ZeroUserMemory function (usermode_accessors.h)

The ZeroUserMemory function fills a user-mode memory region with zeros.

Syntax

void ZeroUserMemory(
  volatile VOID *Destination,
  SIZE_T        Length
);

Parameters

Destination

[out] A pointer to the starting address of the memory block to zero.

Length

[in] The number of bytes to zero.

Return value

None

Remarks

This function provides a safe way to zero a user-mode memory region. This allows for flexible memory operations when kernel-mode code needs to initialize user-mode memory buffers to zero.

The function has the following properties:

• The function performs a volatile zero operation using memory_order_relaxed semantics.

• The function isn't recognized as a compiler intrinsic so the compiler will never optimize away the call (either entirely or replace the call with an equivalent sequence of instructions).

• When the call returns, the buffer has been overwritten with zeros. This function's memory accesses to the Destination will only be performed within the function (for example, the compiler can't move memory accesses out of this function).

• The function might perform unaligned memory accesses if the platform allows for it.

• The function might access memory locations more than once as part of its zero operation.

The function raises a structured exception if the zero operation fails, such as when the destination address is not a valid user-mode address or is inaccessible.

This function will never be optimized away by the compiler, nor will the compiler create additional accesses to this memory location before the function is called or after the function returns (unless the source code explicitly performs these accesses).

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.

Requirements

See also

ZeroModeMemory

SetUserMemory

FillUserMemory

CopyToUser