                 ec->data = jent_rol64(ec->data, 1);
 525
 526                 /*
 527                  * We multiply the loop value with ->osr to obtain the
 528                  * oversampling rate requested by the caller
 529                  */
 530                 if (++k >= (DATA_SIZE_BITS * ec->osr))
 531                         break;
 532         }
 533         if (ec->stir)
 534                 jent_stir_pool(ec);
 535 }
 536
 537 /**
 538  * The continuous test required by FIPS 140-2 -- the function automatically
 539  * primes the test if needed.
 540  *
 541  * Return:
 542  * 0 if FIPS test passed
 543  * < 0 if FIPS test failed
 544  */
 545 static void jent_fips_test(struct rand_data *ec)
 546 {
 547         if (!jent_fips_enabled())
 548                 return;
 549
 550         /* prime the FIPS test */
 551         if (!ec->old_data) {
 552                 ec->old_data = ec->data;
 553                 jent_gen_entropy(ec);
 554         }
 555
 556         if (ec->data == ec->old_data)
 557                 jent_panic("jitterentropy: Duplicate output detected\n");
 558
 559         ec->old_data = ec->data;
 560 }
 561
 562 /**
 563  * Entry function: Obtain entropy for the caller.
 564  *
 565  * This function invokes the entropy gathering logic as often to generate
 566  * as many bytes as requested by the caller. The entropy gathering logic
 567  * creates 64 bit per invocation.
 568  *
 569  * This function truncates the last 64 bit entropy value output to the exact
 570  * size specified by the caller.
 571  *
 572  * Input:
 573  * @ec Reference to entropy collector
 574  * @data pointer to buffer for storing random data -- buffer must already
 575  *       exist
 576  * @len size of the buffer, specifying also the requested number of random
 577  *      in bytes
 578  *
 579  * @return 0 when request is fulfilled or an error
 580  *
 581  * The following error codes can occur:
 582  *      -1      entropy_collector is NULL
 583  */
 584 int jent_read_entropy(struct rand_data *ec, unsigned char *data,
 585                       unsigned int len)
 586 {
 587         unsigned char *p = data;
 588
 589         if (!ec)
 590                 return -1;
 591
 592         while (0 < len) {
 593                 unsigned int tocopy;
 594
 595                 jent_gen_entropy(ec);
 596                 jent_fips_test(ec);
 597                 if ((DATA_SIZE_BITS / 8) < len)
 598                         tocopy = (DATA_SIZE_BITS / 8);
 599                 else
 600                         tocopy = len;
 601                 jent_memcpy(p, &ec->data, tocopy);
 602
 603                 len -= tocopy;
 604                 p += tocopy;
 605         }
 606
 607         return 0;
 608 }
 609
 610 /***************************************************************************
 611  * Initialization logic
 612  ***************************************************************************/
 613
 614 struct rand_data *jent_entropy_collector_alloc(unsigned int osr,
 615                                                unsigned int flags)
 616 {
 617         struct rand_data *entropy_collector;
 618
 619         entropy_collector = jent_zalloc(sizeof(struct rand_data));
 620         if (!entropy_collector)
 621                 return NULL;
 622
 623         if (!(flags & JENT_DISABLE_MEMORY_ACCESS)) {
 624                 /* Allocate memory for adding variations based on memory
 625                  * access
 626                  */
 627                 entropy_collector->mem = jent_zalloc(JENT_MEMORY_SIZE);
 628                 if (!entropy_collector->mem) {
 629                         jent_zfree(entropy_collector);
 630                         return NULL;
 631                 }
 632                 entropy_collector->memblocksize = JENT_MEMORY_BLOCKSIZE;
 633                 entropy_collector->memblocks = JENT_MEMORY_BLOCKS;
 634                 entropy_collector->memaccessloops = JENT_MEMORY_ACCESSLOOPS;
 635         }
 636
 637         /* verify and set the oversampling rate */
 638         if (0 == osr)
 639                 osr = 1; /* minimum sampling rate is 1 */
 640         entropy_collector->osr = osr;
 641
 642         entropy_collector->stir = 1;
 643         if (flags & JENT_DISABLE_STIR)
 644                 entropy_collector->stir = 0;
 645         if (flags & JENT_DISABLE_UNBIAS)
 646                 entropy_collector->disable_unbias = 1;
 647
 648         /* fill the data pad with non-zero values */
 649         jent_gen_entropy(entropy_collector);
 650
 651         return entropy_collector;
 652 }
 653
 654 void jent_entropy_collector_free(struct rand_data *entropy_collector)
 655 {
 656         jent_zfree(entropy_collector->mem);
 657         entropy_collector->mem = NULL;
 658         jent_zfree(entropy_collector);
 659         entropy_collector = NULL;
 660 }
 661
 662 int jent_entropy_init(void)
 663 {
 664         int i;
 665         __u64 delta_sum = 0;
 666         __u64 old_delta = 0;
 667         int time_backwards = 0;
 668         int count_var = 0;
 669         int count_mod = 0;
 670
 671         /* We could perform statistical tests here, but the problem is
 672          * that we only have a few loop counts to do testing. These
 673          * loop counts may show some slight skew and we produce
 674          * false positives.
