Improve ASLR for arm64

src/platform-posix.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Platform-specific code for POSIX goes here. This is not a platform on its
 // own, but contains the parts which are the same across the POSIX platforms
 // Linux, MacOS, FreeBSD, OpenBSD, NetBSD and QNX.
 
 #include <dlfcn.h>
 #include <pthread.h>
@@ skipping 187 matching lines @@
   // CpuFeatures::Probe. We don't care about randomization in this case because
   // the code page is immediately freed.
   if (isolate != NULL) {
     uintptr_t raw_addr;
     isolate->random_number_generator()->NextBytes(&raw_addr, sizeof(raw_addr));
 #if V8_TARGET_ARCH_X64
     // Currently available CPUs have 48 bits of virtual addressing.  Truncate
     // the hint address to 46 bits to give the kernel a fighting chance of
     // fulfilling our placement request.
     raw_addr &= V8_UINT64_C(0x3ffffffff000);
+#elif V8_HOST_ARCH_ARM64
+    // Currently available CPUs have 40 bits of virtual addressing with 39 for

[Rodolph Perfetta, 2014/05/21 08:00:08]

DBC: arm64 has 48-bit virtual addresses

+    // user space.  Truncate the hint address to 38 bits to give the kernel a
+    // fighting chance of fulfilling our placement request.
+    raw_addr &= V8_UINT64_C(0x3ffffff000);
 #else
     raw_addr &= 0x3ffff000;
 
 # ifdef __sun
     // For our Solaris/illumos mmap hint, we pick a random address in the bottom
     // half of the top half of the address space (that is, the third quarter).
     // Because we do not MAP_FIXED, this will be treated only as a hint -- the
     // system will not fail to mmap() because something else happens to already
     // be mapped at our random address. We deliberately set the hint high enough
     // to get well above the system's break (that is, the heap); Solaris and
@@ skipping 533 matching lines @@
 
 void Thread::SetThreadLocal(LocalStorageKey key, void* value) {
   pthread_key_t pthread_key = LocalKeyToPthreadKey(key);
   int result = pthread_setspecific(pthread_key, value);
   ASSERT_EQ(0, result);
   USE(result);
 }
 
 
 } }  // namespace v8::internal