# mkkmod

Pack a binary into a self-contained, self-executing Linux kernel module using the usermode driver infrastructure.

Adapted from [an example by Richard Weinberger](https://sigma-star.at/blog/2023/07/embedded-go-prog/).

License: GPL-2.0-only

## Usage

- Build sample binary to embed: `./build-sample.sh`
- Build kernel module: `./build-module.sh ./sample`
    - To build for the non-running kernel: `KERN_VER=6.9.8-200.fc40.x86_64 ./build-module.sh ./sample`
- Run: `insmod ./eprog.ko`

## Requirements

- The generated module must have a GPL-compatible license to use `EXPORT_SYMBOL_GPL` functions.
- Requires kernel 5.9 or later.
- Kernel version needs to export the umd functionality.

If you get errors of the form `modpost: "fork_usermode_driver" [...] undefined!` check if your kernel exposes the functions in `/usr/src/linux-headers-$(uname -r)/Module.symvers` and/or that the functions are present in `/proc/kallsyms`.

Compatibility tests:

|Distro|Kernel version|Notes
|---|---|---
|Debian 12|6.1.0-22|❌ Missing symbols
|Fedora 40|6.9.8-200|✅ Features are present

## Reference

- https://sigma-star.at/blog/2023/07/embedded-go-prog/
- https://git.kernel.org/pub/scm/linux/kernel/git/rw/misc.git/tree/drivers/misc/embedded_prog?h=embedded_go_prog
- https://medium.com/@adityapatnaik27/linux-kernel-module-in-tree-vs-out-of-tree-build-77596fc35891
- https://github.com/torvalds/linux/blob/master/include/linux/usermode_driver.h
- https://github.com/torvalds/linux/blob/master/kernel/usermode_driver.c