Synchronizing Kernel with User mode

Plese help!

I’m making a File filter driver to check for viruses on files. But the
functions to check the files are in a DLL. I can’t call the DLL from
Kernel mode. So I synchronize the driver with an application, when a file
is open the driver comunicates with the application via an event. But I
want the driver to wait for application’s answer to deny or permit file
access, I’m using an Event here too but it’s not working. What do I have
to do?
Thanks in advance