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 "llvm/Support/Windows/WindowsSupport.h"
21#else
22#include "Unix/Unix.h"
23#endif
24
25using namespace llvm;
26
27#define DEBUG_TYPE "rng"
28
29static cl::opt<uint64_t> Seed("rng-seed", cl::value_desc("seed"), cl::Hidden,
30                              cl::desc("Seed for the random number generator"),
31                              cl::init(0));
32
33RandomNumberGenerator::RandomNumberGenerator(StringRef Salt) {
34  LLVM_DEBUG(if (Seed == 0) dbgs()
35             << "Warning! Using unseeded random number generator.\n");
36
37  // Combine seed and salts using std::seed_seq.
38  // Data: Seed-low, Seed-high, Salt
39  // Note: std::seed_seq can only store 32-bit values, even though we
40  // are using a 64-bit RNG. This isn't a problem since the Mersenne
41  // twister constructor copies these correctly into its initial state.
42  std::vector<uint32_t> Data;
43  Data.resize(2 + Salt.size());
44  Data[0] = Seed;
45  Data[1] = Seed >> 32;
46
47  llvm::copy(Salt, Data.begin() + 2);
48
49  std::seed_seq SeedSeq(Data.begin(), Data.end());
50  Generator.seed(SeedSeq);
51}
52
53RandomNumberGenerator::result_type RandomNumberGenerator::operator()() {
54  return Generator();
55}
56
57// Get random vector of specified size
58std::error_code llvm::getRandomBytes(void *Buffer, size_t Size) {
59#ifdef _WIN32
60  HCRYPTPROV hProvider;
61  if (CryptAcquireContext(&hProvider, 0, 0, PROV_RSA_FULL,
62                           CRYPT_VERIFYCONTEXT | CRYPT_SILENT)) {
63    ScopedCryptContext ScopedHandle(hProvider);
64    if (CryptGenRandom(hProvider, Size, static_cast<BYTE *>(Buffer)))
65      return std::error_code();
66  }
67  return std::error_code(GetLastError(), std::system_category());
68#else
69  int Fd = open("/dev/urandom", O_RDONLY);
70  if (Fd != -1) {
71    std::error_code Ret;
72    ssize_t BytesRead = read(Fd, Buffer, Size);
73    if (BytesRead == -1)
74      Ret = std::error_code(errno, std::system_category());
75    else if (BytesRead != static_cast<ssize_t>(Size))
76      Ret = std::error_code(EIO, std::system_category());
77    if (close(Fd) == -1)
78      Ret = std::error_code(errno, std::system_category());
79
80    return Ret;
81  }
82  return std::error_code(errno, std::system_category());
83#endif
84}
85