Overview
Muen is an Open Source separation kernel (SK) for the Intel x86/64 architecture that has been formally proven to contain no runtime errors at the source code level. It is developed in Switzerland by codelabs GmbH. Muen was designed specifically to meet the challenging requirements of high-assurance systems on the Intel x86/64 platform. To ensure Muen is suitable for highly critical systems and advanced national security platforms, codelabs closely cooperates with the high-security specialist secunet Security Networks AG in Germany.
A separation kernel is a specialized microkernel that provides an execution environment for components that exclusively communicate according to a given security policy and are otherwise strictly isolated from each other. The covert channel problem, largely ignored by other platforms, is addressed explicitly by these kernels. SKs are generally more static and smaller than dynamic microkernels, which minimizes the possibility of kernel failure, enables the application of formal verification techniques and the mitigation of covert channels.
Muen uses Intel’s hardware-assisted virtualization technology VT-x as core mechanism to separate components. The kernel executes in VMX root mode, while user components, so called subjects, run in VMX non-root mode. Hardware passthrough is realized using Intel’s VT-d DMA and interrupt remapping technology. This enables the secure assignment of PCI devices to subjects.
Muen is under active development and verification of kernel properties is ongoing. |
Features
Kernel
The following list outlines the most-prominent features of the Muen kernel:
-
Minimal SK for the Intel x86/64 architecture written in SPARK 2014
-
Full availability of source code and documentation
-
Proof of absence of runtime errors
-
Multicore support
-
Nested paging (EPT) and memory typing (PAT)
-
Fixed cyclic scheduling using Intel VMX preemption timer
-
Static assignment of resources according to system policy
-
PCI device passthrough using Intel VT-d (DMAR and IR)
-
PCI config space emulation
-
Support for Message Signaled Interrupts (MSI)
-
Minimal Zero-Footprint Run-Time (RTS)
-
Event mechanism
-
Shared memory channels for inter-subject communication
-
Crash Audit
-
Support for 64-bit native and 32/64-bit VM subjects
-
Native 64-bit Ada subjects
-
Native 64-bit SPARK 2014 subjects
-
Linux 32/64-bit VMs
-
SMP for Linux VMs
-
MirageOS unikernels [mirageos]
-
Tau0
Tau0 (τ₀) is the Muen System Composer. In its current static mode of operation, the task of Tau0 is to compose a system image while making sure that certain invariants are not violated. The Tau0 concept is a mechanism to gradually increase the flexibility of component-based systems running on top of Muen, while keeping a high level of assurance regarding the correctness of isolation enforcement. Read more about Tau0 here.
Components
The Muen platform includes re-usable components which implement common services:
-
AHCI (SATA) driver subject written in SPARK 2014
-
Device Manager (DM) written in SPARK 2014
-
Subject Monitor (SM) written in SPARK 2014
-
Subject Loader (SL) written in SPARK 2014
-
Subject Lifecycle Controller written in SPARK 2014
-
Timeserver subject written in SPARK 2014
-
Debugserver subject written in Ada 2012
-
PS/2 driver subject written in Ada 2012
-
Virtual Terminal (VT) subject written in Ada 2012
Furthermore the [muenfs], [muennet] and [muenblock] Linux kernel modules provide virtual filesystem, network interface and block I/O drivers based on inter-subject memory channels.
Toolchain
The Muen platform includes a versatile toolchain which facilitates the specification and construction of component-based systems in different application domains.
The [mugenhwcfg] tool for automated hardware description generation simplifies the addition of support for new target machines. There is also a Debian Live-based bootable image [mugenhwcfg-live] with persistence to simplify the collection of hardware configurations from new targets.
Resources
Documentation
The following detailed project documentation is available:
-
Muen System Specification
https://muen.sk/muen-system-spec.pdf -
Muen Kernel Specification
https://muen.sk/muen-kernel-spec.pdf -
Muen Component Specification
https://muen.sk/muen-component-spec.pdf -
Bootloader Signed Block Stream of Commands Specification
https://muen.sk/bsbsc-spec.pdf -
Original Muen master thesis
https://muen.sk/muen-report.pdf -
Muen project presentation
https://muen.sk/muen-slides.pdf -
Presentation given at High Integrity Software Conference HIS 2014
http://www.slideshare.net/AdaCore/slides-his-2014secunethsr -
Technical articles on Muen
https://muen.sk/articles.html
Mailing list
The muen-dev@googlegroups.com mailing list is used for project announcements and discussions regarding the Muen separation kernel.
