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Implementation of GetProcAddress
for Windows NT4/2000/XP/2003 kernel mode

I'm asonished, 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 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.


KernelGetModuleBase

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()

KernelGetProcAddress

PVOID
KernelGetProcAddress(
    PVOID ModuleBase,
    PCHAR pFunctionName
    )
{
    PVOID pFunctionAddress = NULL;
    
    __try
    {
        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                 size = expdir->Size;
        ULONG                 addr = expdir->VirtualAddress;

        PIMAGE_EXPORT_DIRECTORY exports =(PIMAGE_EXPORT_DIRECTORY)((ULONG) ModuleBase + addr);

        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 < exports->AddressOfNames; 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()
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