XF86(4)                   OpenBSD Programmer's Manual                  XF86(4)

NAME
     xf86 - X Window System aperture driver

SYNOPSIS
     option APERTURE

DESCRIPTION
     On the alpha, amd64, i386, macppc, and sparc64 architectures, the
     /dev/xf86 driver provides access to the memory and I/O ports of a VGA
     board and to the PCI configuration registers for use by the X servers
     when running with a kernel security level greater than 0.

     The X servers require the use of this driver for isa(4) or pci(4) video
     cards on alpha, amd64, i386, macppc, and sparc64.

ACCESS CONTROL
     Access to the /dev/xf86 device is allowed when the sysctl(8) variable
     machdep.allowaperture is greater than or equal to 1.  This variable
     (which has a default value of 0) can only be raised when the security
     level is less than or equal to 0, so it should be set in
     /etc/sysctl.conf.  The possible values for machdep.allowaperture are:

     0       the aperture driver is disabled.  Opening it returns EPERM.

     1       the aperture driver allows access to standard VGA framebuffer and
             BIOS.  Access to pci(4) configuration registers is also allowed.

     2       in addition to allowing access to pci(4) configuration registers,
             the aperture driver allows access to the whole first megabyte of
             physical memory, permitting use of the int10 emulation in X.Org
             6.8 and later.  Note that this can cause some security problems,
             since the process that has access to the aperture driver can also
             access part of the kernel memory.  This mode is not supported on
             alpha or sparc64.

SEE ALSO
     Xorg(1), options(4), pci(4), sysctl.conf(5), securelevel(7), config(8),
     sysctl(8)

HISTORY
     /dev/xf86 was integrated as an in-kernel device on OpenBSD 2.3.  It is
     required in order to allow access to I/O ports for all X servers since
     OpenBSD 2.4.

AUTHORS
     The aperture driver was written by Matthieu Herrb.

BUGS
     This driver allows access to all addresses above physmem.  It should be
     restricted to the actual address range of the video memory.

OpenBSD 4.7                    November 1, 2008                              1
