blob: cc00aaaf744ac3a17f4cc3054890b578908a933a [file] [log] [blame]
// 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 {
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)
{
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 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;
}
// 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;
#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 CPU(ARM64)
// ARM64 on Linux has 39-bit user space.
random &= 0x3fffffffffUL;
random += 0x1000000000UL;
#else // !CPU(X86_64) && !CPU(ARM64)
#if 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 // 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 // CPU(X86_64)
random &= kPageAllocationGranularityBaseMask;
return reinterpret_cast<void*>(random);
}
}