crypto/rand/rand_unix.c

   1 /*
   2  * Copyright 1995-2018 The OpenSSL Project Authors. All Rights Reserved.
   3  *
   4  * Licensed under the Apache License 2.0 (the "License").  You may not use
   5  * this file except in compliance with the License.  You can obtain a copy
   6  * in the file LICENSE in the source distribution or at
   7  * https://www.openssl.org/source/license.html
   8  */
   9
  10 #ifndef _GNU_SOURCE
  11 # define _GNU_SOURCE
  12 #endif
  13 #include "e_os.h"
  14 #include <stdio.h>
  15 #include "internal/cryptlib.h"
  16 #include <openssl/rand.h>
  17 #include "rand_lcl.h"
  18 #include "internal/rand_int.h"
  19 #include <stdio.h>
  20 #include "internal/dso.h"
  21 #if defined(__linux)
  22 # include <sys/syscall.h>
  23 #endif
  24 #if defined(__FreeBSD__)
  25 # include <sys/types.h>
  26 # include <sys/sysctl.h>
  27 # include <sys/param.h>
  28 #endif
  29 #if defined(__OpenBSD__) || defined(__NetBSD__)
  30 # include <sys/param.h>
  31 #endif
  32
  33 #if defined(OPENSSL_SYS_UNIX) || defined(__DJGPP__)
  34 # include <sys/types.h>
  35 # include <sys/stat.h>
  36 # include <fcntl.h>
  37 # include <unistd.h>
  38 # include <sys/time.h>
  39
  40 static uint64_t get_time_stamp(void);
  41 static uint64_t get_timer_bits(void);
  42
  43 /* Macro to convert two thirty two bit values into a sixty four bit one */
  44 # define TWO32TO64(a, b) ((((uint64_t)(a)) << 32) + (b))
  45
  46 /*
  47  * Check for the existence and support of POSIX timers.  The standard
  48  * says that the _POSIX_TIMERS macro will have a positive value if they
  49  * are available.
  50  *
  51  * However, we want an additional constraint: that the timer support does
  52  * not require an extra library dependency.  Early versions of glibc
  53  * require -lrt to be specified on the link line to access the timers,
  54  * so this needs to be checked for.
  55  *
  56  * It is worse because some libraries define __GLIBC__ but don't
  57  * support the version testing macro (e.g. uClibc).  This means
  58  * an extra check is needed.
  59  *
  60  * The final condition is:
  61  *      "have posix timers and either not glibc or glibc without -lrt"
  62  *
  63  * The nested #if sequences are required to avoid using a parameterised
  64  * macro that might be undefined.
  65  */
  66 # undef OSSL_POSIX_TIMER_OKAY
  67 # if defined(_POSIX_TIMERS) && _POSIX_TIMERS > 0
  68 #  if defined(__GLIBC__)
  69 #   if defined(__GLIBC_PREREQ)
  70 #    if __GLIBC_PREREQ(2, 17)
  71 #     define OSSL_POSIX_TIMER_OKAY
  72 #    endif
  73 #   endif
  74 #  else
  75 #   define OSSL_POSIX_TIMER_OKAY
  76 #  endif
  77 # endif
  78 #endif /* defined(OPENSSL_SYS_UNIX) || defined(__DJGPP__) */
  79
  80 #if defined(OPENSSL_RAND_SEED_NONE)
  81 /* none means none. this simplifies the following logic */
  82 # undef OPENSSL_RAND_SEED_OS
  83 # undef OPENSSL_RAND_SEED_GETRANDOM
  84 # undef OPENSSL_RAND_SEED_LIBRANDOM
