initdata-processor: gate insecure attestation via cmdline

Author: msanft

initdata-processor/main.go

@@ -15,6 +15,8 @@ import (
 	"net/http"
 	"os"
 	"path/filepath"
+	"slices"
+	"strings"
 
 	"github.com/edgelesssys/contrast/initdata-processor/policy"
 	"github.com/edgelesssys/contrast/initdata-processor/validator"
@@ -27,7 +29,10 @@ const (
 	insecureConfigPath = "/run/insecure-cfg"
 )
 
-var version = "0.0.0-dev"
+var (
+	version           = "0.0.0-dev"
+	kernelCmdlinePath = "/proc/cmdline"
+)
 
 // We always exit with status code 0 so that the Kata agent can start and propagate errors to
 // the runtime.
@@ -100,10 +105,17 @@ func handleInitdata(doc initdata.Raw) (hostdata []byte, insecurePlatform bool, r
 		return nil, false, fmt.Errorf("computing initdata digest: %w", err)
 	}
 
+	allowInsecure, err := allowInsecureAttestation()
+	if err != nil {
+		return nil, false, err
+	}
+
 	v, verr := validator.New()
 	if errors.Is(verr, validator.ErrNoPlatform) {
+		if !allowInsecure {
+			return nil, false, fmt.Errorf("no TEE platform detected and insecure attestation is not allowed")
+		}
 		log.Print("WARNING: No TEE platform detected, skipping initdata digest validation. This is expected on insecure platforms.")
-		insecurePlatform = true
 	} else if verr != nil {
 		return nil, false, fmt.Errorf("creating validator: %w", verr)
 	} else if err := v.ValidateDigest(digest); err != nil {
@@ -121,7 +133,18 @@ func handleInitdata(doc initdata.Raw) (hostdata []byte, insecurePlatform bool, r
 			return nil, false, fmt.Errorf("writing file %q: %w", path, err)
 		}
 	}
-	return digest, insecurePlatform, nil
+	return digest, allowInsecure, nil
+}
+
+func allowInsecureAttestation() (bool, error) {
+	cmdline, err := os.ReadFile(kernelCmdlinePath)
+	if err != nil {
+		return false, fmt.Errorf("reading kernel command line: %w", err)
+	}
+	if slices.Contains(strings.Fields(string(cmdline)), "contrast.allow_insecure_attestation=1") {
+		return true, nil
+	}
+	return false, nil
 }
 
 // serveHostdata starts an HTTP server that serves the hostdata digest.

initdata-processor/main_test.go

@@ -0,0 +1,47 @@
+// Copyright 2026 Edgeless Systems GmbH
+// SPDX-License-Identifier: BUSL-1.1
+
+package main
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestAllowInsecureAttestation(t *testing.T) {
+	oldKernelCmdlinePath := kernelCmdlinePath
+	t.Cleanup(func() { kernelCmdlinePath = oldKernelCmdlinePath })
+
+	testCases := map[string]struct {
+		cmdline string
+		want    bool
+	}{
+		"absent": {
+			cmdline: "console=hvc0",
+			want:    false,
+		},
+		"disabled": {
+			cmdline: "console=hvc0 contrast.allow_insecure_attestation=0",
+			want:    false,
+		},
+		"enabled": {
+			cmdline: "console=hvc0 contrast.allow_insecure_attestation=1 quiet",
+			want:    true,
+		},
+	}
+
+	for name, tc := range testCases {
+		t.Run(name, func(t *testing.T) {
+			kernelCmdlinePath = filepath.Join(t.TempDir(), "cmdline")
+			require.NoError(t, os.WriteFile(kernelCmdlinePath, []byte(tc.cmdline), 0o644))
+
+			got, err := allowInsecureAttestation()
+			require.NoError(t, err)
+			assert.Equal(t, tc.want, got)
+		})
+	}
+}