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 - 2020
   6  *
   7  * Design
   8  * ======
   9  *
  10  * See https://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 2.2.0 provided at https://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         /* Repetition Count Test */
  88         int rct_count;                  /* Number of stuck values */
  89
  90         /* Adaptive Proportion Test for a significance level of 2^-30 */
  91 #define JENT_APT_CUTOFF         325     /* Taken from SP800-90B sec 4.4.2 */
  92 #define JENT_APT_WINDOW_SIZE    512     /* Data window size */
  93         /* LSB of time stamp to process */
  94 #define JENT_APT_LSB            16
  95 #define JENT_APT_WORD_MASK      (JENT_APT_LSB - 1)
  96         unsigned int apt_observations;  /* Number of collected observations */
  97         unsigned int apt_count;         /* APT counter */
  98         unsigned int apt_base;          /* APT base reference */
  99         unsigned int apt_base_set:1;    /* APT base reference set? */
 100
 101         unsigned int health_failure:1;  /* Permanent health failure */
 102 };
 103
 104 /* Flags that can be used to initialize the RNG */
 105 #define JENT_DISABLE_MEMORY_ACCESS (1<<2) /* Disable memory access for more
 106                                            * entropy, saves MEMORY_SIZE RAM for
 107                                            * entropy collector */
 108
 109 /* -- error codes for init function -- */
 110 #define JENT_ENOTIME            1 /* Timer service not available */
 111 #define JENT_ECOARSETIME        2 /* Timer too coarse for RNG */
 112 #define JENT_ENOMONOTONIC       3 /* Timer is not monotonic increasing */
 113 #define JENT_EVARVAR            5 /* Timer does not produce variations of
 114                                    * variations (2nd derivation of time is
 115                                    * zero). */
 116 #define JENT_ESTUCK             8 /* Too many stuck results during init. */
 117 #define JENT_EHEALTH            9 /* Health test failed during initialization */
 118 #define JENT_ERCT               10 /* RCT failed during initialization */
 119
 120 #include "jitterentropy.h"
 121
 122 /***************************************************************************
 123  * Adaptive Proportion Test
 124  *
 125  * This test complies with SP800-90B section 4.4.2.
 126  ***************************************************************************/
 127
 128 /**
 129  * Reset the APT counter
 130  *
 131  * @ec [in] Reference to entropy collector
 132  */
 133 static void jent_apt_reset(struct rand_data *ec, unsigned int delta_masked)
 134 {
 135         /* Reset APT counter */
 136         ec->apt_count = 0;
 137         ec->apt_base = delta_masked;
 138         ec->apt_observations = 0;
 139 }
 140
 141 /**
 142  * Insert a new entropy event into APT
 143  *
 144  * @ec [in] Reference to entropy collector
 145  * @delta_masked [in] Masked time delta to process
 146  */
 147 static void jent_apt_insert(struct rand_data *ec, unsigned int delta_masked)
 148 {
 149         /* Initialize the base reference */
 150         if (!ec->apt_base_set) {
 151                 ec->apt_base = delta_masked;
 152                 ec->apt_base_set = 1;
 153                 return;
 154         }
 155
 156         if (delta_masked == ec->apt_base) {
 157                 ec->apt_count++;
 158
 159                 if (ec->apt_count >= JENT_APT_CUTOFF)
 160                         ec->health_failure = 1;
 161         }
 162
 163         ec->apt_observations++;
 164
 165         if (ec->apt_observations >= JENT_APT_WINDOW_SIZE)
 166                 jent_apt_reset(ec, delta_masked);
 167 }
 168
 169 /***************************************************************************
 170  * Stuck Test and its use as Repetition Count Test
 171  *
 172  * The Jitter RNG uses an enhanced version of the Repetition Count Test
 173  * (RCT) specified in SP800-90B section 4.4.1. Instead of counting identical
 174  * back-to-back values, the input to the RCT is the counting of the stuck
 175  * values during the generation of one Jitter RNG output block.
 176  *
 177  * The RCT is applied with an alpha of 2^{-30} compliant to FIPS 140-2 IG 9.8.