  85 # undef OPENSSL_RAND_SEED_DEVRANDOM
  86 # undef OPENSSL_RAND_SEED_RDTSC
  87 # undef OPENSSL_RAND_SEED_RDCPU
  88 # undef OPENSSL_RAND_SEED_EGD
  89 #endif
  90
  91 #if (defined(OPENSSL_SYS_VXWORKS) || defined(OPENSSL_SYS_UEFI)) && \
  92         !defined(OPENSSL_RAND_SEED_NONE)
  93 # error "UEFI and VXWorks only support seeding NONE"
  94 #endif
  95
  96 #if defined(OPENSSL_SYS_VXWORKS)
  97 /* empty implementation */
  98 int rand_pool_init(void)
  99 {
 100     return 1;
 101 }
 102
 103 void rand_pool_cleanup(void)
 104 {
 105 }
 106
 107 void rand_pool_keep_random_devices_open(int keep)
 108 {
 109 }
 110
 111 size_t rand_pool_acquire_entropy(RAND_POOL *pool)
 112 {
 113     return rand_pool_entropy_available(pool);
 114 }
 115 #endif
 116
 117 #if !(defined(OPENSSL_SYS_WINDOWS) || defined(OPENSSL_SYS_WIN32) \
 118     || defined(OPENSSL_SYS_VMS) || defined(OPENSSL_SYS_VXWORKS) \
 119     || defined(OPENSSL_SYS_UEFI))
 120
 121 # if defined(OPENSSL_SYS_VOS)
 122
 123 #  ifndef OPENSSL_RAND_SEED_OS
 124 #   error "Unsupported seeding method configured; must be os"
 125 #  endif
 126
 127 #  if defined(OPENSSL_SYS_VOS_HPPA) && defined(OPENSSL_SYS_VOS_IA32)
 128 #   error "Unsupported HP-PA and IA32 at the same time."
 129 #  endif
 130 #  if !defined(OPENSSL_SYS_VOS_HPPA) && !defined(OPENSSL_SYS_VOS_IA32)
 131 #   error "Must have one of HP-PA or IA32"
 132 #  endif
 133
 134 /*
 135  * The following algorithm repeatedly samples the real-time clock (RTC) to
 136  * generate a sequence of unpredictable data.  The algorithm relies upon the
 137  * uneven execution speed of the code (due to factors such as cache misses,
 138  * interrupts, bus activity, and scheduling) and upon the rather large
 139  * relative difference between the speed of the clock and the rate at which
 140  * it can be read.  If it is ported to an environment where execution speed
 141  * is more constant or where the RTC ticks at a much slower rate, or the
 142  * clock can be read with fewer instructions, it is likely that the results
 143  * would be far more predictable.  This should only be used for legacy
 144  * platforms.
 145  *
 146  * As a precaution, we assume only 2 bits of entropy per byte.
 147  */
 148 size_t rand_pool_acquire_entropy(RAND_POOL *pool)
 149 {
 150     short int code;
 151     int i, k;
 152     size_t bytes_needed;
 153     struct timespec ts;
 154     unsigned char v;
 155 #  ifdef OPENSSL_SYS_VOS_HPPA
 156     long duration;
 157     extern void s$sleep(long *_duration, short int *_code);
 158 #  else
 159     long long duration;
 160     extern void s$sleep2(long long *_duration, short int *_code);
 161 #  endif
 162
 163     bytes_needed = rand_pool_bytes_needed(pool, 4 /*entropy_factor*/);
 164
 165     for (i = 0; i < bytes_needed; i++) {
 166         /*
 167          * burn some cpu; hope for interrupts, cache collisions, bus
 168          * interference, etc.
