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lunatik

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Lunatik is a framework for scripting the Linux kernel with Lua.

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# Lunatik

Lunatik is a framework for scripting the Linux kernel with [Lua](https://www.lua.org/).
It is composed by the Lua interpreter modified to run in the kernel;
a [device driver](driver.lua) (written in Lua =)) and a [command line tool](bin/lunatik)
to load and run scripts and manage runtime environments from the user space;
a [C API](doc/capi.md) to load and run scripts and manage runtime environments from the kernel;
and [Lua APIs](#lunatik-lua-apis) for binding kernel facilities to Lua scripts.

> Note: Lunatik supports Linux Kernel versions 5.15 and later

Feel free to join us on [Matrix](https://matrix.to/#/#lunatik:matrix.org).

Here is an example of a character device driver written in Lua using Lunatik
to generate random ASCII printable characters:
```Lua
-- /lib/modules/lua/passwd.lua
--
-- implements /dev/passwd for generate passwords
-- usage: $ sudo lunatik run passwd
--        $ head -c <width> /dev/passwd

local device = require("device")
local linux  = require("linux")
local stat   = require("linux.stat")

local driver = {name = "passwd", mode = stat.IRUGO}

function driver:read() -- read(2) callback
	-- generate random ASCII printable characters
	return string.char(linux.random(32, 126))
end

-- creates a new character device
device.new(driver)
```

## Setup

Install dependencies (here for Debian/Ubuntu, to be adapted to one's distribution):

```sh
sudo apt install git build-essential lua5.4 dwarves clang llvm libelf-dev linux-headers-$(uname -r) linux-tools-common linux-tools-$(uname -r) pkg-config libpcap-dev m4
```

Install dependencies (here for Arch Linux):

```sh
sudo pacman -S git lua clang llvm m4 libpcap pkg-config build2 linux-tools linux-headers
```

The `lua-readline` package is optional. When installed, the REPL gains line editing and command history:

```sh
sudo apt install lua-readline  # Debian/Ubuntu
```

Compile and install `lunatik`:

```sh
LUNATIK_DIR=~/lunatik  # to be adapted
mkdir "${LUNATIK_DIR}" ; cd "${LUNATIK_DIR}"
git clone --depth 1 --recurse-submodules https://github.com/luainkernel/lunatik.git
cd lunatik
make
sudo make install
```

Once done, the `debian_kernel_postinst_lunatik.sh` script from tools/ may be copied into
`/etc/kernel/postinst.d/`: this ensures `lunatik` (and also the `xdp` needed libs) will get
compiled on kernel upgrade.

### OpenWRT

Install Lunatik from our [package feed](https://github.com/luainkernel/openwrt_feed/tree/openwrt-23.05).

## Usage

```
sudo lunatik # execute Lunatik REPL
Lunatik 4.4  Copyright (C) 2023-2026 Ring Zero Desenvolvimento de Software LTDA.
> return 42 -- execute this line in the kernel
42
```

### lunatik

* `load`: load Lunatik kernel modules
* `unload`: unload Lunatik kernel modules
* `reload`: reload Lunatik kernel modules
* `status`: show which Lunatik kernel modules are currently loaded
* `test [suite]`: run installed test suites (see [Testing](#testing))
* `list`: show which runtime environments are currently running
* `run [softirq|hardirq]`: create a new runtime environment to run the script `/lib/modules/lua/<script>.lua`; pass `softirq` for hooks that fire in softirq context (netfilter, XDP), or `hardirq` for hooks that fire in hardirq context (kprobes); optionally pass `percpu` to create one runtime instance per CPU id, for scripts dispatched by the eBPF bindings, which resolve to the instance of the CPU the hook runs on. The script runs once per instance and can read its id with `lunatik.cpu()`; netfilter hooks and constructors whose registration is global fail at load in a percpu instance
* `spawn`: create a new runtime environment and spawn a thread to run the script `/lib/modules/lua/<script>.lua`
* `stop`: stop the runtime environment created to run the script `<script>`
* `default`: start a _REPL (Read–Eval–Print Loop)_

### Testing

Install and run the test suites:

```sh
sudo make install
sudo lunatik test           # run all suites
sudo lunatik test thread    # run a specific suite (bpf, crypto, io, monitor,
                            # netlink, notifier, probe, rcu, runtime, set, skb,
                            # socket, struct, thread, xdp)
```

`lunatik test` reloads the modules before the run and unloads them
afterwards, so each invocation exercises the currently-installed kernel
code. See [tests/README.md](tests/README.md) for the full list of suites
and individual tests.

