Oilpan: Improve address space randomization for the Oilpan heap.

Source/wtf/AddressSpaceRandomization.h

+/*
+ * Copyright (C) 2013 Google Inc. All rights reserved.

[Tom Sepez, 2014/06/26 17:06:54]

Nit: no (C), 2014.

+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "wtf/PageAllocator.h"
+#include "wtf/ProcessID.h"
+#include "wtf/SpinLock.h"
+
+namespace WTF {
+
+// 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;
+}
+
+// Calculates a random preferred mapping address. In calculating an
+// address, we balance good ASLR against not fragmenting the address
+// space too badly.
+void* getRandomPageBase()
+{
+    static struct ranctx s_ranctx;
+    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);
+}
+
+}