 169          */
 170         for (k = 0; k < 99; k++)
 171             ts.tv_nsec = random();
 172
 173 #  ifdef OPENSSL_SYS_VOS_HPPA
 174         /* sleep for 1/1024 of a second (976 us).  */
 175         duration = 1;
 176         s$sleep(&duration, &code);
 177 #  else
 178         /* sleep for 1/65536 of a second (15 us).  */
 179         duration = 1;
 180         s$sleep2(&duration, &code);
 181 #  endif
 182
 183         /* Get wall clock time, take 8 bits. */
 184         clock_gettime(CLOCK_REALTIME, &ts);
 185         v = (unsigned char)(ts.tv_nsec & 0xFF);
 186         rand_pool_add(pool, arg, &v, sizeof(v) , 2);
 187     }
 188     return rand_pool_entropy_available(pool);
 189 }
 190
 191 void rand_pool_cleanup(void)
 192 {
 193 }
 194
 195 void rand_pool_keep_random_devices_open(int keep)
 196 {
 197 }
 198
 199 # else
 200
 201 #  if defined(OPENSSL_RAND_SEED_EGD) && \
 202         (defined(OPENSSL_NO_EGD) || !defined(DEVRANDOM_EGD))
 203 #   error "Seeding uses EGD but EGD is turned off or no device given"
 204 #  endif
 205
 206 #  if defined(OPENSSL_RAND_SEED_DEVRANDOM) && !defined(DEVRANDOM)
 207 #   error "Seeding uses urandom but DEVRANDOM is not configured"
 208 #  endif
 209
 210 #  if defined(OPENSSL_RAND_SEED_OS)
 211 #   if !defined(DEVRANDOM)
 212 #    error "OS seeding requires DEVRANDOM to be configured"
 213 #   endif
 214 #   define OPENSSL_RAND_SEED_GETRANDOM
 215 #   define OPENSSL_RAND_SEED_DEVRANDOM
 216 #  endif
 217
 218 #  if defined(OPENSSL_RAND_SEED_LIBRANDOM)
 219 #   error "librandom not (yet) supported"
 220 #  endif
 221
 222 #  if (defined(__FreeBSD__) || defined(__NetBSD__)) && defined(KERN_ARND)
 223 /*
 224  * sysctl_random(): Use sysctl() to read a random number from the kernel
 225  * Returns the number of bytes returned in buf on success, -1 on failure.
 226  */
 227 static ssize_t sysctl_random(char *buf, size_t buflen)
 228 {
 229     int mib[2];
 230     size_t done = 0;
 231     size_t len;
 232
 233     /*
 234      * Note: sign conversion between size_t and ssize_t is safe even
 235      * without a range check, see comment in syscall_random()
 236      */
 237
 238     /*
 239      * On FreeBSD old implementations returned longs, newer versions support
 240      * variable sizes up to 256 byte. The code below would not work properly
 241      * when the sysctl returns long and we want to request something not a
 242      * multiple of longs, which should never be the case.
 243      */
 244     if (!ossl_assert(buflen % sizeof(long) == 0)) {
 245         errno = EINVAL;
 246         return -1;
 247     }
 248
 249     /*
 250      * On NetBSD before 4.0 KERN_ARND was an alias for KERN_URND, and only
 251      * filled in an int, leaving the rest uninitialized. Since NetBSD 4.0
 252      * it returns a variable number of bytes with the current version supporting
 253      * up to 256 bytes.
 254      * Just return an error on older NetBSD versions.
 255      */
 256 #if   defined(__NetBSD__) && __NetBSD_Version__ < 400000000
 257     errno = ENOSYS;
 258     return -1;
 259 #endif
 260
 261     mib[0] = CTL_KERN;
 262     mib[1] = KERN_ARND;
 263
 264     do {
 265         len = buflen;
 266         if (sysctl(mib, 2, buf, &len, NULL, 0) == -1)
 267             return done > 0 ? done : -1;
 268         done += len;
 269         buf += len;
 270         buflen -= len;
 271     } while (buflen > 0);
 272
 273     return done;
 274 }
 275 #  endif
 276
 277 #  if defined(OPENSSL_RAND_SEED_GETRANDOM)
 278 /*
 279  * syscall_random(): Try to get random data using a system call
 280  * returns the number of bytes returned in buf, or < 0 on error.
