Windows NT Kernel mode GetProcAddress and GetModuleHandle

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Implementation of GetProcAddress and GetModuleHandle
for Windows NT3.51/NT4/2000/XP/2003 kernel mode

Methods description
Functions and Appliance table
Sources
Samples

Methods description

I'm astonished, so many people ask questions like "How to get address of some exported function from ntdll.dll dynamically, when we know only the name of this function ?". People, please find the answer below. These are sources of kernel-mode implementation of Win32 GetModuleHandle() and GetProcAddress(). In general, this code (except KernelGetModuleBase3()) should work not only for kernel-mode, but for user-mode too if you use ntdll.dll.

Main appliance of these functions is writing drivers with unified binary (.SYS) those work under different NT OS versions. Together with PsGetVersion() they give you a power to work wonders. Lets go.

KernelGetModuleBase()

Standard and the most legal solution is to use Nt/ZwQuerySystemInformation(SystemModuleInfo, ...). We obtain list of loaded modules, walk through it looking for required name and parse its export section. Thats all - golden key is in our pocket. The only limitation is presence of adequate NtQuerySystemInformation() implementation in ntdll.dll. NT3 has not it at all. ReactOS has dummy do-nothing implementation. Not too good.

KernelGetModuleBase3()

There is another implementation of GetModuleHandle() (thanks to Egor Yuzik). It doesn't use NtQuerySystemInformation which appeared in NT4. The implementation itself - KernelGetModuleBase3(), is universal for all Windows NT-family OS'es. The main idea is to use undocumented filed PVOID SectionHandle from DRIVER_OBJECT structure. This is actually pointer to LDR_DATA_TABLE_ENTRY describing corresponding driver. All such structures are linked in bidirectional list (see LoadOrder member in LDR_DATA_TABLE_ENTRY structure) and cover all modules loaded in memory. The root record of the list (also called PsLoadedModuleList) is located just before LDR_DATA_TABLE_ENTRY structure corresponding to NTOSKRNL.EXE.

Note: Some interesting issues were found during further testing of new code.

Issue 1

When looking for ntoskrnl.exe and hal.dll modules with KernelGetModuleBase3(), these modules always have such names (e.g. kernel is always named ntoskrnl.exe and HAL - always hal.dll). But when we use KernelGetModuleBase(), modules are named according to their real file names. For example if ntkrnlpa.exe or ntkrnlmp.exe is loaded as kernel, KernelGetModuleBase("ntoskrnl.exe") shall return NULL, while KernelGetModuleBase("ntkrnlpa.exe") - proper address. But KernelGetModuleBase("ntoskrnl.exe") works always. The same policy is applied to HAL. Rather useful feature, I should say.

Issue 2

KernelGetModuleBase3() seemed to be an ultimate solution. But in Windows prior to Win 2000 for BOOT-drivers (those are loaded by ntldr and have Start=0 in registry) PVOID SectionHandle member of DRIVER_OBJECT is always NULL. In this case KernelGetModuleBase3() doesn't work (see above why). So, you cannot use this function from your BOOT-driver. I've also found that NtUnloadDriver() checks this value to determine if the driver can be unloaded. It is assumed, that BOOT-drivers are not unloadable and the sign of BOOT-drivers is SectionHandle == NULL.

Issue 3

ReactOS source review shown, that they use SectionHandle in a different way. Thus, such approach is inapplicable there.

KernelGetModuleBaseByPtr()

I had to invent still one approach - KernelGetModuleBaseByPtr(). The idea: we build our driver so that it imports at least one function (or variable) from the module we are interested in. Let it be ntoskrnl.exe. The function is chosen to be present in all versions on Windows NT, e.g. DbgPrint(). We take its address and start looking for valid MZ/PE header at descending addresses. Very helpful fact: header is always aligned on page boundary (PAGE_SIZE=4096 for x86 family). Address of the first valid header would ModuleHandle of required module. You can use it in KernelGetProcAddress() calls. This technique shall work under all NT- and 9x-compatible OSes, in both kernel- and user-modes in 32-bit addressing mode.

