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The Bareflank Hypervisor is an open source, hypervisor Software Development Toolkit (SDK), led by Assured Information Security, Inc. (AIS), that provides a set of APIs needed to rapidly prototype and create new hypervisors. To ease development, Bareflank is written in C/C++, and includes support for C++ exceptions, JSON, the GSL and the C++ Standard Template Library (STL).

The Bareflank Hypervisor uses a layered, modular approach.

  • hypervisor: provides the base SDK, hypervisor implementation, the build system, and architecture specific intrinsics.
  • boxy: leverages the Bareflank SDK to provide a fully functional hypervisor with guest support.

To support Bareflank's design approach, the hypervisor is licensed under MIT, specifically enabling users of the project to both contribute back to the project, but also create proprietary versions of the hypervisor if so desired.

In addition, the project comes complete with a set of unit tests to validate that the provided SDK works as expected. Furthermore, Travis CI has been set up to test source code formatting via Astyle, and static / dynamic analysis via Clang Tidy, Codacy, and Google's Sanitizers. Finally, we adhere to the CII Best Practices, the High Integrity C++ Guidelines and the C++ Core Guidelines including support for the Guideline Support Library.

Currently, we have support for the following 64bit host operating systems on Intel Sandy Bridge and above hardware:

  • Arch Linux
  • Ubuntu 17.10+
  • Windows 10
  • Windows 7
  • UEFI

In the future, we would also like to support:

  • macOS
  • BSD
  • ARM64 (still under development)


Most people think that hypervisors are meant to virtualize servers and provide a means to run Windows on a Mac, but there is a whole field of research where hypervisors are used without guest virtual machines. Since a hypervisor is capable of controlling the host OS running underneath it (so-called "ring -1"), host-only hypervisors support introspection, reverse engineering, anti-virus, containerization, diversity, and even architectural research like MoRE. All of these use cases start the same way, by spending months standing up the hypervisor itself before you can start working on your actual project. Existing open source hypervisors are burdened with legacy support and unnecessary complexity that make them painful to work with when conducting hypervisor research.


Bareflank Hypervisor Website
Bareflank Hypervisor API Documentation


Check out the latest demo for how to compile and use the Bareflank Hypervisor on Ubuntu 18.04:

Bareflank Demonstration Video

Additional Videos

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

CppCon 2019 CppCon 2017 CppCon 2016

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.



Although Bareflank can be made to run on most systems, the following are the supported platforms and their dependencies:

Arch Linux:

sudo pacman -S git base-devel linux-headers nasm clang cmake

Ubuntu 17.10 (or Higher):

sudo apt-get install git build-essential linux-headers-$(uname -r) nasm clang cmake libelf-dev

Windows (Visual Studio):

  • Visual Studio 2019 / WDK 10
    • Check "Desktop development with C++"
    • Check "C++ CLI / Support"
    • Check "VC++ 2019 version xxx Libs for Spectre (x86 and x64)"

After installing the above packages, you must enable test signing mode. This can be done from a command prompt with admin privileges:

bcdedit.exe /set testsigning ON

Windows (Cygwin):

  • All of the Windows (Visual Studio) instructions
  • Cygwin

To install Cygwin, simply install using all default settings, and then copy setup-x86_64.exe to C:\cygwin64\bin. From there, open a Cygwin terminal and run the following:

setup-x86_64.exe -q -P git,make,gcc-core,gcc-g++,nasm,clang,clang++,cmake,python,gettext,bash-completion,flex,bison,texinfo

This build environment provides a complete toolchain for building and running Bareflank. Most developers using Bareflank on Windows will need Cygwin for this reason. The remaining compilation instructions follow below.

Compilation Instructions

To compile with default settings for your host environment, run the following commands:

git clone
mkdir build; cd build
cmake ../hypervisor
make -j<# cores + 1>

For more detailed build instructions, see the detailed build instructions. For instructions on building and creating Bareflank extensions, see the extension build instructions

Usage Instructions

To use the hypervisor, run the following commands:

make driver_quick
make quick

to get status information, use the following:

make status
make dump

to reverse this:

make unload
make driver_unload

to clean up:

make distclean

Example Extensions

As stated above, the Bareflank Hypervisor is an SDK to create your own, more complicated hypervisors. One example of an extension is the boxy hypervisor, which provides support for Linux based guest virtual machines. There are several other examples in our examples folder.

To use one of these examples, you must tell the build system which Virtual Machine Monitor (VMM) you wish to use. By default, the build system will use "bfvmm", but you can override this by defining DEFAULT_VMM variable when running cmake. Each example has its own VMM target. For example, the CPUID count example's VMM is "example_cpuidcount_vmm" which can be seen in the following CMakeLists.txt file. So for example, to compile Bareflank and test out the CPUID count example, you would configure Bareflank using the following:

cmake -DDEFAULT_VMM=example_cpuidcount_vmm ..

In addition to setting the DEFAULT_VMM, if you are using the example_config.cmake config file you would set the OVERRIDE_VMM variable which will set the DEFAULT_VMM for you.

Finally, if you are creating your own out-of-tree extension, you must tell the build system where your extension is located so that it can include it when building the hypervisor. To do this, you must define the EXTENSION variable. So for example, if you are creating your own extension, with your own VMM target, you would use the following when configuring cmake:

cmake -DDEFAULT_VMM=<vmm target name> -DEXTENSION=<path to extension> ..


A UEFI application version of Bareflank may be compiled on Linux and used to boot both Linux and Windows The following describes how to build and execute Bareflank with EFI. For additional information, please see the following YouTube video

To compile for UEFI, add the following to CMake when configuring:


It should be noted that unit tests must be disabled, and static builds are currently required (the example config provides an example of how to configure Bareflank as needed for more complex builds).

To boot Windows or Linux you will need to provide your own extension that enables EPT. To see an example of this type of extension, please see the following integration test:

Once you have your own extension, the example config is required to tell the build system which VMM and target to use. The example config can be found here:

Our front page video on YouTube explains how to use this config, and the instructions are also in the config itself. To enable EFI, turn on the EFI flag. You will also need to set the following:

set(OVERRIDE_VMM <name>)

If for example, you are using the integration test listed above, these setting would be as follows:

set(OVERRIDE_VMM integration_intel_x64_efi_test_efi)
set(OVERRIDE_VMM_TARGET integration)

The first variable defines the VMM's name and the second variable defines the target that builds this VMM (which tells the build system what dependency EFI has). From there build as normal.

The resulting UEFI application can be found here:


Place this binary in your EFI partition (e.g., on Ubuntu this is /boot/efi/EFI/BOOT/bareflank.efi) and execute it like any other EFI application. Once Bareflank is running, you can start Windows or Linux if you included the above. Also note that utilities like "make dump" do not work when using EFI as the driver doesn't have access to the debug ring. You can, however, use "make ack" to get the hypervisor to say "hi".

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"

Cygwin SSH Instructions

You might find it useful to setup SSH if you are using Cygwin. The instructions for setting up SSH on Cygwin are as follows:

setup-x86_64.exe -q -P getent,cygrunsrv,openssl,openssh

ssh-host-config -y

net start sshd
netsh advfirewall firewall add rule name='SSH Port' dir=in action=allow protocol=TCP localport=22


The Bareflank Hypervisor is licensed under the MIT License.


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




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