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// OpenVPN -- An application to securely tunnel IP networks
// over a single port, with support for SSL/TLS-based
// session authentication and key exchange,
// packet encryption, packet authentication, and
// packet compression.
//
// Copyright (C) 2012- OpenVPN Inc.
//
// SPDX-License-Identifier: MPL-2.0 OR AGPL-3.0-only WITH openvpn3-openssl-exception
//
#pragma once
#include <openvpn/common/arch.hpp>
#include <openvpn/common/size.hpp>
#include <atomic>
#if defined(USE_OPENSSL)
#include <openssl/crypto.h>
#endif
// Does this architecture allow efficient unaligned access?
#if defined(OPENVPN_ARCH_x86_64) || defined(OPENVPN_ARCH_i386)
#define OPENVPN_HAVE_EFFICIENT_UNALIGNED_ACCESS
#endif
// Define a portable compiler memory access fence (from Boost).
#if defined(__INTEL_COMPILER)
#define OPENVPN_COMPILER_FENCE __memory_barrier();
#elif defined(_MSC_VER) && _MSC_VER >= 1310
extern "C" void _ReadWriteBarrier();
#pragma intrinsic(_ReadWriteBarrier)
#define OPENVPN_COMPILER_FENCE _ReadWriteBarrier();
#elif defined(__GNUC__)
#define OPENVPN_COMPILER_FENCE __asm__ __volatile__("" \
: \
: \
: "memory");
#else
#error need memory fence definition for this compiler
#endif
// C++ doesn't allow increment of void *
#define OPENVPN_INCR_VOID_PTR(var, incr) (var) = static_cast<const unsigned char *>(var) + (incr)
namespace openvpn::crypto {
/**
* memneq - Compare two areas of memory in constant time
*
* @param a first area of memory
* @param b second area of memory
* @param size The length of the memory area to compare
*
* @return Returns false when data is equal, true otherwise
*/
inline bool memneq(const void *a, const void *b, size_t size);
#if defined(USE_OPENSSL)
inline bool memneq(const void *a, const void *b, size_t size)
{
// memcmp does return 0 (=false) when the memory is equal. It normally
// returns the position of first mismatch otherwise but the crypto
// variants only promise to return something != 0 (=true)
return (bool)(CRYPTO_memcmp(a, b, size));
}
#else
inline bool memneq(const void *a, const void *b, size_t size)
{
// This is inspired by mbedtls' internal safer_memcmp function:
const unsigned char *x = (const unsigned char *)a;
const unsigned char *y = (const unsigned char *)b;
unsigned char diff = 0;
for (size_t i = 0; i < size; i++)
{
unsigned char u = x[i], v = y[i];
diff |= u ^ v;
}
atomic_thread_fence(std::memory_order_release);
return bool(diff);
}
#endif
} // namespace openvpn::crypto
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