| // 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 "config.h" |
| #include "wtf/AddressSpaceRandomization.h" |
| |
| #include "wtf/PageAllocator.h" |
| #include "wtf/SpinLock.h" |
| |
| #if OS(WIN) |
| #include <windows.h> |
| #else |
| #include <sys/time.h> |
| #include <unistd.h> |
| #endif |
| |
| namespace WTF { |
| |
| namespace { |
| |
| // This is the same PRNG as used by tcmalloc for mapping address randomness; |
| // see http://burtleburtle.net/bob/rand/smallprng.html |
| struct ranctx { |
| int 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) |
| { |
| spinLockLock(&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 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); |
| spinLockUnlock(&x->lock); |
| return ret; |
| } |
| |
| static struct ranctx s_ranctx; |
| |
| } |
| |
| // 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 CPU(X86_64) |
| random <<= 32UL; |
| random |= static_cast<uintptr_t>(ranval(&s_ranctx)); |
| // This address mask gives a low liklihood of address space collisions. |
| // We handle the situation gracefully if there is a collision. |
| #if OS(WIN) |
| // 64-bit Windows has a bizarrely small 8TB user address space. |
| // Allocates in the 1-5TB region. |
| // TODO(cevans): I think Win 8.1 has 47-bits like Linux. |
| random &= 0x3ffffffffffUL; |
| random += 0x10000000000UL; |
| #else |
| // Linux and OS X support the full 47-bit user space of x64 processors. |
| random &= 0x3fffffffffffUL; |
| #endif |
| #elif CPU(ARM64) |
| // ARM64 on Linux has 39-bit user space. |
| random &= 0x3fffffffffUL; |
| random += 0x1000000000UL; |
| #else // !CPU(X86_64) && !CPU(ARM64) |
| // This is a good range on Windows, Linux and Mac. |
| // Allocates in the 0.5-1.5GB region. |
| random &= 0x3fffffff; |
| random += 0x20000000; |
| #endif // CPU(X86_64) |
| random &= kPageAllocationGranularityBaseMask; |
| return reinterpret_cast<void*>(random); |
| } |
| |
| } |