minhook.net's Introduction

MinHook.NET

Introduction

MinHook.NET is a pure managed C# port of the brilliant MinHook library by Tsuda Kageyu (https://github.com/TsudaKageyu/minhook). The library has the capability of inline hooking native API calls, utilising .NET delegates for both the detoured and original function that is commonly called with the detour.

The project has attempted to keep within the simplistic spirit of the original MinHook library.

Quick Start

Simple example demonstrating the hooking of the MessageBoxW Windows API

    [DllImport("user32.dll", SetLastError = true, CharSet = CharSet.Unicode)]
    public static extern int MessageBoxW(IntPtr hWnd, String text, String caption, uint type);

    //We need to declare a delegate that matches the prototype of the hooked function
    [UnmanagedFunctionPointer(CallingConvention.StdCall,CharSet=CharSet.Unicode)]
    delegate int MessageBoxWDelegate(IntPtr hWnd, string text, string caption, uint type);

    //A variable to store the original function so that we can call
    //within our detoured MessageBoxW handler
    MessageBoxWDelegate MessageBoxW_orig;

    //Our actual detour handler function
    int MessageBoxW_Detour(IntPtr hWnd, string text, string caption, uint type) {
        return MessageBoxW_orig(hWnd, "HOOKED: " + text, caption, type);
    }

    void ChangeMessageBoxMessage() {

		using (HookEngine engine = new HookEngine()) {

			MessageBoxW_orig = engine.CreateHook("user32.dll", "MessageBoxW", new MessageBoxWDelegate(MessageBoxW_Detour));
			engine.EnableHooks();

			//Call the PInvoke import to test our hook is in place
			MessageBoxW(IntPtr.Zero, "Text", "Caption", 0);
		}
    }

TOOO

Figure out how to calculate imm length with ModRM based instructions
When enabling hooks, enumerate threads and update thread context if any are running at the hook instructions that are being patched
Implement unit tests

Thanks

The original MinHook library that this project is based on - https://github.com/TsudaKageyu/minhook
The SharpDisasm project and Udis86 disassembler that the project is ported from - https://github.com/spazzarama/SharpDisasm

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minhook.net's Issues

System.MethodAccessException

I have a managed DLL that uses this library.
This is the code I'm trying to run:

try
{
  using (var engine = new HookEngine())
  {
      ... = engine.CreateHook(...);
  }
}
catch (Exception e)
{
  MessageBox.Show("Exception: " + e.ToString());
}