lib/Support/RandomNumberGenerator.cpp

   1 //===-- RandomNumberGenerator.cpp - Implement RNG class -------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This file implements deterministic random number generation (RNG).
  10 // The current implementation is NOT cryptographically secure as it uses
  11 // the C++11 <random> facilities.
  12 //
  13 //===----------------------------------------------------------------------===//
  14
  15 #include "llvm/Support/RandomNumberGenerator.h"
  16 #include "llvm/Support/CommandLine.h"
  17 #include "llvm/Support/Debug.h"
  18 #include "llvm/Support/raw_ostream.h"
  19 #ifdef _WIN32
  20 #include "Windows/WindowsSupport.h"
  21 #else
  22 #include "Unix/Unix.h"
  23 #endif
  24
  25 using namespace llvm;
  26
  27 #define DEBUG_TYPE "rng"
  28
  29 // Tracking BUG: 19665
  30 // http://llvm.org/bugs/show_bug.cgi?id=19665
  31 //
  32 // Do not change to cl::opt<uint64_t> since this silently breaks argument parsing.
  33 static cl::opt<unsigned long long>
  34     Seed("rng-seed", cl::value_desc("seed"), cl::Hidden,
  35          cl::desc("Seed for the random number generator"), cl::init(0));
  36
  37 RandomNumberGenerator::RandomNumberGenerator(StringRef Salt) {
  38   LLVM_DEBUG(if (Seed == 0) dbgs()
  39              << "Warning! Using unseeded random number generator.\n");
  40
  41   // Combine seed and salts using std::seed_seq.
  42   // Data: Seed-low, Seed-high, Salt
  43   // Note: std::seed_seq can only store 32-bit values, even though we
  44   // are using a 64-bit RNG. This isn't a problem since the Mersenne
  45   // twister constructor copies these correctly into its initial state.
  46   std::vector<uint32_t> Data;
  47   Data.resize(2 + Salt.size());
  48   Data[0] = Seed;
  49   Data[1] = Seed >> 32;
  50
  51   llvm::copy(Salt, Data.begin() + 2);
  52
  53   std::seed_seq SeedSeq(Data.begin(), Data.end());
  54   Generator.seed(SeedSeq);
  55 }
  56
  57 RandomNumberGenerator::result_type RandomNumberGenerator::operator()() {
  58   return Generator();
  59 }
  60
  61 // Get random vector of specified size
  62 std::error_code llvm::getRandomBytes(void *Buffer, size_t Size) {
  63 #ifdef _WIN32
  64   HCRYPTPROV hProvider;
  65   if (CryptAcquireContext(&hProvider, 0, 0, PROV_RSA_FULL,
  66                            CRYPT_VERIFYCONTEXT | CRYPT_SILENT)) {
  67     ScopedCryptContext ScopedHandle(hProvider);
  68     if (CryptGenRandom(hProvider, Size, static_cast<BYTE *>(Buffer)))
  69       return std::error_code();
  70   }
  71   return std::error_code(GetLastError(), std::system_category());
  72 #else
  73   int Fd = open("/dev/urandom", O_RDONLY);
  74   if (Fd != -1) {
  75     std::error_code Ret;
  76     ssize_t BytesRead = read(Fd, Buffer, Size);
  77     if (BytesRead == -1)
  78       Ret = std::error_code(errno, std::system_category());
  79     else if (BytesRead != static_cast<ssize_t>(Size))
  80       Ret = std::error_code(EIO, std::system_category());
  81     if (close(Fd) == -1)
  82       Ret = std::error_code(errno, std::system_category());
  83
  84     return Ret;
  85   }
  86   return std::error_code(errno, std::system_category());
  87 #endif
  88 }