Extension Security

im writing an extension to provide shared memory and memory mapped file support to Windows. the latter, however raises the possibility for abuse. how can i, in an extension, ensure that access is limited to files under the user's virtual directory root ? id hate to have someone mapping to \IO.SYS and truncation to zero bytes (even if Windows is smart enough to intercept) -- _____________________________________ "Fried Ice-Cream is a reality !" - George Clinton