 281  */
 282 static ssize_t syscall_random(void *buf, size_t buflen)
 283 {
 284     /*
 285      * Note: 'buflen' equals the size of the buffer which is used by the
 286      * get_entropy() callback of the RAND_DRBG. It is roughly bounded by
 287      *
 288      *   2 * RAND_POOL_FACTOR * (RAND_DRBG_STRENGTH / 8) = 2^14
 289      *
 290      * which is way below the OSSL_SSIZE_MAX limit. Therefore sign conversion
 291      * between size_t and ssize_t is safe even without a range check.
 292      */
 293
 294     /*
 295      * Do runtime detection to find getentropy().
 296      *
 297      * Known OSs that should support this:
 298      * - Darwin since 16 (OSX 10.12, IOS 10.0).
 299      * - Solaris since 11.3
 300      * - OpenBSD since 5.6
 301      * - Linux since 3.17 with glibc 2.25
 302      * - FreeBSD since 12.0 (1200061)
 303      */
 304 #  if defined(__GNUC__) && __GNUC__>=2 && defined(__ELF__) && !defined(__hpux)
 305     extern int getentropy(void *buffer, size_t length) __attribute__((weak));
 306
 307     if (getentropy != NULL)
 308         return getentropy(buf, buflen) == 0 ? (ssize_t)buflen : -1;
 309 #  else
 310     union {
 311         void *p;
 312         int (*f)(void *buffer, size_t length);
 313     } p_getentropy;
 314
 315     /*
 316      * We could cache the result of the lookup, but we normally don't
 317      * call this function often.
 318      */
 319     ERR_set_mark();
 320     p_getentropy.p = DSO_global_lookup("getentropy");
 321     ERR_pop_to_mark();
 322     if (p_getentropy.p != NULL)
 323         return p_getentropy.f(buf, buflen) == 0 ? (ssize_t)buflen : -1;
 324 #  endif
 325
 326     /* Linux supports this since version 3.17 */
 327 #  if defined(__linux) && defined(SYS_getrandom)
 328     return syscall(SYS_getrandom, buf, buflen, 0);
 329 #  elif (defined(__FreeBSD__) || defined(__NetBSD__)) && defined(KERN_ARND)
 330     return sysctl_random(buf, buflen);
 331 #  else
 332     errno = ENOSYS;
 333     return -1;
 334 #  endif
 335 }
 336 #  endif    /* defined(OPENSSL_RAND_SEED_GETRANDOM) */
 337
 338 #  if defined(OPENSSL_RAND_SEED_DEVRANDOM)
 339 static const char *random_device_paths[] = { DEVRANDOM };
 340 static struct random_device {
 341     int fd;
 342     dev_t dev;
 343     ino_t ino;
 344     mode_t mode;
 345     dev_t rdev;
 346 } random_devices[OSSL_NELEM(random_device_paths)];
 347 static int keep_random_devices_open = 1;
 348
 349 /*
 350  * Verify that the file descriptor associated with the random source is
 351  * still valid. The rationale for doing this is the fact that it is not
 352  * uncommon for daemons to close all open file handles when daemonizing.
 353  * So the handle might have been closed or even reused for opening
 354  * another file.
