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ProbeForWrite routine

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.

Syntax


VOID ProbeForWrite(
  _Inout_  PVOID Address,
  _In_     SIZE_T Length,
  _In_     ULONG Alignment
);

Parameters

Address [in, out]

Specifies the beginning of the user-mode buffer.

Length [in]

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

Alignment [in]

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

Return value

None

Remarks

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.

Requirements

Version

Available starting with Windows 2000.

Header

Wdm.h (include Wdm.h, Ntddk.h, or Ntifs.h)

Library

Ntoskrnl.lib

IRQL

<= APC_LEVEL

DDI compliance rules

IrqlExApcLte2, HwStorPortProhibitedDDIs

See also

ProbeForRead

 

 

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