feat: proxy and cmdline config

Author: natesales

.goreleaser.yaml

@@ -13,7 +13,7 @@ builds:
 
 nfpms:
   - package_name: tinfoil-sev-shim
-    file_name_template: "{{ .ProjectName }}_{{ .Version }}"
+    file_name_template: tinfoil-sev-shim
     vendor: Tinfoil
     maintainer: Tinfoil <[email protected]>
     section: utils

main.go

@@ -10,6 +10,10 @@ import (
 	"fmt"
 	"log"
 	"net/http"
+	"net/http/httputil"
+	"net/url"
+	"os"
+	"strings"
 
 	"github.com/caddyserver/certmagic"
 	"github.com/google/go-sev-guest/abi"
@@ -18,13 +22,33 @@ import (
 	"github.com/tinfoilanalytics/verifier/pkg/attestation"
 )
 
+var version = "dev"
+
 var (
 	listenAddr = flag.String("l", ":443", "listen address")
-	domain     = flag.String("d", "", "TLS domain name")
-	email      = flag.String("e", "", "TLS email address")
 	staging    = flag.Bool("s", false, "use staging CA")
+	upstream   = flag.Int("u", 8080, "upstream port")
+
+	email = "[email protected]"
 )
 
+// cmdlineParam returns the value of a parameter from the kernel command line
+func cmdlineParam(key string) (string, error) {
+	cmdline, err := os.ReadFile("/proc/cmdline")
+	if err != nil {
+		return "", err
+	}
+
+	for _, p := range strings.Split(string(cmdline), " ") {
+		if strings.HasPrefix(p, key+"=") {
+			return strings.TrimPrefix(p, key+"="), nil
+		}
+	}
+
+	return "", fmt.Errorf("missing %s", key)
+}
+
+// attestationReport gets a SEV-SNP signed attestation report over a TLS certificate fingerprint
 func attestationReport(certFP string) (*attestation.Document, error) {
 	var userData [64]byte
 	copy(userData[:], certFP)
@@ -48,44 +72,69 @@ func attestationReport(certFP string) (*attestation.Document, error) {
 	}, nil
 }
 
+func cors(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("Access-Control-Allow-Origin", "*")
+	w.Header().Set("Access-Control-Allow-Methods", "*")
+	w.Header().Set("Access-Control-Allow-Headers", "*")
+
+	if r.Method == "OPTIONS" {
+		w.WriteHeader(http.StatusOK)
+		return
+	}
+}
+
 func main() {
 	flag.Parse()
-	if *domain == "" {
-		log.Fatal("domain is required")
-	}
-	if *email == "" {
-		log.Fatal("email is required")
+
+	domain, err := cmdlineParam("tinfoil-domain")
+	if err != nil {
+		log.Fatal(err)
 	}
 
+	log.Printf("Starting SEV-SNP attestation shim %s domain %s", version, domain)
+
 	mux := http.NewServeMux()
 
-	certmagic.DefaultACME.Email = *email
+	// Request TLS certificate
+	certmagic.DefaultACME.Email = email
 	if *staging {
 		certmagic.DefaultACME.CA = certmagic.LetsEncryptStagingCA
 	} else {
 		certmagic.DefaultACME.CA = certmagic.LetsEncryptProductionCA
 	}
-	tlsConfig, err := certmagic.TLS([]string{*domain})
+	tlsConfig, err := certmagic.TLS([]string{domain})
 	if err != nil {
 		log.Fatalf("Failed to get TLS config: %v", err)
 	}
 
+	// Get certificate from TLS config
 	cert, err := tlsConfig.GetCertificate(&tls.ClientHelloInfo{
-		ServerName: *domain,
+		ServerName: domain,
 	})
 	if err != nil {
 		log.Fatalf("Failed to get certificate: %v", err)
 	}
 	certFP := sha256.Sum256(cert.Leaf.Raw)
 	certFPHex := hex.EncodeToString(certFP[:])
 
+	// Request SEV-SNP attestation
 	log.Printf("Fetching attestation over %s", certFPHex)
 	att, err := attestationReport(certFPHex)
 	if err != nil {
 		log.Fatal(err)
 	}
 
 	mux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
+		cors(w, r)
+		proxy := httputil.NewSingleHostReverseProxy(&url.URL{
+			Scheme: "http",
+			Host:   fmt.Sprintf("localhost:%d", *upstream),
+		})
+		proxy.ServeHTTP(w, r)
+	})
+
+	mux.HandleFunc("/.well-known/tinfoil-attestation", func(w http.ResponseWriter, r *http.Request) {
+		cors(w, r)
 		w.WriteHeader(http.StatusOK)
 		w.Header().Set("Content-Type", "application/json")
 		json.NewEncoder(w).Encode(att)