 675          *
 676          * Moreover, only old systems show potentially problematic
 677          * jitter entropy that could potentially be caught here. But
 678          * the RNG is intended for hardware that is available or widely
 679          * used, but not old systems that are long out of favor. Thus,
 680          * no statistical tests.
 681          */
 682
 683         /*
 684          * We could add a check for system capabilities such as clock_getres or
 685          * check for CONFIG_X86_TSC, but it does not make much sense as the
 686          * following sanity checks verify that we have a high-resolution
 687          * timer.
 688          */
 689         /*
 690          * TESTLOOPCOUNT needs some loops to identify edge systems. 100 is
 691          * definitely too little.
 692          */
 693 #define TESTLOOPCOUNT 300
 694 #define CLEARCACHE 100
 695         for (i = 0; (TESTLOOPCOUNT + CLEARCACHE) > i; i++) {
 696                 __u64 time = 0;
 697                 __u64 time2 = 0;
 698                 __u64 folded = 0;
 699                 __u64 delta = 0;
 700                 unsigned int lowdelta = 0;
 701
 702                 jent_get_nstime(&time);
 703                 jent_fold_time(NULL, time, &folded, 1<<MIN_FOLD_LOOP_BIT);
 704                 jent_get_nstime(&time2);
 705
 706                 /* test whether timer works */
 707                 if (!time || !time2)
 708                         return JENT_ENOTIME;
 709                 delta = time2 - time;
 710                 /*
 711                  * test whether timer is fine grained enough to provide
 712                  * delta even when called shortly after each other -- this
 713                  * implies that we also have a high resolution timer
 714                  */
 715                 if (!delta)
 716                         return JENT_ECOARSETIME;
 717
 718                 /*
 719                  * up to here we did not modify any variable that will be
 720                  * evaluated later, but we already performed some work. Thus we
 721                  * already have had an impact on the caches, branch prediction,
 722                  * etc. with the goal to clear it to get the worst case
 723                  * measurements.
 724                  */
 725                 if (CLEARCACHE > i)
 726                         continue;
 727
 728                 /* test whether we have an increasing timer */
 729                 if (!(time2 > time))
 730                         time_backwards++;
 731
 732                 /*
 733                  * Avoid modulo of 64 bit integer to allow code to compile
 734                  * on 32 bit architectures.
 735                  */
 736                 lowdelta = time2 - time;
 737                 if (!(lowdelta % 100))
 738                         count_mod++;
 739
 740                 /*
 741                  * ensure that we have a varying delta timer which is necessary
 742                  * for the calculation of entropy -- perform this check
 743                  * only after the first loop is executed as we need to prime
 744                  * the old_data value
 745                  */
 746                 if (i) {
 747                         if (delta != old_delta)
 748                                 count_var++;
 749                         if (delta > old_delta)
 750                                 delta_sum += (delta - old_delta);
 751                         else
 752                                 delta_sum += (old_delta - delta);
 753                 }
 754                 old_delta = delta;
 755         }
 756
 757         /*
 758          * we allow up to three times the time running backwards.
 759          * CLOCK_REALTIME is affected by adjtime and NTP operations. Thus,
 760          * if such an operation just happens to interfere with our test, it
 761          * should not fail. The value of 3 should cover the NTP case being
 762          * performed during our test run.
 763          */
 764         if (3 < time_backwards)
 765                 return JENT_ENOMONOTONIC;
 766         /* Error if the time variances are always identical */
 767         if (!delta_sum)
 768                 return JENT_EVARVAR;
 769
 770         /*
 771          * Variations of deltas of time must on average be larger
 772          * than 1 to ensure the entropy estimation
 773          * implied with 1 is preserved
 774          */
 775         if (delta_sum <= 1)
 776                 return JENT_EMINVARVAR;
 777
 778         /*
 779          * Ensure that we have variations in the time stamp below 10 for at
 780          * least 10% of all checks -- on some platforms, the counter
 781          * increments in multiples of 100, but not always
 782          */
 783         if ((TESTLOOPCOUNT/10 * 9) < count_mod)
 784                 return JENT_ECOARSETIME;
 785
 786         return 0;
 787 }