[wasm] Add guard regions to end of WebAssembly.Memory buffers

src/base/platform/platform.h

 // 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.
 
 // This module contains the platform-specific code. This make the rest of the
 // code less dependent on operating system, compilers and runtime libraries.
 // This module does specifically not deal with differences between different
 // processor architecture.
 // The platform classes have the same definition for all platforms. The
 // implementation for a particular platform is put in platform_<os>.cc.
@@ skipping 160 matching lines @@
   static PRINTF_FORMAT(1, 0) void VPrintError(const char* format, va_list args);
 
   // Allocate/Free memory used by JS heap. Pages are readable/writable, but
   // they are not guaranteed to be executable unless 'executable' is true.
   // Returns the address of allocated memory, or NULL if failed.
   static void* Allocate(const size_t requested,
                         size_t* allocated,
                         bool is_executable);
   static void Free(void* address, const size_t size);
 
+  // Allocates a region of memory that is inaccessible. On Windows this reserves
+  // but does not commit the memory. On Linux, it is equivalent to a call to
+  // Allocate() followed by Guard().
+  static void* AllocateGuarded(const size_t requested);
+
   // This is the granularity at which the ProtectCode(...) call can set page
   // permissions.
   static intptr_t CommitPageSize();
 
   // Mark code segments non-writable.
   static void ProtectCode(void* address, const size_t size);
 
   // Assign memory as a guard page so that access will cause an exception.
   static void Guard(void* address, const size_t size);
 
+  // Make a region of memory readable and writable.
+  static void Unprotect(void* address, const size_t size);
+
   // Generate a random address to be used for hinting mmap().
   static void* GetRandomMmapAddr();
 
   // Get the Alignment guaranteed by Allocate().
   static size_t AllocateAlignment();
 
   // Sleep for a specified time interval.
   static void Sleep(TimeDelta interval);
 
   // Abort the current process.
@@ skipping 312 matching lines @@
   int stack_size_;
   Semaphore* start_semaphore_;
 
   DISALLOW_COPY_AND_ASSIGN(Thread);
 };
 
 }  // namespace base
 }  // namespace v8
 
 #endif  // V8_BASE_PLATFORM_PLATFORM_H_