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// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "third_party/base/allocator/partition_allocator/address_space_randomization.h"
#include "build/build_config.h"
#include "third_party/base/allocator/partition_allocator/page_allocator.h"
#include "third_party/base/allocator/partition_allocator/random.h"
#include "third_party/base/allocator/partition_allocator/spin_lock.h"
#include "third_party/base/logging.h"
#if defined(OS_WIN)
#include <windows.h> // Must be in front of other Windows header files.
#include <VersionHelpers.h>
#endif
namespace pdfium {
namespace base {
void* GetRandomPageBase() {
uintptr_t random = static_cast<uintptr_t>(RandomValue());
#if defined(ARCH_CPU_64_BITS)
random <<= 32ULL;
random |= static_cast<uintptr_t>(RandomValue());
// The kASLRMask and kASLROffset constants will be suitable for the
// OS and build configuration.
#if defined(OS_WIN) && !defined(MEMORY_TOOL_REPLACES_ALLOCATOR)
// Windows >= 8.1 has the full 47 bits. Use them where available.
static bool windows_81 = false;
static bool windows_81_initialized = false;
if (!windows_81_initialized) {
windows_81 = IsWindows8Point1OrGreater();
windows_81_initialized = true;
}
if (!windows_81) {
random &= internal::kASLRMaskBefore8_10;
} else {
random &= internal::kASLRMask;
}
random += internal::kASLROffset;
#else
random &= internal::kASLRMask;
random += internal::kASLROffset;
#endif // defined(OS_WIN) && !defined(MEMORY_TOOL_REPLACES_ALLOCATOR)
#else // defined(ARCH_CPU_32_BITS)
#if defined(OS_WIN)
// On win32 host systems the randomization plus huge alignment causes
// excessive fragmentation. Plus most of these systems lack ASLR, so the
// randomization isn't buying anything. In that case we just skip it.
// TODO(palmer): Just dump the randomization when HE-ASLR is present.
static BOOL is_wow64 = -1;
if (is_wow64 == -1 && !IsWow64Process(GetCurrentProcess(), &is_wow64))
is_wow64 = FALSE;
if (!is_wow64)
return nullptr;
#endif // defined(OS_WIN)
random &= internal::kASLRMask;
random += internal::kASLROffset;
#endif // defined(ARCH_CPU_32_BITS)
DCHECK_EQ(0ULL, (random & kPageAllocationGranularityOffsetMask));
return reinterpret_cast<void*>(random);
}
} // namespace base
} // namespace pdfium
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