Use VSOCK with libzmq

AF_VSOCK VSOCK is not new anymore it has been around in Linux kernel since 4.8. For those who do not know what this is, it was previously developed by VMware under the name VMCI. AF_VSOCK is a socket address family like AF_INET or AF_UNIX. It’s an address family designed for communication between a VM (guest) and the underlying hypervisor (host), you can also build communication between multiple guests on the same host. Previously, this kind of communication was done with a serial port, a great example is https://pve.proxmox.com/wiki/Qemu-guest-agent. AF_VSOCK looks and feels like a Unix socket with TCP/UDP-like features. You have addresses and ports, you also have stream and datagram. The man page https://man7.org/linux/man-pages/man7/vsock.7.html You have 32-bit addresses that are called “context identifier”, with reserved CID: VMADDR_CID_ANY, VMADDR_CID_HYPERVISOR, VMADDR_CID_LOCAL (new in 5.6), VMADDR_CID_HOST. Regarding port numbers, you can allocate 32-bit ports and those under 1024 need root access. just like TCP/UDP you can then have different communication with the same CID by using different port. VSOCK has been around for some time, but the support is growing slowly. Python/C/Golang/rust support it and you have some basic tools and SDK. https://stefano-garzarella.github.io/posts/2021-01-22-socat-vsock/ https://github.com/rust-vsock/tokio-vsock https://mdlayher.com/blog/linux-vm-sockets-in-go/ https://docs.python.org/3/library/socket.html#socket.AF_VSOCK https://gitlab.com/vsock/vsock AWS uses it for its Nitro Enclaves feature https://docs.aws.amazon.com/enclaves/latest/user/developing-applications-linux.html Support in libzmq If you are planning to use vsock, you’ll quickly notice that you only have low-level bindings available, there is no magical library that abstracts the socket for you. You probably have not opened a socket yourself in a long time, you are trying to remember how to: poll, recv, send, open, listen, bind. Fortunately there is a great library for that https://zeromq.org/, it implements basic patterns and good practices over almost any kind of socket, it even has security features http://curvezmq.org/. To my great surprise, there was a VMCI implementation https://libzmq.readthedocs.io/en/latest/zmq_vmci.html, but no VSOCK. Proposing something was straightforward; I almost just copied and pasted the code from VMCI. https://github.com/zeromq/libzmq/pull/4822 Having VSOCK in libzmq offers numerous advantages. use AF_VSOCK in every language that has a libzmq binding: python, ruby, nodejs, perl, java, lua … use libzmq features over AF_VSOCK : authentication with curve, different message pattern, req/rep, pub/sub. libzmq does not make regular releases because it is stable and does not move that much. It is also a library made for embedded software it’s easy to build it statically over a specific commit. VSOCK will certainly be available in a stable release someday, in the meantime i have forked pyzmq to build it with the latest libzmq commit, https://github.com/remijouannet/pyzmq-vsock. libzmq documentation on vsock https://github.com/zeromq/libzmq/blob/master/doc/zmq_vsock.adoc. pyzmq-vsock examples Hello world Since Linux 5.6 there is a loopback CID (VMADDR_CID_LOCAL) so you can test VSOCK without running a VM. Use @ in ZMQ to directly bind on this loopback. Here is a basic example of using req/rep socket pair over VSOCK loopback. if you ever want to test VSOCK in real condition with guest and host, your QEMU command line must add vsock device (or your libvirt configuration https://libvirt.org/formatdomain.html#vsock). 1export CID=100 2/usr/local/bin/qemu-system-x86_64 \ 3... 4 -device vhost-vsock-pci,id=vhost-vsock-pci0,guest-cid=$CID 5... 1 2# vsock_loopback is probably not loaded on your machine 3# sudo modprobe vsock_loopback 4 5python3 -m venv venv 6 7venv/bin/pip install \ 8 https://github.com/remijouannet/pyzmq-vsock/releases/download/27.2.0.dev0%2B4649337/pyzmq-27.2.0.dev0+4649337-cp312-abi3-manylinux_2_26_x86_64.manylinux_2_28_x86_64.whl 9 10# Examples from https://zeromq.org/get-started/?language=python# adapted for vsock 11cat <<EOF > rep.py 12# 13# Hello World server in Python 14# Binds REP socket to vsock://@:5555 15# Expects b"Hello" from client, replies with b"World" 16# 17 18import time 19import zmq 20 21context = zmq.Context() 22socket = context.socket(zmq.REP) 23socket.bind("vsock://@:5555") 24 25while True: 26 # Wait for next request from client 27 message = socket.recv() 28 print(f"Received request: {message}") 29 30 # Do some 'work' 31 time.sleep(1) 32 33 # Send reply back to client 34 socket.send(b"World") 35EOF 36 37cat <<EOF > req.py 38# 39# Hello World client in Python 40# Connects REQ socket to vsock://@:5555 41# Sends "Hello" to server, expects "World" back 42# 43 44import zmq 45 46context = zmq.Context() 47 48# Socket to talk to server 49print("Connecting to hello world server…") 50socket = context.socket(zmq.REQ) 51socket.connect("vsock://@:5555") 52 53# Do 5 requests, waiting each time for a response 54for request in range(5): 55 print(f"Sending request {request} …") 56 socket.send(b"Hello") 57 58 # Get the reply. 