Note: Do not forget, that when you write code for getting address of imported function like this:

  PVOID f_ptr=DbgPrint;

f_ptr may receive address of the call-stub, that belongs to your module:

  yourmodule!DbgPrint:
  jmp  [yourmodule!__imp__DbgPrint]

but it is also possible, that the function you chosen, really begins with such instruction. For example starting from Windows 2000

  ntoskrnl!IofCallDriver:
  jmp  [ptr_IopCallDriver]

Plus, some antivuruses, firewalls and other useful (and not) drivers can insert at the very beginning of system functions JMP to themselves. And some other guys hook module load procedure and patch import addresses directly inside your module. I tell this to show, that there is no universal solution and you must be careful when using described mothods. And I also tell this for those people, who write such clever and tricky drivers: please, think about compatibility with other cunning ones ;).

For better reliability I would recommend to check if derived ModuleHandle is not equal to our own. If it is equal, we got stub address inside our module instead of real exported function entry point. In this case we shall extract real address from the stub. For example with SkipImportStub(). When we alredy think, that ModuleHandle is in our hands, it would be nice to check, that this module actually exports the function we have started from. If we start from address of DbgPrint and get to module which doesn't export such function, somethig goes wrong.

Note 2: Exkurs proposed better way - to import NtBuildNumber from ntoskrnl.exe. This constant is available in all versions of WinNT and we need not to check if address of NtBuildNumber is a call stub.

Limitations: along with the fact that this is a hack, significant weakness of this method is impossibility of finding in memory arbitrary module by its name.

ModuleBaseByPeb()

To draw full picture, I'll mention still one way - KernelGetModuleBaseByPeb(). It is similar to KernelGetModuleBase3(). The difference is that, LDR_DATA_TABLE_ENTRY is taken from PEB - Process Environment Block. Since PEB belongs to Win32 processes, we can use this method in appropriate execution context only (e.g. in context of Win32 or Native aplication). It shall not work in system threads.

Note: Since Windows 2003 R2 KTHREAD_HDR structure is changed This is the structure where we take PEB pointer. Look here for new definition.

MiLocateExportName

Just for education: the following function (not exported) exists since Win 2000:

PVOID
MiLocateExportName (
    IN PVOID DllBase,
    IN PCHAR FunctionName
    );

It has same functionality as KernelGetProcAddress().

Thanks to DeastSoft for reference.

Functions and Appliance table

Function	OS			Kernel mode	32bit User mode (Win32/native)
Function	NT	ReactOS	9x	Kernel mode	32bit User mode (Win32/native)
KernelGetProcAddress()	+	+	+	+	+
SkipImportStub()	+	+	+	+	+
KernelGetModuleBase()	4.0+	-	-	+	+
KernelGetModuleBase3()	3.51+	-	-	w2k+ 3.51,4.0 except for boot drivers	-
KernelGetModuleBaseByPtr()	3.51+	+	+	+	+
KernelGetModuleBaseByPeb()	3.51(?) 4.0+	?	-	in context of user-mode thread only (e.g. IoControl handler)	+

Sources

KernelGetModuleBase() (NT 4.0+)
KernelGetProcAddress()
RtlImageDirectoryEntryToData() (NT family)
LDR_DATA_TABLE_ENTRY (NT family)
KernelGetModuleBase3() (NT 3.51+)
SkipImportStub()
KernelGetModuleBaseByPtr()
KTHREAD_HDR (NT3 - 2003)
KTHREAD_HDR_2003_R2 (2003 R2)
TEB
PEB
PEB_LDR_DATA
KernelGetModuleBaseByPeb()

KernelGetModuleBase

NT 4.0 and higher

PVOID
KernelGetModuleBase(
    PCHAR  pModuleName
    )
{
    PVOID pModuleBase = NULL;
    PULONG pSystemInfoBuffer = NULL;

