feat: add Firecracker guest execution transport

guest/firecracker-supervisor/build.sh

@@ -0,0 +1,22 @@
+#!/bin/sh
+set -eu
+
+ROOT=$(CDPATH= cd -- "$(dirname -- "$0")" && pwd)
+GO_VERSION=go1.25.0
+VERSION=${VERSION:-dev}
+OUTPUT=${OUTPUT:-"$ROOT/firecracker-supervisor"}
+
+actual=$(go env GOVERSION)
+if [ "$actual" != "$GO_VERSION" ]; then
+  echo "required Go toolchain: $GO_VERSION (found $actual)" >&2
+  exit 1
+fi
+
+cd "$ROOT"
+CGO_ENABLED=0 GOOS=linux GOARCH="${GOARCH:-amd64}" \
+  go build -trimpath -buildvcs=false -ldflags="-s -w -X main.version=$VERSION" -o "$OUTPUT" .
+if command -v sha256sum >/dev/null 2>&1; then
+  sha256sum "$OUTPUT" > "$OUTPUT.sha256"
+else
+  shasum -a 256 "$OUTPUT" > "$OUTPUT.sha256"
+fi

guest/firecracker-supervisor/config.go

@@ -0,0 +1,83 @@
+package main
+
+import (
+	"fmt"
+	"net"
+	"path/filepath"
+	"strconv"
+	"strings"
+)
+
+type bootConfig struct {
+	WorkspaceDevice string
+	WorkspaceMount  string
+	VsockPort       uint32
+	GuestIP         net.IP
+	GuestPrefix     int
+	Gateway         net.IP
+	Interface       string
+}
+
+func parseBootConfig(cmdline string) (bootConfig, error) {
+	values := make(map[string]string)
+	for _, token := range strings.Fields(cmdline) {
+		key, value, ok := strings.Cut(token, "=")
+		if !ok || !strings.HasPrefix(key, "awf.") {
+			continue
+		}
+		if _, duplicate := values[key]; duplicate {
+			return bootConfig{}, fmt.Errorf("duplicate boot argument %q", key)
+		}
+		values[key] = value
+	}
+	required := []string{
+		"awf.workspace-device", "awf.workspace-mount", "awf.vsock-port",
+		"awf.guest-ip", "awf.guest-prefix", "awf.guest-gateway", "awf.guest-interface",
+	}
+	for _, key := range required {
+		if values[key] == "" {
+			return bootConfig{}, fmt.Errorf("missing required boot argument %q", key)
+		}
+	}
+	port, err := strconv.ParseUint(values["awf.vsock-port"], 10, 32)
+	if err != nil || port == 0 {
+		return bootConfig{}, fmt.Errorf("invalid awf.vsock-port")
+	}
+	prefix, err := strconv.Atoi(values["awf.guest-prefix"])
+	if err != nil || prefix < 0 || prefix > 32 {
+		return bootConfig{}, fmt.Errorf("invalid awf.guest-prefix")
+	}
+	ip := net.ParseIP(values["awf.guest-ip"]).To4()
+	gateway := net.ParseIP(values["awf.guest-gateway"]).To4()
+	if ip == nil || gateway == nil {
+		return bootConfig{}, fmt.Errorf("guest IP and gateway must be IPv4 addresses")
+	}
+	device := values["awf.workspace-device"]
+	if !strings.HasPrefix(device, "/dev/") || filepath.Clean(device) != device || strings.Contains(device, "..") {
+		return bootConfig{}, fmt.Errorf("invalid awf.workspace-device")
+	}
+	mount := values["awf.workspace-mount"]
+	if !filepath.IsAbs(mount) || filepath.Clean(mount) != mount || mount == "/" {
+		return bootConfig{}, fmt.Errorf("invalid awf.workspace-mount")
+	}
+	iface := values["awf.guest-interface"]
+	if !validInterface(iface) {
+		return bootConfig{}, fmt.Errorf("invalid awf.guest-interface")
+	}
+	return bootConfig{
+		WorkspaceDevice: device, WorkspaceMount: mount, VsockPort: uint32(port),
+		GuestIP: ip, GuestPrefix: prefix, Gateway: gateway, Interface: iface,
+	}, nil
+}
+
+func validInterface(name string) bool {
+	if name == "" || len(name) > 15 {
+		return false
+	}
+	for i, r := range name {
+		if !(r == '-' || r == '_' || r == '.' || r >= 'a' && r <= 'z' || r >= 'A' && r <= 'Z' || (i > 0 && r >= '0' && r <= '9')) {
+			return false
+		}
+	}
+	return true
+}

