Add guard pages in front of executable allocations

BUG=89247

Review URL: http://codereview.chromium.org/7379004
Patch from Chris Neckar <cdn@chromium.org>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@8687 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/platform-nullos.cc

@@ -217,6 +217,11 @@ void OS::Free(void* buf, const size_t length) {
 }
 
 
+void OS::Guard(void* address, const size_t size) {
+  UNIMPLEMENTED();
+}
+
+
 void OS::Sleep(int milliseconds) {
   UNIMPLEMENTED();
 }

src/platform-posix.cc

@@ -33,6 +33,7 @@
 #include <errno.h>
 #include <time.h>
 
+#include <sys/mman.h>
 #include <sys/socket.h>
 #include <sys/resource.h>
 #include <sys/time.h>
@@ -43,6 +44,8 @@
 #include <netinet/in.h>
 #include <netdb.h>
 
+#undef MAP_TYPE
+
 #if defined(ANDROID)
 #define LOG_TAG "v8"
 #include <utils/Log.h>  // LOG_PRI_VA
@@ -67,6 +70,12 @@ intptr_t OS::MaxVirtualMemory() {
 }
 
 
+// Create guard pages.
+void OS::Guard(void* address, const size_t size) {
+  mprotect(address, size, PROT_NONE);
+}
+
+
 // ----------------------------------------------------------------------------
 // Math functions
 

src/platform-win32.cc

@@ -957,6 +957,12 @@ void OS::Free(void* address, const size_t size) {
 }
 
 
+void OS::Guard(void* address, const size_t size) {
+  DWORD oldprotect;
+  VirtualProtect(address, size, PAGE_READONLY | PAGE_GUARD, &oldprotect);
+}
+
+
 void OS::Sleep(int milliseconds) {
   ::Sleep(milliseconds);
 }

src/platform.h

@@ -206,6 +206,10 @@ class OS {
                         size_t* allocated,
                         bool is_executable);
   static void Free(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);
+
   // Get the Alignment guaranteed by Allocate().
   static size_t AllocateAlignment();
 

src/spaces.cc

@@ -402,7 +402,9 @@ void MemoryAllocator::FreeRawMemory(void* mem,
                                     size_t length,
                                     Executability executable) {
 #ifdef DEBUG
-  ZapBlock(reinterpret_cast<Address>(mem), length);
+  // Do not try to zap the guard page.
+  size_t guard_size = (executable == EXECUTABLE) ? Page::kPageSize : 0;
+  ZapBlock(reinterpret_cast<Address>(mem) + guard_size, length - guard_size);
 #endif
   if (isolate_->code_range()->contains(static_cast<Address>(mem))) {
     isolate_->code_range()->FreeRawMemory(mem, length);
@@ -504,14 +506,28 @@ Page* MemoryAllocator::AllocatePages(int requested_pages,
   LOG(isolate_, NewEvent("PagedChunk", chunk, chunk_size));
 
   *allocated_pages = PagesInChunk(static_cast<Address>(chunk), chunk_size);
+
   // We may 'lose' a page due to alignment.
   ASSERT(*allocated_pages >= kPagesPerChunk - 1);
-  if (*allocated_pages == 0) {
-    FreeRawMemory(chunk, chunk_size, owner->executable());
+
+  size_t guard_size = (owner->executable() == EXECUTABLE) ? Page::kPageSize : 0;
+
+  // Check that we got at least one page that we can use.
+  if (*allocated_pages <= ((guard_size != 0) ? 1 : 0)) {
+    FreeRawMemory(chunk,
+                  chunk_size,
+                  owner->executable());
     LOG(isolate_, DeleteEvent("PagedChunk", chunk));
     return Page::FromAddress(NULL);
   }
 
+  if (guard_size != 0) {
+    OS::Guard(chunk, guard_size);
+    chunk_size -= guard_size;
+    chunk = static_cast<Address>(chunk) + guard_size;
+    --*allocated_pages;
+  }
+
   int chunk_id = Pop();
   chunks_[chunk_id].init(static_cast<Address>(chunk), chunk_size, owner);
 
