Driver Verifier has two levels of I/O Verification:
Level 1 I/O Verification is always active whenever I/O Verification is selected.
Level 2 I/O Verification is always active whenever I/O Verification is selected in Windows XP and later.
See Also: Enhanced I/O Verification In Windows 7 and later versions of the Windows operating system, Enhanced I/O Verification is automatically activated when you select I/O Verification. It is not available or necessary to select it as a separate option.
Level 1 I/O Verification
When Level 1 I/O Verification is enabled, all IRPs obtained through IoAllocateIrp are allocated from a special pool and their use is tracked.
Additionally, Driver Verifier checks for invalid I/O calls, including:
Attempts to free an IRP whose type is not IO_TYPE_IRP
Passes of invalid device objects to IoCallDriver
Passes of an IRP to IoCompleteRequest that contains invalid status or that still has a cancel routine set
Changes to the IRQL across a call to the driver dispatch routine
Attempts to free an IRP that remains associated with a thread
Passes of a device object to IoInitializeTimer that already contains an initialized timer
Passes of an invalid buffer to IoBuildAsynchronousFsdRequest or IoBuildDeviceIoControlRequest
Passes of an I/O status block to an IRP, when this I/O status block is allocated on a stack that has unwound too far
Passes of an event object to an IRP, when this event object is allocated on a stack that has unwound too far
Because the special IRP pool is of limited size, I/O Verification is most effective when it is only used on one driver at a time.
I/O Verification Level 1 failures cause bug check 0xC9 to be issued. The first parameter of this bug check indicates what violation has occurred. See Bug Check 0xC9 (DRIVER_VERIFIER_IOMANAGER_VIOLATION) for a full parameter listing.
Level 2 I/O Verification
I/O Verification Level 2 errors are displayed in different ways: on the blue screen, in a crash dump file, and in a kernel debugger.
On the blue screen, these errors are noted by the message IO SYSTEM VERIFICATION ERROR and the string WDM DRIVER ERRORXXX, where XXX is an I/O error code.
In a crash dump file, most of these errors are noted by the message BugCheck 0xC9 (DRIVER_VERIFIER_IOMANAGER_VIOLATION), along with the I/O error code. In this case, the I/O error code appears as the first parameter of the bug check 0xC9. The remainder are noted by the message Bug Check 0xC4 (DRIVER_VERIFIER_DETECTED_VIOLATION), along with a Driver Verifier error code. In this case, the Driver Verifier error code appears as the first parameter of the bug check 0xC4.
In a kernel debugger (KD or WinDbg), these errors are noted by the message WDM DRIVER ERROR and a descriptive text string. When the kernel debugger is active, it is possible to ignore the Level 2 errors and resume system operation. (This is not possible with any other bug checks.)
The blue screen, the crash dump file, and the kernel debugger each display additional information as well. For a full description of most I/O Verification Level 2 error messages, see Bug Check 0xC9. For the remainder, see Bug Check 0xC4.
Starting in Window Vista, the I/O Verification option checks for the following driver errors:
Taking too long to complete and cancel IRPs that originated in user-mode applications.
Releasing a remove lock that has not yet been acquired.
Calling IoReleaseRemoveLock or IoReleaseRemoveLockAndWait with a tag parameter that differs from the tag parameter used in the corresponding IoAcquireRemoveLock call.
Calling IoCallDriver with interrupts disabled.
Calling IoCallDriver at IRQL greater than DISPATCH_LEVEL.
Returning from a driver dispatch routine with interrupts disabled.
Returning from a driver dispatch routine with a changed IRQL.
Returning from a driver dispatch routine with APCs disabled. In this case, the driver might have called KeEnterCriticalRegion more times than KeLeaveCriticalRegion, which is the primary cause for Bug Check 0x20 (KERNEL_APC_PENDING_DURING_EXIT) and Bug Check 0x1 (APC_INDEX_MISMATCH).
Starting in Windows 7, the I/O Verification option checks for the following driver errors:
- Attempts to free IRPs by calling ExFreePool. IRPs must be freed with IoFreeIrp.
In addition, you can use this option to detect another common driver bug—reinitializing remove locks. Remove locks data structures should be allocated inside device extensions. This ensures that the I/O manager frees the memory that holds the IO_REMOVE_LOCK structure only when the device object is deleted. If the driver performs the following three steps, it is possible that after step 2, an application or driver still holds a reference to Device1:
- Allocates the IO_REMOVE_LOCK structure that corresponds to Device1, but does the allocation outside of Device1’s extension.
- Calls IoReleaseRemoveLockAndWait when Device1 is being removed.
- Calls IoInitializeRemoveLock for the same lock to reuse it as a remove lock for Device2.
It is possible that after step 2 an application or driver still holds a reference to Device1. The application or driver can still send requests to Device1, even though this device was removed. Therefore, it is not safe to reuse the same memory as a new remove lock until I/O manager deletes Device1. Reinitializing the same lock while another thread is trying to acquire it can result in the corruption of the lock, with unpredictable results for the driver and the entire system.
In Windows 7 and later versions of the Windows operating system, Enhanced I/O Verification is automatically activated when you select I/O Verification.
Activating This Option
You can activate the I/O Verification feature for one or more drivers by using Driver Verifier Manager or the Verifier.exe command line. For details, see Selecting Driver Verifier Options.
At the command line.
At the command line, the I/O Verification option is represented by Bit 4 (0x10). To activate I/O Verification, use a flag value of 0x10 or add 0x10 to the flag value. For example:
verifier /flags 0x10 /driver MyDriver.sys
The feature will be active after the next boot.
You can also activate and deactivate I/O Verification without rebooting the computer by adding the /volatile parameter to the command. For example:
verifier /volatile /flags 0x10 /adddriver MyDriver.sys
This setting is effective immediately, but is lost when you shut down or reboot the computer. For details, see Using Volatile Settings.
The I/O Verification feature is also included in the standard settings. For example:
verifier /standard /driver MyDriver.sys
Using Driver Verifier Manager
- Select Create custom settings (for code developers) and then click Next.
- Select Select individual settings from a full list.
- Select (check) I/O verification.
The I/O Verification feature is also included in the standard settings. To use this feature, in Driver Verifier Manager, click Create Standard Settings.
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