NoRegPatch.c

/*
 * No-Registry Patch for Fallout New Vegas
 *
 * Copyright (C) 2021-2024 Thamatip Chitpong <tangaming123456@outlook.com>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

#include <windows.h>
#include <strsafe.h>

#include <MinHook.h>

#define CONST_STR_LEN(str) ((sizeof(str) / sizeof(str[0])) - 1)

typedef LONG (WINAPI *PFREGOPENKEYEXW)(HKEY, LPCWSTR, DWORD, REGSAM, PHKEY);
typedef LONG (WINAPI *PFREGQUERYVALUEEXW)(HKEY, LPCWSTR, LPDWORD, LPDWORD, LPBYTE, LPDWORD);
typedef LONG (WINAPI *PFREGCLOSEKEY)(HKEY);

/* For calling original functions */
static PFREGOPENKEYEXW Real_RegOpenKeyExW = NULL;
static PFREGQUERYVALUEEXW Real_RegQueryValueExW = NULL;
static PFREGCLOSEKEY Real_RegCloseKey = NULL;

/* A dummy registry key for hooked calls */
static BYTE dummyKey[1];
static HKEY hDummyKey = INVALID_HANDLE_VALUE;

/* Installed folder path of the game, initialize only once */
static LPWSTR pszGameDir = NULL;

/* NOTE: The installed path must be in the following format: "c:\gog games\fallout new vegas/" */
static LPWSTR
NoRegPatch_GetGameDir(void)
{
    DWORD dwLength;
    LPWSTR pszPath;

    /* Get game folder path */
    dwLength = GetCurrentDirectoryW(0, NULL);
    if (dwLength == 0)
        return NULL;

    dwLength += CONST_STR_LEN(L"/");
    pszPath = HeapAlloc(GetProcessHeap(), 0, dwLength * sizeof(WCHAR));
    if (!pszPath)
        return NULL;

    if (GetCurrentDirectoryW(dwLength - CONST_STR_LEN(L"/"), pszPath) == 0)
    {
        HeapFree(GetProcessHeap(), 0, pszPath);
        return NULL;
    }

    /* Convert all chars in the path to lowercase */
    CharLowerBuffW(pszPath, dwLength - CONST_STR_LEN(L"/"));

    /* Append the trailing "/" */
    StringCchCatW(pszPath, dwLength, L"/");

    return pszPath;
}

/* Hooked RegOpenKeyExW */
LONG WINAPI
Hooked_RegOpenKeyExW(HKEY hKey, LPCWSTR lpSubKey, DWORD ulOptions, REGSAM samDesired, PHKEY phkResult)
{
    if (_wcsicmp(lpSubKey, L"Software\\Bethesda Softworks\\FalloutNV") == 0)
    {
        *phkResult = hDummyKey;
        return ERROR_SUCCESS;
    }

    return Real_RegOpenKeyExW(hKey, lpSubKey, ulOptions, samDesired, phkResult);
}

/* Hooked RegQueryValueExW */
LONG WINAPI
Hooked_RegQueryValueExW(HKEY hKey, LPCWSTR lpValueName, LPDWORD lpReserved, LPDWORD lpType, LPBYTE lpData, LPDWORD lpcbData)
{
    if (hKey == hDummyKey)
    {
        /* Opening the dummy key, assume success */
        LONG lError = ERROR_SUCCESS;

        if (_wcsicmp(lpValueName, L"Installed Path") == 0)
        {
            if (lpcbData)
            {
                DWORD cbData = (wcslen(pszGameDir) + 1) * sizeof(WCHAR);

                if (lpData)
                {
                    HRESULT hr = StringCbCopyW((LPWSTR)lpData, *lpcbData, pszGameDir);
                    if (hr == STRSAFE_E_INSUFFICIENT_BUFFER)
                    {
                        lError = ERROR_MORE_DATA;
                    }
                }

                /* Return the size (in bytes) to the caller */
                *lpcbData = cbData;
            }
        }

        return lError;
    }

    return Real_RegQueryValueExW(hKey, lpValueName, lpReserved, lpType, lpData, lpcbData);
}

/* Hooked RegCloseKey */
LONG WINAPI
Hooked_RegCloseKey(HKEY hKey)
{
    if (hKey == hDummyKey)
    {
        return ERROR_SUCCESS;
    }

    return Real_RegCloseKey(hKey);
}

static void
NoRegPatch_Init(void)
{
    /* Get game folder path */
    pszGameDir = NoRegPatch_GetGameDir();
    if (!pszGameDir)
    {
        MessageBoxW(NULL, L"Failed to create game install data.", L"NoRegPatch", MB_ICONERROR | MB_OK);
        TerminateProcess(GetCurrentProcess(), 0);
    }

    /* Initialize MinHook */
    if (MH_Initialize() != MH_OK)
    {
        MessageBoxW(NULL, L"Failed to initialize MinHook.", L"NoRegPatch", MB_ICONERROR | MB_OK);
        TerminateProcess(GetCurrentProcess(), 0);
    }

    /* Get fake handle for the dummy registry key */
    hDummyKey = (HKEY)(PVOID)dummyKey;

    MH_CreateHook((LPVOID*)(&RegOpenKeyExW), (LPVOID*)(&Hooked_RegOpenKeyExW), (LPVOID*)(&Real_RegOpenKeyExW));
    MH_CreateHook((LPVOID*)(&RegQueryValueExW), (LPVOID*)(&Hooked_RegQueryValueExW), (LPVOID*)(&Real_RegQueryValueExW));
    MH_CreateHook((LPVOID*)(&RegCloseKey), (LPVOID*)(&Hooked_RegCloseKey), (LPVOID*)(&Real_RegCloseKey));

    MH_EnableHook(MH_ALL_HOOKS);
}

static void
NoRegPatch_Uninit(void)
{
    MH_DisableHook(MH_ALL_HOOKS);

    /* Uninitialize MinHook */
    MH_Uninitialize();

    HeapFree(GetProcessHeap(), 0, pszGameDir);
}

/* DLL entry point */
BOOL WINAPI DllMain(HINSTANCE hInstDLL, DWORD dwReason, LPVOID lpReserved)
{
    if (dwReason == DLL_PROCESS_ATTACH)
    {
        NoRegPatch_Init();
    }
    else if (dwReason == DLL_PROCESS_DETACH)
    {
        NoRegPatch_Uninit();
    }

    return TRUE;
}