zircon/system/ulib/explicit-memory/include/explicit-memory/bytes.h

// Copyright 2017 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#pragma once

#include <zircon/compiler.h>
#include <stddef.h>

__BEGIN_CDECLS

// See memcpy().  Invocations of this implementation are guaranteed to not be optimized
// away.  I.e. if you invoke mandatory_memcpy(dst, src, n), and then access
// |dst|, the compiler will not issue an access to |src|.  The intention is that
// this is suitable for copying shared data from an untrusted source.  The
// untrusted source should not be able to modify |dst| after the
// mandatory_memcpy() completes.
void* mandatory_memcpy(void* dst, const void* src, size_t n);

// See memset().  Invocations of this implementation are guaranteed to not be optimized
// away.  I.e. if you invoke mandatory_memset(dst, c, n), |dst| will be
// written to, even if |dst| will not be read from again for the rest of its
// lifetime.  The intention is that this is suitable for zeroing a buffer
// containing sensitive data.
void* mandatory_memset(void* dst, int c, size_t n);

__END_CDECLS

#ifdef __cplusplus

#include <fbl/macros.h>
#include <type_traits>

namespace explicit_memory {

// This class guarantees that the wrapped array will be filled with zeroes when
// the wrapping ZeroDtor object goes out of scope.  See mandatory_memset() for
// discussion on what this guarantee entails.
template <typename T, typename = typename std::enable_if<std::is_pod<T>::value>::type>
class ZeroDtor {
public:
    ZeroDtor(T* array, size_t len) : array_(array), len_(len) { }
    ~ZeroDtor() {
        mandatory_memset(static_cast<void*>(array_), 0, sizeof(T) * len_);
    }
    DISALLOW_COPY_ASSIGN_AND_MOVE(ZeroDtor);
private:
     T* const array_;
     const size_t len_;
};

} // namespace explicit_memory

#endif