 178  *
 179  * During the counting operation, the Jitter RNG always calculates the RCT
 180  * cut-off value of C. If that value exceeds the allowed cut-off value,
 181  * the Jitter RNG output block will be calculated completely but discarded at
 182  * the end. The caller of the Jitter RNG is informed with an error code.
 183  ***************************************************************************/
 184
 185 /**
 186  * Repetition Count Test as defined in SP800-90B section 4.4.1
 187  *
 188  * @ec [in] Reference to entropy collector
 189  * @stuck [in] Indicator whether the value is stuck
 190  */
 191 static void jent_rct_insert(struct rand_data *ec, int stuck)
 192 {
 193         /*
 194          * If we have a count less than zero, a previous RCT round identified
 195          * a failure. We will not overwrite it.
 196          */
 197         if (ec->rct_count < 0)
 198                 return;
 199
 200         if (stuck) {
 201                 ec->rct_count++;
 202
 203                 /*
 204                  * The cutoff value is based on the following consideration:
 205                  * alpha = 2^-30 as recommended in FIPS 140-2 IG 9.8.
 206                  * In addition, we require an entropy value H of 1/OSR as this
 207                  * is the minimum entropy required to provide full entropy.
 208                  * Note, we collect 64 * OSR deltas for inserting them into
 209                  * the entropy pool which should then have (close to) 64 bits
 210                  * of entropy.
 211                  *
 212                  * Note, ec->rct_count (which equals to value B in the pseudo
 213                  * code of SP800-90B section 4.4.1) starts with zero. Hence
 214                  * we need to subtract one from the cutoff value as calculated
 215                  * following SP800-90B.
 216                  */
 217                 if ((unsigned int)ec->rct_count >= (31 * ec->osr)) {
 218                         ec->rct_count = -1;
 219                         ec->health_failure = 1;
 220                 }
 221         } else {
 222                 ec->rct_count = 0;
 223         }
 224 }
 225
 226 /**
 227  * Is there an RCT health test failure?
 228  *
 229  * @ec [in] Reference to entropy collector
 230  *
 231  * @return
 232  *      0 No health test failure
 233  *      1 Permanent health test failure
 234  */
 235 static int jent_rct_failure(struct rand_data *ec)
 236 {
 237         if (ec->rct_count < 0)
 238                 return 1;
 239         return 0;
 240 }
 241
 242 static inline __u64 jent_delta(__u64 prev, __u64 next)
 243 {
 244 #define JENT_UINT64_MAX         (__u64)(~((__u64) 0))
 245         return (prev < next) ? (next - prev) :
 246                                (JENT_UINT64_MAX - prev + 1 + next);
 247 }
 248
 249 /**
 250  * Stuck test by checking the:
 251  *      1st derivative of the jitter measurement (time delta)
 252  *      2nd derivative of the jitter measurement (delta of time deltas)
 253  *      3rd derivative of the jitter measurement (delta of delta of time deltas)
 254  *
 255  * All values must always be non-zero.
 256  *
 257  * @ec [in] Reference to entropy collector
 258  * @current_delta [in] Jitter time delta
 259  *
 260  * @return
 261  *      0 jitter measurement not stuck (good bit)
 262  *      1 jitter measurement stuck (reject bit)
 263  */
 264 static int jent_stuck(struct rand_data *ec, __u64 current_delta)
 265 {
 266         __u64 delta2 = jent_delta(ec->last_delta, current_delta);
 267         __u64 delta3 = jent_delta(ec->last_delta2, delta2);
 268         unsigned int delta_masked = current_delta & JENT_APT_WORD_MASK;
 269
 270         ec->last_delta = current_delta;
 271         ec->last_delta2 = delta2;
 272
 273         /*
 274          * Insert the result of the comparison of two back-to-back time
 275          * deltas.
