1996-01-01 11:01:13 +00:00
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.\"
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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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1997-01-14 07:20:47 +00:00
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.\" $FreeBSD$
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1996-01-01 11:01:13 +00:00
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.\"
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.Dd Jan 1, 1996
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.Dt IO 4 i386
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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 DESCRIPTION
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The special file
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.Nm /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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.Pq which are normally reserved for kernel-internal code .
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Any process that holds a file descriptor on
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.Nm /dev/io
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open will get its
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.Em IOPL
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bits in the flag register set, thus allowing it to perform direct
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I/O operations. 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 entire access control is handled by the file access permissions
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of
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.Nm /dev/io ,
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so care should be taken in granting rights for this device. Note
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that even read/only access will grant the full I/O privileges.
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.Sh FILES
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.Bl -tag -width Pa -compact
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.It Pa /dev/io
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.El
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.Sh SEE ALSO
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.Xr mem 4
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.Sh HISTORY
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The
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.Nm io
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file appeared in
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FreeBSD 1.0.
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