mfbt/RandomNum.cpp

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
   6
   7 #include "mozilla/RandomNum.h"
   8
   9 #include <fcntl.h>
  10 #ifdef XP_UNIX
  11 #  include <unistd.h>
  12 #endif
  13
  14 #if defined(XP_WIN)
  15
  16 // Microsoft doesn't "officially" support using RtlGenRandom() directly
  17 // anymore, and the Windows headers assume that __stdcall is
  18 // the default calling convention (which is true when Microsoft uses this
  19 // function to build their own CRT libraries).
  20
  21 // We will explicitly declare it with the proper calling convention.
  22
  23 #  include "minwindef.h"
  24 #  define RtlGenRandom SystemFunction036
  25 extern "C" BOOLEAN NTAPI RtlGenRandom(PVOID RandomBuffer,
  26                                       ULONG RandomBufferLength);
  27
  28 #endif
  29
  30 #if defined(ANDROID) || defined(XP_DARWIN) || defined(__DragonFly__) ||    \
  31     defined(__FreeBSD__) || defined(__NetBSD__) || defined(__OpenBSD__) || \
  32     defined(__wasi__)
  33 #  include <stdlib.h>
  34 #  define USE_ARC4RANDOM
  35 #endif
  36
  37 #if defined(__linux__)
  38 #  include <linux/random.h>  // For GRND_NONBLOCK.
  39 #  include <sys/syscall.h>   // For SYS_getrandom.
  40
  41 // Older glibc versions don't define SYS_getrandom, so we define it here if
  42 // it's not available. See bug 995069.
  43 #  if defined(__x86_64__)
  44 #    define GETRANDOM_NR 318
  45 #  elif defined(__i386__)
  46 #    define GETRANDOM_NR 355
  47 #  elif defined(__aarch64__)
  48 #    define GETRANDOM_NR 278
  49 #  elif defined(__arm__)
  50 #    define GETRANDOM_NR 384
  51 #  elif defined(__powerpc__)
  52 #    define GETRANDOM_NR 359
  53 #  elif defined(__s390__)
  54 #    define GETRANDOM_NR 349
  55 #  elif defined(__mips__)
  56 #    include <sgidefs.h>
  57 #    if _MIPS_SIM == _MIPS_SIM_ABI32
  58 #      define GETRANDOM_NR 4353
  59 #    elif _MIPS_SIM == _MIPS_SIM_ABI64
  60 #      define GETRANDOM_NR 5313
  61 #    elif _MIPS_SIM == _MIPS_SIM_NABI32
  62 #      define GETRANDOM_NR 6317
  63 #    endif
  64 #  endif
  65
  66 #  if defined(SYS_getrandom)
  67 // We have SYS_getrandom. Use it to check GETRANDOM_NR. Only do this if we set
  68 // GETRANDOM_NR so tier 3 platforms with recent glibc are not forced to define
  69 // it for no good reason.
  70 #    if defined(GETRANDOM_NR)
  71 static_assert(GETRANDOM_NR == SYS_getrandom,
  72               "GETRANDOM_NR should match the actual SYS_getrandom value");
  73 #    endif
  74 #  else
  75 #    define SYS_getrandom GETRANDOM_NR
  76 #  endif
  77
  78 #  if defined(GRND_NONBLOCK)
  79 static_assert(GRND_NONBLOCK == 1,
  80               "If GRND_NONBLOCK is not 1 the #define below is wrong");
  81 #  else
  82 #    define GRND_NONBLOCK 1
  83 #  endif
  84
  85 #endif  // defined(__linux__)
  86
  87 namespace mozilla {
  88
  89 MFBT_API bool GenerateRandomBytesFromOS(void* aBuffer, size_t aLength) {
  90   MOZ_ASSERT(aBuffer);
  91   MOZ_ASSERT(aLength > 0);
  92
  93 #if defined(XP_WIN)
  94
  95   return !!RtlGenRandom(aBuffer, aLength);
  96
  97 #elif defined(USE_ARC4RANDOM)  // defined(XP_WIN)
  98
  99   arc4random_buf(aBuffer, aLength);
 100   return true;
 101
 102 #elif defined(XP_UNIX)  // defined(USE_ARC4RANDOM)
 103
 104 #  if defined(__linux__)
 105
 106   long bytesGenerated = syscall(SYS_getrandom, aBuffer, aLength, GRND_NONBLOCK);
 107
 108   if (static_cast<unsigned long>(bytesGenerated) == aLength) {
 109     return true;
 110   }
 111
 112   // Fall-through to UNIX behavior if failed
 113
 114 #  endif  // defined(__linux__)
 115
 116   int fd = open("/dev/urandom", O_RDONLY);
 117   if (fd < 0) {
 118     return false;
 119   }
 120
 121   ssize_t bytesRead = read(fd, aBuffer, aLength);
 122
 123   close(fd);
 124
 125   return (static_cast<size_t>(bytesRead) == aLength);
 126
 127 #else  // defined(XP_UNIX)
 128 #  error "Platform needs to implement GenerateRandomBytesFromOS()"
 129 #endif
 130 }
 131
 132 MFBT_API Maybe<uint64_t> RandomUint64() {
 133   uint64_t randomNum;
 134   if (!GenerateRandomBytesFromOS(&randomNum, sizeof(randomNum))) {
 135     return Nothing();
 136   }
 137
 138   return Some(randomNum);
 139 }
 140
 141 MFBT_API uint64_t RandomUint64OrDie() {
 142   uint64_t randomNum;
 143   MOZ_RELEASE_ASSERT(GenerateRandomBytesFromOS(&randomNum, sizeof(randomNum)));
 144   return randomNum;
 145 }
 146
 147 }  // namespace mozilla