ep_extra: Implemented an ep_extra-based loader

ExplorerPatcher includes a mechanism which allows the user to load a single DLL, named `ep_extra.dll` and placed in `C:\Windows` when `explorer.exe` loads. This was long requested by some users who wanted to perform their own code/initializations/hooks when `explorer` started. In the mean time, I thought `ep_extra.dll` would work nicely as a loader for any number of modules. I could've included this functionality in the main ExplorerPatcher code, but I decided to take it up as a challenge instead and offer a robust implementation without changing ExplorerPatcher's main code. Thus, when using this as `ep_extra.dll`, it will also load DLLs that match the `ep_extra_*.dll` pattern. These DLLs must export a function called `setup` which the loader will execute on the thread that is loading the DLLs. Although not currently checked, return 0 from this function if your initialization succeeded, or some error code when it fails. What's up with the assembly and shell codes and weird threads that I create? Well, I realized I kind of did a mistake when coding ExplorerPatcher, in that I should have loaded and executed `ep_extra` on a seprate thread, not in `explorer`'s main thread. But since I said I'd do this challenge without changing EP, this was my solution towards having this `ep_extra` loader do its work, load the other DLLs, if any, and then unload itself from memory safely and (almost) cleanly without disturbing the main application right after it does its job. This way, you can update it seamlessly when `explorer` is running, which is much more convenient than having to kill `explorer`, replace the DLL, and then manually reload `explorer`. I don't know if this is the best way, but it is the way I thought about when realizing that I cannot call `FreeLibrary` simply, since the "next line" (which would have been a "return") is well outside of valid memory at that point. `FreeLibraryAndExitThread` also can't be used since I do not want to exit `explorer`'s main thread which the loader's function is called on.
valinet · Mar 1, 2023 · 1f4b586 · 1f4b586
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diff --git a/ep_extra/README.md b/ep_extra/README.md
@@ -0,0 +1,5 @@
+# ExplorerPatcher Custom Libraries Chainloader
+
+ExplorerPatcher has a simple, built-in mechanism that allows users to load their own DLL into `explorer.exe` right after ExplorerPatcher finishes initializing its hooks. Interested users hould place a DLL called `ep_extra.dll` in `C:\Windows`. When ExplorerPatcher finishes its setup, it loads the `ep_extra.dll` library and calls the `ep_extra_EntryPoint` function. Although this is very useful so that users can load their custom code, it is quite limited at the moment, as it loads just one DLL.
+
+This project is a solution to this issue. A chainloader is implemented here, that looks for other modules matching the `ep_extra_*.dll` pattern in `C:\Windows` as well, and loads them one after the other.
diff --git a/ep_extra/ep_extra.rc b/ep_extra/ep_extra.rc
@@ -0,0 +1,100 @@
+// Microsoft Visual C++ generated resource script.
+//
+#include "resource.h"
+
+#define APSTUDIO_READONLY_SYMBOLS
+/////////////////////////////////////////////////////////////////////////////
+//
+// Generated from the TEXTINCLUDE 2 resource.
+//
+#include "winres.h"
+
+/////////////////////////////////////////////////////////////////////////////
+#undef APSTUDIO_READONLY_SYMBOLS
+
+/////////////////////////////////////////////////////////////////////////////
+// English (United States) resources
+
+#if !defined(AFX_RESOURCE_DLL) || defined(AFX_TARG_ENU)
+LANGUAGE LANG_ENGLISH, SUBLANG_ENGLISH_US
+#pragma code_page(1252)
+
+#ifdef APSTUDIO_INVOKED
+/////////////////////////////////////////////////////////////////////////////
+//
+// TEXTINCLUDE
+//
+
+1 TEXTINCLUDE 
+BEGIN
+    "resource.h\0"
+END
+
+2 TEXTINCLUDE 
+BEGIN
+    "#include ""winres.h""\r\n"
+    "\0"
+END
+
+3 TEXTINCLUDE 
+BEGIN
+    "\r\n"
+    "\0"
+END
+
+#endif    // APSTUDIO_INVOKED
+
+
+/////////////////////////////////////////////////////////////////////////////
+//
+// Version
+//
+
+VS_VERSION_INFO VERSIONINFO
+ FILEVERSION 1,0,0,1
+ PRODUCTVERSION 1,0,0,1
+ FILEFLAGSMASK 0x3fL
+#ifdef _DEBUG
+ FILEFLAGS 0x1L
+#else
+ FILEFLAGS 0x0L
+#endif
+ FILEOS 0x40004L
+ FILETYPE 0x2L
+ FILESUBTYPE 0x0L
+BEGIN
+    BLOCK "StringFileInfo"
+    BEGIN
+        BLOCK "040904b0"
+        BEGIN
+            VALUE "CompanyName", "VALINET Solutions SRL"
+            VALUE "FileDescription", "ExplorerPatcher Custom Libraries Chainloader"
+            VALUE "FileVersion", "1.0.0.0"
+            VALUE "InternalName", "ep_extra.dll"
+            VALUE "LegalCopyright", "Copyright (C) 2006-2022 VALINET Solutions SRL. All rights reserved."
