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-common.h"
  14 #include "qemu/cutils.h"
  15 #include "qapi/error.h"
  16 #include "qemu/guest-random.h"
  17 #include "crypto/random.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, i - len);
  42     }
  43     return 0;
  44 }
  45
  46 int qemu_guest_getrandom(void *buf, size_t len, Error **errp)
  47 {
  48     if (unlikely(deterministic)) {
  49         /* Deterministic implementation using Glib's Mersenne Twister.  */
  50         return glib_random_bytes(buf, len);
  51     } else {
  52         /* Non-deterministic implementation using crypto routines.  */
  53         return qcrypto_random_bytes(buf, len, errp);
  54     }
  55 }
  56
  57 void qemu_guest_getrandom_nofail(void *buf, size_t len)
  58 {
  59     qemu_guest_getrandom(buf, len, &error_fatal);
  60 }
  61
  62 uint64_t qemu_guest_random_seed_thread_part1(void)
  63 {
  64     if (deterministic) {
  65         uint64_t ret;
  66         glib_random_bytes(&ret, sizeof(ret));
  67         return ret;
  68     }
  69     return 0;
  70 }
  71
  72 void qemu_guest_random_seed_thread_part2(uint64_t seed)
  73 {
  74     g_assert(thread_rand == NULL);
  75     if (deterministic) {
  76         thread_rand =
  77             g_rand_new_with_seed_array((const guint32 *)&seed,
  78                                        sizeof(seed) / sizeof(guint32));
  79     }
  80 }
  81
  82 int qemu_guest_random_seed_main(const char *optarg, Error **errp)
  83 {
  84     unsigned long long seed;
  85     if (parse_uint_full(optarg, &seed, 0)) {
  86         error_setg(errp, "Invalid seed number: %s", optarg);
  87         return -1;
  88     } else {
  89         deterministic = true;
  90         qemu_guest_random_seed_thread_part2(seed);
  91         return 0;
  92     }
  93 }