    __try
    {
        NTSTATUS status = STATUS_INSUFFICIENT_RESOURCES;
        ULONG    SystemInfoBufferSize = 0;

        status = ZwQuerySystemInformation(SystemModuleInfo,
            &SystemInfoBufferSize,
            0,
            &SystemInfoBufferSize);

        if (!SystemInfoBufferSize)
            return NULL;

        pSystemInfoBuffer = (PULONG)ExAllocatePool(NonPagedPool, SystemInfoBufferSize*2);

        if (!pSystemInfoBuffer)
            return NULL;

        memset(pSystemInfoBuffer, 0, SystemInfoBufferSize*2);

        status = ZwQuerySystemInformation(SystemModuleInfo,
            pSystemInfoBuffer,
            SystemInfoBufferSize*2,
            &SystemInfoBufferSize);

        if (NT_SUCCESS(status))
        {
            PSYSTEM_MODULE_ENTRY pSysModuleEntry =
                ((PSYSTEM_MODULE_INFORMATION)(pSystemInfoBuffer))->Module;
            ULONG i;
            
            for (i = 0; i <((PSYSTEM_MODULE_INFORMATION)(pSystemInfoBuffer))->Count; i++)
            {
                if (_stricmp(pSysModuleEntry[i].ModuleName +
                             pSysModuleEntry[i].ModuleNameOffset, pModuleName) == 0)
                {
                    pModuleBase = pSysModuleEntry[i].ModuleBaseAddress;
                    break;
                }
            }
        }

    }
    __except(EXCEPTION_EXECUTE_HANDLER)
    {
        pModuleBase = NULL;
    }
    if(pSystemInfoBuffer) {
        ExFreePool(pSystemInfoBuffer);
    }

    return pModuleBase;
} // end KernelGetModuleBase()

RtlImageDirectoryEntryToData

PVOID
RtlImageDirectoryEntryToData(
    IN PVOID Base,
    IN BOOLEAN MappedAsImage,
    IN USHORT DirectoryEntry,
    OUT PULONG Size
    );

KernelGetProcAddress

PVOID
KernelGetProcAddress(
    PVOID ModuleBase,
    PCHAR pFunctionName
    )
{
    PVOID pFunctionAddress = NULL;
    
    __try
    {
#ifndef WIN9X_SUPPORT
        ULONG                 size = 0;
        PIMAGE_EXPORT_DIRECTORY exports =(PIMAGE_EXPORT_DIRECTORY)
            RtlImageDirectoryEntryToData(ModuleBase, TRUE, IMAGE_DIRECTORY_ENTRY_EXPORT, &size);

        ULONG                 addr = (PUCHAR)((ULONG)exports-(ULONG)ModuleBase);
#else
        PIMAGE_DOS_HEADER dos =(PIMAGE_DOS_HEADER) ModuleBase;
        PIMAGE_NT_HEADERS nt  =(PIMAGE_NT_HEADERS)((ULONG) ModuleBase + dos->e_lfanew);

        PIMAGE_DATA_DIRECTORY expdir = (PIMAGE_DATA_DIRECTORY)
                                (nt->OptionalHeader.DataDirectory + IMAGE_DIRECTORY_ENTRY_EXPORT);
        ULONG                 addr = expdir->VirtualAddress;
        PIMAGE_EXPORT_DIRECTORY exports =(PIMAGE_EXPORT_DIRECTORY)((ULONG) ModuleBase + addr);
#endif
        PULONG functions =(PULONG)((ULONG) ModuleBase + exports->AddressOfFunctions);
        PSHORT ordinals  =(PSHORT)((ULONG) ModuleBase + exports->AddressOfNameOrdinals);
        PULONG names     =(PULONG)((ULONG) ModuleBase + exports->AddressOfNames);
        ULONG  max_name  =exports->NumberOfNames;
        ULONG  max_func  =exports->NumberOfFunctions;

        ULONG i;

        for (i = 0; i < max_name; i++)
        {
            ULONG ord = ordinals[i];
            if(i >= max_name || ord >= max_func) {
                return NULL;
            }
            if (functions[ord] < addr || functions[ord] >= addr + size)
            {
                if (strcmp((PCHAR) ModuleBase + names[i], pFunctionName)  == 0)
                {
                    pFunctionAddress =(PVOID)((PCHAR) ModuleBase + functions[ord]);
                    break;
                }
            }
        }
    }
    __except(EXCEPTION_EXECUTE_HANDLER)
    {
        pFunctionAddress = NULL;
    }

    return pFunctionAddress;
} // end KernelGetProcAddress()

