Determining Whether the Operating System Is Running in Safe Mode

This topic describes how a device driver can determine whether the operating system that it is running on was started in Safe Mode. This topic also describes how to prevent a driver from operating in Safe Mode.

The Microsoft Windows operating system kernel exports a pointer named InitSafeBootMode. InitSafeBootMode points to a ULONG variable that contains the Safe Mode settings that are currently in effect. A device driver can examine these settings to determine whether the operating system is running in Safe Mode.

The following table lists the modes for values of the InitSafeBootMode variable.

Value	Mode
0	The operating system is not in Safe Mode.
1	SAFEBOOT_MINIMAL
2	SAFEBOOT_NETWORK
3*	SAFEBOOT_DSREPAIR

Note  * The value 3 applies to Windows domain controllers only.

To use the InitSafeBootMode variable, you must declare it in your driver, as the following code example shows.

extern PULONG InitSafeBootMode;

After you declare InitSafeBootMode, you can use the following code example to determine whether the operating system is running in Safe Mode.

if (*InitSafeBootMode > 0) {
    // The operating system is in Safe Mode.
    // Take appropriate action.
    //
}

To prevent a driver from operating in Safe Mode, use the technique in the following list that matches your driver type:

• Function drivers

  If your function driver has a service start type of SERVICE_BOOT_START, check the value of InitSafeBootMode in the function driver's AddDevice routine. If the system is in Safe Mode, return a failure status.

  Note   You must never return failure from the DriverEntry routine.

• Filter drivers

  If your filter driver starts during system startup, check the value of InitSafeBootMode in the filter driver's AddDevice routine. If the operating system is in Safe Mode, do the following:

  1. Do not attach the filter device object to the device stack.
  2. Return success from the filter driver's AddDevice routine.

• Other drivers

  For drivers other than function or filter drivers, check the value of InitSafeBootMode in the driver's DriverEntry routine. If the operating system is in Safe Mode, return a failure status.