168 lines
6.0 KiB
Groff
168 lines
6.0 KiB
Groff
.\" $NetBSD: lkm.4,v 1.18 2003/02/14 15:20:19 grant Exp $
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.\"
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.\" Copyright (c) 1993 Christopher G. Demetriou
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.\" All rights reserved.
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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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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed for the
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.\" NetBSD Project. See http://www.NetBSD.org/ for
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.\" information about NetBSD.
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.\" 4. The name of the author may not be used to endorse or promote products
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.\" derived from this software without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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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.\" <<Id: LICENSE,v 1.2 2000/06/14 15:57:33 cgd Exp>>
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.\"
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.Dd September 4, 1993
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.Dt LKM 4
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.Os
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.Sh NAME
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.Nm lkm
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.Nd Loadable Kernel Modules interface
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.Sh SYNOPSIS
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.Cd "options LKM"
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.Sh DESCRIPTION
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Loadable kernel modules allow the system administrator to
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dynamically add and remove functionality from a running system.
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This ability also helps software developers to develop
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new parts of the kernel without constantly rebooting to
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test their changes.
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.Pp
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Various types of modules can be loaded into the system.
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There are several defined module types, listed below, which can
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be added to the system in a predefined way. In addition, there
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is a generic type, for which the module itself handles loading and
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unloading.
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.Pp
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The
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.Nm
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interface is used by performing
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.Xr ioctl 2
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calls on the
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.Pa /dev/lkm
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device. Normally all operations involving
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Loadable Kernel Modules are handled by the
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.Xr modload 8 ,
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.Xr modunload 8 ,
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and
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.Xr modstat 8
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programs. Users should never have to interact with
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.Pa /dev/lkm
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directly.
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.Sh MODULE TYPES
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.Ss System Call modules
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System calls may be replaced by loading
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new ones via the
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.Nm
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interface. All system calls may be
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replaced, but special care should
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be taken with the
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.Xr ioctl 2
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system call, as it is used to load and
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unload modules.
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.Pp
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When a system call module is unloaded,
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the system call which
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was replaced by the loadable module
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is returned to its rightful place
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in the system call table by LKM code.
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.Ss Virtual File System modules
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Virtual file systems may be added via the
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.Nm
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interface.
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.Ss Device Driver modules
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New block and character device
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drivers may be loaded into the system with
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.Li "options LKM" .
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A problem with loading a device driver is that the driver's device
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nodes must be exist for the devices to be accessed. They are
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usually created by instructing
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.Xr modload 8
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to run an appropriate program when the driver has been successfully loaded.
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.Ss Emulation modules
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Emulation modules allow to load an emulation support for foreign
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operating systems.
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.Ss Execution Interpreters
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Execution interpreters allow to load support for execution of new type
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of binaries, not normally supported by kernel. This also allows to load
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support for executing foreign system binaries.
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Execution Interpreters normally depend on
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Emulation modules, in that appropriate Emulation module has to
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be loaded before Execution Interpreter can be.
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.Ss Miscellaneous modules
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Miscellaneous modules are modules for which there are not currently
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well-defined or well-used interfaces for extension.
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They are provided for extension, and the user is expected to
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write their own loader to handle the kernel pointer/table
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manipulation to "wire in" their loaded module (and "unwire"
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it on uload).
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An example of a "miscellaneous module" might be a loader for
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card-specific VGA drivers or alternate terminal emulations in
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an appropriately layered console driver.
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.Sh NOTES
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.Ss Security considerations
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Loaded kernel module can do anything with kernel structures. There is
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no memory protection between module and rest of kernel. Hence, potential
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attacker controlling
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.Pa /dev/lkm
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can do anything they want with the system.
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.Pp
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To avoid associated security risk, new LKMs cannot be loaded on
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.Pa securelevel
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higher than zero.
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.Ss Module might crash system
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Loading and using a buggy module is likely to crash operating system -
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since the module becomes part of kernel, a code error is much more
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fatal than for userland programs. If you are doing kernel development,
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this would hopefully end up happening
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less frequently than changing, recompiling, installing, and
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rebooting would normally occur. This should speed development
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considerably for a lot of the in-kernel work that is currently
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taking place.
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.Sh FILES
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.Bl -tag -width /usr/include/sys/lkm.h -compact
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.It Pa /dev/lkm
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.Nm
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interface device
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.It Pa /usr/include/sys/lkm.h
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file containing definitions of module types
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.It Pa lkm/*
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subdirectory
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.Pa lkm
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within kernel source tree contains many LKMs which are suitable as a base
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for new ones
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.El
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.Sh SEE ALSO
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.Xr modload 8 ,
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.Xr modstat 8 ,
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.Xr modunload 8
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.Sh HISTORY
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The
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.Nm
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facility was designed to be similar in functionality
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to the loadable kernel modules facility provided by
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.Tn "SunOS 4.1.3" .
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.Sh AUTHORS
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.Bl -tag
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Terrence R. Lambert, terry@cs.weber.edu
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.El
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