libkrun is a dynamic library that allows programs to easily acquire the ability to run processes in a partially isolated environment using KVM Virtualization.

It integrates a VMM (Virtual Machine Monitor, the userspace side of an Hypervisor) with the minimum amount of emulated devices required to its purpose, abstracting most of the complexity that comes from Virtual Machine management, offering users a simple C API.

• Adding VM-isolation capabilities to an OCI runtime.
• Implementing a lightweight jailer for serverless workloads.
• Bringing additional self-isolation capabilities to conventional services (think of something as simple as chroot, but more powerful).

• Enable other projects to easily gain KVM-based process isolation capabilities.
• Be self-sufficient (no need for calling to an external VMM) and very simple to use.
• Be as small as possible, implementing only the features required to achieve its goals.
• Have the smallest possible footprint in every aspect (RAM consumption, CPU usage and boot time).
• Be compatible with a reasonable amount of workloads.

• Become a generic VMM.
• Be compatible with all kinds of workloads.
• Provide the best possible performance.

• virtio-console
• virtio-fs
• virtio-vsock
• virtio-balloon (only free-page reporting)

In libkrun, networking is implemented using a novel technique called socket-to-vsock impersonation. This allows the VM to have network connectivity without a virtual interface (hence, virtio-net is not among the list of supported devices).

The current implementation of this technique, found part in this repository and the other part in the kernel patches included with libkrunfw is just a proof-of-concept. It's limited to IPv4 TCP and UNIX connections, only supports recv/send operations, and the implementation itself is still quite hacky. We expect this technique to mature within libkrun, so it can be eventually upstreamed into the Linux kernel and other VMMs.

As, by default, glibc will use UDP for DNS requests, which is not yet supported by the socket-to-vsock impersonation technique described above, name resolution will fail with the default configuration. To work around this, you need to add the following line to the /etc/resolv.conf of the root filesystem servicing the isolated process:

options use-vc

• libkrunfw
• A working Rust toolchain

make

sudo make install

Despite being written in Rust, this library provides a simple C API defined in include/libkrun.h

This is a simple example providing chroot-like functionality using libkrun.

cd examples
make

To be able to chroot_vm, you need first a directory to act as the root filesystem for your isolated program. An easy way to prepare one, is by using podman:

podman create --name chroot_vm fedora
mkdir rootfs
podman export chroot_vm | tar xpf - -C rootfs
podman rm chroot_vm

Now you can use chroot_vm to run a process within this new root filesystem:

./chroot_vm ./rootfs /bin/sh

If the libkrun and/or libkrunfw libraries were installed on a path that's not included in your /etc/ld.so.conf configuration, you may get an error like this one:

./chroot_vm: error while loading shared libraries: libkrun.so: cannot open shared object file: No such file or directory

To avoid this problem, use the LD_LIBRARY_PATH environment variable to point to the location where the libraries were installed. For example, if the libraries were installed in /usr/local/lib64, use something like this:

LD_LIBRARY_PATH=/usr/local/lib64 ./chroot_vm rootfs/ /bin/sh

While functional, libkrun is still in a very early development stage.

Our first priority now is getting feedback from potential users of the library, to build a Community around it that would help us set the priorities and shape it to be useful for them.

libkrun incorporates code from Firecracker, rust-vmm and Cloud-Hypervisor.