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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 "base/allocator/partition_allocator/address_space_randomization.h"
- #include "base/allocator/partition_allocator/partition_alloc_check.h"
- #include "base/allocator/partition_allocator/random.h"
- #include "build/build_config.h"
- #if BUILDFLAG(IS_WIN)
- #include <windows.h> // Must be in front of other Windows header files.
- #include <versionhelpers.h>
- #endif
- namespace partition_alloc {
- uintptr_t GetRandomPageBase() {
- uintptr_t random = static_cast<uintptr_t>(internal::RandomValue());
- #if defined(ARCH_CPU_64_BITS)
- random <<= 32ULL;
- random |= static_cast<uintptr_t>(internal::RandomValue());
- // The ASLRMask() and ASLROffset() constants will be suitable for the
- // OS and build configuration.
- #if BUILDFLAG(IS_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::ASLRMaskBefore8_10();
- } else {
- random &= internal::ASLRMask();
- }
- random += internal::ASLROffset();
- #else
- random &= internal::ASLRMask();
- random += internal::ASLROffset();
- #endif // BUILDFLAG(IS_WIN) && !defined(MEMORY_TOOL_REPLACES_ALLOCATOR)
- #else // defined(ARCH_CPU_32_BITS)
- #if BUILDFLAG(IS_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 0;
- #endif // BUILDFLAG(IS_WIN)
- random &= internal::ASLRMask();
- random += internal::ASLROffset();
- #endif // defined(ARCH_CPU_32_BITS)
- PA_DCHECK(!(random & internal::PageAllocationGranularityOffsetMask()));
- return random;
- }
- } // namespace partition_alloc
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