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Windows Driver Kit DDI reference (nf-usermode_accessors-umaexceptionfilter)

Description

The UmaExceptionFilter function provides mode-dependent exception filtering for structured exception handling.

Parameters

`Mode`

[in] The processor mode that determines the exception handling behavior. Mode can be one of the following values.

Value	Meaning
KernelMode	The exception should continue searching for a handler. Returns EXCEPTION_CONTINUE_SEARCH.
UserMode	The exception should be handled by the current handler. Returns EXCEPTION_EXECUTE_HANDLER.

Return value

The function returns one of the following exception filter values:

Return code	Description
EXCEPTION_EXECUTE_HANDLER	Returned when Mode is UserMode. Indicates that the exception handler should execute and the exception is considered handled.
EXCEPTION_CONTINUE_SEARCH	Returned when Mode is KernelMode. Indicates that the exception should propagate up the call stack to find another handler.

Remarks

This function provides a standardized way to handle structured exceptions differently depending on whether the code is dealing with user-mode or kernel-mode memory access. It's designed to be used in __except() clauses within usermode accessor functions.

The behavior depends on the processor mode specified:

When Mode is UserMode, the function returns EXCEPTION_EXECUTE_HANDLER, indicating that exceptions should be handled gracefully. This is appropriate for user-mode memory access where exceptions are expected and should not crash the system.
When Mode is KernelMode, the function returns EXCEPTION_CONTINUE_SEARCH, indicating that exceptions should propagate to higher-level handlers. This is appropriate for kernel-mode memory access where exceptions typically indicate serious bugs that should not be silently ignored.

This design pattern ensures that user-mode memory access failures are handled safely while kernel-mode memory access failures are treated as serious errors requiring appropriate debugging and error handling.

This function works on all versions of Windows, not just the latest. You need to consume the latest WDK to get the function declaration from the usermode_accessors.h header. You also need the library (umaccess.lib) from the latest WDK. However, the resulting driver will run fine on older versions of Windows.

View the official Windows Driver Kit DDI reference

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