One of the prominant design goals throughout KMDF's development cycle was to create a system that had a built in and deeply integrated verifier from the start. Furthermore, we had a goal to create a system that was easier to verify (as compared to WDM) at runtime and at compile time. The WDM driver verifier (DV) is phenomenal at checking for many common mistakes and is a very powerful tool, but there are some things it cannot check for because the initial design decisions made in creating WDM (and really when creating previous versions of NT) preclude these checks. For instance, you can create and initialize a PIRP out of your own buffer (via IoInitializeIrp(), so DV cannot validate PIRP pointer values when they are passed to a kernel routine.

So, in that light, KMDF has its own verifier (KMDFDV). KMDFDV verifiers KMDF specific contracts and behaviors, it is meant to be an addition to DV; KMDFDV is not meant to replace DV. KMDFDV can be enabled with or without DV being enabled on the driver. Just like DV, you should enable KMDFDV while developing your driver so that you can catch your mistakes ealier rather then later.

There are two new whitepapers on WHDC that describes how to build a KMDF driver and how to use the KMDF debugger extension. Currently, there is no UI to enable KMDFDV so you must edit the registry directly. First, navigate to this path:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\[your driver]\Parameters\WDF

If Parameters\WDF does not exist, you must create this sub path yourself. Under this path, add the following value:

"VerifierOn" : REG_DWORD : 0x1

The value must be added before the driver loads. This means that unlike the currently released versions of DV you do not need to reboot to enable KMDFDV. If you cannot unload your driver, you must reboot for this value to take effect. Once added, KMDFDV will be enabled on your driver until the value is removed and your driver is unloaded. To verify that the KMDF verifier has been enabled on your driver, break into the debugger and run !wdfkd.wdfdriverinfo. Here is the output right after before I am returned from my driver's DriverEntry() routine.

1: kd> !wdfdriverinfo wdfrawbusenumtest fff
Default driver image name:   wdfrawbusenumtest
WDF Verifier settings for wdfrawbusenumtest.sys is ON
  Pool tracking is ON
  Handle verification is ON
  IO verification is ON
  Lock verification is ON

Tomorrow I'll talk about the different checks that KMDFDV does and how to track your object refereces while KMDFDV is enabled.