## Lua Version

Lunatik 4.4 is based on
[Lua 5.5 adapted](https://github.com/luainkernel/lua)
to run in the kernel.

### Floating-point numbers

Lunatik **does not** support floating-point arithmetic,
thus it **does not** support `__div` nor `__pow`
[metamethods](https://www.lua.org/manual/5.5/manual.html#2.4)
and the type _number_ has only the subtype _integer_.

### Lua API

Lunatik **does not** support the [os](https://www.lua.org/manual/5.5/manual.html#6.9) library,
floating-point arithmetic (`__div`, `__pow`), or `debug.debug`.
The `math` library is present but all floating-point functions are absent —
only integer operations are supported.

The [io](https://www.lua.org/manual/5.5/manual.html#6.8) library is supported with the
following limitations: there are no default streams (`io.stdin`, `io.stdout`, `io.stderr`),
no default input/output (`io.read`, `io.write`, `io.input`, `io.output`), no process pipes
(`io.popen`), no temporary files (`io.tmpfile`), and no buffering control (`file:setvbuf`).
The available functions are `io.open`, `io.lines`, `io.type`, and the file handle methods
`read`, `write`, `lines`, `flush`, `seek`, and `close`.
On failure, error messages always read `"I/O error"` regardless of the underlying errno.

Lunatik **modifies** the following identifiers:
* [\_VERSION](https://www.lua.org/manual/5.5/manual.html#pdf-_VERSION): is defined as `"Lua 5.5-kernel"`.
* [collectgarbage("count")](https://www.lua.org/manual/5.5/manual.html#pdf-collectgarbage): returns the total memory in use by Lua in **bytes**, instead of _Kbytes_.
* [package.path](https://www.lua.org/manual/5.5/manual.html#pdf-package.path): is defined as `"/lib/modules/lua/?.lua;/lib/modules/lua/?/init.lua"`.
* [require](https://www.lua.org/manual/5.5/manual.html#pdf-require): only supports built-in or already linked C modules, that is, Lunatik **cannot** load kernel modules dynamically.

## Lunatik Lua APIs

Lua APIs are documented with [LDoc](https://stevedonovan.github.io/ldoc/) and can be browsed at
[luainkernel.github.io/lunatik](https://luainkernel.github.io/lunatik/).

The table below lists the available kernel Lua modules:

| Module | Description |
|--------|-------------|
| `linux` | Kernel utilities: `schedule`, `time`, `random`, `stat` flags |
| `thread` | Kernel threads: spawn, stop, `shouldstop` |
| `socket` | Kernel sockets: TCP, UDP, AF\_PACKET, AF\_UNIX |
| `netlink` | Netlink namespace: rtnetlink and generic-netlink sessions, softirq-safe channel |
| `data` | Raw memory buffer for binary data read/write |
| `device` | Character device drivers |
| `rcu` | RCU-protected shared hash table |
| `set` | Compact immutable string set: exact membership, plus a suffix-matched labeled flavor |
| `netfilter` | Netfilter hooks: register packet processing callbacks |
| `skb` | Socket buffer (`sk_buff`): inspect and modify packets |
| `xdp` | XDP (eXpress Data Path) hooks |
| `bpf` | Pinned eBPF map access (hash, array, LRU hash, queue, stack) |
| `crypto` | Kernel crypto API: hash, cipher, AEAD, RNG, compression |
| `hid` | HID device drivers |
| `probe` | Kernel probes (kprobe / tracepoint) |
| `fifo` | Kernel FIFO queues |
| `signal` | POSIX signal management |
| `byteorder` | Network byte order conversions |
| `darken` | AES-256-CTR encrypted script execution |
| `lighten` | Lua interface for running encrypted scripts via `darken` |
| `notifier` | Kernel notifier chain registration |
| `lunatik.runner` | Run, spawn, and stop scripts from within Lua |
| `net` | Networking helpers |
| `mailbox` | Asynchronous inter-runtime messaging |

## Lunatik C API

The [C API](doc/capi.md) allows kernel modules to create and manage Lunatik runtime
environments, define new object classes, and expose kernel facilities to Lua scripts.
See [doc/capi.md](doc/capi.md) for the full reference.

