ring3下的IAT HOOK

IAT hooking
当应用程序使用另一个动态库的函数时，PE装载器会找到每个IAMGE_IMPORT_BY_NAME结构所指向的输入函数的地址，然后把这些地址存储在一个叫做IAT的表。当函数CALL一个输入函数的时候，会先在IAT找到对应的函数地址，紧接着再进入该函数空间。熟悉PE结构的朋友应该清楚，IAT是一个IMAGE_THUNK_DATAj结构的数组。只要程序装载进内存中，就只与IAT查询信息，所以可见IAT表是一个非常重要的位置。
如果在IAT表中把某个函数的地址修改为钩子函数的地址，当调用到函数的时候，就会执行到该钩子函数中去。示例代码如下：
钩子函数，这里只是简单的弹出个窗口：

int
WINAPI
MyMessageBoxW(
/* __in_opt HWND hWnd,
__in_opt LPCWSTR lpText,
__in_opt LPCWSTR lpCaption,
__in UINT uType*/)
{
//todo yourself
return MessageBox(NULL, "hello world", "caption", MB_OK);
}

ROOKIT函数，获取目标函数的地址，然后调用IAT HOOK函数ImportAddressTableHook，修改IAT表的值。

 

BOOL Rookits
(
IN HMODULE hModule,
IN LPCTSTR pImageName,
IN LPCTSTR pTargetFuncName
)
{
LPDWORD pTargetFuncAddr = NULL;
HMODULE hLib = LoadLibrary(pImageName);
if (NULL != hLib)
{
pTargetFuncAddr = (LPDWORD)GetProcAddress(hLib, pTargetFuncName);
return ImportAddressTableHook(hModule, pImageName, pTargetFuncAddr, MyMessageBoxW);
}
 
return FALSE;
}

修改IAT表的函数，通过所在模块的基地址hModule找到输入表的数据目录项，获取IAT的首指针，查询目标函数地址所在的位置，然后修改为钩子函数的地址。

BOOL ImportAddressTableHook
(
 IN HMODULE hModule,
 IN LPCTSTR pImageName,
 IN LPCVOID pTargetFuncAddr,
 IN LPCVOID pReplaceFuncAddr
 )
{
    IMAGE_DOS_HEADER* pImageDosHearder = (IMAGE_DOS_HEADER*)hModule;
    IMAGE_OPTIONAL_HEADER* pImageOptionalHeader = (IMAGE_OPTIONAL_HEADER*)((DWORD)hModule+pImageDosHearder->e_lfanew+24);    
    IMAGE_IMPORT_DESCRIPTOR* pImageImportDescriptor = (IMAGE_IMPORT_DESCRIPTOR*)
        ((DWORD)hModule+
        pImageOptionalHeader->DataDirectory[IMAGE_DIRECTORY_ENTRY_IMPORT].VirtualAddress);
    IMAGE_THUNK_DATA* pImageThunkData = NULL;
    string TargetLibraryName;
    DWORD Value = 0, OldProtect = 0， NewProtect = 0;
    LPDWORD FunctionAddress = NULL;
    MEMORY_BASIC_INFORMATION InforMation;
 
 
    while(pImageImportDescriptor->Characteristics  != 0)   
    {   
        TargetLibraryName=(LPCTSTR)((DWORD)hModule+pImageImportDescriptor->Name);
        if(TargetLibraryName.compare(pImageName) == 0)
        {   
            pImageThunkData = (IMAGE_THUNK_DATA*)((DWORD)hModule + pImageImportDescriptor->FirstThunk);
            break; 
        } 
        pImageImportDescriptor++;   
    }  
    if (pImageThunkData == NULL)
    {
        return FALSE;
    } 
    while(pImageThunkData->u1.Function)   
    {   
        //循环查找目标函数地址所在的位置
        FunctionAddress = (LPDWORD)&(pImageThunkData->u1.Function);
        if(*FunctionAddress == (DWORD)pTargetFuncAddr)
        {    
            //找到目标函数的地址，然后修改为钩子函数的地址
            VirtualProtect(FunctionAddress, sizeof(DWORD), PAGE_READWRITE, &OldProtect);
            if(!WriteProcessMemory((HANDLE)-1, FunctionAddress, &pReplaceFuncAddr, 4, NULL))
            {
                return FALSE;
            }
            VirtualProtect(FunctionAddress, sizeof(DWORD), OldProtect, NewProtect );   
            return TRUE; 
        }  
        pImageThunkData++;   
    }
    return FALSE;
} 

也许你会注意到，如果使用了延迟装入数据，那么示例代码是无效的，因为程序会使用___delayLoadHelper2来加载，具体代码可在delayhlp.cpp查看，里面直接GetProcAddress获取该函数地址，对于这种情况只能再HOOK多一个函数，即GetProcAddress。
___delayLoadHelper2代码片段：

// Go for the procedure now.
//
dli.hmodCur = hmod;
if (__pfnDliNotifyHook2) {
pfnRet = (*__pfnDliNotifyHook2)(dliNotePreGetProcAddress, &dli);
}
if (pfnRet == 0) {
if (pidd->rvaBoundIAT && pidd->dwTimeStamp) {
// bound imports exist...check the timestamp from the target image
//
PIMAGE_NT_HEADERS pinh(PinhFromImageBase(hmod));
 
if (pinh->Signature == IMAGE_NT_SIGNATURE &&
TimeStampOfImage(pinh) == idd.dwTimeStamp &&
FLoadedAtPreferredAddress(pinh, hmod)) {
 
// Everything is good to go, if we have a decent address
// in the bound IAT!
//
pfnRet = FARPROC(UINT_PTR(idd.pBoundIAT[iIAT].u1.Function));
if (pfnRet != 0) {
goto SetEntryHookBypass;
}
}
}
 
pfnRet = ::GetProcAddress(hmod, dli.dlp.szProcName);
}