io(4)
NAME
io - I/O privilege file
SYNOPSIS
device io
DESCRIPTION
- The special file /dev/io is a controlled security hole that
- allows a process to gain I/O privileges (which are normally reserved for
- kernelinternal code). Any process that holds a file descriptor on
- /dev/io open
will get its IOPL bits in the flag register set, thus allow - ing it to perform direct I/O operations. This can be useful in order to
- write userland programs that handle some hardware directly. Note that
- even readonly access will grant the full I/O privileges.
- In addition to any file access permissions on /dev/io, the
- kernel
enforces that only the super-user may open this device.
FILES
/dev/io
SEE ALSO
i386_get_ioperm(2), i386_set_ioperm(2), mem(4)
HISTORY
- The io file appeared in FreeBSD 1.0.
- BSD October 3, 2004