Improve ASLR for arm64

src/platform-posix.cc

Index: src/platform-posix.cc
diff --git a/src/platform-posix.cc b/src/platform-posix.cc
index bc315b2e7e15ade647f0a92b121669eb69aaeb8f..5a149bc9119782e75646f4263392eff8290e7c93 100644
--- a/src/platform-posix.cc
+++ b/src/platform-posix.cc
@@ -205,6 +205,11 @@ void* OS::GetRandomMmapAddr() {
     // 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;