+            VALUE "OriginalFilename", "ep_extra.dll"
+            VALUE "ProductName", "ExplorerPatcher"
+            VALUE "ProductVersion", "1.0.0.0"
+        END
+    END
+    BLOCK "VarFileInfo"
+    BEGIN
+        VALUE "Translation", 0x409, 1200
+    END
+END
+
+#endif    // English (United States) resources
+/////////////////////////////////////////////////////////////////////////////
+
+
+
+#ifndef APSTUDIO_INVOKED
+/////////////////////////////////////////////////////////////////////////////
+//
+// Generated from the TEXTINCLUDE 3 resource.
+//
+
+
+/////////////////////////////////////////////////////////////////////////////
+#endif    // not APSTUDIO_INVOKED
+
diff --git a/ep_extra/ep_extra.vcxproj b/ep_extra/ep_extra.vcxproj
@@ -0,0 +1,179 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <ItemGroup Label="ProjectConfigurations">
+    <ProjectConfiguration Include="Debug|Win32">
+      <Configuration>Debug</Configuration>
+      <Platform>Win32</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="Release|Win32">
+      <Configuration>Release</Configuration>
+      <Platform>Win32</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="Debug|x64">
+      <Configuration>Debug</Configuration>
+      <Platform>x64</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="Release|x64">
+      <Configuration>Release</Configuration>
+      <Platform>x64</Platform>
+    </ProjectConfiguration>
+  </ItemGroup>
+  <PropertyGroup Label="Globals">
+    <VCProjectVersion>16.0</VCProjectVersion>
+    <Keyword>Win32Proj</Keyword>
+    <ProjectGuid>{93fa47cc-7753-4f86-b583-69048f51c5ab}</ProjectGuid>
+    <RootNamespace>epextra</RootNamespace>
+    <WindowsTargetPlatformVersion>10.0</WindowsTargetPlatformVersion>
+  </PropertyGroup>
+  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.Default.props" />
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'" Label="Configuration">
+    <ConfigurationType>DynamicLibrary</ConfigurationType>
+    <UseDebugLibraries>true</UseDebugLibraries>
+    <PlatformToolset>v142</PlatformToolset>
+    <CharacterSet>Unicode</CharacterSet>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|Win32'" Label="Configuration">
+    <ConfigurationType>DynamicLibrary</ConfigurationType>
+    <UseDebugLibraries>false</UseDebugLibraries>
+    <PlatformToolset>v142</PlatformToolset>
+    <WholeProgramOptimization>true</WholeProgramOptimization>
+    <CharacterSet>Unicode</CharacterSet>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|x64'" Label="Configuration">
+    <ConfigurationType>DynamicLibrary</ConfigurationType>
+    <UseDebugLibraries>true</UseDebugLibraries>
+    <PlatformToolset>v142</PlatformToolset>
+    <CharacterSet>Unicode</CharacterSet>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|x64'" Label="Configuration">
+    <ConfigurationType>DynamicLibrary</ConfigurationType>
+    <UseDebugLibraries>false</UseDebugLibraries>
+    <PlatformToolset>v142</PlatformToolset>
+    <WholeProgramOptimization>true</WholeProgramOptimization>
+    <CharacterSet>Unicode</CharacterSet>
+  </PropertyGroup>
+  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.props" />
+  <ImportGroup Label="ExtensionSettings">
+    <Import Project="$(VCTargetsPath)\BuildCustomizations\masm.props" />
+  </ImportGroup>
+  <ImportGroup Label="Shared">
+  </ImportGroup>
+  <ImportGroup Label="PropertySheets" Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">
+    <Import Project="$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props" Condition="exists('$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props')" Label="LocalAppDataPlatform" />
+  </ImportGroup>