 355  */
 356 static int check_random_device(struct random_device * rd)
 357 {
 358     struct stat st;
 359
 360     return rd->fd != -1
 361            && fstat(rd->fd, &st) != -1
 362            && rd->dev == st.st_dev
 363            && rd->ino == st.st_ino
 364            && ((rd->mode ^ st.st_mode) & ~(S_IRWXU | S_IRWXG | S_IRWXO)) == 0
 365            && rd->rdev == st.st_rdev;
 366 }
 367
 368 /*
 369  * Open a random device if required and return its file descriptor or -1 on error
 370  */
 371 static int get_random_device(size_t n)
 372 {
 373     struct stat st;
 374     struct random_device * rd = &random_devices[n];
 375
 376     /* reuse existing file descriptor if it is (still) valid */
 377     if (check_random_device(rd))
 378         return rd->fd;
 379
 380     /* open the random device ... */
 381     if ((rd->fd = open(random_device_paths[n], O_RDONLY)) == -1)
 382         return rd->fd;
 383
 384     /* ... and cache its relevant stat(2) data */
 385     if (fstat(rd->fd, &st) != -1) {
 386         rd->dev = st.st_dev;
 387         rd->ino = st.st_ino;
 388         rd->mode = st.st_mode;
 389         rd->rdev = st.st_rdev;
 390     } else {
 391         close(rd->fd);
 392         rd->fd = -1;
 393     }
 394
 395     return rd->fd;
 396 }
 397
 398 /*
 399  * Close a random device making sure it is a random device
 400  */
 401 static void close_random_device(size_t n)
 402 {
 403     struct random_device * rd = &random_devices[n];
 404
 405     if (check_random_device(rd))
 406         close(rd->fd);
 407     rd->fd = -1;
 408 }
 409
 410 int rand_pool_init(void)
 411 {
 412     size_t i;
 413
 414     for (i = 0; i < OSSL_NELEM(random_devices); i++)
 415         random_devices[i].fd = -1;
 416
 417     return 1;
 418 }
 419
 420 void rand_pool_cleanup(void)
 421 {
 422     size_t i;
 423
 424     for (i = 0; i < OSSL_NELEM(random_devices); i++)
 425         close_random_device(i);
 426 }
 427
 428 void rand_pool_keep_random_devices_open(int keep)
 429 {
 430     if (!keep)
 431         rand_pool_cleanup();
 432
 433     keep_random_devices_open = keep;
 434 }
 435
 436 #  else     /* !defined(OPENSSL_RAND_SEED_DEVRANDOM) */
 437
 438 int rand_pool_init(void)
 439 {
 440     return 1;
 441 }
 442
 443 void rand_pool_cleanup(void)
 444 {
 445 }
 446
 447 void rand_pool_keep_random_devices_open(int keep)
 448 {
 449 }
 450
 451 #  endif    /* defined(OPENSSL_RAND_SEED_DEVRANDOM) */
 452
 453 /*
 454  * Try the various seeding methods in turn, exit when successful.
 455  *
 456  * TODO(DRBG): If more than one entropy source is available, is it
 457  * preferable to stop as soon as enough entropy has been collected
 458  * (as favored by @rsalz) or should one rather be defensive and add
 459  * more entropy than requested and/or from different sources?
 460  *
 461  * Currently, the user can select multiple entropy sources in the
 462  * configure step, yet in practice only the first available source
 463  * will be used. A more flexible solution has been requested, but
 464  * currently it is not clear how this can be achieved without
 465  * overengineering the problem. There are many parameters which
 466  * could be taken into account when selecting the order and amount
 467  * of input from the different entropy sources (trust, quality,
 468  * possibility of blocking).
 469  */
 470 size_t rand_pool_acquire_entropy(RAND_POOL *pool)
 471 {
 472 #  if defined(OPENSSL_RAND_SEED_NONE)
 473     return rand_pool_entropy_available(pool);
 474 #  else
 475     size_t bytes_needed;
 476     size_t entropy_available = 0;
 477     unsigned char *buffer;
 478
 479 #   if defined(OPENSSL_RAND_SEED_GETRANDOM)
 480     {
 481         ssize_t bytes;
 482         /* Maximum allowed number of consecutive unsuccessful attempts */
 483         int attempts = 3;
 484
 485         bytes_needed = rand_pool_bytes_needed(pool, 1 /*entropy_factor*/);
 486         while (bytes_needed != 0 && attempts-- > 0) {
 487             buffer = rand_pool_add_begin(pool, bytes_needed);
 488             bytes = syscall_random(buffer, bytes_needed);
