ProbeForWrite

The ProbeForWrite routine checks that a user-mode buffer actually resides in the user-mode portion of the address space, is writable, and is correctly aligned.

VOID 
  ProbeForWrite(
    IN CONST VOID  *Address,
    IN SIZE_T  Length,
    IN ULONG  Alignment
    );

Parameters

Address

Specifies the beginning of the user-mode buffer.

Length

Specifies the length, in bytes, of the user-mode buffer.

Alignment

Specifies the required alignment, in bytes, of the beginning of the user-mode buffer.

Return Value

None

Headers

Declared in wdm.h and ntddk.h. Include wdm.h or ntddk.h.

Comments

If the specified range of memory is not a valid user-mode address range or is not writable (no access, read-only, and so on), ProbeForWrite raises the STATUS_ACCESS_VIOLATION exception. If the beginning of the address range is not aligned on the byte boundary that is specified by Alignment, ProbeForWrite raises the STATUS_DATATYPE_MISALIGNMENT exception.

Kernel-mode drivers must use ProbeForWrite to validate write access to buffers allocated in user space. It is most commonly used during METHOD_NEITHER I/O to validate the user buffer pointed to by Irp -> UserBuffer.

Drivers must call ProbeForWrite inside a try/except block. If the routine raises an exception, the driver should complete the IRP with the appropriate error. Note that subsequent accesses by the driver to the user-mode buffer must also be encapsulated within a try/except block: a malicious application could have another thread deleting, substituting, or changing the protection of user address ranges at any time (even after or during a call to ProbeForRead or ProbeForWrite). For more information, see Handling Exceptions.

Do not use this routine on kernel-mode addresses; it will raise an exception.

Callers of ProbeForWrite must be running at IRQL <= APC_LEVEL.

See Also

ProbeForRead