# Examples

### spyglass

[spyglass](examples/spyglass)
is a kernel script that implements a _keylogger_ inspired by the
[spy](https://github.com/jarun/spy) kernel module.
This kernel script logs the _keysym_ of the pressed keys in a device (`/dev/spyglass`).
If the _keysym_ is a printable character, `spyglass` logs the _keysym_ itself;
otherwise, it logs a mnemonic of the ASCII code, (e.g., `<del>` stands for `127`).

The keyboard notifier fires in hardirq context, whereas the device requires
process context; spyglass splits across two runtimes
([`device.lua`](examples/spyglass/device.lua) in process and
[`notifier.lua`](examples/spyglass/notifier.lua) in hardirq) sharing captured
chars via a [`fifo`](lib/luafifo.c).

#### Usage

```
sudo make examples_install                 # installs examples
sudo lunatik run examples/spyglass/device  # runs spyglass
sudo tail -f /dev/spyglass                 # prints the key log
```

### keylocker

[keylocker](examples/keylocker.lua)
is a kernel script that implements
[Konami Code](https://en.wikipedia.org/wiki/Konami_Code)
for locking and unlocking the console keyboard.
When the user types `↑ ↑ ↓ ↓ ← → ← → LCTRL LALT`,
the keyboard will be _locked_; that is, the system will stop processing any key pressed
until the user types the same key sequence again.

The keyboard notifier fires in hardirq context, so keylocker must run in a
`hardirq` runtime (passed as the third argument to `lunatik run`).

#### Usage

```
sudo make examples_install                         # installs examples
sudo lunatik run examples/keylocker hardirq        # runs keylocker
<↑> <↑> <↓> <↓> <←> <→> <←> <→> <LCTRL> <LALT>     # locks keyboard
<↑> <↑> <↓> <↓> <←> <→> <←> <→> <LCTRL> <LALT>     # unlocks keyboard
```

### tap

[tap](examples/tap.lua)
is a kernel script that implements a _sniffer_ using `AF_PACKET` socket.
It prints destination and source MAC addresses followed by Ethernet type and the frame size.

#### Usage

```
sudo make examples_install    # installs examples
sudo lunatik run examples/tap # runs tap
cat /dev/tap
```

### shared

[shared](examples/shared.lua)
is a kernel script that implements an in-memory key-value store using
[rcu](https://github.com/luainkernel/lunatik#rcu),
[data](https://github.com/luainkernel/lunatik#data),
[socket](https://github.com/luainkernel/lunatik#socket) and
[thread](https://github.com/luainkernel/lunatik#thread).

#### Usage

```
sudo make examples_install         # installs examples
sudo lunatik spawn examples/shared # spawns shared
nc 127.0.0.1 90                    # connects to shared
foo=bar                            # assigns "bar" to foo
foo                                # retrieves foo
bar
^C                                 # finishes the connection
```

### echod

[echod](examples/echod)
is an echo server implemented as kernel scripts.

#### Usage

```
sudo make examples_install               # installs examples
sudo lunatik spawn examples/echod/daemon # runs echod
nc 127.0.0.1 1337
hello kernel!
hello kernel!
```

### systrack

[systrack](examples/systrack/probe.lua)
is a kernel script that uses kprobes to count every system call on the
running architecture. [systrack/device](examples/systrack/device.lua)
exposes the live counters as a character device readable with `cat`.

The device runtime creates the probe runtime via `runner.run`, passing the
RCU counter table via `runtime:resume()`. Stopping the device runtime also
stops the probe runtime.

#### Usage

```
sudo make examples_install                            # installs examples
sudo lunatik run examples/systrack/device             # starts device and probe runtimes
cat /dev/systrack
close: 473
openat: 515
read: 1066
write: 438
sudo lunatik stop examples/systrack/device            # stops device and probe runtimes
```

### ifquarantine

[ifquarantine](examples/ifquarantine) composes two notifier chains to build
an interface-level default-deny policy: every new network interface
(NETDEV_REGISTER) is automatically added to a shared RCU set whose contents
a netfilter hook uses to decide the verdict on each packet. An interface is
released from quarantine by writing `allow=<name>` to `/dev/ifquarantine`;
re-denied with `deny=<name>`; inspected with `cat /dev/ifquarantine`.

