| // 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 "third_party/base/allocator/partition_allocator/page_allocator.h" |
| #include "third_party/base/allocator/partition_allocator/spin_lock.h" |
| #include "third_party/build/build_config.h" |
| |
| #if defined(OS_WIN) |
| #include <windows.h> |
| #else |
| #include <sys/time.h> |
| #include <unistd.h> |
| #endif |
| |
| namespace pdfium { |
| 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 ranctx { |
| subtle::SpinLock lock; |
| bool initialized; |
| uint32_t a; |
| uint32_t b; |
| uint32_t c; |
| uint32_t d; |
| }; |
| |
| #define rot(x, k) (((x) << (k)) | ((x) >> (32 - (k)))) |
| |
| uint32_t ranvalInternal(ranctx* 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 ranval(ranctx* x) { |
| subtle::SpinLock::Guard guard(x->lock); |
| if (UNLIKELY(!x->initialized)) { |
| x->initialized = true; |
| char c; |
| uint32_t seed = static_cast<uint32_t>(reinterpret_cast<uintptr_t>(&c)); |
| uint32_t pid; |
| uint32_t usec; |
| #if defined(OS_WIN) |
| pid = GetCurrentProcessId(); |
| SYSTEMTIME st; |
| GetSystemTime(&st); |
| usec = static_cast<uint32_t>(st.wMilliseconds * 1000); |
| #else |
| pid = static_cast<uint32_t>(getpid()); |
| struct timeval tv; |
| gettimeofday(&tv, 0); |
| usec = static_cast<uint32_t>(tv.tv_usec); |
| #endif |
| seed ^= pid; |
| seed ^= usec; |
| x->a = 0xf1ea5eed; |
| x->b = x->c = x->d = seed; |
| for (int i = 0; i < 20; ++i) { |
| (void)ranvalInternal(x); |
| } |
| } |
| uint32_t ret = ranvalInternal(x); |
| return ret; |
| } |
| |
| static struct ranctx s_ranctx; |
| |
| } // namespace |
| |
| // Calculates a random preferred mapping address. In calculating an address, we |
| // balance good ASLR against not fragmenting the address space too badly. |
| void* GetRandomPageBase() { |
| uintptr_t random; |
| random = static_cast<uintptr_t>(ranval(&s_ranctx)); |
| #if defined(ARCH_CPU_X86_64) |
| random <<= 32UL; |
| random |= static_cast<uintptr_t>(ranval(&s_ranctx)); |
| // This address mask gives a low likelihood of address space collisions. We |
| // handle the situation gracefully if there is a collision. |
| #if defined(OS_WIN) |
| // 64-bit Windows has a bizarrely small 8TB user address space. Allocates in |
| // the 1-5TB region. TODO(palmer): See if Windows >= 8.1 has the full 47 bits, |
| // and use it if so. crbug.com/672219 |
| random &= 0x3ffffffffffUL; |
| random += 0x10000000000UL; |
| #elif defined(MEMORY_TOOL_REPLACES_ALLOCATOR) |
| // This range is copied from the TSan source, but works for all tools. |
| random &= 0x007fffffffffUL; |
| random += 0x7e8000000000UL; |
| #else |
| // Linux and OS X support the full 47-bit user space of x64 processors. |
| random &= 0x3fffffffffffUL; |
| #endif |
| #elif defined(ARCH_CPU_ARM64) |
| // ARM64 on Linux has 39-bit user space. |
| random &= 0x3fffffffffUL; |
| random += 0x1000000000UL; |
| #else // !defined(ARCH_CPU_X86_64) && !defined(ARCH_CPU_ARM64) |
| #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 isWow64 = -1; |
| if (isWow64 == -1 && !IsWow64Process(GetCurrentProcess(), &isWow64)) |
| isWow64 = FALSE; |
| if (!isWow64) |
| return nullptr; |
| #endif // defined(OS_WIN) |
| // This is a good range on Windows, Linux and Mac. |
| // Allocates in the 0.5-1.5GB region. |
| random &= 0x3fffffff; |
| random += 0x20000000; |
| #endif // defined(ARCH_CPU_X86_64) |
| random &= kPageAllocationGranularityBaseMask; |
| return reinterpret_cast<void*>(random); |
| } |
| |
| } // namespace base |
| } // namespace pdfium |