Xdp Ebpf Fw

3 minute read

XDP/eBPF IP-layer firewall in Rust!

One of the option available today to do sub-millisecond packet filtering at scale is to harness the facilities afforded by XDP, eBPF, Linux kernel and support provided by various NIC manufacturers.

The two (XDP and eBPF) have grown quite rapidly in the 5.x release of the Linux kernel and there is absolutely no reason you would not want to use it for your low-latency, high-performance use case.

In this post, I will be demonstrating a sample XDP code that performs IP-layer firewall function traditionally done by Netfilter/IPtables (thanks for all the fish Rusty Russell!) but ran as a offloaded XDP program by the eBPF VM in the Linux kernel. The walk-through was thoroughly tested on Ubuntu 20.10 with LLVM version 11.0.0 on QEMU/virtio. LLVM is required today because it can produce eBPF targets.

According to XDP developers, on a benchmark they conducted, XDP far out-performed traditional kernel network stack on Linux on all fronts - tx, rx and forward (in the order of 12-25x!) when used with a NIC that that offloads XDP such as the ones from Intel/Mellanox/Netronome (mlx/ixgbe/nfp etc).

Dependencies Installation and Rust setup

Install dependencies:

$ sudo apt-get install          \
    build-essential             \    
    libelf-dev                  \
    ca-certificates             \
    ca-certificates-java        \
    zlib1g-dev                  \
    llvm-11-dev                 \
    libclang-11-dev             \
    linux-headers-$(uname -r)

Install Rust (single user) using rustup

$ curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
$ . ~/.bashrc # or logout then login.
$ rustup install nightly
$ rustup default nightly
$ rustc --version

Install Rust (system-wide) using rustup

$ sudo -i
$ curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs |       \
    env RUSTUP_HOME=/opt/rust/rustup CARGO_HOME=/opt/rust/cargo     \
    sh -s -- --default-toolchain stable --profile default --no-modify-path -y
$ tee -a /root/.bashrc <<HD
# setup Rust environment
export RUSTUP_HOME=/opt/rust/rustup
export PATH=${PATH}:/opt/rust/cargo/bin
$ . /root/.bashrc # or logout then login.
$ rustup install nightly
$ rustup default nightly
$ rustc --version

Install carfgo-bpf:

$ cargo install cargo-bpf


Create the eBPF project:

$ cargo bpf new xdp-ebpf-fw

Add a new eBPF program called fw:

$ cd xdp-ebpf-fw
$ cargo bpf add fw

Source for xdp-ebpf-fw/Cargo.toml:

name = "xdp-ebpf-fw"
version = "0.1.0"
edition = '2018'

cty = "0.2"
redbpf-macros = "1.3"
redbpf-probes = "1.3"

cargo-bpf = { version = "1.3", default-features = false }

default = []
probes = []

path = "src/lib.rs"

name = "fw"
path = "src/fw/main.rs"
required-features = ["probes"]

Source for fw/main.rs:


use core::fmt::Error;
use cty::*;
use redbpf_probes::xdp::prelude::*;

program!(0xFFFFFFFE, "GPL");

const TCP_XDP_DROP: XdpAction = XdpAction::Drop;
const UDP_XDP_DROP: XdpAction = XdpAction::Drop;
const XDP_PASS: XdpAction = XdpAction::Pass;

// XDP/eBPF based IP-layer firewall to drop all UDP packets.
// And, also drop all TCP packets destined to port 80.
pub fn xdp_ip_firewall(ctx: XdpContext) -> XdpResult {
    if let Ok(ip_protocol) = get_ip_protocol(&ctx) {
        match ip_protocol as u32 {
            IPPROTO_UDP => return Ok(UDP_XDP_DROP), // drop it on the floor
            IPPROTO_TCP => {
                if let Ok(transport) = ctx.transport() {
                    if transport.dest() == 80 {
                        return Ok(TCP_XDP_DROP);  // drop it on the floor
            _ => return Ok(XDP_PASS), // pass it up the protocol stack
    return Ok(XDP_PASS); // pass it up the protocol stack

fn get_ip_protocol(ctx: &XdpContext) -> Result<u32, Error> {
    if let Ok(ip) = ctx.ip() {
        // We need to make raw pointer into a u32 so `unsafe` is required.
        unsafe {
            return Ok((*ip).protocol as u32);
    // Anything above `255` is reserved.
    return Ok(0x10000);

Build eBPF program:

$ cargo bpf build 

Network queues on QEMU/virtio for XDP

On QEMU, we need to add 2N queues (where N is the number of vCPUs). The following <driver> section is required inside <interface> (use virsh edit [vmname]) is required (for 4 vCPUs, allocate 8 queues) as of QEMU version 4.2.1.

<interface ...>
[ ... ]
<driver name='vhost' txmode='iothread' ioeventfd='on' event_idx='off' queues='8' rx_queue_size='256' tx_queue_size='256'>
    <host csum='off' gso='off' tso4='off' tso6='off' ecn='off' ufo='off' mrg_rxbuf='off'/>
    <guest csum='off' tso4='off' tso6='off' ecn='off' ufo='off'/>
[ ... ]

Load the compiled eBPF program!

Load the compiled eBPF program:

$ cd xdp-ebpf-fw
$ cargo bpf load -i eth0 target/bpf/programs/fw/fw.elf



External resources


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