Windows Kernel Drivers 101

Work In Progress This living document captures some of the Kernel Driver and OS related concepts that I encounter as I study Windows kernel driver development.

Driver Types

There are many different types of drivers, but I am mostly interested in Sofware Drivers.

Software Driver

• Not associated with any device

• Useful for running code in the kernel mode

• Can also be a user mode driver

• Drivers can be developed with Kernel-Mode Driver Framework (KMDF) and Windows Driver Model (WDM)

KMDF vs WDM

• WDM is very closely tied to the OS and interacts with the it calling system service routines directly

• KMDF is a framework that abstracts a lot of driver development and allows the developer to focus on his/her driver rather than focusing on OS programming intricacies

• KMDF is recommended and a preferred driver development model over WDM in most cases

I/O Manager

• Is an interface enabling communication between userland applications and kernel drivers

• Creates a driver object (DRIVER_OBJECT) for each installed and loaded driver

• Defines a set of standard mandatory driver routines that drivers must support such as DriverEntry

• Calls driver's DriverEntry routine, which supplies the driver's DRIVER_OBJECT address

• Accepts I/O requests, which usually originate from user-mode applications

• Creates IRPs to represent the I/O requests

• Transfers IRPs to the appropriate drivers

Uncategorized Notes

• All drivers contain DriverEntry routine - similary to main routine of an executable and DllMain of a DLL. This routine gets called once the driver is loaded and started by the OS.

• Memory allocated in paged pool can be paged out to a disk, whereas memory allocated from a nonpaged pool cannot

• Requests sent to drivers are encapsulated in I/O Request Packets (IRP)

• DRIVER_OBJECT represents the image of a loaded kernel-mode driver:

  • typedef struct _DRIVER_OBJECT {
      CSHORT             Type;
      CSHORT             Size;
      PDEVICE_OBJECT     DeviceObject;
      ULONG              Flags;
      PVOID              DriverStart;
      ULONG              DriverSize;
      PVOID              DriverSection;
      PDRIVER_EXTENSION  DriverExtension;
      UNICODE_STRING     DriverName;
      PUNICODE_STRING    HardwareDatabase;
      PFAST_IO_DISPATCH  FastIoDispatch;
      PDRIVER_INITIALIZE DriverInit;
      PDRIVER_STARTIO    DriverStartIo;
      PDRIVER_UNLOAD     DriverUnload;
      PDRIVER_DISPATCH   MajorFunction[IRP_MJ_MAXIMUM_FUNCTION + 1];
    } DRIVER_OBJECT, *PDRIVER_OBJECT;

• DRIVER_OBJECT contains references to entry points of driver's standard routines (i.e Unload)

• Driver standard routines receive IRPs as input as well as a pointer to the target device object

• Drivers must create at least one device object (DEVICE_OBJECT) for each device

• Device objects serve as a target of operations performed on a the device

• Software only drivers that only handle I/O requests and do not pass them to hardware, still must create a device object to represent the target of its operations

References

Packet-Driven I/O with Reusable IRPs - Windows driversdocsmsft