Write protect executable pages in the VM.

runtime/vm/virtual_memory_linux.cc

Index: runtime/vm/virtual_memory_linux.cc
diff --git a/runtime/vm/virtual_memory_linux.cc b/runtime/vm/virtual_memory_linux.cc
index 7a0d02b8078cfcf5964a0772583031727bfb269b..7c6cff8f6d05f9a16bcfb6b5cc0055d90f38426a 100644
--- a/runtime/vm/virtual_memory_linux.cc
+++ b/runtime/vm/virtual_memory_linux.cc
@@ -13,6 +13,7 @@
 
 #include "platform/assert.h"
 #include "platform/utils.h"
+// #include "vm/os.h"
 
 namespace dart {
 
@@ -76,7 +77,10 @@ bool VirtualMemory::Commit(uword addr, intptr_t size, bool executable) {
 }
 
 
-bool VirtualMemory::Protect(Protection mode) {
+bool VirtualMemory::Protect(void* address, intptr_t size, Protection mode) {
+  uword start_address = reinterpret_cast<uword>(address);
+  uword end_address = start_address + size;
+  uword page_address = start_address & ~(PageSize() - 1);
   int prot = 0;
   switch (mode) {
     case kNoAccess:
@@ -95,9 +99,12 @@ bool VirtualMemory::Protect(Protection mode) {
       prot = PROT_READ | PROT_WRITE | PROT_EXEC;
       break;
   }
-  return (mprotect(address(), size(), prot) == 0);
+  return (mprotect(reinterpret_cast<void*>(page_address),
+                   end_address - page_address,
+                   prot) == 0);
 }
 
+
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_LINUX)