Add hinting to improve ASLR for macos (all allocations) and linux (newly added allocation types).

src/platform-macos.cc

Index: src/platform-macos.cc
===================================================================
--- src/platform-macos.cc	(revision 9508)
+++ src/platform-macos.cc	(working copy)
@@ -92,14 +92,32 @@
 
 static Mutex* limit_mutex = NULL;
 
+static void* GetRandomMmapAddr() {

[Vyacheslav Egorov (Chromium), 2011/10/04 09:18:33]

consider moving somewhere (e.g. platfrom-posix.cc) to avoid duplication.

platform can define the range of unpopular addresses which shared implementation
would use.

[Cris Neckar, 2011/10/04 19:20:47]

Done.

+  Isolate* isolate = Isolate::UncheckedCurrent();
+  // Note that the current isolate isn't set up in a call path via
+  // CpuFeatures::Probe. We don't care about randomization in this case because
+  // the code page is immediately freed.
+  if (isolate != NULL) {
+#ifdef V8_TARGET_ARCH_X64
+    uint64_t rnd1 = V8::RandomPrivate(isolate);
+    uint64_t rnd2 = V8::RandomPrivate(isolate);
+    uint64_t rnd2 = V8::RandomPrivate(isolate);
+    raw_addr &= V8_UINT64_C(0x3ffffffff000);
+#else
+    uint32_t raw_addr = V8::RandomPrivate(isolate);
+    // The range 0x20000000 - 0x60000000 is relatively unpopulated on macos
+    // 10.6 and 10.7.
+    raw_addr &= 0x3ffff000;
+    raw_addr += 0x20000000;
+#endif
+    return reinterpret_cast<void*>(raw_addr);
+  }
+  return NULL;
+}
 
 void OS::Setup() {
-  // Seed the random number generator.
-  // Convert the current time to a 64-bit integer first, before converting it
-  // to an unsigned. Going directly will cause an overflow and the seed to be
-  // set to all ones. The seed will be identical for different instances that
-  // call this setup code within the same millisecond.
-  uint64_t seed = static_cast<uint64_t>(TimeCurrentMillis());
+  // Seed the random number generator. We preserve microsecond resolution.
+  uint64_t seed = Ticks() ^ (getpid() << 16);
   srandom(static_cast<unsigned int>(seed));
   limit_mutex = CreateMutex();
 }
@@ -148,7 +166,7 @@
                    bool is_executable) {
   const size_t msize = RoundUp(requested, getpagesize());
   int prot = PROT_READ | PROT_WRITE | (is_executable ? PROT_EXEC : 0);
-  void* mbase = mmap(NULL, msize, prot,
+  void* mbase = mmap(GetRandomMmapAddr(), msize, prot,

[Vyacheslav Egorov (Chromium), 2011/10/04 09:18:33]

formatting: one argument per line

[Cris Neckar, 2011/10/04 19:20:47]

Done.

                      MAP_PRIVATE | MAP_ANON,
                      kMmapFd, kMmapFdOffset);
   if (mbase == MAP_FAILED) {
@@ -207,7 +225,8 @@
   int size = ftell(file);
 
   void* memory =
-      mmap(0, size, PROT_READ | PROT_WRITE, MAP_SHARED, fileno(file), 0);
+      mmap(GetRandomMmapAddr(), size, PROT_READ | PROT_WRITE,

[Vyacheslav Egorov (Chromium), 2011/10/04 09:18:33]

formatting: one argument per line

[Cris Neckar, 2011/10/04 19:20:47]

Done.

+           MAP_SHARED, fileno(file), 0);
   return new PosixMemoryMappedFile(file, memory, size);
 }
 
@@ -222,7 +241,8 @@
     return NULL;
   }
   void* memory =
-      mmap(0, size, PROT_READ | PROT_WRITE, MAP_SHARED, fileno(file), 0);
+      mmap(GetRandomMmapAddr(), size, PROT_READ | PROT_WRITE,

[Vyacheslav Egorov (Chromium), 2011/10/04 09:18:33]

formatting: one argument per line

[Cris Neckar, 2011/10/04 19:20:47]

Done.

+           MAP_SHARED, fileno(file), 0);
   return new PosixMemoryMappedFile(file, memory, size);
 }
 
@@ -346,7 +366,7 @@
   ASSERT(IsAligned(alignment, static_cast<intptr_t>(OS::AllocateAlignment())));
   size_t request_size = RoundUp(size + alignment,
                                 static_cast<intptr_t>(OS::AllocateAlignment()));
-  void* reservation = mmap(NULL,
+  void* reservation = mmap(GetRandomMmapAddr(),
                            request_size,
                            PROT_NONE,
                            MAP_PRIVATE | MAP_ANON | MAP_NORESERVE,
@@ -397,7 +417,7 @@
 
 
 void* VirtualMemory::ReserveRegion(size_t size) {
-  void* result = mmap(NULL,
+  void* result = mmap(GetRandomMmapAddr(),
                       size,
                       PROT_NONE,
                       MAP_PRIVATE | MAP_ANON | MAP_NORESERVE,