Make chrome_elf use thunks instead of function pointers.

chrome_elf/ntdll_cache.cc

Index: chrome_elf/ntdll_cache.cc
diff --git a/chrome_elf/ntdll_cache.cc b/chrome_elf/ntdll_cache.cc
index e5504421ae420cf6d78b281d4c859df6c0ac2a0b..5393513a6007666da08dc05917c766c6b82a2b6c 100644
--- a/chrome_elf/ntdll_cache.cc
+++ b/chrome_elf/ntdll_cache.cc
@@ -2,15 +2,26 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#include "chrome_elf/ntdll_cache.h"
+
 #include <stdint.h>
 #include <windows.h>
 
-#include "chrome_elf/ntdll_cache.h"
+#include "base/basictypes.h"
+#include "chrome_elf/thunk_getter.h"
+#include "sandbox/win/src/interception_internal.h"
+#include "sandbox/win/src/internal_types.h"
+#include "sandbox/win/src/service_resolver.h"
+
+// Allocate storage for thunks in a page of this module to save on doing
+// an extra allocation at run time.
+#pragma section(".crthunk", read, execute)
+__declspec(allocate(".crthunk")) sandbox::ThunkData g_nt_thunk_storage;
 
 FunctionLookupTable g_ntdll_lookup;
 
 void InitCache() {
-  HMODULE ntdll_handle = ::GetModuleHandle(L"ntdll.dll");
+  HMODULE ntdll_handle = ::GetModuleHandle(sandbox::kNtdllName);
 
   // To find the Export Address Table address, we start from the DOS header.
   // The module handle is actually the address of the header.
@@ -48,4 +59,42 @@ void InitCache() {
     FARPROC func_addr = reinterpret_cast<FARPROC>(func + base_addr);
     g_ntdll_lookup[std::string(name)] = func_addr;
   }
+
+  const bool kRelaxed = true;
+
+  // Create a thunk via the appropriate ServiceResolver instance.
+  sandbox::ServiceResolverThunk* thunk = GetThunk(kRelaxed);
+
+  if (thunk) {
+    BYTE* thunk_storage = reinterpret_cast<BYTE*>(&g_nt_thunk_storage);
+
+    // Mark the thunk storage as readable and writeable, since we
+    // ready to write to it.
+    DWORD old_protect = 0;
+    if (!::VirtualProtect(&g_nt_thunk_storage,
+                          sizeof(g_nt_thunk_storage),
+                          PAGE_EXECUTE_READWRITE,
+                          &old_protect)) {
+      return;
+    }
+
+    size_t storage_used = 0;
+    NTSTATUS ret = thunk->CopyThunk(::GetModuleHandle(sandbox::kNtdllName),
+                                    "NtCreateFile",
+                                    thunk_storage,
+                                    sizeof(sandbox::ThunkData),
+                                    &storage_used);
+
+    // Ensure that the pointer to the old function can't be changed.
+    ::VirtualProtect(&g_nt_thunk_storage,
+                     sizeof(g_nt_thunk_storage),
+                     PAGE_EXECUTE_READ,
+                     &old_protect);
+
+    if (NT_SUCCESS(ret)) {
+      // Add an entry in the lookup table for the thunk.
+      g_ntdll_lookup["NtCreateFile"] =
+          reinterpret_cast<FARPROC>(&g_nt_thunk_storage);
+    }
+  }
 }