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// Copyright 2016 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package bpf_test
import (
// A virtualMachine is a BPF virtual machine which can process an
// input packet against a BPF program and render a verdict.
type virtualMachine interface {
Run(in []byte) (int, error)
// canUseOSVM indicates if the OS BPF VM is available on this platform.
func canUseOSVM() bool {
// OS BPF VM can only be used on platforms where x/net/ipv4 supports
// attaching a BPF program to a socket.
switch runtime.GOOS {
case "linux":
return true
return false
// All BPF tests against both the Go VM and OS VM are assumed to
// be used with a UDP socket. As a result, the entire contents
// of a UDP datagram is sent through the BPF program, but only
// the body after the UDP header will ever be returned in output.
// testVM sets up a Go BPF VM, and if available, a native OS BPF VM
// for integration testing.
func testVM(t *testing.T, filter []bpf.Instruction) (virtualMachine, func(), error) {
goVM, err := bpf.NewVM(filter)
if err != nil {
// Some tests expect an error, so this error must be returned
// instead of fatally exiting the test
return nil, nil, err
mvm := &multiVirtualMachine{
goVM: goVM,
t: t,
// If available, add the OS VM for tests which verify that both the Go
// VM and OS VM have exactly the same output for the same input program
// and packet.
done := func() {}
if canUseOSVM() {
osVM, osVMDone := testOSVM(t, filter)
done = func() { osVMDone() }
mvm.osVM = osVM
return mvm, done, nil
// udpHeaderLen is the length of a UDP header.
const udpHeaderLen = 8
// A multiVirtualMachine is a virtualMachine which can call out to both the Go VM
// and the native OS VM, if the OS VM is available.
type multiVirtualMachine struct {
goVM virtualMachine
osVM virtualMachine
t *testing.T
func (mvm *multiVirtualMachine) Run(in []byte) (int, error) {
if len(in) < udpHeaderLen {
mvm.t.Fatalf("input must be at least length of UDP header (%d), got: %d",
udpHeaderLen, len(in))
// All tests have a UDP header as part of input, because the OS VM
// packets always will. For the Go VM, this output is trimmed before
// being sent back to tests.
goOut, goErr := mvm.goVM.Run(in)
if goOut >= udpHeaderLen {
goOut -= udpHeaderLen
// If Go output is larger than the size of the packet, packet filtering
// interop tests must trim the output bytes to the length of the packet.
// The BPF VM should not do this on its own, as other uses of it do
// not trim the output byte count.
trim := len(in) - udpHeaderLen
if goOut > trim {
goOut = trim
// When the OS VM is not available, process using the Go VM alone
if mvm.osVM == nil {
return goOut, goErr
// The OS VM will apply its own UDP header, so remove the pseudo header
// that the Go VM needs.
osOut, err := mvm.osVM.Run(in[udpHeaderLen:])
if err != nil {
mvm.t.Fatalf("error while running OS VM: %v", err)
// Verify both VMs return same number of bytes
var mismatch bool
if goOut != osOut {
mismatch = true
mvm.t.Logf("output byte count does not match:\n- go: %v\n- os: %v", goOut, osOut)
if mismatch {
mvm.t.Fatal("Go BPF and OS BPF packet outputs do not match")
return goOut, goErr
// An osVirtualMachine is a virtualMachine which uses the OS's BPF VM for
// processing BPF programs.
type osVirtualMachine struct {
l net.PacketConn
s net.Conn
// testOSVM creates a virtualMachine which uses the OS's BPF VM by injecting
// packets into a UDP listener with a BPF program attached to it.
func testOSVM(t *testing.T, filter []bpf.Instruction) (virtualMachine, func()) {
l, err := nettest.NewLocalPacketListener("udp")
if err != nil {
t.Fatalf("failed to open OS VM UDP listener: %v", err)
prog, err := bpf.Assemble(filter)
if err != nil {
t.Fatalf("failed to compile BPF program: %v", err)
ip := l.LocalAddr().(*net.UDPAddr).IP
if ip.To4() != nil && ip.To16() == nil {
err = ipv4.NewPacketConn(l).SetBPF(prog)
} else {
err = ipv6.NewPacketConn(l).SetBPF(prog)
if err != nil {
t.Fatalf("failed to attach BPF program to listener: %v", err)
s, err := net.Dial(l.LocalAddr().Network(), l.LocalAddr().String())
if err != nil {
t.Fatalf("failed to dial connection to listener: %v", err)
done := func() {
_ = s.Close()
_ = l.Close()
return &osVirtualMachine{
l: l,
s: s,
}, done
// Run sends the input bytes into the OS's BPF VM and returns its verdict.
func (vm *osVirtualMachine) Run(in []byte) (int, error) {
go func() {
_, _ = vm.s.Write(in)
vm.l.SetDeadline(time.Now().Add(50 * time.Millisecond))
var b [512]byte
n, _, err := vm.l.ReadFrom(b[:])
if err != nil {
// A timeout indicates that BPF filtered out the packet, and thus,
// no input should be returned.
if nerr, ok := err.(net.Error); ok && nerr.Timeout() {
return n, nil
return n, err
return n, nil