The control runtime (process context) owns `notifier.netdevice` and the
device; it spawns a child softirq runtime with the netfilter hook, sharing
the quarantine set via `rcu.table` through `runtime:resume()`. Illustrates
cross-subsystem composition between two notifier chains of different
execution contexts.

#### Usage

```
sudo make examples_install                         # installs examples
sudo lunatik run examples/ifquarantine/control     # starts control+filter
sudo cat /dev/ifquarantine                         # lists known interfaces and verdict
sudo sh -c "echo 'allow=eth0' > /dev/ifquarantine" # lift quarantine on eth0
sudo sh -c "echo 'deny=eth0'  > /dev/ifquarantine" # re-apply quarantine
sudo lunatik stop examples/ifquarantine/control    # stops both runtimes
```

Pre-existing interfaces are covered as well: `register_netdevice_notifier`
synchronously replays `NETDEV_REGISTER` (and `NETDEV_UP`) for each existing
netdev when the notifier block is registered, so they enter quarantine at
script start too.

### filter

[filter](examples/filter) is a kernel extension composed by
a XDP/eBPF program to filter HTTPS sessions and
a Lua kernel script to filter [SNI](https://datatracker.ietf.org/doc/html/rfc3546#section-3.1) TLS extension.
This kernel extension drops any HTTPS request destinated to a
[blacklisted](examples/filter/sni.lua#L35) server.

#### Usage

Usage requires `libbpf` and `bpftool` installed.

Come back to this repository, install and load the filter:

```sh
cd ${LUNATIK_DIR}/lunatik    # cf. above
sudo make btf_install        # needed to export the 'bpf_luaxdp_run' kfunc
sudo make examples_install   # installs examples
make ebpf                    # builds the XDP/eBPF program
sudo make ebpf_install       # installs the XDP/eBPF program
# Run the Lua kernel script, one runtime per CPU
sudo lunatik run examples/filter/sni softirq percpu
# Load the compiled XDP/eBPF program and attach to interface <ifname>
sudo bpftool prog load examples/filter/https.o /sys/fs/bpf/lunatik_filter type xdp
sudo bpftool net attach xdp pinned /sys/fs/bpf/lunatik_filter dev <ifname>
```

For example, testing is easy thanks to [docker](https://www.docker.com).
Assuming docker is installed and running:

- in a terminal:
```sh
sudo bpftool prog load example/filter/https.o /sys/fs/bpf/lunatik_filter type xdp
sudo bpftool net attach xdp pinned /sys/fs/bpf/lunatik_filter dev docker0
sudo journalctl -ft kernel
```
- in another one:
```sh
docker run --rm -it alpine/curl https://ebpf.io
```

The system logs (in the first terminal) should display `filter_sni: ebpf.io DROP`, and the
`docker run…` should return `curl: (35) OpenSSL SSL_connect: SSL_ERROR_SYSCALL in connection to ebpf.io:443`.

### filter in MoonScript

[This other sni filter](https://github.com/luainkernel/snihook) uses netfilter api.

### dnsblock

[dnsblock](examples/dnsblock) is a kernel script that uses the netfilter framework ([luanetfilter](https://github.com/luainkernel/lunatik#netfilter)) to filter DNS packets.
This script drops any outbound DNS packet with question matching the blacklist provided by the user. By default, it will block DNS resolutions for the domains `github.com` and `gitlab.com`.

#### Usage

```
sudo make examples_install              # installs examples
sudo lunatik run examples/dnsblock/nf_dnsblock softirq	# runs the Lua kernel script
```

### dnsdoctor

[dnsdoctor](examples/dnsdoctor) is a kernel script that uses the netfilter framework ([luanetfilter](https://github.com/luainkernel/lunatik#netfilter)) to change the DNS response
from Public IP to a Private IP if the destination IP matches the one provided by the user. For example, if the user
wants to change the DNS response from `192.168.10.1` to `10.1.2.3` for the domain `lunatik.com` if the query is being sent to `10.1.1.2` (a private client), this script can be used.

