Oilpan: Improve address space randomization for the Oilpan heap.

Source/wtf/AddressSpaceRandomization.cpp

Index: Source/wtf/AddressSpaceRandomization.cpp
diff --git a/Source/wtf/AddressSpaceRandomization.cpp b/Source/wtf/AddressSpaceRandomization.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..daaa1fd73c495f40c3ede4b8da28311edded6ed3
--- /dev/null
+++ b/Source/wtf/AddressSpaceRandomization.cpp
@@ -0,0 +1,99 @@
+// 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/ProcessID.h"
+#include "wtf/SpinLock.h"
+
+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));
+        seed ^= static_cast<uint32_t>(getCurrentProcessID());
+        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.
+    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);
+}
+
+}