-
To subscribe to the list, send a (blank) mail to muen-dev+subscribe@googlegroups.com. Note: A Google account is not required, any email address should work.
-
To post a message to the list write an email to muen-dev@googlegroups.com.
-
The list has a Google Groups web interface: https://groups.google.com/group/muen-dev.
Download
The Muen sources are available through the following git repository:
$ git clone --recursive https://git.codelabs.ch/git/muen.git
A browsable version of the repository is available here:
A ZIP archive of the current Muen sources can be downloaded here:
The ZIP archive cannot be used to build the example system since it does not contain all sub-projects. |
Build
Environment
The Muen SK has been developed and successfully tested using the development environment listed in the following table.
Operating systems |
Debian GNU/Linux 12 x86_64 |
Linux kernel/KVM |
>= 5.2.0 with GUEST_CR3 fix [lnxcr3] |
Ada compiler |
GNAT FSF 12.2 |
GCC version |
gcc (GCC) 12.2 |
SPARK version |
12.1 |
Emulator |
qemu-system-x86_64 (>= 3.1.0) |
Intel AMT SoL client |
amtterm (>= commit 0ece513…) |
Intel vPro AMT / WSMan |
amtc (github.com/schnoddelbotz/amtc) |
The following hardware is used for the development of Muen. There is a good chance similar hardware works out-of-the box if the microarchitecture is Ivy Bridge or newer.
ASUS Prime Z690-P D4 |
Alder Lake |
i5-125000 |
iBASE MI995VF-X27 |
Coffee Lake |
Xeon E-2176M |
Lenovo ThinkPad T480s |
Kaby Lake |
i7-8650U |
HPE DL380 Gen10 Server |
Skylake |
Xeon Gold 6130 |
Lenovo ThinkPad X260 |
Skylake |
i7-6500U |
Intel NUC 6i7KYK |
Skylake |
i7-6770HQ |
UP2 maker board |
Apollo Lake |
Atom E3950 |
Intel NUC 6CAYH |
Apollo Lake |
Celeron J3455 |
Intel NUC 5i5MYHE |
Broadwell |
i5-5300U |
Cirrus7 Nimbus |
Haswell |
i7-4765T |
Lenovo ThinkPad T440s |
Haswell |
i7-4600U |
Lenovo ThinkPad T430s |
Ivy Bridge |
i7-3520M |
Kontron Technology KTQM77/mITX |
Ivy Bridge |
i7-3610QE |
The first step to build Muen is to install the required packages. See the
tools/docker/Dockerfile.muen-dev-env
file in the project repository for the
current list of required packages:
acpica-tools amtterm autoconf automake autopoint bc bison bzip2 \ ca-certificates ccache cpio curl file flex gawk gettext git-core \ gnupg inotify-tools iputils-ping iucode-tool kmod lcov libc6-dev \ libcurl4-gnutls-dev libelf-dev libfreetype6-dev libgmp10-dev libiberty-dev \ libncurses-dev libseccomp-dev libssl-dev libxml2-utils lighttpd make mtools \ openssh-client patch picocom pkg-config python3-minimal python3-lxml \ python3-colorlog python3-setuptools python3-pip python3-rangehttpserver \ python3-wheel qemu-system-x86 rsync screen tidy unzip vim wget \ xfonts-unifont xorriso xsltproc xxd xz-utils zlib1g-dev
Muen is built using a GNAT FSF toolchain provided via [alire], see the
project’s website about instructions on how to install the alr
command-line
tool for your distribution. Then clone and build the Muen meta crate for alire,
which takes care of installing and configuring the toolchain:
$ git clone https://git.codelabs.ch/alire/muen-dev-env.git $ cd muen-dev-env $ make $ source ./env
Docker
There is also a ready-made Docker image which contains all necessary tools for Muen development. You can install it using the following command:
$ docker pull ghcr.io/codelabs-ch/muen-dev-env
Compilation
To build the Muen tools, RTS, kernel and example components change to the Muen source directory and issue the following command:
$ make
This will create a bootable ISO image containing the example system. See below for deployment instructions.