#### Usage

```
sudo make examples_install              # installs examples
examples/dnsdoctor/setup.sh             # sets up the environment

# test the setup, a response with IP 192.168.10.1 should be returned
dig lunatik.com

# run the Lua kernel script
sudo lunatik run examples/dnsdoctor/nf_dnsdoctor softirq

# test the setup, a response with IP 10.1.2.3 should be returned
dig lunatik.com

# cleanup
sudo lunatik unload
examples/dnsdoctor/cleanup.sh
```

### tcpreject

[tcpreject](examples/tcpreject) is a kernel script that uses the
netfilter framework ([luanetfilter](https://github.com/luainkernel/lunatik#netfilter))
and the socket buffer API ([luaskb](https://github.com/luainkernel/lunatik#skb))
to inject a TCP RST toward the origin of forwarded packets.

It intercepts packets marked by an `nft` rule, builds a RST+ACK by
copying the original packet, inverting IP, MAC, and port addresses,
trimming the payload, and recomputing the checksums.
It supports both IPv4 and IPv6.
By default, it rejects forwarded HTTPS (TCP/443) connections to `8.8.8.8` (IPv4)
and `2001:4860:4860::8888` (IPv6).

#### Usage

```
sudo make examples_install              # installs examples
sudo examples/tcpreject/setup.sh        # sets up namespace, nft mark rule, and loads the hook

# connection is reset immediately (IPv4)
ip netns exec tcpreject curl --connect-timeout 2 https://8.8.8.8

# connection is reset immediately (IPv6)
ip netns exec tcpreject curl --connect-timeout 2 https://[2001:4860:4860::8888]

# cleanup
sudo examples/tcpreject/cleanup.sh
```

### gesture

[gesture](examples/gesture.lua)
is a kernel script that implements a HID driver for QEMU USB Mouse (0627:0001).
It supports gestures: swiping right locks the mouse, and swiping left unlocks it.

#### Usage

1. You need to change the display protocal into `VNC` and enable USB mouse device in QEMU, the following configuration can help you disable PS2 mouse & enable USB mouse:

```
<features>
	
	<ps2 state="off"/>
	
</features>
```

2. run the gesture script:

```
sudo make examples_install 			# installs examples
sudo lunatik run examples/gesture softirq 	# runs gesture
# In QEMU window:
# Drag right to lock the mouse
# Drag left to unlock the mouse
```

### xiaomi

[xiaomi](examples/xiaomi.lua)
is a kernel script that ports the Xiaomi Silent Mouse driver to Lua using `luahid`.
It fixes the report descriptor for the device (`0x2717`:`0x5014`).

#### Usage

```
sudo make examples_install 		# installs examples
sudo lunatik run examples/xiaomi softirq 	# runs xiaomi driver
```

Then insert the Xiaomi Silent Mouse with bluetooth mode on and it should work properly.

### lldpd

[lldpd](examples/lldpd.lua) shows how to implement a simple LLDP transmitter in kernel space using Lunatik.
It periodically emits LLDP frames on a given interface using an AF_PACKET socket.

#### Usage

```
sudo make examples_install                  # installs examples

# the LLDP daemon sends frames on a single Ethernet interface
# you may use an existing interface, or create a virtual one for testing

# create a veth pair (the example uses veth0 by default)
ip link add veth0 type veth peer name veth1
ip link set veth0 up
ip link set veth1 up

sudo lunatik spawn examples/lldpd           # runs lldpd

# verify LLDP frames are being transmitted
sudo tcpdump -i veth0 -e ether proto 0x88cc -vv
```

### cpuexporter

[cpuexporter](examples/cpuexporter.lua) will gather CPU usage statistics and expose using [OpenMetrics text format](https://github.com/prometheus/OpenMetrics/blob/main/specification/OpenMetrics.md#text-format) at a UNIX socket file.

