Difference between revisions of "LKM"
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Linux kernel modules are written in C and compiled from one or more source files into a kernel object (.ko) file. In order to write an LKM, you will need a strong grasp of the fundamentals of [[C|C programming]] and at least a basic understanding of the way linux manages files, processes and devices. | Linux kernel modules are written in C and compiled from one or more source files into a kernel object (.ko) file. In order to write an LKM, you will need a strong grasp of the fundamentals of [[C|C programming]] and at least a basic understanding of the way linux manages files, processes and devices. | ||
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= Creating character devices = | = Creating character devices = | ||
Revision as of 21:33, 21 June 2016
LKM stands for "Linux Kernel Module" or "Loadable Kernel Module". As the name implies, it is a way to allow code to interact directly with the kernel and extend its functionality. The ability to insert modular components into the kernel allows it to remain relatively lightweight, as it does not need to include every driver ever created. The ability to load modules on-the-fly also saves us from having to recompile every time a change needs to be made.
It goes without saying that you need root to modify the kernel. With this restriction in mind, however, LKMs can be very powerful if used correctly, since the kernel operates under significantly elevated privileges compared to userland. In particular, the functionality provided by extending the kernel can be used to great effect in the development of Rootkits.
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LKMs interact with your system on the kernel level, executing with the highest possible level of privilege. A poorly-designed kernel module may make your OS unstable, corrupt your filesystem and even brick your computer. You have been warned. |
Contents
You can see a list of currently loaded kernel modules in two ways:
$ lsmod $ cat /proc/modules |
You can (as root) add new modules to your kernel with the insmod and rmmod commands:
$ insmod modname.ko $ rmmod modname |
These two utilities provide a simple, clean way to insert or remove modules from the kernel. If you need more advanced control over the insertion, removal and alteration of modules in the kernel, use the more fully-featured modprobe utility instead.
Writing a basic LKM
Linux kernel modules are written in C and compiled from one or more source files into a kernel object (.ko) file. In order to write an LKM, you will need a strong grasp of the fundamentals of C programming and at least a basic understanding of the way linux manages files, processes and devices.
Differences from normal C programming
Creating character devices
Device operations
Hooking system calls
See also
The Linux Kernel Module Programming Guide- an outdated but solid tutorial covering many of the concepts that will help you to understand the linux kernel.
