Write protect executable pages in the VM.

runtime/vm/code_patcher.cc

Index: runtime/vm/code_patcher.cc
diff --git a/runtime/vm/code_patcher.cc b/runtime/vm/code_patcher.cc
index 6fda035f4047783368cc8dffa9e299c6d09d6b20..8fa4785a686081f05935a747cbe5b5d679b5bc3c 100644
--- a/runtime/vm/code_patcher.cc
+++ b/runtime/vm/code_patcher.cc
@@ -6,9 +6,30 @@
 #include "vm/cpu.h"
 #include "vm/instructions.h"
 #include "vm/object.h"
+#include "vm/virtual_memory.h"
 
 namespace dart {
 
+WritableInstructionsScope::WritableInstructionsScope(uword address,
+                                                     intptr_t size)
+    : address_(address), size_(size) {
+  bool status =
+      VirtualMemory::Protect(reinterpret_cast<void*>(address),
+                             size,
+                             VirtualMemory::kReadWriteExecute);
+  ASSERT(status);
+}
+
+
+WritableInstructionsScope::~WritableInstructionsScope() {
+  bool status =
+      VirtualMemory::Protect(reinterpret_cast<void*>(address_),
+                             size_,
+                             VirtualMemory::kReadExecute);
+  ASSERT(status);
+}
+
+
 static void SwapCode(intptr_t num_bytes, char* code, char* buffer) {
   uword code_address = reinterpret_cast<uword>(code);
   for (intptr_t i = 0; i < num_bytes; i++) {
@@ -36,10 +57,15 @@ void CodePatcher::PatchEntry(const Code& code) {
   JumpPattern jmp_patch(patch_buffer, code);
   ASSERT(jmp_patch.IsValid());
   const uword jump_target = jmp_patch.TargetAddress();
-  SwapCode(jmp_patch.pattern_length_in_bytes(),
-           reinterpret_cast<char*>(patch_addr),
-           reinterpret_cast<char*>(patch_buffer));
-  jmp_entry.SetTargetAddress(jump_target);
+  intptr_t length = jmp_patch.pattern_length_in_bytes();
+  {
+    WritableInstructionsScope writable_code(patch_addr, length);
+    WritableInstructionsScope writable_buffer(patch_buffer, length);
+    SwapCode(jmp_patch.pattern_length_in_bytes(),
+             reinterpret_cast<char*>(patch_addr),
+             reinterpret_cast<char*>(patch_buffer));
+    jmp_entry.SetTargetAddress(jump_target);
+  }
 }
 
 
@@ -57,11 +83,16 @@ void CodePatcher::RestoreEntry(const Code& code) {
   // 'patch_buffer' contains original entry code.
   JumpPattern jmp_patch(patch_buffer, code);
   ASSERT(!jmp_patch.IsValid());
-  SwapCode(jmp_patch.pattern_length_in_bytes(),
-           reinterpret_cast<char*>(patch_addr),
-           reinterpret_cast<char*>(patch_buffer));
-  ASSERT(jmp_patch.IsValid());
-  jmp_patch.SetTargetAddress(jump_target);
+  intptr_t length = jmp_patch.pattern_length_in_bytes();
+  {
+    WritableInstructionsScope writable_code(patch_addr, length);
+    WritableInstructionsScope writable_buffer(patch_buffer, length);
+    SwapCode(jmp_patch.pattern_length_in_bytes(),
+             reinterpret_cast<char*>(patch_addr),
+             reinterpret_cast<char*>(patch_buffer));
+    ASSERT(jmp_patch.IsValid());
+    jmp_patch.SetTargetAddress(jump_target);
+  }
 }