Bug 1676913 - Restrict a caller of GetDependentModulePaths to xul.dll. r=mhowell

Bug 1659438 introduced an exported function `GetDependentModulePaths` in firefox.exe
so that our sandboxBroker can easily access the shared section whose handle is owned
by firefox.exe.

This patch disallows `GetDependentModulePaths` to be called from someone other than
xul.dll in order to harden the attack to tamper our shared section.  This cannot
prevent all possible attacks, but it's better than nothing.

Differential Revision: https://phabricator.services.mozilla.com/D97377

browser/app/winlauncher/NtLoaderAPI.cpp

@@ -6,34 +6,15 @@
 
 #include "mozilla/LoaderAPIInterfaces.h"
 
+#include "freestanding/CheckForCaller.h"
 #include "freestanding/LoaderPrivateAPI.h"
 
-#if defined(_MSC_VER)
-#  include <intrin.h>
-#  pragma intrinsic(_ReturnAddress)
-#  define RETURN_ADDRESS() _ReturnAddress()
-#elif defined(__GNUC__) || defined(__clang__)
-#  define RETURN_ADDRESS() \
-    __builtin_extract_return_addr(__builtin_return_address(0))
-#endif
-
-static bool CheckForMozglue(void* aReturnAddress) {
-  HMODULE callingModule;
-  if (!::GetModuleHandleExW(GET_MODULE_HANDLE_EX_FLAG_FROM_ADDRESS |
-                                GET_MODULE_HANDLE_EX_FLAG_UNCHANGED_REFCOUNT,
-                            reinterpret_cast<LPCWSTR>(aReturnAddress),
-                            &callingModule)) {
-    return false;
-  }
-
-  return callingModule && callingModule == ::GetModuleHandleW(L"mozglue.dll");
-}
-
 namespace mozilla {
 
 extern "C" MOZ_EXPORT nt::LoaderAPI* GetNtLoaderAPI(
     nt::LoaderObserver* aNewObserver) {
-  const bool isCallerMozglue = CheckForMozglue(RETURN_ADDRESS());
+  const bool isCallerMozglue =
+      CheckForAddress(RETURN_ADDRESS(), L"mozglue.dll");
   MOZ_ASSERT(isCallerMozglue);
   if (!isCallerMozglue) {
     return nullptr;

browser/app/winlauncher/freestanding/CheckForCaller.h

@@ -0,0 +1,36 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_freestanding_CheckForCaller_h
+#define mozilla_freestanding_CheckForCaller_h
+
+namespace mozilla {
+
+#if defined(_MSC_VER)
+#  include <intrin.h>
+#  pragma intrinsic(_ReturnAddress)
+#  define RETURN_ADDRESS() _ReturnAddress()
+#elif defined(__GNUC__) || defined(__clang__)
+#  define RETURN_ADDRESS() \
+    __builtin_extract_return_addr(__builtin_return_address(0))
+#endif
+
+template <int N>
+bool CheckForAddress(void* aReturnAddress, const wchar_t (&aName)[N]) {
+  HMODULE callingModule;
+  if (!::GetModuleHandleExW(GET_MODULE_HANDLE_EX_FLAG_FROM_ADDRESS |
+                                GET_MODULE_HANDLE_EX_FLAG_UNCHANGED_REFCOUNT,
+                            reinterpret_cast<LPCWSTR>(aReturnAddress),
+                            &callingModule)) {
+    return false;
+  }
+
+  return callingModule && callingModule == ::GetModuleHandleW(aName);
+}
+
+}  // namespace mozilla
+
+#endif  // mozilla_freestanding_CheckForCaller_h

browser/app/winlauncher/freestanding/SharedSection.cpp

@@ -6,6 +6,8 @@
 
 #include "SharedSection.h"
 
+#include "CheckForCaller.h"
+
 namespace mozilla {
 namespace freestanding {
 
@@ -214,6 +216,15 @@ LauncherVoidResult SharedSection::TransferHandle(
 }
 
 extern "C" MOZ_EXPORT uint32_t GetDependentModulePaths(uint32_t** aOutArray) {
+  const bool isCallerXul = CheckForAddress(RETURN_ADDRESS(), L"xul.dll");
+  MOZ_ASSERT(isCallerXul);
+  if (!isCallerXul) {
+    if (aOutArray) {
+      *aOutArray = nullptr;
+    }
+    return 0;
+  }
+
   LauncherResult<SharedSection::Layout*> resultView = gSharedSection.GetView();
   if (resultView.isErr()) {
     if (aOutArray) {

browser/app/winlauncher/test/TestCrossProcessWin.cpp

@@ -68,30 +68,10 @@ static bool VerifySharedSection(SharedSection& aSharedSection) {
   VERIFY_FUNCTION_RESOLVED(k32mod, view->mK32Exports, GetSystemInfo);
   VERIFY_FUNCTION_RESOLVED(k32mod, view->mK32Exports, VirtualProtect);
 
-  Span<uint32_t> modulePaths = []() -> Span<uint32_t> {
-    auto getDependentModulePaths =
-        reinterpret_cast<uint32_t (*)(uint32_t**)>(::GetProcAddress(
-            ::GetModuleHandleW(nullptr), "GetDependentModulePaths"));
-    if (!getDependentModulePaths) {
-      printf(
-          "TEST-FAILED | TestCrossProcessWin | "
-          "Failed to get a pointer to GetDependentModulePaths - %08lx.\n",
-          ::GetLastError());
-      return nullptr;
-    }
-
-    uint32_t* modulePathArray;
-    uint32_t modulePathArrayLen = getDependentModulePaths(&modulePathArray);
-    return Span(modulePathArray, modulePathArrayLen);
-  }();
-
-  if (modulePaths.IsEmpty()) {
-    return false;
-  }
-
-  const uint8_t* arrayBase =
-      reinterpret_cast<const uint8_t*>(modulePaths.data());
-  for (const uint32_t& offset : modulePaths) {
+  const uint8_t* const arrayBase =
+      reinterpret_cast<const uint8_t*>(view->mModulePathArray);
+  for (uint32_t i = 0; i < view->mModulePathArrayLength; ++i) {
+    uint32_t offset = view->mModulePathArray[i];
     // Use NtQueryAttributesFile to check the validity of an NT path.
     UNICODE_STRING ntpath;
     ::RtlInitUnicodeString(
@@ -152,6 +132,30 @@ class ChildProcess final {
       return 1;
     }
 
+    auto getDependentModulePaths =
+        reinterpret_cast<uint32_t (*)(uint32_t**)>(::GetProcAddress(
+            ::GetModuleHandleW(nullptr), "GetDependentModulePaths"));
+    if (!getDependentModulePaths) {
+      printf(
+          "TEST-FAILED | TestCrossProcessWin | "
+          "Failed to get a pointer to GetDependentModulePaths - %08lx.\n",
+          ::GetLastError());
+      return 1;
+    }
+
+#if !defined(DEBUG)
+    // GetDependentModulePaths does not allow a caller other than xul.dll.
+    // Skip on Debug build because it hits MOZ_ASSERT.
+    uint32_t* modulePathArray;
+    if (getDependentModulePaths(&modulePathArray) || modulePathArray) {
+      printf(
+          "TEST-FAILED | TestCrossProcessWin | "
+          "GetDependentModulePaths should return zero if the caller is "
+          "not xul.dll.\n");
+      return 1;
+    }
+#endif  // !defined(DEBUG)
+
     if (!VerifySharedSection(gSharedSection)) {
       return 1;
     }