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The Bareflank Hypervisor is an open source hypervisor Software Development Toolkit (SDK) for Rust and C++, led by Assured Information Security, Inc. (AIS), that provides the tools needed to rapidly prototype and create your own hypervisor on 64bit versions of Intel and AMD (ARMv8 CPUs, RISC-V and PowerPC also planned). The Bareflank SDK is intended for instructional/research purposes as it only provides enough virtualization support to start/stop a hypervisor. Bareflank can also be used as the foundation to create your own, fully functional hypervisor as it uses the MIT license, includes 100% unit test coverage and compliance for AUTOSAR. If you are looking for a complete hypervisor (and not an SDK), please see MicroV. If you are looking for a minimal SDK for education or to perform research, this is the project for you. If you are simply looking for a reference hypervisor, please see SimpleVisor.

Bareflank uses a layered, modular approach, that lets you pick just how much complexity you need in your project when creating your own custom hypervisor:

  • BSL: provides a header-only, AUTOSAR compliant implementation of a subset of the C++ Standard Library, used to implement Bareflank's C++ components ensuring Bareflank and projects built using Bareflank can support critical systems applications.
  • LLVM: provides our custom implementation of the LLVM Clang-Tidy static analysis tool to ensure compliance with AUTOSAR.
  • PAL: provides auto-generated intrinsics APIs for Intel, AMD and ARM on any combination of OS and language.
  • hypervisor: provides the base SDK including the loader, the Bareflank microkernel and support applications. Although this repo is labeled "hypervisor", this repo only provides the base scaffolding for creating your own hypervisor. If you are in education or performing research and do not want to deal with the complexity of a fully functional hypervisor, this repo would be your starting point. By itself, the code in this repo only implements enough virtualization to start/stop a hypervisor.
  • MicroV: This is the project led by Assured Information Security, Inc. (AIS) the provides a fully functional hypervisor that uses the Bareflank SDK as it's foundation. If you are looking for an actual hypervisor and not an SDK, this is the project you are looking for.

Quick start

GitHub release (latest by date)

Get the latest version of the Bareflank Hypervisor SDK from GitHub:

git clone
mkdir hypervisor/build && cd hypervisor/build
cmake ..


make driver_quick
make start
make dump
make stop

Interested In Working For AIS?

Check out our Can You Hack It?® challenge and test your skills! Submit your score to show us what you’ve got. We have offices across the country and offer competitive pay and outstanding benefits. Join a team that is not only committed to the future of cyberspace, but to our employee’s success as well.



Check out the latest demo for how to compile and use the Bareflank Hypervisor on Ubuntu 20.04:

Additional Videos

Check out our YouTube Channel for more great content as well as the following videos at CppCon below:

CppCon 2019 CppCon 2017 CppCon 2016

Important Tips

Before attempting to use Bareflank, please review the following tips as they can make a huge difference in your initial experience:

  • Make sure you are running on a system with a serial port. Which serial port Bareflank uses can be configured by setting HYPERVISOR_SERIAL_PORT on x86 or HYPERVISOR_SERIAL_PORTH and HYPERVISOR_SERIAL_PORTL on ARMv8. Cables like these work great. Bareflank uses the following settings (115200 baud rate, 8 data bits, no parity bits, one stop bit).
  • Using PCI serial addon cards will not work with UEFI. These cards need to be initialized by the OS, logic that Bareflank does not currently contain. If you are using Bareflank directly from Windows/Linux, these cards will work fine, but from UEFI, you need a serial port provided on the motherboard.
  • The serial output might contain a lot of ANSI color codes if you are using a terminal that doesn't support ANSI color. To remove these, configure CMake with -DENABLE_COLOR=OFF.
  • Windows Subsystem For Linux v2 is not supported. When this is turned on, Windows runs under HyperV, which currently does not support nested virtualization. Furthermore, if you have ever enabled the WSL2, you must turn HyperV off using bcdedit /set hypervisorlaunchtype off as HyperV will continue to run even if you are no longer using the WSL2.
  • When running under Windows, driver issues can be seen by using DbgView. This tool must be run with Admin rights, and you need to turn on kernel output. Once this is working, you will see error messages coming from the Windows driver if needed.
  • Nested virtualization (i.e., attempting to run Bareflank inside a VM) is not officially supported, but does work if you know what you are doing. Specifically, a headless version of Linux 20.04 or higher in VMWare works with the proper configuration. VirtualBox does not work due to a lack of supported features and KVM may or may not work (your milage may vary). In general, you should be using real hardware.
  • If you need to compile Bareflank on older versions of Linux, it is possible, but you will need to update the build tools manually including LLVM 10+ and CMake 3.13+.

