ProbeForWrite function

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(
  volatile VOID *Address,
  SIZE_T        Length,
  ULONG         Alignment



Specifies the beginning of the user-mode buffer.


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


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

Return value



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.

If Irp->RequestorMode = KernelMode, the Irp->AssociatedIrp.SystemBuffer and Irp->UserBuffer fields do not contain user-mode addresses, and a call to ProbeForWrite to probe a buffer pointed to by either field will raise an exception.

If Length = 0, ProbeForWrite does no checking of the address. In this case, the routine does not raise an exception for an address that is misaligned or is outside the range of valid user addresses.


Minimum supported client Available starting with Windows 2000.
Target Platform Universal
Header wdm.h (include Wdm.h, Ntddk.h, Ntifs.h)
Library NtosKrnl.lib
DLL NtosKrnl.exe
DDI compliance rules IrqlExApcLte2, HwStorPortProhibitedDDIs

See also