131 lines
3.6 KiB
Groff
131 lines
3.6 KiB
Groff
.\"
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.\" Copyright (c) 1996 Joerg Wunsch
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.\"
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.\" All rights reserved.
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.\"
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.\" This program is free software.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd June 1, 2010
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.Dt IO 4
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.Os
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.Sh NAME
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.Nm io
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.Nd I/O privilege file
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.Sh SYNOPSIS
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.Cd "device io"
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.Pp
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.In sys/types.h
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.In sys/ioctl.h
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.In dev/io/iodev.h
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.In machine/iodev.h
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.Bd -literal
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struct iodev_pio_req {
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u_int access;
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u_int port;
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u_int width;
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u_int val;
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};
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.Ed
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.Sh DESCRIPTION
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The special file
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.Pa /dev/io
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is a controlled security hole that allows a process to gain I/O
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privileges
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(which are normally reserved for kernel-internal code).
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This can be useful in order to write userland
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programs that handle some hardware directly.
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.Pp
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The usual operations on the device are to open it via the
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.Xr open 2
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interface and to send I/O requests to the file descriptor using the
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.Xr ioctl 2
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syscall.
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.Pp
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The
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.Xr ioctl 2
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requests available for
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.Pa /dev/io
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are mostly platform dependent, but there are also some in common between
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all of them.
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The
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.Dv IODEV_PIO
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is used by all the architectures in order to request that an I/O operation
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be performed.
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It takes a 'struct iodev_pio_req' argument that must be previously setup.
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.Pp
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The
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.Fa access
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member specifies the type of operation requested.
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It may be:
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.Bl -tag -width IODEV_PIO_WRITE
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.It Dv IODEV_PIO_READ
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The operation is an "in" type.
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A value will be read from the specified port
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(retrieved from the
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.Fa port
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member) and the result will be stored in the
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.Fa val
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member.
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.It Dv IODEV_PIO_WRITE
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The operation is a "out" type.
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The value will be fetched from the
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.Fa val
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member and will be written out to the specified port (defined as the
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.Fa port
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member).
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.El
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.Pp
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Finally, the
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.Fa width
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member specifies the size of the operand to be read/written, expressed
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in bytes.
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.Pp
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In addition to any file access permissions on
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.Pa /dev/io ,
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the kernel enforces that only the super-user may open this device.
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.Sh LEGACY
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The
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.Pa /dev/io
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interface used to be very i386 specific and worked differently.
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The initial implementation simply raised the
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.Em IOPL
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of the current thread when
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.Xr open 2
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was called on the device.
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This behaviour is retained in the current implementation as legacy
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support for both i386 and amd64 architectures.
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.Sh SEE ALSO
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.Xr close 2 ,
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.Xr i386_get_ioperm 2 ,
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.Xr i386_set_ioperm 2 ,
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.Xr ioctl 2 ,
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.Xr open 2 ,
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.Xr mem 4
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.Sh HISTORY
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The
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.Nm
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file appeared in
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.Fx 1.0 .
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