 489             if (bytes > 0) {
 490                 rand_pool_add_end(pool, bytes, 8 * bytes);
 491                 bytes_needed -= bytes;
 492                 attempts = 3; /* reset counter after successful attempt */
 493             } else if (bytes < 0 && errno != EINTR) {
 494                 break;
 495             }
 496         }
 497     }
 498     entropy_available = rand_pool_entropy_available(pool);
 499     if (entropy_available > 0)
 500         return entropy_available;
 501 #   endif
 502
 503 #   if defined(OPENSSL_RAND_SEED_LIBRANDOM)
 504     {
 505         /* Not yet implemented. */
 506     }
 507 #   endif
 508
 509 #   if defined(OPENSSL_RAND_SEED_DEVRANDOM)
 510     bytes_needed = rand_pool_bytes_needed(pool, 1 /*entropy_factor*/);
 511     {
 512         size_t i;
 513
 514         for (i = 0; bytes_needed > 0 && i < OSSL_NELEM(random_device_paths); i++) {
 515             ssize_t bytes = 0;
 516             /* Maximum allowed number of consecutive unsuccessful attempts */
 517             int attempts = 3;
 518             const int fd = get_random_device(i);
 519
 520             if (fd == -1)
 521                 continue;
 522
 523             while (bytes_needed != 0 && attempts-- > 0) {
 524                 buffer = rand_pool_add_begin(pool, bytes_needed);
 525                 bytes = read(fd, buffer, bytes_needed);
 526
 527                 if (bytes > 0) {
 528                     rand_pool_add_end(pool, bytes, 8 * bytes);
 529                     bytes_needed -= bytes;
 530                     attempts = 3; /* reset counter after successful attempt */
 531                 } else if (bytes < 0 && errno != EINTR) {
 532                     break;
 533                 }
 534             }
 535             if (bytes < 0 || !keep_random_devices_open)
 536                 close_random_device(i);
 537
 538             bytes_needed = rand_pool_bytes_needed(pool, 1 /*entropy_factor*/);
 539         }
 540         entropy_available = rand_pool_entropy_available(pool);
 541         if (entropy_available > 0)
 542             return entropy_available;
 543     }
 544 #   endif
 545
 546 #   if defined(OPENSSL_RAND_SEED_RDTSC)
 547     entropy_available = rand_acquire_entropy_from_tsc(pool);
 548     if (entropy_available > 0)
 549         return entropy_available;
 550 #   endif
 551
 552 #   if defined(OPENSSL_RAND_SEED_RDCPU)
 553     entropy_available = rand_acquire_entropy_from_cpu(pool);
 554     if (entropy_available > 0)
 555         return entropy_available;
 556 #   endif
 557
 558 #   if defined(OPENSSL_RAND_SEED_EGD)
 559     bytes_needed = rand_pool_bytes_needed(pool, 1 /*entropy_factor*/);
 560     if (bytes_needed > 0) {
 561         static const char *paths[] = { DEVRANDOM_EGD, NULL };
 562         int i;
 563
 564         for (i = 0; paths[i] != NULL; i++) {
 565             buffer = rand_pool_add_begin(pool, bytes_needed);
 566             if (buffer != NULL) {
 567                 size_t bytes = 0;
 568                 int num = RAND_query_egd_bytes(paths[i],
 569                                                buffer, (int)bytes_needed);
 570                 if (num == (int)bytes_needed)
 571                     bytes = bytes_needed;
 572
 573                 rand_pool_add_end(pool, bytes, 8 * bytes);
 574                 entropy_available = rand_pool_entropy_available(pool);
 575             }
 576             if (entropy_available > 0)
 577                 return entropy_available;
 578         }
 579     }
 580 #   endif
 581
 582     return rand_pool_entropy_available(pool);
 583 #  endif
 584 }
 585 # endif
 586 #endif
 587
 588 #if defined(OPENSSL_SYS_UNIX) || defined(__DJGPP__)
 589 int rand_pool_add_nonce_data(RAND_POOL *pool)
 590 {
 591     struct {
 592         pid_t pid;
 593         CRYPTO_THREAD_ID tid;
 594         uint64_t time;
 595     } data = { 0 };
 596
 597     /*
 598      * Add process id, thread id, and a high resolution timestamp to
 599      * ensure that the nonce is unique with high probability for
 600      * different process instances.
