gvisor-tap-vsock

A replacement for libslirp and VPNKit, written in pure Go. It is based on the network stack of gVisor.

Compared to libslirp, gvisor-tap-vsock brings a configurable DNS server and dynamic port forwarding.

Build

make

Run with Qemu (Linux or macOS)

Usually with Qemu, to not run as root, you would have to use -netdev user,id=n0. With this project, this is the same but you have to run a daemon on the host.

There 2 ways for the VM to communicate with the daemon: with a tcp port or with a unix socket.

With gvproxy and the VM discussing on a tcp port:

(terminal 1) $ bin/gvproxy -debug -listen unix:///tmp/network.sock -listen-qemu tcp://0.0.0.0:1234
(terminal 2) $ qemu-system-x86_64 (all your qemu options) -netdev socket,id=vlan,connect=127.0.0.1:1234 -device virtio-net-pci,netdev=vlan,mac=5a:94:ef:e4:0c:ee

With gvproxy and the VM discussing on a unix socket:

(terminal 1) $ bin/gvproxy -debug -listen unix:///tmp/network.sock -listen-qemu unix:///tmp/qemu.sock
(terminal 2) $ bin/qemu-wrapper /tmp/qemu.sock qemu-system-x86_64 (all your qemu options) -netdev socket,id=vlan,fd=3 -device virtio-net-pci,netdev=vlan,mac=5a:94:ef:e4:0c:ee

Run with vsock

Made for Windows but also works for Linux and macOS with HyperKit.

Host

Windows prerequisites

$service = New-Item -Path "HKLM:\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Virtualization\GuestCommunicationServices" -Name "00000400-FACB-11E6-BD58-64006A7986D3"
$service.SetValue("ElementName", "gvisor-tap-vsock")

More docs: https://docs.microsoft.com/en-us/virtualization/hyper-v-on-windows/user-guide/make-integration-service

In the VM, be sure to have hv_sock module loaded.

Linux prerequisites

On Fedora 32, it worked out of the box. On others distros, you might have to look at https://github.com/mdlayher/vsock#requirements.

macOS prerequisites

Please locate the hyperkit state (there is a file called connect inside) folder and launch gvproxy with the following listen argument: --listen vsock://null:1024/path_to_connect_directory

Run

(host) $ sudo bin/gvproxy -debug -listen vsock://:1024 -listen unix:///tmp/network.sock

VM

With a container:

(vm) # docker run -d --name=gvisor-tap-vsock --privileged --net=host -it quay.io/crcont/gvisor-tap-vsock:latest
(vm) $ ping -c1 192.168.127.1
(vm) $ curl http://redhat.com

With the executable:

(vm) # ./vm -debug

Services

API

The executable running on the host, gvproxy, exposes a HTTP API. It can be used with curl.

$ curl  --unix-socket /tmp/network.sock http:/unix/stats 
{
  "BytesSent": 0,
  "BytesReceived": 0,
  "UnknownProtocolRcvdPackets": 0,
  "MalformedRcvdPackets": 0,
...

Gateway

The executable running on the host runs a virtual gateway that can be used by the VM.

DNS

The gateway also runs a DNS server. It can be configured to serve static zones.

Activate it by changing the /etc/resolv.conf file inside the VM with:

nameserver 192.168.127.1

Port forwarding

Dynamic port forwarding is supported.

Expose a port:

$ curl  --unix-socket /tmp/network.sock http:/unix/services/forwarder/expose -X POST -d '{"local":":6443","remote":"192.168.127.2:6443"}'

Unexpose a port:

$ curl  --unix-socket /tmp/network.sock http:/unix/services/forwarder/expose -X POST -d '{"local":":6443"}'

List exposed ports:

$ curl  --unix-socket /tmp/network.sock http:/foo/services/forwarder/all | jq .
[
  {
    "local": ":2222",
    "remote": "192.168.127.2:22"
  },
  {
    "local": ":6443",
    "remote": "192.168.127.2:6443"
  }
]

Tunneling

The HTTP API exposed on the host can be used to connect to a specific IP and port inside the virtual network. A working example for SSH can be found here.

Limitations

• ICMP is not forwarded outside the network.

Performance

Using iperf3, running the server on the host and the client in the VM, it can achieve 600Mbits/s.

How it works with vsock

Internet access

0. A tap network interface is running in the VM. It's the default gateway.
1. User types curl redhat.com
2. Linux kernel sends raw Ethernet packets to the tap device.
3. Tap device sends these packets to a process on the host using vsock
4. The process on the host maintains both internal (host to VM) and external (host to Internet endpoint) connections. It uses regular syscalls to connect to external endpoints.

This is the same behaviour as slirp.

Expose a port

1. The process on the host binds the port 80.
2. Each time, a client sends a http request, the process creates and sends the appropriate Ethernet packets to the VM.
3. The tap device receives the packets and injects them in the kernel.
4. The http server receives the request and send back the response.