LDR_DATA_TABLE_ENTRY

typedef struct _LDR_DATA_TABLE_ENTRY {
    LIST_ENTRY     LoadOrder;
    LIST_ENTRY     MemoryOrder;
    LIST_ENTRY     InitializationOrder;
    PVOID          ModuleBaseAddress;
    PVOID          EntryPoint;
    ULONG          ModuleSize;
    UNICODE_STRING FullModuleName;
    UNICODE_STRING ModuleName;
    ULONG          Flags;
    USHORT         LoadCount;
    USHORT         TlsIndex;
    union {
        LIST_ENTRY Hash;
        struct {
            PVOID SectionPointer;
            ULONG CheckSum;
        };
    };
    ULONG   TimeStamp;
} LDR_DATA_TABLE_ENTRY, *PLDR_DATA_TABLE_ENTRY;

KernelGetModuleBase3

NT 3.51 and higher

PLIST_ENTRY g_LoadOrderListHead = NULL;

PVOID
KernelGetModuleBase3(
    PDRIVER_OBJECT DriverObject,
    PCHAR  pModuleName
    )
{
    PVOID pModuleBase = NULL;
    PLIST_ENTRY Next;
    PLIST_ENTRY LoadOrderListHead;
    UNICODE_STRING uStr;
    PLDR_DATA_TABLE_ENTRY LdrDataTableEntry;
    PLDR_DATA_TABLE_ENTRY LdrDataTableEntry0;
    ULONG len;
    BOOLEAN FreeUstr = FALSE;

    uStr.Buffer = NULL;

    __try
    {
        if(!g_LoadOrderListHead) {
            LdrDataTableEntry0 = (PLDR_DATA_TABLE_ENTRY)DriverObject->DriverSection;

            uStr.Length = sizeof(L"NTOSKRNL.EXE")-sizeof(WCHAR);
            uStr.MaximumLength = sizeof(L"NTOSKRNL.EXE");
            uStr.Buffer = L"NTOSKRNL.EXE";

            Next = LdrDataTableEntry0->LoadOrder.Blink;
            while ( TRUE ) {
                LdrDataTableEntry = CONTAINING_RECORD( Next,
                                                       LDR_DATA_TABLE_ENTRY,
                                                       LoadOrder
                                                     );
                Next = Next->Blink;
                if(!LdrDataTableEntry->ModuleName.Buffer) {
                    return NULL;
                }
                if(RtlCompareUnicodeString(&LdrDataTableEntry->ModuleName, &uStr, TRUE) == 0)
                {
                    LoadOrderListHead = Next;
                    break;
                }
                if(LdrDataTableEntry == LdrDataTableEntry0)
                    return NULL;
            }
            g_LoadOrderListHead = LoadOrderListHead;
        } else {
            LoadOrderListHead = g_LoadOrderListHead;
        }
        len = strlen(pModuleName);
        if(!len)
            return NULL;
        len = (len+1)*sizeof(WCHAR);

        uStr.MaximumLength = (USHORT)len;
        uStr.Length = (USHORT)len - sizeof(WCHAR);
        uStr.Buffer = (PWCHAR)ExAllocatePool(NonPagedPool, len);
        FreeUstr = TRUE;
        swprintf(uStr.Buffer, L"%S", pModuleName);

        Next = LoadOrderListHead->Flink;
        while ( Next != LoadOrderListHead ) {
            LdrDataTableEntry = CONTAINING_RECORD( Next,
                                                   LDR_DATA_TABLE_ENTRY,
                                                   LoadOrder
                                                 );
            if(RtlCompareUnicodeString(&LdrDataTableEntry->ModuleName, &uStr, TRUE) == 0)
            {
                pModuleBase = LdrDataTableEntry->ModuleBaseAddress;
                break;
            }
            Next = Next->Flink;
        }
    }
    __except(EXCEPTION_EXECUTE_HANDLER)
    {
        pModuleBase = NULL;
    }
    if(FreeUstr && uStr.Buffer) {
        ExFreePool(uStr.Buffer);
    }

    return pModuleBase;
} // end KernelGetModuleBase3()

SkipImportStub

For entire 32-bit Windows family on x86 (e.g. ReactOS, Win9x)

PVOID
SkipImportStub(
    PVOID p
    )
{
    if(((PUCHAR)p)[0] == 0xff && ((PUCHAR)p)[1] == 0x25) {
        p = (PVOID)(*(PULONG)(*(PULONG)((ULONG)p+2)));
    }
    return p;
} // end SkipImportStub()

KernelGetModuleBaseByPtr