 276          */
 277         jent_apt_insert(ec, delta_masked);
 278
 279         if (!current_delta || !delta2 || !delta3) {
 280                 /* RCT with a stuck bit */
 281                 jent_rct_insert(ec, 1);
 282                 return 1;
 283         }
 284
 285         /* RCT with a non-stuck bit */
 286         jent_rct_insert(ec, 0);
 287
 288         return 0;
 289 }
 290
 291 /**
 292  * Report any health test failures
 293  *
 294  * @ec [in] Reference to entropy collector
 295  *
 296  * @return
 297  *      0 No health test failure
 298  *      1 Permanent health test failure
 299  */
 300 static int jent_health_failure(struct rand_data *ec)
 301 {
 302         /* Test is only enabled in FIPS mode */
 303         if (!jent_fips_enabled())
 304                 return 0;
 305
 306         return ec->health_failure;
 307 }
 308
 309 /***************************************************************************
 310  * Noise sources
 311  ***************************************************************************/
 312
 313 /**
 314  * Update of the loop count used for the next round of
 315  * an entropy collection.
 316  *
 317  * Input:
 318  * @ec entropy collector struct -- may be NULL
 319  * @bits is the number of low bits of the timer to consider
 320  * @min is the number of bits we shift the timer value to the right at
 321  *      the end to make sure we have a guaranteed minimum value
 322  *
 323  * @return Newly calculated loop counter
 324  */
 325 static __u64 jent_loop_shuffle(struct rand_data *ec,
 326                                unsigned int bits, unsigned int min)
 327 {
 328         __u64 time = 0;
 329         __u64 shuffle = 0;
 330         unsigned int i = 0;
 331         unsigned int mask = (1<<bits) - 1;
 332
 333         jent_get_nstime(&time);
 334         /*
 335          * Mix the current state of the random number into the shuffle
 336          * calculation to balance that shuffle a bit more.
 337          */
 338         if (ec)
 339                 time ^= ec->data;
 340         /*
 341          * We fold the time value as much as possible to ensure that as many
 342          * bits of the time stamp are included as possible.
 343          */
 344         for (i = 0; ((DATA_SIZE_BITS + bits - 1) / bits) > i; i++) {
 345                 shuffle ^= time & mask;
 346                 time = time >> bits;
 347         }
 348
 349         /*
 350          * We add a lower boundary value to ensure we have a minimum
 351          * RNG loop count.
 352          */
 353         return (shuffle + (1<<min));
 354 }
 355
 356 /**
 357  * CPU Jitter noise source -- this is the noise source based on the CPU
 358  *                            execution time jitter
 359  *
 360  * This function injects the individual bits of the time value into the
 361  * entropy pool using an LFSR.
 362  *
 363  * The code is deliberately inefficient with respect to the bit shifting
 364  * and shall stay that way. This function is the root cause why the code
 365  * shall be compiled without optimization. This function not only acts as
 366  * folding operation, but this function's execution is used to measure
 367  * the CPU execution time jitter. Any change to the loop in this function
 368  * implies that careful retesting must be done.
 369  *
 370  * @ec [in] entropy collector struct
 371  * @time [in] time stamp to be injected
 372  * @loop_cnt [in] if a value not equal to 0 is set, use the given value as
 373  *                number of loops to perform the folding
 374  * @stuck [in] Is the time stamp identified as stuck?
 375  *
 376  * Output:
 377  * updated ec->data
 378  *
 379  * @return Number of loops the folding operation is performed
 380  */
 381 static void jent_lfsr_time(struct rand_data *ec, __u64 time, __u64 loop_cnt,
 382                            int stuck)
 383 {
 384         unsigned int i;
 385         __u64 j = 0;
 386         __u64 new = 0;
 387 #define MAX_FOLD_LOOP_BIT 4
 388 #define MIN_FOLD_LOOP_BIT 0
 389         __u64 fold_loop_cnt =
 390                 jent_loop_shuffle(ec, MAX_FOLD_LOOP_BIT, MIN_FOLD_LOOP_BIT);
 391
 392         /*
 393          * testing purposes -- allow test app to set the counter, not
 394          * needed during runtime
 395          */
 396         if (loop_cnt)
 397                 fold_loop_cnt = loop_cnt;
 398         for (j = 0; j < fold_loop_cnt; j++) {
 399                 new = ec->data;
 400                 for (i = 1; (DATA_SIZE_BITS) >= i; i++) {
 401                         __u64 tmp = time << (DATA_SIZE_BITS - i);
 402
 403                         tmp = tmp >> (DATA_SIZE_BITS - 1);
 404
 405                         /*
 406                         * Fibonacci LSFR with polynomial of
 407                         *  x^64 + x^61 + x^56 + x^31 + x^28 + x^23 + 1 which is
 408                         *  primitive according to
 409                         *   http://poincare.matf.bg.ac.rs/~ezivkovm/publications/primpol1.pdf
 410                         * (the shift values are the polynomial values minus one
 411                         * due to counting bits from 0 to 63). As the current
 412                         * position is always the LSB, the polynomial only needs
 413                         * to shift data in from the left without wrap.
