OpenBSD-4.6/share/man/man4/xf86.4

.\"	$OpenBSD: xf86.4,v 1.17 2008/11/01 22:36:05 jmc Exp $
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.\" Copyright (c) 1998 Matthieu Herrb
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.Dd $Mdocdate: November 1 2008 $
.Dt XF86 4
.Os
.Sh NAME
.Nm xf86
.Nd X Window System aperture driver
.Sh SYNOPSIS
.Cd "option APERTURE"
.Sh DESCRIPTION
On
the alpha, amd64, i386, macppc, and sparc64 architectures,
the
.Pa /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.
.Pp
The X servers require the use of this driver for
.Xr isa 4
or
.Xr pci 4
video cards on
.Ar alpha ,
.Ar amd64 ,
.Ar i386 ,
.Ar macppc ,
and
.Ar sparc64 .
.Sh ACCESS CONTROL
Access to the
.Pa /dev/xf86
device is allowed when the
.Xr sysctl 8
variable
.Va 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
.Pa /etc/sysctl.conf .
The possible values for
.Va machdep.allowaperture
are:
.Bl -tag -width Ds
.It 0
the aperture driver is disabled.
Opening it returns
.Dv EPERM .
.It 1
the aperture driver allows access to standard VGA framebuffer and BIOS.
Access to
.Xr pci 4
configuration registers is also allowed.
.It 2
in addition to allowing access to
.Xr 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.
.El
.Sh SEE ALSO
.Xr Xorg 1 ,
.Xr options 4 ,
.Xr pci 4 ,
.Xr sysctl.conf 5 ,
.Xr securelevel 7 ,
.Xr config 8 ,
.Xr sysctl 8
.Sh HISTORY
.Pa /dev/xf86
was integrated as an in-kernel device on
.Ox 2.3 .
It is required in order to allow access to I/O ports for all X servers since
.Ox 2.4 .
.Sh AUTHORS
The aperture driver was written by Matthieu Herrb.
.Sh BUGS
This driver allows access to all addresses above
.Va physmem .
It should be restricted to the actual address range of the video
memory.