+  <ImportGroup Label="PropertySheets" Condition="'$(Configuration)|$(Platform)'=='Release|Win32'">
+    <Import Project="$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props" Condition="exists('$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props')" Label="LocalAppDataPlatform" />
+  </ImportGroup>
+  <ImportGroup Label="PropertySheets" Condition="'$(Configuration)|$(Platform)'=='Debug|x64'">
+    <Import Project="$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props" Condition="exists('$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props')" Label="LocalAppDataPlatform" />
+  </ImportGroup>
+  <ImportGroup Label="PropertySheets" Condition="'$(Configuration)|$(Platform)'=='Release|x64'">
+    <Import Project="$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props" Condition="exists('$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props')" Label="LocalAppDataPlatform" />
+  </ImportGroup>
+  <PropertyGroup Label="UserMacros" />
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">
+    <LinkIncremental>true</LinkIncremental>
+    <OutDir>$(SolutionDir)\build\$(Configuration)</OutDir>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|Win32'">
+    <LinkIncremental>false</LinkIncremental>
+    <OutDir>$(SolutionDir)\build\$(Configuration)</OutDir>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|x64'">
+    <LinkIncremental>true</LinkIncremental>
+    <OutDir>$(SolutionDir)\build\$(Configuration)</OutDir>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|x64'">
+    <LinkIncremental>false</LinkIncremental>
+    <OutDir>$(SolutionDir)\build\$(Configuration)</OutDir>
+  </PropertyGroup>
+  <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">
+    <ClCompile>
+      <WarningLevel>Level3</WarningLevel>
+      <SDLCheck>true</SDLCheck>
+      <PreprocessorDefinitions>WIN32;_DEBUG;_CONSOLE;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <ConformanceMode>true</ConformanceMode>
+      <RuntimeLibrary>MultiThreadedDebug</RuntimeLibrary>
+    </ClCompile>
+    <Link>
+      <SubSystem>Console</SubSystem>
+      <GenerateDebugInformation>true</GenerateDebugInformation>
+      <ModuleDefinitionFile>
+      </ModuleDefinitionFile>
+      <AdditionalOptions>/EXPORT:ep_extra_EntryPoint %(AdditionalOptions)</AdditionalOptions>
+    </Link>
+  </ItemDefinitionGroup>
+  <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Release|Win32'">
+    <ClCompile>
+      <WarningLevel>Level3</WarningLevel>
+      <FunctionLevelLinking>true</FunctionLevelLinking>
+      <IntrinsicFunctions>true</IntrinsicFunctions>
+      <SDLCheck>true</SDLCheck>
+      <PreprocessorDefinitions>WIN32;NDEBUG;_CONSOLE;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <ConformanceMode>true</ConformanceMode>
+      <RuntimeLibrary>MultiThreaded</RuntimeLibrary>
+    </ClCompile>
+    <Link>
+      <SubSystem>Console</SubSystem>
+      <EnableCOMDATFolding>true</EnableCOMDATFolding>
+      <OptimizeReferences>true</OptimizeReferences>
+      <GenerateDebugInformation>true</GenerateDebugInformation>
+      <ModuleDefinitionFile>
+      </ModuleDefinitionFile>
+      <AdditionalOptions>/EXPORT:ep_extra_EntryPoint %(AdditionalOptions)</AdditionalOptions>
+    </Link>
+  </ItemDefinitionGroup>
+  <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Debug|x64'">
+    <ClCompile>
+      <WarningLevel>Level3</WarningLevel>
+      <SDLCheck>true</SDLCheck>
+      <PreprocessorDefinitions>_DEBUG;_CONSOLE;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <ConformanceMode>true</ConformanceMode>
+      <RuntimeLibrary>MultiThreadedDebug</RuntimeLibrary>
+    </ClCompile>
+    <Link>
+      <SubSystem>Console</SubSystem>
+      <GenerateDebugInformation>true</GenerateDebugInformation>
