Bug 1603974 - Part 5: Introduce WindowsDllEntryPointInterceptor. r=mhowell

This patch introduces a new DLL interceptor `WindowsDllEntryPointInterceptor`
which applies a hook to a target function without backing up the original
function code.

Depends on D68345

Differential Revision: https://phabricator.services.mozilla.com/D68346

--HG--
extra : moz-landing-system : lando

mozglue/misc/NativeNt.h

@@ -764,6 +764,12 @@ class MOZ_RAII PEHeaders final {
 
   void SetImportDirectoryTampered() { mIsImportDirectoryTampered = true; }
 
+  FARPROC GetEntryPoint() const {
+    // Use the unchecked version because the entrypoint may be tampered.
+    return RVAToPtrUnchecked<FARPROC>(
+        mPeHeader->OptionalHeader.AddressOfEntryPoint);
+  }
+
  private:
   enum class BoundsCheckPolicy { Default, Skip };
 

mozglue/misc/interceptor/PatcherDetour.h

@@ -100,6 +100,21 @@ class WindowsDllDetourPatcherPrimitive {
       const WindowsDllDetourPatcherPrimitive&) = delete;
   WindowsDllDetourPatcherPrimitive& operator=(
       WindowsDllDetourPatcherPrimitive&&) = delete;
+
+  bool AddIrreversibleHook(const MMPolicyT& aMMPolicy, FARPROC aTargetFn,
+                           intptr_t aHookDest) {
+    ReadOnlyTargetFunction<MMPolicyT> targetReadOnly(aMMPolicy, aTargetFn);
+
+    WritableTargetFunction<MMPolicyT> targetWritable(
+        targetReadOnly.Promote(GetWorstCaseRequiredBytesToPatch()));
+    if (!targetWritable) {
+      return false;
+    }
+
+    ApplyDefaultPatch(targetWritable, aHookDest);
+
+    return targetWritable.Commit();
+  }
 };
 
 template <typename VMPolicy>

mozglue/misc/nsWindowsDllInterceptor.h

@@ -717,6 +717,33 @@ class MOZ_ONLY_USED_TO_AVOID_STATIC_CONSTRUCTORS
   FuncPtrT mOrigFunc;
 };
 
+/**
+ * This class applies an irreversible patch to jump to a target function
+ * without backing up the original function.
+ */
+class WindowsDllEntryPointInterceptor final {
+  using DllMainFn = BOOL(WINAPI*)(HINSTANCE, DWORD, LPVOID);
+  using MMPolicyT = MMPolicyInProcessEarlyStage;
+
+  MMPolicyT mMMPolicy;
+
+ public:
+  explicit WindowsDllEntryPointInterceptor(
+      const MMPolicyT::Kernel32Exports& aK32Exports)
+      : mMMPolicy(aK32Exports) {}
+
+  bool Set(const nt::PEHeaders& aHeaders, DllMainFn aDestination) {
+    if (!aHeaders) {
+      return false;
+    }
+
+    WindowsDllDetourPatcherPrimitive<MMPolicyT> patcher;
+    return patcher.AddIrreversibleHook(
+        mMMPolicy, aHeaders.GetEntryPoint(),
+        reinterpret_cast<uintptr_t>(aDestination));
+  }
+};
+
 }  // namespace interceptor
 
 using WindowsDllInterceptor = interceptor::WindowsDllInterceptor<>;