util/guest-random.c

   1 /*
   2  * QEMU guest-visible random functions
   3  *
   4  * Copyright 2019 Linaro, Ltd.
   5  *
   6  * This program is free software; you can redistribute it and/or modify it
   7  * under the terms of the GNU General Public License as published by the Free
   8  * Software Foundation; either version 2 of the License, or (at your option)
   9  * any later version.
  10  */
  11
  12 #include "qemu/osdep.h"
  13 #include "qemu/cutils.h"
  14 #include "qapi/error.h"
  15 #include "qemu/guest-random.h"
  16 #include "crypto/random.h"
  17 #include "exec/replay-core.h"
  18
  19
  20 static __thread GRand *thread_rand;
  21 static bool deterministic;
  22
  23
  24 static int glib_random_bytes(void *buf, size_t len)
  25 {
  26     GRand *rand = thread_rand;
  27     size_t i;
  28     uint32_t x;
  29
  30     if (unlikely(rand == NULL)) {
  31         /* Thread not initialized for a cpu, or main w/o -seed.  */
  32         thread_rand = rand = g_rand_new();
  33     }
  34
  35     for (i = 0; i + 4 <= len; i += 4) {
  36         x = g_rand_int(rand);
  37         __builtin_memcpy(buf + i, &x, 4);
  38     }
  39     if (i < len) {
  40         x = g_rand_int(rand);
  41         __builtin_memcpy(buf + i, &x, len - i);
  42     }
  43     return 0;
  44 }
  45
  46 int qemu_guest_getrandom(void *buf, size_t len, Error **errp)
  47 {
  48     int ret;
  49     if (replay_mode == REPLAY_MODE_PLAY) {
  50         return replay_read_random(buf, len);
  51     }
  52     if (unlikely(deterministic)) {
  53         /* Deterministic implementation using Glib's Mersenne Twister.  */
  54         ret = glib_random_bytes(buf, len);
  55     } else {
  56         /* Non-deterministic implementation using crypto routines.  */
  57         ret = qcrypto_random_bytes(buf, len, errp);
  58     }
  59     if (replay_mode == REPLAY_MODE_RECORD) {
  60         replay_save_random(ret, buf, len);
  61     }
  62     return ret;
  63 }
  64
  65 void qemu_guest_getrandom_nofail(void *buf, size_t len)
  66 {
  67     (void)qemu_guest_getrandom(buf, len, &error_fatal);
  68 }
  69
  70 uint64_t qemu_guest_random_seed_thread_part1(void)
  71 {
  72     if (deterministic) {
  73         uint64_t ret;
  74         glib_random_bytes(&ret, sizeof(ret));
  75         return ret;
  76     }
  77     return 0;
  78 }
  79
  80 void qemu_guest_random_seed_thread_part2(uint64_t seed)
  81 {
  82     g_assert(thread_rand == NULL);
  83     if (deterministic) {
  84         thread_rand =
  85             g_rand_new_with_seed_array((const guint32 *)&seed,
  86                                        sizeof(seed) / sizeof(guint32));
  87     }
  88 }
  89
  90 int qemu_guest_random_seed_main(const char *optarg, Error **errp)
  91 {
  92     uint64_t seed;
  93     if (parse_uint_full(optarg, 0, &seed)) {
  94         error_setg(errp, "Invalid seed number: %s", optarg);
  95         return -1;
  96     } else {
  97         deterministic = true;
  98         qemu_guest_random_seed_thread_part2(seed);
  99         return 0;
 100     }
 101 }