X Window System aperture driver
On the alpha, amd64, i386, macppc, and sparc64 architectures, the
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
pci(4) video cards on
i386, macppc, and
Access to the /dev/xf86 device is allowed when the
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
/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.
The aperture driver was written by Matthieu Herrb.
This driver allows access to all addresses above physmem.
It should be restricted to the actual address range of the video memory.
- the aperture driver is disabled. Opening it returns
- the aperture driver allows access to standard VGA framebuffer and BIOS.
Access to pci(4) configuration
registers is also allowed.
- in addition to allowing access to
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.
- the aperture driver allows multiple processes to concurrently access
pci(4) configuration registers
and the whole first megabyte of physical memory.