59 message = socket.recv() 60 print(f"Received reply {request} [ {message} ]") 61EOF 62 63venv/bin/python3 rep.py & 64[1] 88069 65 66venv/bin/python3 req.py 67Connecting to hello world server… 68Sending request 0 … 69Received request: b'Hello' 70Received reply 0 [ b'World' ] 71Sending request 1 … 72Received request: b'Hello' 73Received reply 1 [ b'World' ] 74Sending request 2 … 75Received request: b'Hello' 76Received reply 2 [ b'World' ] 77Sending request 3 … 78Received request: b'Hello' 79Received reply 3 [ b'World' ] 80Sending request 4 … 81Received request: b'Hello' 82Received reply 4 [ b'World' ] Curve with asyncio Hello World is great, but you’re probably going to use asyncio and curve in production. The following example is taken from pyzmq https://github.com/zeromq/pyzmq/blob/main/examples/security/asyncio-ironhouse.py. Script to generate Curve keys 1#!/usr/bin/env python 2 3import json 4 5import zmq 6import zmq.auth 7 8keys_file = "keys.json" 9 10client_pub, client_priv = zmq.curve_keypair() 11client2_pub, client2_priv = zmq.curve_keypair() 12server_pub, server_priv = zmq.curve_keypair() 13 14with open(keys_file, "w") as f: 15 json.dump( 16 { 17 "client": [client_pub.decode(), client_priv.decode()], 18 "client2": [client2_pub.decode(), client2_priv.decode()], 19 "server": [server_pub.decode(), server_priv.decode()], 20 }, 21 f, 22 sort_keys=True, 23 indent=4, 24 ) REP server 1#!/usr/bin/env python 2 3import asyncio 4import json 5import logging 6 7import zmq 8import zmq.auth 9from zmq.asyncio import Context 10from zmq.auth.asyncio import AsyncioAuthenticator 11 12LOGGER = logging.getLogger(__name__) 13 14 15async def run(keys: dict) -> None: 16 ctx = Context.instance() 17 18 # Start an authenticator for this context. 19 auth = AsyncioAuthenticator(ctx) 20 auth.start() 21 auth.certs["*"] = {keys["client"][0].encode(): True} 22 23 server = ctx.socket(zmq.REP) 24 25 server.curve_publickey = zmq.utils.z85.decode(keys['server'][0]) 26 server.curve_secretkey = zmq.utils.z85.decode(keys['server'][1]) 27 server.curve_server = True # must come before bind 28 server.bind('vsock://@:9000') 29 30 msg = await server.recv() 31 LOGGER.info(f"Received {msg!r}") 32 if msg == b"Hello": 33 LOGGER.info("Ironhouse test OK") 34 await server.send(b"World") 35 36 # close sockets 37 server.close() 38 auth.stop() 39 40 41if __name__ == '__main__': 42 if not zmq.has("vsock") or not zmq.has("curve"): 43 raise RuntimeError( 44 f"Security is not supported in libzmq version < 4.0. libzmq version {zmq.zmq_version()}" 45 ) 46 47 level = logging.DEBUG 48 49 logging.basicConfig(level=level, format="[%(levelname)s] %(message)s") 50 51 with open("keys.json") as f: 52 keys = json.load(f) 53 54 asyncio.run(run(keys)) REQ client 1#!/usr/bin/env python 2 3import asyncio 4import json 5import logging 6 7import zmq 8import zmq.auth 9from zmq.asyncio import Context 10from zmq.auth.asyncio import AsyncioAuthenticator 11 12LOGGER = logging.getLogger(__name__) 13 14 15async def run(keys: dict) -> None: 16 ctx = Context.instance() 17 18 # Start an authenticator for this context. 19 auth = AsyncioAuthenticator(ctx) 20 auth.start() 21 22 client = ctx.socket(zmq.REQ) 23 client.curve_publickey = zmq.utils.z85.decode(keys['client'][0]) 24 client.curve_secretkey = zmq.utils.z85.decode(keys['client'][1]) 25 26 client.curve_serverkey = zmq.utils.z85.decode(keys['server'][0]) 27 client.connect('vsock://@:9000') 28 29 await client.send(b"Hello") 30 reply = await client.recv() 31 LOGGER.info(f"Received reply {reply!r}") 32 33 client.close() 34 auth.stop() 35 36 37if __name__ == '__main__': 38 if not zmq.has("vsock") or not zmq.has("curve"): 39 raise RuntimeError( 40 f"Security is not supported in libzmq version < 4.0. libzmq version {zmq.zmq_version()}" 41 ) 42 43 level = logging.DEBUG 44 45 logging.basicConfig(level=level, format="[%(levelname)s] %(message)s") 46 47 with open("keys.json") as f: 48 keys = json.load(f) 49 50 asyncio.run(run(keys)) The output when authentication succeeds 1venv/bin/python generate_keys.py 2 3venv/bin/python rep_asyncio_curve.py 4[DEBUG] Using selector: EpollSelector 5[DEBUG] Starting 6[DEBUG] version: b'1.0', request_id: b'1', domain: '', address: '', identity: b'', mechanism: b'CURVE' 7[DEBUG] ALLOWED (CURVE) domain=* client_key=b'HhdIwzo4=a}1F#eL{}rs4C1Hgx.Z4nd#/JqIasmP' 8[DEBUG] ZAP reply code=b'200' text=b'OK' 9[INFO] Received b'Hello' 10[INFO] Ironhouse test OK 11 12venv/bin/python req_asyncio_curve.py