Build Requirements

Currently, the Bareflank hypervisor only supports the Clang/LLVM 10+ compiler. This, however, ensures that the hypervisor can be natively compiled on Windows including support for cross-compiling. Support for other C++20 compilers can be added if needed, just let us know if that is something you need.


To compile the BSL on Windows, you must first disable UEFI SecureBoot and enable test signing mode. Note that this might require you to reinstall Windows (you have been warned). This can be done from a command prompt with admin privileges:

bcdedit.exe /set testsigning ON

Next, install the following:

Visual Studio is needed as it contains Windows specific libraries that are needed during compilation. Instead of using the Clang/LLVM project that natively ships with Visual Studio, we use the standard Clang/LLVM binaries provided by the LLVM project which ensures we get all of the tools including LLD, Clang Tidy and Clang Format. Also note that you must put Ninja somewhere in your path (we usually drop into CMake's bin folder). Finally, make sure you follow all of the instructions when installing the WDK. These instructions change frequently, and each step must be installed correctly and in the order provided by the instructions. Skipping a step, or installing a package in the wrong order will result in a WDK installation that doesn't work.

To compile the BSL, we are going to use Bash. There are many ways to start Bash including opening a CMD prompt and typing "bash". Once running bash, make sure you add the following to your PATH:

  • MSBuild
  • devcon
  • certmgr

For example, in your .bashrc, you might add the following (depending on where Visual Studio put these files):

export PATH="/c/Program Files (x86)/Microsoft Visual Studio/2019/Community/MSBuild/Current/Bin:/c/Program Files (x86)/Windows Kits/10/Tools/x64:/c/Program Files (x86)/Windows Kits/10/bin/10.0.19041.0/x64:$PATH"

Finally, run the following from Bash:

git clone
mkdir hypervisor/build && cd hypervisor/build
cmake ..
ninja info

Ubuntu Linux

To compile the BSL on Ubuntu (20.04 or higher) you must first install the following dependencies:

sudo apt-get install -y clang cmake lld

To compile the BSL, use the following:

git clone
mkdir hypervisor/build && cd hypervisor/build
cmake ..
make info


To compile for UEFI, simply follow the steps for your OS above, but add the following to the cmake:


You can then build the hypervisor as normal and the UEFI loader will be compiled for you automatically. Once the kernel, extensions and UEFI loader are compiled, you can copy them to your UEFI FS0 partition. Note that all binaries must be copied to your FS0 partition, and on some systems, this might be a USB stick. To aid in this copy process, the build system includes the following command:

make copy_to_efi_partition

By default this uses the EFI partition, but it can be relocated using:


Some systems require you to provide the UEFI shell, and so Bareflank contains a copy of this shell which will be copied along with the kernel, extensions and UEFI loader. Once you have rebooted into the UEFI shell, you can start the hypervisor using


Note that by default, the hypervisor is not able to boot an OS. You must either use a non-default example that provides more complete UEFI support, or provide your own extension that is capable of successfully booting an OS. Finally, we currently do not provide any of the other vmmctl functions like stop or dump.