 414                         */
 415                         tmp ^= ((new >> 63) & 1);
 416                         tmp ^= ((new >> 60) & 1);
 417                         tmp ^= ((new >> 55) & 1);
 418                         tmp ^= ((new >> 30) & 1);
 419                         tmp ^= ((new >> 27) & 1);
 420                         tmp ^= ((new >> 22) & 1);
 421                         new <<= 1;
 422                         new ^= tmp;
 423                 }
 424         }
 425
 426         /*
 427          * If the time stamp is stuck, do not finally insert the value into
 428          * the entropy pool. Although this operation should not do any harm
 429          * even when the time stamp has no entropy, SP800-90B requires that
 430          * any conditioning operation (SP800-90B considers the LFSR to be a
 431          * conditioning operation) to have an identical amount of input
 432          * data according to section 3.1.5.
 433          */
 434         if (!stuck)
 435                 ec->data = new;
 436 }
 437
 438 /**
 439  * Memory Access noise source -- this is a noise source based on variations in
 440  *                               memory access times
 441  *
 442  * This function performs memory accesses which will add to the timing
 443  * variations due to an unknown amount of CPU wait states that need to be
 444  * added when accessing memory. The memory size should be larger than the L1
 445  * caches as outlined in the documentation and the associated testing.
 446  *
 447  * The L1 cache has a very high bandwidth, albeit its access rate is  usually
 448  * slower than accessing CPU registers. Therefore, L1 accesses only add minimal
 449  * variations as the CPU has hardly to wait. Starting with L2, significant
 450  * variations are added because L2 typically does not belong to the CPU any more
 451  * and therefore a wider range of CPU wait states is necessary for accesses.
 452  * L3 and real memory accesses have even a wider range of wait states. However,
 453  * to reliably access either L3 or memory, the ec->mem memory must be quite
 454  * large which is usually not desirable.
 455  *
 456  * @ec [in] Reference to the entropy collector with the memory access data -- if
 457  *          the reference to the memory block to be accessed is NULL, this noise
 458  *          source is disabled
 459  * @loop_cnt [in] if a value not equal to 0 is set, use the given value
 460  *                number of loops to perform the LFSR
 461  */
 462 static void jent_memaccess(struct rand_data *ec, __u64 loop_cnt)
 463 {
 464         unsigned int wrap = 0;
 465         __u64 i = 0;
 466 #define MAX_ACC_LOOP_BIT 7
 467 #define MIN_ACC_LOOP_BIT 0
 468         __u64 acc_loop_cnt =
 469                 jent_loop_shuffle(ec, MAX_ACC_LOOP_BIT, MIN_ACC_LOOP_BIT);
 470
 471         if (NULL == ec || NULL == ec->mem)
 472                 return;
 473         wrap = ec->memblocksize * ec->memblocks;
 474
 475         /*
 476          * testing purposes -- allow test app to set the counter, not
 477          * needed during runtime
 478          */
 479         if (loop_cnt)
 480                 acc_loop_cnt = loop_cnt;
 481
 482         for (i = 0; i < (ec->memaccessloops + acc_loop_cnt); i++) {
 483                 unsigned char *tmpval = ec->mem + ec->memlocation;
 484                 /*
 485                  * memory access: just add 1 to one byte,
 486                  * wrap at 255 -- memory access implies read
 487                  * from and write to memory location
 488                  */
 489                 *tmpval = (*tmpval + 1) & 0xff;
 490                 /*
 491                  * Addition of memblocksize - 1 to pointer
 492                  * with wrap around logic to ensure that every
 493                  * memory location is hit evenly
 494                  */
 495                 ec->memlocation = ec->memlocation + ec->memblocksize - 1;
 496                 ec->memlocation = ec->memlocation % wrap;
 497         }
 498 }
 499
 500 /***************************************************************************
 501  * Start of entropy processing logic
 502  ***************************************************************************/
 503 /**
 504  * This is the heart of the entropy generation: calculate time deltas and
 505  * use the CPU jitter in the time deltas. The jitter is injected into the
 506  * entropy pool.
 507  *
 508  * WARNING: ensure that ->prev_time is primed before using the output
 509  *          of this function! This can be done by calling this function
 510  *          and not using its result.
 511  *
 512  * @ec [in] Reference to entropy collector
 513  *
 514  * @return result of stuck test
 515  */
 516 static int jent_measure_jitter(struct rand_data *ec)
 517 {
 518         __u64 time = 0;
 519         __u64 current_delta = 0;
 520         int stuck;
 521
 522         /* Invoke one noise source before time measurement to add variations */
 523         jent_memaccess(ec, 0);
 524
 525         /*
 526          * Get time stamp and calculate time delta to previous
 527          * invocation to measure the timing variations
 528          */
 529         jent_get_nstime(&time);
 530         current_delta = jent_delta(ec->prev_time, time);
 531         ec->prev_time = time;
 532
 533         /* Check whether we have a stuck measurement. */
 534         stuck = jent_stuck(ec, current_delta);
 535
 536         /* Now call the next noise sources which also injects the data */
 537         jent_lfsr_time(ec, current_delta, 0, stuck);
 538
 539         return stuck;
 540 }
 541
 542 /**
 543  * Generator of one 64 bit random number
 544  * Function fills rand_data->data
 545  *
 546  * @ec [in] Reference to entropy collector
 547  */
 548 static void jent_gen_entropy(struct rand_data *ec)
 549 {
 550         unsigned int k = 0;
 551
 552         /* priming of the ->prev_time value */
 553         jent_measure_jitter(ec);
 554
 555         while (1) {
 556                 /* If a stuck measurement is received, repeat measurement */
 557                 if (jent_measure_jitter(ec))
 558                         continue;
 559
 560                 /*
 561                  * We multiply the loop value with ->osr to obtain the
 562                  * oversampling rate requested by the caller
 563                  */
 564                 if (++k >= (DATA_SIZE_BITS * ec->osr))
 565                         break;
 566         }
 567 }
 568
 569 /**
 570  * Entry function: Obtain entropy for the caller.
 571  *
 572  * This function invokes the entropy gathering logic as often to generate
 573  * as many bytes as requested by the caller. The entropy gathering logic
 574  * creates 64 bit per invocation.
 575  *
 576  * This function truncates the last 64 bit entropy value output to the exact
 577  * size specified by the caller.
 578  *
 579  * @ec [in] Reference to entropy collector
 580  * @data [in] pointer to buffer for storing random data -- buffer must already
 581  *            exist
 582  * @len [in] size of the buffer, specifying also the requested number of random
 583  *           in bytes
 584  *
 585  * @return 0 when request is fulfilled or an error
 586  *
 587  * The following error codes can occur:
 588  *      -1      entropy_collector is NULL
 589  *      -2      RCT failed
 590  *      -3      APT test failed
 591  */
 592 int jent_read_entropy(struct rand_data *ec, unsigned char *data,
 593                       unsigned int len)
 594 {
 595         unsigned char *p = data;
 596
 597         if (!ec)
 598                 return -1;
 599
 600         while (0 < len) {
 601                 unsigned int tocopy;
 602
 603                 jent_gen_entropy(ec);
 604
 605                 if (jent_health_failure(ec)) {
 606                         int ret;
 607
 608                         if (jent_rct_failure(ec))
 609                                 ret = -2;
 610                         else
 611                                 ret = -3;
 612
 613                         /*
 614                          * Re-initialize the noise source
 615                          *
 616                          * If the health test fails, the Jitter RNG remains
 617                          * in failure state and will return a health failure
 618                          * during next invocation.
