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// Copyright 2012 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "base/rand_util.h"
#include <windows.h>
#include <stddef.h>
#include <stdint.h>
#include <algorithm>
#include <atomic>
#include <limits>
#include "base/check.h"
#include "base/feature_list.h"
#include "third_party/boringssl/src/include/openssl/rand.h"
// Prototype for ProcessPrng.
// See: https://learn.microsoft.com/en-us/windows/win32/seccng/processprng
extern "C" {
BOOL WINAPI ProcessPrng(PBYTE pbData, SIZE_T cbData);
}
namespace base {
namespace internal {
namespace {
// The BoringSSl helpers are duplicated in rand_util_fuchsia.cc and
// rand_util_posix.cc.
std::atomic<bool> g_use_boringssl;
BASE_FEATURE(kUseBoringSSLForRandBytes,
"UseBoringSSLForRandBytes",
FEATURE_DISABLED_BY_DEFAULT);
} // namespace
void ConfigureBoringSSLBackedRandBytesFieldTrial() {
g_use_boringssl.store(FeatureList::IsEnabled(kUseBoringSSLForRandBytes),
std::memory_order_relaxed);
}
bool UseBoringSSLForRandBytes() {
return g_use_boringssl.load(std::memory_order_relaxed);
}
} // namespace internal
namespace {
// Import bcryptprimitives!ProcessPrng rather than cryptbase!RtlGenRandom to
// avoid opening a handle to \\Device\KsecDD in the renderer.
decltype(&ProcessPrng) GetProcessPrng() {
HMODULE hmod = LoadLibraryW(L"bcryptprimitives.dll");
CHECK(hmod);
decltype(&ProcessPrng) process_prng_fn =
reinterpret_cast<decltype(&ProcessPrng)>(
GetProcAddress(hmod, "ProcessPrng"));
CHECK(process_prng_fn);
return process_prng_fn;
}
void RandBytesInternal(span<uint8_t> output, bool avoid_allocation) {
if (!avoid_allocation && internal::UseBoringSSLForRandBytes()) {
// BoringSSL's RAND_bytes always returns 1. Any error aborts the program.
(void)RAND_bytes(output.data(), output.size());
return;
}
static decltype(&ProcessPrng) process_prng_fn = GetProcessPrng();
BOOL success =
process_prng_fn(static_cast<BYTE*>(output.data()), output.size());
// ProcessPrng is documented to always return TRUE.
CHECK(success);
}
} // namespace
void RandBytes(span<uint8_t> output) {
RandBytesInternal(output, /*avoid_allocation=*/false);
}
namespace internal {
double RandDoubleAvoidAllocation() {
uint64_t number;
RandBytesInternal(byte_span_from_ref(number),
/*avoid_allocation=*/true);
// This transformation is explained in rand_util.cc.
return (number >> 11) * 0x1.0p-53;
}
} // namespace internal
} // namespace base
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