#### Usage

```shell
sudo make examples_install         	# installs examples
sudo lunatik spawn examples/cpuexporter # runs cpuexporter
sudo socat - UNIX-CONNECT:/tmp/cpuexporter.sock <<<""
# TYPE cpu_usage_system gauge
cpu_usage_system{cpu="cpu1"} 0.0000000000000000 1764094519529162
cpu_usage_system{cpu="cpu0"} 0.0000000000000000 1764094519529162
# TYPE cpu_usage_idle gauge
cpu_usage_idle{cpu="cpu1"} 100.0000000000000000 1764094519529162
cpu_usage_idle{cpu="cpu0"} 100.0000000000000000 1764094519529162
...
```

## References

### Talks and Papers
* [Scripting the Linux Routing Table with Lua](https://netdevconf.info/0x17/sessions/talk/scripting-the-linux-routing-table-with-lua.html) — Netdev 0x17 (2023)
* [Linux Network Scripting with Lua](https://legacy.netdevconf.info/0x14/session.html?talk-linux-network-scripting-with-lua) — Netdev 0x14 (2020)
* [Lua no Núcleo](https://www.youtube.com/watch?v=-ufBgy044HI) — Lua Workshop 2023, PUC-Rio (Portuguese)
* [Scriptable Operating Systems with Lua](https://www.netbsd.org/~lneto/dls14.pdf) — DLS 2014
* [Lua in Kernel](https://events.canonical.com/event/89/contributions/506/attachments/265/393/Lua%20in%20Kernel%20-%20OOSC%202024%20(2).pdf) — Opportunity Open Source Conference 2024

### Articles
* [From the Kernel to the Moon: A Journey into Lunatik Bindings](https://medium.com/@lourival.neto/from-the-kernel-to-the-moon-a-journey-into-lunatik-bindings-c2cac8816f9e) — Medium (2025)
* [Is eBPF driving you crazy? Let it run Lunatik instead!](https://medium.com/@lourival.neto/is-ebpf-driving-you-crazy-let-it-run-lunatik-instead-4aca7d63e6fd) — Medium (2024)
* [Lua in the kernel?](https://lwn.net/Articles/830154/) — LWN.net (2020)

### GSoC Projects
* [LuaHID](https://github.com/qrsikno2/GSoC2025) — LabLua (2025), Jieming Zhou
* [Lunatik binding for Netfilter](https://summerofcode.withgoogle.com/archive/2024/projects/BIJAPZjf) — LabLua (2024), Mohammad Shehar Yaar Tausif
* [Lua hook on kTLS](https://luainkernel.github.io/ktls/) — LabLua (2020), Xinzhe Wang
* [Lunatik States Management](https://github.com/luainkernel/lunatik/pull/20) — LabLua (2020), Matheus Rodrigues
* [XDP Lua](https://victornogueirario.github.io/xdplua/) — LabLua (2019), Victor Nogueira
* [RCU binding for Lunatik](https://github.com/cmessias/lunatik) — LabLua (2018), Caio Messias
* [Lunatik Socket Library](https://github.com/luainkernel/lunatik/pull/4) — LabLua (2018), Chengzhi Tan
* [Port Lua Test Suite to the NetBSD Kernel](https://www.google-melange.com/archive/gsoc/2015/orgs/lablua/projects/gmesalazar.html) — LabLua (2015), Guilherme Salazar
* [Lua scripting in the NetBSD kernel](http://netbsd-soc.sourceforge.net/projects/luakern/) — The NetBSD Foundation (2010), Lourival Vieira Neto

## Contributing

Conventions for contributors, and for AI coding assistants working on this repository, are in
[AGENTS.md](AGENTS.md): build and test loop, execution contexts, object model, code style, and commit
discipline. Design notes for work in progress live under [doc/design](doc/design); what is being
worked on, and how far along it is, lives in the
[project boards](https://github.com/orgs/luainkernel/projects).

## License

Lunatik is dual-licensed under [MIT](LICENSE-MIT) or [GPL-2.0-only](LICENSE-GPL).

[Lua](https://github.com/luainkernel/lua) submodule is licensed under MIT.
For more details, see its [Copyright Notice](https://github.com/luainkernel/lua/blob/lunatik/lua.h#L530-L556).

[Klibc](https://github.com/luainkernel/klibc) submodule is dual-licensed under BSD 3-Clause or GPL-2.0-only.
For more details, see its [LICENCE](https://github.com/luainkernel/klibc/blob/lunatik/usr/klibc/LICENSE) file.

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