 619                          */
 620                         if (jent_entropy_init())
 621                                 return ret;
 622
 623                         /* Set APT to initial state */
 624                         jent_apt_reset(ec, 0);
 625                         ec->apt_base_set = 0;
 626
 627                         /* Set RCT to initial state */
 628                         ec->rct_count = 0;
 629
 630                         /* Re-enable Jitter RNG */
 631                         ec->health_failure = 0;
 632
 633                         /*
 634                          * Return the health test failure status to the
 635                          * caller as the generated value is not appropriate.
 636                          */
 637                         return ret;
 638                 }
 639
 640                 if ((DATA_SIZE_BITS / 8) < len)
 641                         tocopy = (DATA_SIZE_BITS / 8);
 642                 else
 643                         tocopy = len;
 644                 jent_memcpy(p, &ec->data, tocopy);
 645
 646                 len -= tocopy;
 647                 p += tocopy;
 648         }
 649
 650         return 0;
 651 }
 652
 653 /***************************************************************************
 654  * Initialization logic
 655  ***************************************************************************/
 656
 657 struct rand_data *jent_entropy_collector_alloc(unsigned int osr,
 658                                                unsigned int flags)
 659 {
 660         struct rand_data *entropy_collector;
 661
 662         entropy_collector = jent_zalloc(sizeof(struct rand_data));
 663         if (!entropy_collector)
 664                 return NULL;
 665
 666         if (!(flags & JENT_DISABLE_MEMORY_ACCESS)) {
 667                 /* Allocate memory for adding variations based on memory
 668                  * access
 669                  */
 670                 entropy_collector->mem = jent_zalloc(JENT_MEMORY_SIZE);
 671                 if (!entropy_collector->mem) {
 672                         jent_zfree(entropy_collector);
 673                         return NULL;
 674                 }
 675                 entropy_collector->memblocksize = JENT_MEMORY_BLOCKSIZE;
 676                 entropy_collector->memblocks = JENT_MEMORY_BLOCKS;
 677                 entropy_collector->memaccessloops = JENT_MEMORY_ACCESSLOOPS;
 678         }
 679
 680         /* verify and set the oversampling rate */
 681         if (0 == osr)
 682                 osr = 1; /* minimum sampling rate is 1 */
 683         entropy_collector->osr = osr;
 684
 685         /* fill the data pad with non-zero values */
 686         jent_gen_entropy(entropy_collector);
 687
 688         return entropy_collector;
 689 }
 690
 691 void jent_entropy_collector_free(struct rand_data *entropy_collector)
 692 {
 693         jent_zfree(entropy_collector->mem);
 694         entropy_collector->mem = NULL;
 695         jent_zfree(entropy_collector);
 696 }
 697
 698 int jent_entropy_init(void)
 699 {
 700         int i;
 701         __u64 delta_sum = 0;
 702         __u64 old_delta = 0;
 703         unsigned int nonstuck = 0;
 704         int time_backwards = 0;
 705         int count_mod = 0;
 706         int count_stuck = 0;
 707         struct rand_data ec = { 0 };
 708
 709         /* Required for RCT */
 710         ec.osr = 1;
 711
 712         /* We could perform statistical tests here, but the problem is
 713          * that we only have a few loop counts to do testing. These
 714          * loop counts may show some slight skew and we produce
 715          * false positives.
 716          *
 717          * Moreover, only old systems show potentially problematic
 718          * jitter entropy that could potentially be caught here. But
 719          * the RNG is intended for hardware that is available or widely
 720          * used, but not old systems that are long out of favor. Thus,
 721          * no statistical tests.
 722          */
 723
 724         /*
 725          * We could add a check for system capabilities such as clock_getres or
 726          * check for CONFIG_X86_TSC, but it does not make much sense as the
 727          * following sanity checks verify that we have a high-resolution
 728          * timer.
 729          */
 730         /*
 731          * TESTLOOPCOUNT needs some loops to identify edge systems. 100 is
 732          * definitely too little.
 733          *
 734          * SP800-90B requires at least 1024 initial test cycles.
