chromium/components/gwp_asan/client/thread_local_random_bit_generator.h

// Copyright 2023 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef COMPONENTS_GWP_ASAN_CLIENT_THREAD_LOCAL_RANDOM_BIT_GENERATOR_H_
#define COMPONENTS_GWP_ASAN_CLIENT_THREAD_LOCAL_RANDOM_BIT_GENERATOR_H_

#include <limits>

#include "base/compiler_specific.h"
#include "base/rand_util.h"
#include "components/gwp_asan/client/thread_local_state.h"

namespace gwp_asan::internal {

namespace {
template <std::size_t N>
struct XorShiftImpl;

template <>
struct XorShiftImpl<8> { … };

template <>
struct XorShiftImpl<4> { … };

template <typename result_type>
result_type XorShift(result_type x) { … }
}  // namespace

// Efficient pseudo-random number generator (PRNG) tailored for Thread-Local
// Storage (TLS) slots. Chooses between XorShift 64 and XorShift 32 based on
// TLS slot size.
//
// Note: GWP-ASan previously relied on a high-entropy source with the intent of
// preventing attackers from identifying allocations originating from GWP-ASan.
// However, it seems like there are more practical methods for attackers to
// achieve this, bypassing the need to crack the PRNG state. Additionally, an
// attacker can simply neutralize GWP-ASan by making numerous small allocations,
// exhausting all available slots.
class ThreadLocalRandomBitGenerator
    : ThreadLocalState<ThreadLocalRandomBitGenerator> { … };

}  // namespace gwp_asan::internal

#endif  // COMPONENTS_GWP_ASAN_CLIENT_THREAD_LOCAL_RANDOM_BIT_GENERATOR_H_