C Loadable Kernel Module Template

A simple template to get started with writing a C LKM. Supports hot-reloading and a qemu VM.

Setup

The default paths for scripts in this template are:

• KERNEL: ../linux
• BUSYBOX: ../busybox

So, you should have a KERNEL dir with a rust enabled kernel already built and a BUSYBOX dir with a ALREADY built and configured busybox.

For automating the setup of the environment, run the setup script:

./scripts/setup

Refer to the script for more info.

Building

I wrote a simple wrapper script for the make command for compiling this LKM. It is located in the scripts directory. You can use it like this:

./scripts/build
./scripts/build -t help
./scripts/build -t clean
./scripts/build -k /path/to/linux -b /path/to/busybox
# ... and so on

Please refer to the kernel docs for more info on basic Kbuild usage.

Running

First, build the LKM. Then, you can use the run script to run it in a qemu VM:

# Default locations: KERNEL=../linux, BUSYBOX=../busybox
./scripts/run
# Custom locations
./scripts/run -k /path/to/linux -b /path/to/busybox

This script will simply copy all the .ko files to the initramfs and run the VM.

Hot-reloading

You can use the hot-reload script to hot-reload the LKM in the running VM:

./scripts/hot-reload

It uses the entr utility to watch for changes in the source code and then running ./scripts/build to build the LKM and ./scripts/run to run it in the VM. Please refer to the script for more info.

References

• Linux Kernel Docs
• Linux Kernel Module Programming Guide
• Linux Kernel Development
• Linux Device Drivers