@@ -681,7 +697,8 @@ void MemoryAllocator::DeleteChunk(int chunk_id) {
     LOG(isolate_, DeleteEvent("PagedChunk", c.address()));
     ObjectSpace space = static_cast<ObjectSpace>(1 << c.owner_identity());
     size_t size = c.size();
-    FreeRawMemory(c.address(), size, c.executable());
+    size_t guard_size = (c.executable() == EXECUTABLE) ? Page::kPageSize : 0;
+    FreeRawMemory(c.address() - guard_size, size + guard_size, c.executable());
     PerformAllocationCallback(space, kAllocationActionFree, size);
   }
   c.init(NULL, 0, NULL);
@@ -2672,9 +2689,10 @@ LargeObjectChunk* LargeObjectChunk::New(int size_in_bytes,
                                         Executability executable) {
   size_t requested = ChunkSizeFor(size_in_bytes);
   size_t size;
+  size_t guard_size = (executable == EXECUTABLE) ? Page::kPageSize : 0;
   Isolate* isolate = Isolate::Current();
   void* mem = isolate->memory_allocator()->AllocateRawMemory(
-      requested, &size, executable);
+      requested + guard_size, &size, executable);
   if (mem == NULL) return NULL;
 
   // The start of the chunk may be overlayed with a page so we have to
@@ -2682,13 +2700,19 @@ LargeObjectChunk* LargeObjectChunk::New(int size_in_bytes,
   ASSERT((size & Page::kPageFlagMask) == 0);
 
   LOG(isolate, NewEvent("LargeObjectChunk", mem, size));
-  if (size < requested) {
+  if (size < requested + guard_size) {
     isolate->memory_allocator()->FreeRawMemory(
         mem, size, executable);
     LOG(isolate, DeleteEvent("LargeObjectChunk", mem));
     return NULL;
   }
 
+  if (guard_size != 0) {
+    OS::Guard(mem, guard_size);
+    size -= guard_size;
+    mem = static_cast<Address>(mem) + guard_size;
+  }
+
   ObjectSpace space = (executable == EXECUTABLE)
       ? kObjectSpaceCodeSpace
       : kObjectSpaceLoSpace;
@@ -2742,8 +2766,10 @@ void LargeObjectSpace::TearDown() {
     ObjectSpace space = kObjectSpaceLoSpace;
     if (executable == EXECUTABLE) space = kObjectSpaceCodeSpace;
     size_t size = chunk->size();
-    heap()->isolate()->memory_allocator()->FreeRawMemory(chunk->address(),
-                                                         size,
+    size_t guard_size = (executable == EXECUTABLE) ? Page::kPageSize : 0;
+    heap()->isolate()->memory_allocator()->FreeRawMemory(
+        chunk->address() - guard_size,
+        size + guard_size,
         executable);
     heap()->isolate()->memory_allocator()->PerformAllocationCallback(
         space, kAllocationActionFree, size);
@@ -2941,9 +2967,14 @@ void LargeObjectSpace::FreeUnmarkedObjects() {
       objects_size_ -= object->Size();
       page_count_--;
       ObjectSpace space = kObjectSpaceLoSpace;
-      if (executable == EXECUTABLE) space = kObjectSpaceCodeSpace;
-      heap()->isolate()->memory_allocator()->FreeRawMemory(chunk_address,
-                                                           chunk_size,
+      size_t guard_size = 0;
+      if (executable == EXECUTABLE) {
+        space = kObjectSpaceCodeSpace;
+        guard_size = Page::kPageSize;
+      }
+      heap()->isolate()->memory_allocator()->FreeRawMemory(
+          chunk_address - guard_size,
+          chunk_size + guard_size,
           executable);
       heap()->isolate()->memory_allocator()->PerformAllocationCallback(
           space, kAllocationActionFree, size_);

src/spaces.h

@@ -647,13 +647,11 @@ class MemoryAllocator {
 #ifdef V8_TARGET_ARCH_X64
   static const int kPagesPerChunk = 32;
   // On 64 bit the chunk table consists of 4 levels of 4096-entry tables.
-  static const int kPagesPerChunkLog2 = 5;
   static const int kChunkTableLevels = 4;
   static const int kChunkTableBitsPerLevel = 12;
 #else
   static const int kPagesPerChunk = 16;
   // On 32 bit the chunk table consists of 2 levels of 256-entry tables.
-  static const int kPagesPerChunkLog2 = 4;
   static const int kChunkTableLevels = 2;
   static const int kChunkTableBitsPerLevel = 8;
 #endif
@@ -662,7 +660,6 @@ class MemoryAllocator {
   MemoryAllocator();
 
   static const int kChunkSize = kPagesPerChunk * Page::kPageSize;
-  static const int kChunkSizeLog2 = kPagesPerChunkLog2 + kPageSizeBits;
 
   // Maximum space size in bytes.
   intptr_t capacity_;