| // 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/page_allocator.h" |
| #include "base/allocator/partition_allocator/spin_lock.h" |
| #include "base/lazy_instance.h" |
| #include "base/rand_util.h" |
| #include "build/build_config.h" |
| |
| #if defined(OS_WIN) |
| #include <windows.h> // Must be in front of other Windows header files. |
| |
| #include <VersionHelpers.h> |
| |
| #include "starboard/types.h" |
| #endif |
| |
| namespace base { |
| |
| namespace { |
| |
| // This is the same PRNG as used by tcmalloc for mapping address randomness; |
| // see http://burtleburtle.net/bob/rand/smallprng.html |
| struct RandomContext { |
| subtle::SpinLock lock; |
| bool initialized; |
| uint32_t a; |
| uint32_t b; |
| uint32_t c; |
| uint32_t d; |
| }; |
| |
| static LazyInstance<RandomContext>::Leaky s_RandomContext = |
| LAZY_INSTANCE_INITIALIZER; |
| |
| #define rot(x, k) (((x) << (k)) | ((x) >> (32 - (k)))) |
| |
| uint32_t RandomValueInternal(RandomContext* x) { |
| uint32_t e = x->a - rot(x->b, 27); |
| x->a = x->b ^ rot(x->c, 17); |
| x->b = x->c + x->d; |
| x->c = x->d + e; |
| x->d = e + x->a; |
| return x->d; |
| } |
| |
| #undef rot |
| |
| uint32_t RandomValue(RandomContext* x) { |
| subtle::SpinLock::Guard guard(x->lock); |
| if (UNLIKELY(!x->initialized)) { |
| const uint64_t r1 = RandUint64(); |
| const uint64_t r2 = RandUint64(); |
| |
| x->a = static_cast<uint32_t>(r1); |
| x->b = static_cast<uint32_t>(r1 >> 32); |
| x->c = static_cast<uint32_t>(r2); |
| x->d = static_cast<uint32_t>(r2 >> 32); |
| |
| x->initialized = true; |
| } |
| |
| return RandomValueInternal(x); |
| } |
| |
| } // namespace |
| |
| void SetRandomPageBaseSeed(int64_t seed) { |
| RandomContext* x = s_RandomContext.Pointer(); |
| subtle::SpinLock::Guard guard(x->lock); |
| // Set RNG to initial state. |
| x->initialized = true; |
| x->a = x->b = static_cast<uint32_t>(seed); |
| x->c = x->d = static_cast<uint32_t>(seed >> 32); |
| } |
| |
| void* GetRandomPageBase() { |
| uintptr_t random = |
| static_cast<uintptr_t>(RandomValue(s_RandomContext.Pointer())); |
| |
| #if defined(ARCH_CPU_64_BITS) |
| random <<= 32ULL; |
| random |= static_cast<uintptr_t>(RandomValue(s_RandomContext.Pointer())); |
| |
| // 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(jschuh): 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 |