ZwQueryKey function (wdm.h)

Article
01/13/2023

The ZwQueryKey routine provides information about the class of a registry key, and the number and sizes of its subkeys.

Syntax

NTSYSAPI NTSTATUS ZwQueryKey(
  [in]            HANDLE                KeyHandle,
  [in]            KEY_INFORMATION_CLASS KeyInformationClass,
  [out, optional] PVOID                 KeyInformation,
  [in]            ULONG                 Length,
  [out]           PULONG                ResultLength
);

Parameters

[in] KeyHandle

Handle to the registry key to obtain information about. This handle is created by a successful call to ZwCreateKey or ZwOpenKey.

[in] KeyInformationClass

Specifies a KEY_INFORMATION_CLASS value that determines the type of information returned in the KeyInformation buffer.

[out, optional] KeyInformation

Pointer to a caller-allocated buffer that receives the requested information.

[in] Length

Specifies the size, in bytes, of the KeyInformation buffer.

[out] ResultLength

Pointer to a variable that receives the size, in bytes, of the requested key information. If ZwQueryKey returns STATUS_SUCCESS, the variable contains the amount of data returned. If ZwQueryKey returns STATUS_BUFFER_OVERFLOW or STATUS_BUFFER_TOO_SMALL, you can use the value of the variable to determine the required buffer size.

Return value

ZwQueryKey returns STATUS_SUCCESS on success, or the appropriate error code on failure. Possible error code values include:

Return code	Description
STATUS_BUFFER_OVERFLOW	The buffer supplied is too small, and only partial data has been written to the buffer. *ResultLength is set to the minimum size required to hold the requested information.
STATUS_BUFFER_TOO_SMALL	The buffer supplied is too small, and no data has been written to the buffer. *ResultLength is set to the minimum size required to hold the requested information.
STATUS_INVALID_PARAMETER	The KeyInformationClass parameter is not a valid KEY_INFORMATION_CLASS value.

Remarks

The KeyHandle passed to ZwQueryKey must have been opened with KEY_QUERY_VALUE access. This is accomplished by passing KEY_QUERY_VALUE, KEY_READ, or KEY_ALL_ACCESS as the DesiredAccess parameter to ZwCreateKey or ZwOpenKey.

If KeyInformationClass is KeyNameInformation or KeyHandleTagsInformation, the KEY_QUERY_VALUE requirement does not apply.

ZwQueryKey can be used to obtain information that you can use to allocate buffers to hold registry data, such as the maximum size of a key's value entries or subkey names, or the number of subkeys. For example, you can call ZwQueryKey, use the returned information to allocate a buffer for a subkey, call ZwEnumerateKey to get the name of the subkey, and pass that name to an RtlXxxRegistry routine.

For more information about working with registry keys, see Using the Registry in a Driver.

If the call to this function occurs in user mode, you should use the name "NtQueryKey" instead of "ZwQueryKey".

For calls from kernel-mode drivers, the NtXxx and ZwXxx versions of a Windows Native System Services routine can behave differently in the way that they handle and interpret input parameters. For more information about the relationship between the NtXxx and ZwXxx versions of a routine, see Using Nt and Zw Versions of the Native System Services Routines.

Requirements

Requirement	Value
Target Platform	Universal
Header	wdm.h (include Wdm.h, Ntddk.h, Ntifs.h)
Library	NtosKrnl.lib
DLL	NtosKrnl.exe
IRQL	PASSIVE_LEVEL
DDI compliance rules	HwStorPortProhibitedDDIs(storport), IrqlZwPassive(wdm), PowerIrpDDis(wdm), ZwRegistryCreate(storport), ZwRegistryCreate(storport), ZwRegistryCreate(wdm), ZwRegistryOpen(storport), ZwRegistryOpen(storport), ZwRegistryOpen(wdm)