 601      */
 602     data.pid = getpid();
 603     data.tid = CRYPTO_THREAD_get_current_id();
 604     data.time = get_time_stamp();
 605
 606     return rand_pool_add(pool, (unsigned char *)&data, sizeof(data), 0);
 607 }
 608
 609 int rand_pool_add_additional_data(RAND_POOL *pool)
 610 {
 611     struct {
 612         CRYPTO_THREAD_ID tid;
 613         uint64_t time;
 614     } data = { 0 };
 615
 616     /*
 617      * Add some noise from the thread id and a high resolution timer.
 618      * The thread id adds a little randomness if the drbg is accessed
 619      * concurrently (which is the case for the <master> drbg).
 620      */
 621     data.tid = CRYPTO_THREAD_get_current_id();
 622     data.time = get_timer_bits();
 623
 624     return rand_pool_add(pool, (unsigned char *)&data, sizeof(data), 0);
 625 }
 626
 627
 628 /*
 629  * Get the current time with the highest possible resolution
 630  *
 631  * The time stamp is added to the nonce, so it is optimized for not repeating.
 632  * The current time is ideal for this purpose, provided the computer's clock
 633  * is synchronized.
 634  */
 635 static uint64_t get_time_stamp(void)
 636 {
 637 # if defined(OSSL_POSIX_TIMER_OKAY)
 638     {
 639         struct timespec ts;
 640
 641         if (clock_gettime(CLOCK_REALTIME, &ts) == 0)
 642             return TWO32TO64(ts.tv_sec, ts.tv_nsec);
 643     }
 644 # endif
 645 # if defined(__unix__) \
 646      || (defined(_POSIX_C_SOURCE) && _POSIX_C_SOURCE >= 200112L)
 647     {
 648         struct timeval tv;
 649
 650         if (gettimeofday(&tv, NULL) == 0)
 651             return TWO32TO64(tv.tv_sec, tv.tv_usec);
 652     }
 653 # endif
 654     return time(NULL);
 655 }
 656
 657 /*
 658  * Get an arbitrary timer value of the highest possible resolution
 659  *
 660  * The timer value is added as random noise to the additional data,
 661  * which is not considered a trusted entropy sourec, so any result
 662  * is acceptable.
 663  */
 664 static uint64_t get_timer_bits(void)
 665 {
 666     uint64_t res = OPENSSL_rdtsc();
 667
 668     if (res != 0)
 669         return res;
 670
 671 # if defined(__sun) || defined(__hpux)
 672     return gethrtime();
 673 # elif defined(_AIX)
 674     {
 675         timebasestruct_t t;
 676
 677         read_wall_time(&t, TIMEBASE_SZ);
 678         return TWO32TO64(t.tb_high, t.tb_low);
 679     }
 680 # elif defined(OSSL_POSIX_TIMER_OKAY)
 681     {
 682         struct timespec ts;
 683
 684 #  ifdef CLOCK_BOOTTIME
 685 #   define CLOCK_TYPE CLOCK_BOOTTIME
 686 #  elif defined(_POSIX_MONOTONIC_CLOCK)
 687 #   define CLOCK_TYPE CLOCK_MONOTONIC
 688 #  else
 689 #   define CLOCK_TYPE CLOCK_REALTIME
 690 #  endif
 691
 692         if (clock_gettime(CLOCK_TYPE, &ts) == 0)
 693             return TWO32TO64(ts.tv_sec, ts.tv_nsec);
 694     }
 695 # endif
 696 # if defined(__unix__) \
 697      || (defined(_POSIX_C_SOURCE) && _POSIX_C_SOURCE >= 200112L)
 698     {
 699         struct timeval tv;
 700
 701         if (gettimeofday(&tv, NULL) == 0)
 702             return TWO32TO64(tv.tv_sec, tv.tv_usec);
 703     }
 704 # endif
 705     return time(NULL);
 706 }
 707 #endif /* defined(OPENSSL_SYS_UNIX) || defined(__DJGPP__) */