guest/firecracker-supervisor/config_test.go

@@ -0,0 +1,35 @@
+package main
+
+import "testing"
+
+const validCmdline = "console=ttyS0 awf.workspace-device=/dev/vdb awf.workspace-mount=/workspace awf.vsock-port=1024 awf.guest-ip=192.0.2.2 awf.guest-prefix=24 awf.guest-gateway=192.0.2.1 awf.guest-interface=eth0"
+
+func TestParseBootConfig(t *testing.T) {
+	config, err := parseBootConfig(validCmdline)
+	if err != nil {
+		t.Fatalf("parseBootConfig: %v", err)
+	}
+	if config.VsockPort != 1024 || config.Interface != "eth0" || config.GuestIP.String() != "192.0.2.2" {
+		t.Fatalf("unexpected config: %#v", config)
+	}
+}
+
+func TestParseBootConfigRejectsUnsafeValues(t *testing.T) {
+	cases := []string{
+		"awf.workspace-device=/dev/vdb awf.workspace-mount=/workspace awf.vsock-port=0 awf.guest-ip=192.0.2.2 awf.guest-prefix=24 awf.guest-gateway=192.0.2.1 awf.guest-interface=eth0",
+		"awf.workspace-device=/dev/../etc/passwd awf.workspace-mount=/workspace awf.vsock-port=1 awf.guest-ip=192.0.2.2 awf.guest-prefix=24 awf.guest-gateway=192.0.2.1 awf.guest-interface=eth0",
+		"awf.workspace-device=/dev/vdb awf.workspace-mount=/ awf.vsock-port=1 awf.guest-ip=192.0.2.2 awf.guest-prefix=24 awf.guest-gateway=192.0.2.1 awf.guest-interface=eth0",
+		"awf.workspace-device=/dev/vdb awf.workspace-mount=/workspace awf.vsock-port=1 awf.guest-ip=bad awf.guest-prefix=24 awf.guest-gateway=192.0.2.1 awf.guest-interface=eth0",
+	}
+	for _, cmdline := range cases {
+		if _, err := parseBootConfig(cmdline); err == nil {
+			t.Errorf("unsafe command line accepted: %q", cmdline)
+		}
+	}
+}
+
+func TestParseBootConfigRejectsDuplicateArguments(t *testing.T) {
+	if _, err := parseBootConfig(validCmdline + " awf.vsock-port=1025"); err == nil {
+		t.Fatal("duplicate argument accepted")
+	}
+}

guest/firecracker-supervisor/go.mod

@@ -0,0 +1,5 @@
+module github.com/github/gh-aw-firewall/firecracker-supervisor
+
+go 1.24.0
+
+toolchain go1.25.0

guest/firecracker-supervisor/main.go

@@ -0,0 +1,23 @@
+// firecracker-supervisor is the minimal guest-side command supervisor.
+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+)
+
+var version = "dev"
+
+func main() {
+	showVersion := flag.Bool("version", false, "print version")
+	flag.Parse()
+	if *showVersion {
+		fmt.Println(version)
+		return
+	}
+	if err := runSupervisor(); err != nil {
+		fmt.Fprintln(os.Stderr, "firecracker-supervisor:", err)
+		os.Exit(1)
+	}
+}