 735          */
 736 #define TESTLOOPCOUNT 1024
 737 #define CLEARCACHE 100
 738         for (i = 0; (TESTLOOPCOUNT + CLEARCACHE) > i; i++) {
 739                 __u64 time = 0;
 740                 __u64 time2 = 0;
 741                 __u64 delta = 0;
 742                 unsigned int lowdelta = 0;
 743                 int stuck;
 744
 745                 /* Invoke core entropy collection logic */
 746                 jent_get_nstime(&time);
 747                 ec.prev_time = time;
 748                 jent_lfsr_time(&ec, time, 0, 0);
 749                 jent_get_nstime(&time2);
 750
 751                 /* test whether timer works */
 752                 if (!time || !time2)
 753                         return JENT_ENOTIME;
 754                 delta = jent_delta(time, time2);
 755                 /*
 756                  * test whether timer is fine grained enough to provide
 757                  * delta even when called shortly after each other -- this
 758                  * implies that we also have a high resolution timer
 759                  */
 760                 if (!delta)
 761                         return JENT_ECOARSETIME;
 762
 763                 stuck = jent_stuck(&ec, delta);
 764
 765                 /*
 766                  * up to here we did not modify any variable that will be
 767                  * evaluated later, but we already performed some work. Thus we
 768                  * already have had an impact on the caches, branch prediction,
 769                  * etc. with the goal to clear it to get the worst case
 770                  * measurements.
 771                  */
 772                 if (CLEARCACHE > i)
 773                         continue;
 774
 775                 if (stuck)
 776                         count_stuck++;
 777                 else {
 778                         nonstuck++;
 779
 780                         /*
 781                          * Ensure that the APT succeeded.
 782                          *
 783                          * With the check below that count_stuck must be less
 784                          * than 10% of the overall generated raw entropy values
 785                          * it is guaranteed that the APT is invoked at
 786                          * floor((TESTLOOPCOUNT * 0.9) / 64) == 14 times.
 787                          */
 788                         if ((nonstuck % JENT_APT_WINDOW_SIZE) == 0) {
 789                                 jent_apt_reset(&ec,
 790                                                delta & JENT_APT_WORD_MASK);
 791                                 if (jent_health_failure(&ec))
 792                                         return JENT_EHEALTH;
 793                         }
 794                 }
 795
 796                 /* Validate RCT */
 797                 if (jent_rct_failure(&ec))
 798                         return JENT_ERCT;
 799
 800                 /* test whether we have an increasing timer */
 801                 if (!(time2 > time))
 802                         time_backwards++;
 803
 804                 /* use 32 bit value to ensure compilation on 32 bit arches */
 805                 lowdelta = time2 - time;
 806                 if (!(lowdelta % 100))
 807                         count_mod++;
 808
 809                 /*
 810                  * ensure that we have a varying delta timer which is necessary
 811                  * for the calculation of entropy -- perform this check
 812                  * only after the first loop is executed as we need to prime
 813                  * the old_data value
 814                  */
 815                 if (delta > old_delta)
 816                         delta_sum += (delta - old_delta);
 817                 else
 818                         delta_sum += (old_delta - delta);
 819                 old_delta = delta;
 820         }
 821
 822         /*
 823          * we allow up to three times the time running backwards.
 824          * CLOCK_REALTIME is affected by adjtime and NTP operations. Thus,
 825          * if such an operation just happens to interfere with our test, it
 826          * should not fail. The value of 3 should cover the NTP case being
 827          * performed during our test run.
 828          */
 829         if (3 < time_backwards)
 830                 return JENT_ENOMONOTONIC;
 831
 832         /*
 833          * Variations of deltas of time must on average be larger
 834          * than 1 to ensure the entropy estimation
 835          * implied with 1 is preserved
 836          */
 837         if ((delta_sum) <= 1)
 838                 return JENT_EVARVAR;
 839
 840         /*
 841          * Ensure that we have variations in the time stamp below 10 for at
 842          * least 10% of all checks -- on some platforms, the counter increments
 843          * in multiples of 100, but not always
 844          */
 845         if ((TESTLOOPCOUNT/10 * 9) < count_mod)
 846                 return JENT_ECOARSETIME;
 847
 848         /*
 849          * If we have more than 90% stuck results, then this Jitter RNG is
 850          * likely to not work well.
 851          */
 852         if ((TESTLOOPCOUNT/10 * 9) < count_stuck)
 853                 return JENT_ESTUCK;
 854
 855         return 0;
 856 }