Usage Instructions

The Bareflank Hypervisor SDK consists of the following main components:

  • vmmctl
  • loader
  • kernel
  • extension

The "extension" is where you put your code. It is a ring 3 application that runs on top of our microkernel in so called "ring -1" or VMX root. The "kernel" is the aformentioned microkernel, and it is responsible for executing all of the hypervisor applications that actually implement the hypervisor. In other words, all of the hypervisor logic is implemented in an extension that you provide, and our microkernel is just there to execute your extension in VMX root. The "loader" places our microkernel and your extension in VMX root. It is responsible for starting and stopping the hypervisor, and dumping the contents of its debug ring. The "vmmctl" application is used to control the loader. It provides a simple means for telling the loader what to do.

To start Bareflank, compile the "loader" and run it in your OS's kernel. To do that, run the following (replace make with ninja on Windows):

make driver_build
make driver_load

This builds the "loader" and runs it in the OS's kernel. If you followed the buld instructions above using CMake, you should have already compiled the microkernel, vmmctl and your extension (which by default is our default example). Once these components are compiled, you can run the hypervisor using the following command (replace make with ninja on Windows):

make start

to get debug information, use the following (replace make with ninja on Windows):

make dump

To stop the hypervisor use the following (replace make with ninja on Windows):

make stop

Finally, to unload the "loader" and clean up its build system you can run the following (replace make with ninja on Windows):

make driver_unload
make driver_clean

And that is it. For more information on how to build and use Bareflank, you can run the following core a complete list of commands available to you as well as the complete build configuration (replace make with ninja on Windows):

make info

Writing Your Own Extensions

The Bareflank Hypervisor comes complete with a series of example extensions you can use to create your own custom hypervisor. To start, we will create a working directory, and clone some repos to speed up the build process:

mkdir ~/working
mkdir ~/working/build
git clone ~/working/bsl
git clone ~/working/hypervisor

Next, we will copy an existing example into our working directory (pick the example that provides the best starting point for your project):

cp -R ~/working/hypervisor/example/default ~/working/extension

Finally, we will configure the project, telling the build system how to find our custom extension.

cd ~/working/build
cmake \
  ../hypervisor \

HYPERVISOR_EXTENSIONS_DIR defines the location of your extension. Note that the path must be an absolute path, which is why we used the absolute path of the build folder as a starting point and then worked out the location of the extension folder from there.

FETCHCONTENT_SOURCE_DIR_BSL is optional. This tells the build system where to find the BSL. Since we already cloned the BSL into our working directory, we can use it instead of asking the build system to automatically fetch the BSL for us. This is great for offline builds, or builds where you are rerunning cmake a lot and don't want to wait for the BSL to download each time.

The rest of the usage instructions above can be used to start/stop your custom hypervisor. For more information about what ABIs the microkernel provides your extension with, please see the Microkernel Syscall Specification in the docs folder. We also provide an example implementation of this ABI as a set of C++ APIs that you can use if you would like. This example set of APIs can be seen in the syscall/include/mk_interface.hpp file.

To use the Rust example, you will have to install Rust and switch to the nightly channel.


Join the chat

The Bareflank hypervisor provides a ton of useful resources to learn how to use the library including:

If you have any questions, bugs, or feature requests, please feel free to ask on any of the following:

If you would like to help:


Build Status codecov

The Bareflank hypervisor leverages the following tools to ensure the highest possible code quality. Each pull request undergoes the following rigorous testing and review:

  • Static Analysis: Clang Tidy
  • Dynamic Analysis: Google's ASAN and UBSAN
  • Code Coverage: Code Coverage with CodeCov
  • Coding Standards: AUTOSAR C++14 and C++ Core Guidelines
  • Style: Clang Format
  • Documentation: Doxygen

Serial Instructions

On Windows, serial output might not work, and on some systems (e.g. Intel NUC), the default Windows serial device may prevent Bareflank from starting at all. If this is the case, disable the default serial device using the following:

reg add "HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Serial" /f /v "start" /t REG_DWORD /d "4"

See "Important Tips" above for additional details on how to use serial devices.


The Bareflank Hypervisor is licensed under the MIT License.


If you’re interested in Bareflank, you might also be interested in the following projects: