1 files changed, 94 insertions, 0 deletions
diff --git a/mozglue/misc/ImportDir.h b/mozglue/misc/ImportDir.h
new file mode 100644
index 0000000000..6f7721d966
--- /dev/null
+++ b/mozglue/misc/ImportDir.h
@@ -0,0 +1,94 @@
+/* -*- 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/. */
+
+#include "mozilla/NativeNt.h"
+#include "mozilla/WinHeaderOnlyUtils.h"
+
+namespace mozilla {
+namespace detail {
+
+inline LauncherResult<nt::DataDirectoryEntry> GetImageDirectoryViaFileIo(
+    const nsAutoHandle& aImageFile, const uint32_t aOurImportDirectoryRva) {
+  OVERLAPPED ov = {};
+  ov.Offset = aOurImportDirectoryRva;
+
+  DWORD bytesRead;
+  nt::DataDirectoryEntry result;
+  if (!::ReadFile(aImageFile, &result, sizeof(result), &bytesRead, &ov) ||
+      bytesRead != sizeof(result)) {
+    return LAUNCHER_ERROR_FROM_LAST();
+  }
+
+  return result;
+}
+
+}  // namespace detail
+
+/**
+ * This function ensures that the import directory of a loaded binary image
+ * matches the version that is found in the original file on disk. We do this
+ * to prevent tampering by third-party code.
+ *
+ * Yes, this function may perform file I/O on the critical path during
+ * startup. A mitigating factor here is that this function must be called
+ * immediately after creating a process using the image specified by
+ * |aFullImagePath|; by this point, the system has already paid the price of
+ * pulling the image file's contents into the page cache.
+ *
+ * @param aFullImagePath Wide-character string containing the absolute path
+ *                       to the binary whose import directory we are touching.
+ * @param aTransferMgr   Encapsulating the transfer from the current process to
+ *                       the child process whose import table we are touching.
+ */
+inline LauncherVoidResult RestoreImportDirectory(
+    const wchar_t* aFullImagePath, nt::CrossExecTransferManager& aTransferMgr) {
+  uint32_t importDirEntryRva;
+  PIMAGE_DATA_DIRECTORY importDirEntry =
+      aTransferMgr.LocalPEHeaders().GetImageDirectoryEntryPtr(
+          IMAGE_DIRECTORY_ENTRY_IMPORT, &importDirEntryRva);
+  if (!importDirEntry) {
+    return LAUNCHER_ERROR_FROM_WIN32(ERROR_BAD_EXE_FORMAT);
+  }
+
+  nsAutoHandle file(::CreateFileW(aFullImagePath, GENERIC_READ, FILE_SHARE_READ,
+                                  nullptr, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL,
+                                  nullptr));
+  if (file.get() == INVALID_HANDLE_VALUE) {
+    return LAUNCHER_ERROR_FROM_LAST();
+  }
+
+  // Why do we use file I/O here instead of a memory mapping? The simple reason
+  // is that we do not want any kernel-mode drivers to start tampering with file
+  // contents under the belief that the file is being mapped for execution.
+  // Windows 8 supports creation of file mappings using the SEC_IMAGE_NO_EXECUTE
+  // flag, which may help to mitigate this, but we might as well just support
+  // a single implementation that works everywhere.
+  LauncherResult<nt::DataDirectoryEntry> realImportDirectory =
+      detail::GetImageDirectoryViaFileIo(file, importDirEntryRva);
+  if (realImportDirectory.isErr()) {
+    return realImportDirectory.propagateErr();
+  }
+
+  nt::DataDirectoryEntry toWrite = realImportDirectory.unwrap();
+
+  {  // Scope for prot
+    AutoVirtualProtect prot = aTransferMgr.Protect(
+        importDirEntry, sizeof(IMAGE_DATA_DIRECTORY), PAGE_READWRITE);
+    if (!prot) {
+      return LAUNCHER_ERROR_FROM_MOZ_WINDOWS_ERROR(prot.GetError());
+    }
+
+    LauncherVoidResult writeResult = aTransferMgr.Transfer(
+        importDirEntry, &toWrite, sizeof(IMAGE_DATA_DIRECTORY));
+    if (writeResult.isErr()) {
+      return writeResult.propagateErr();
+    }
+  }
+
+  return Ok();
+}
+
+}  // namespace mozilla