APIフック

hoge.cpp

#define UNICODE
#include <windows.h>
#include <stdio.h>

DWORD OldProtect;
BYTE tmp[6];
BYTE ByteAsm[6];
DWORD * pFunc;


int WINAPI Hook_MessageBoxA(
	_In_opt_ HWND    hWnd,
	_In_opt_ LPCTSTR lpText,
	_In_opt_ LPCTSTR lpCaption,
	_In_     UINT    uType
	)
{
	MessageBoxW(0, L"", L"foo", MB_OK);
	return 0;
}

void StarteHook()
{

	HMODULE hDll = GetModuleHandleW(L"user32.dll");
	pFunc = (DWORD*)GetProcAddress(hDll, "MessageBoxA");

	if (VirtualProtect(pFunc, 6, PAGE_EXECUTE_READWRITE, &OldProtect))
	{
		memcpy(tmp, pFunc, 6);

		ByteAsm[0] = 0x68; //push dword ptr
		DWORD* dwProc = (DWORD*)Hook_MessageBoxA;
		memcpy(&ByteAsm[1], &dwProc, 4);
		ByteAsm[5] = 0xC3; //ret

		memcpy(pFunc, ByteAsm, 6);
	}
}

int CALLBACK WinMain(
	_In_ HINSTANCE hInstance,
	_In_ HINSTANCE hPrevInstance,
	_In_ LPSTR     lpCmdLine,
	_In_ int       nCmdShow
	)
{

	StarteHook();
	MessageBoxA(0, "", "hoge", MB_OK);
	memcpy(pFunc, tmp, 6);
	return 0;

}