The following command gives a short description of the top-level Makefile targets:
$ make help
Deploy
The build system provides two ways to instantly deploy and test the created system image.
Emulation
To ease kernel development and testing, the Muen project makes use of nested
virtualization provided by QEMU/KVM. In order for this to work, a Linux
kernel (>= 5.2.0) with applied KVM GUEST_CR3 fix [lnxcr3] and the
qemu-system-x86_64
binary must be installed on the build machine.
Issue the following command in the Muen project directory to start the nested virtualization of a Muen system:
$ make emulate
The system serial output is written to emulate/serial.out
. Follow the
on-screen instructions on how to connect to the QEMU curses console or how to
SSH into the NIC Linux guest VM.
As the virtual terminal (VT) over curses is timing sensitive and QEMU/KVM cannot guarantee tick-exact timing depending on the host CPU and system load, this console is just an emergency console. Use SSH to interact with the booted Muen system. |
Hardware
The top-level Makefile provides two convenient targets to deploy Muen to real
hardware: iso
and deploy
. The first creates a bootable ISO image which can
be burned on a CD-ROM or dumped on a USB stick, the second uses network boot to
shorten round-trips during development.
USB Stick
To create a bootable USB stick containing the Muen system, enter the following commands in the top-level directory:
$ make HARDWARE=hardware/lenovo-t440s.xml SYSTEM=xml/demo_system_vtd.xml iso
Then follow the instructions on the screen.
Network Boot
For fast deployment of the Muen system image to real hardware, the iPXE [ipxe] boot firmware installed on a USB stick in conjunction with Intel Active Management Technology (AMT) is used. Please refer to the amtterm [amt] documentation on how to configure AMT on the target hardware.
To build and install iPXE with the Muen specific boot script issue the following commands:
$ sudo apt-get install liblzma-dev $ git clone git://git.ipxe.org/ipxe.git $ wget https://muen.sk/muen.ipxe $ cd ipxe/src $ make bin/ipxe.usb EMBED=../../muen.ipxe $ sudo dd if=bin/ipxe.usb of=/dev/sdX
The /dev/sdX
device is the USB stick (e.g. /dev/sdc
, without partition
number). All existing data will be erased.
When booting from the created stick the first NIC (net0) is configured as follows:
IP Address : 192.168.254.2 Netmask : 255.255.255.0 Gateway : 192.168.254.1
After initialization of the network adapter iPXE tries to download and chainload the iPXE configuration from the following URL:
http://192.168.254.1:8000/boot.cfg
The development machine must be connected to the target hardware via an interface with IP address 192.168.254.1. To actually serve the created system image to the bootloader, issue the following command in the top-level Muen directory:
$ export AMT_PASSWORD=<your AMT password> $ make deploy
To view the output of the Muen kernel debug console use the command:
$ amtterm 192.168.254.2
If your hardware differs from the default configuration, additionally specify
the HARDWARE
variable:
$ make deploy HARDWARE=hardware/intel-nuc-dc53427hye.xml
References
-
[lnxcr3] Linux KVM GUEST_CR3 fix, https://patchwork.kernel.org/patch/11165185/
-
[alire] ALIRE: Ada LIbrary REpository, https://alire.ada.dev/
-
[ipxe] iPXE boot firmware, https://ipxe.org/
-
[amt] Intel AMT SoL client + tools, https://www.kraxel.org/cgit/amtterm/
-
[mirageos] MirageOS, https://mirage.io
-
[muenblock] Muenblock Linux kernel module, https://git.codelabs.ch/?p=muen/linux/muenblock.git
-
[muenfs] Muenfs Linux kernel module, https://git.codelabs.ch/?p=muen/linux/muenfs.git
-
[muennet] Muennet Linux kernel module, https://git.codelabs.ch/?p=muen/linux/muennet.git
-
[mugenhwcfg] Muen hardware config generator, https://git.codelabs.ch/?p=muen/mugenhwcfg.git
-
[mugenhwcfg-live] Mugenhwcfg Live, https://github.com/codelabs-ch/mugenhwcfg-live/releases
License
Copyright (C) 2013-2024 Reto Buerki <reet@codelabs.ch> Copyright (C) 2013-2024 Adrian-Ken Rueegsegger <ken@codelabs.ch> This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.