+      <ModuleDefinitionFile>
+      </ModuleDefinitionFile>
+      <AdditionalOptions>/EXPORT:ep_extra_EntryPoint %(AdditionalOptions)</AdditionalOptions>
+    </Link>
+  </ItemDefinitionGroup>
+  <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Release|x64'">
+    <ClCompile>
+      <WarningLevel>Level3</WarningLevel>
+      <FunctionLevelLinking>true</FunctionLevelLinking>
+      <IntrinsicFunctions>true</IntrinsicFunctions>
+      <SDLCheck>true</SDLCheck>
+      <PreprocessorDefinitions>NDEBUG;_CONSOLE;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <ConformanceMode>true</ConformanceMode>
+      <RuntimeLibrary>MultiThreaded</RuntimeLibrary>
+    </ClCompile>
+    <Link>
+      <SubSystem>Console</SubSystem>
+      <EnableCOMDATFolding>true</EnableCOMDATFolding>
+      <OptimizeReferences>true</OptimizeReferences>
+      <GenerateDebugInformation>true</GenerateDebugInformation>
+      <ModuleDefinitionFile>
+      </ModuleDefinitionFile>
+      <AdditionalOptions>%(AdditionalOptions)</AdditionalOptions>
+    </Link>
+    <MASM />
+  </ItemDefinitionGroup>
+  <ItemGroup>
+    <ClCompile Include="worker.c" />
+  </ItemGroup>
+  <ItemGroup>
+    <MASM Include="main.asm" />
+  </ItemGroup>
+  <ItemGroup>
+    <ClInclude Include="resource.h" />
+  </ItemGroup>
+  <ItemGroup>
+    <ResourceCompile Include="ep_extra.rc" />
+  </ItemGroup>
+  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />
+  <ImportGroup Label="ExtensionTargets">
+    <Import Project="$(VCTargetsPath)\BuildCustomizations\masm.targets" />
+  </ImportGroup>
+</Project>
diff --git a/ep_extra/ep_extra.vcxproj.filters b/ep_extra/ep_extra.vcxproj.filters
@@ -0,0 +1,37 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <ItemGroup>
+    <Filter Include="Source Files">
+      <UniqueIdentifier>{4FC737F1-C7A5-4376-A066-2A32D752A2FF}</UniqueIdentifier>
+      <Extensions>cpp;c;cc;cxx;c++;cppm;ixx;def;odl;idl;hpj;bat;asm;asmx</Extensions>
+    </Filter>
+    <Filter Include="Header Files">
+      <UniqueIdentifier>{93995380-89BD-4b04-88EB-625FBE52EBFB}</UniqueIdentifier>
+      <Extensions>h;hh;hpp;hxx;h++;hm;inl;inc;ipp;xsd</Extensions>
+    </Filter>
+    <Filter Include="Resource Files">
+      <UniqueIdentifier>{67DA6AB6-F800-4c08-8B7A-83BB121AAD01}</UniqueIdentifier>
+      <Extensions>rc;ico;cur;bmp;dlg;rc2;rct;bin;rgs;gif;jpg;jpeg;jpe;resx;tiff;tif;png;wav;mfcribbon-ms</Extensions>
+    </Filter>
+  </ItemGroup>
+  <ItemGroup>
+    <ClCompile Include="worker.c">
+      <Filter>Source Files</Filter>
+    </ClCompile>
+  </ItemGroup>
+  <ItemGroup>
+    <MASM Include="main.asm">
+      <Filter>Source Files</Filter>
+    </MASM>
+  </ItemGroup>
+  <ItemGroup>
+    <ClInclude Include="resource.h">
+      <Filter>Header Files</Filter>
+    </ClInclude>
+  </ItemGroup>
+  <ItemGroup>
+    <ResourceCompile Include="ep_extra.rc">
+      <Filter>Resource Files</Filter>
+    </ResourceCompile>
+  </ItemGroup>
+</Project>
diff --git a/ep_extra/main.asm b/ep_extra/main.asm
@@ -0,0 +1,18 @@
+EXTERN worker : PROC
+
+.CODE
+
+ep_extra_EntryPoint PROC EXPORT
+  PUSH RBP
+  MOV RBP, RSP
+  SUB RSP, 30H
+  CALL worker
+  CMP RAX, 0
+  JE finish
+  JMP RAX
+finish:
+  LEAVE
+  RET
+ep_extra_EntryPoint ENDP
+
+END
diff --git a/ep_extra/resource.h b/ep_extra/resource.h
@@ -0,0 +1,14 @@
+//{{NO_DEPENDENCIES}}
+// Microsoft Visual C++ generated include file.
+// Used by ep_extra.rc
+
+// Next default values for new objects
+// 
+#ifdef APSTUDIO_INVOKED
+#ifndef APSTUDIO_READONLY_SYMBOLS
+#define _APS_NEXT_RESOURCE_VALUE        101
+#define _APS_NEXT_COMMAND_VALUE         40001
+#define _APS_NEXT_CONTROL_VALUE         1001
+#define _APS_NEXT_SYMED_VALUE           101
+#endif
+#endif