From be004c971da880a790709661b5e929d76177a8e2 Mon Sep 17 00:00:00 2001
From: Malte Poll <mp@edgeless.systems>
Date: Mon, 11 Apr 2022 10:34:15 +0200
Subject: [PATCH] Coordinator vTPM: add method to check for previous node
 initialization

Signed-off-by: Malte Poll <mp@edgeless.systems>
---
 coordinator/attestation/vtpm/initialize.go    | 57 +++++++++++++++++++
 .../attestation/vtpm/initialize_test.go       | 50 ++++++++++++++++
 2 files changed, 107 insertions(+)

diff --git a/coordinator/attestation/vtpm/initialize.go b/coordinator/attestation/vtpm/initialize.go
index b105a3cd0..9087d7e55 100644
--- a/coordinator/attestation/vtpm/initialize.go
+++ b/coordinator/attestation/vtpm/initialize.go
@@ -1,6 +1,9 @@
 package vtpm
 
 import (
+	"errors"
+	"fmt"
+
 	"github.com/google/go-tpm/tpm2"
 	"github.com/google/go-tpm/tpmutil"
 )
@@ -29,3 +32,57 @@ func MarkNodeAsInitialized(openTPM TPMOpenFunc, ownerID, clusterID []byte) error
 	// clusterID is used to uniquely identify this running instance of Constellation
 	return tpm2.PCREvent(tpm, PCRIndexClusterID, clusterID)
 }
+
+// IsNodeInitialized checks if a node is already initialized by reading PCRs.
+func IsNodeInitialized(openTPM TPMOpenFunc) (bool, error) {
+	tpm, err := openTPM()
+	if err != nil {
+		return false, err
+	}
+	defer tpm.Close()
+
+	idxOwner := int(PCRIndexOwnerID)
+	idxCluster := int(PCRIndexClusterID)
+	selection := tpm2.PCRSelection{
+		Hash: tpm2.AlgSHA256,
+		PCRs: []int{idxOwner, idxCluster},
+	}
+
+	pcrs, err := tpm2.ReadPCRs(tpm, selection)
+	if err != nil {
+		return false, err
+	}
+
+	if len(pcrs[idxOwner]) == 0 {
+		return false, errors.New("owner ID PCR does not exist")
+	}
+	if len(pcrs[idxCluster]) == 0 {
+		return false, errors.New("cluster ID PCR does not exist")
+	}
+
+	ownerInitialized := pcrInitialized(pcrs[idxOwner])
+	clusterInitialized := pcrInitialized(pcrs[idxCluster])
+
+	if ownerInitialized == clusterInitialized {
+		return ownerInitialized && clusterInitialized, nil
+	}
+	ownerState := "not initialized"
+	if ownerInitialized {
+		ownerState = "initialized"
+	}
+	clusterState := "not initialized"
+	if clusterInitialized {
+		clusterState = "initialized"
+	}
+	return false, fmt.Errorf("PCRs %v and %v are not consistent: PCR[%v]=%v (%v), PCR[%v]=%v (%v)", idxOwner, idxCluster, idxOwner, pcrs[idxOwner], ownerState, idxCluster, pcrs[idxCluster], clusterState)
+}
+
+// pcrInitialized checks if a PCR value is set to a non-zero value.
+func pcrInitialized(pcr []byte) bool {
+	for _, b := range pcr {
+		if b != 0 {
+			return true
+		}
+	}
+	return false
+}
diff --git a/coordinator/attestation/vtpm/initialize_test.go b/coordinator/attestation/vtpm/initialize_test.go
index c010a7058..a2db1ac1d 100644
--- a/coordinator/attestation/vtpm/initialize_test.go
+++ b/coordinator/attestation/vtpm/initialize_test.go
@@ -6,6 +6,7 @@ import (
 	"testing"
 
 	"github.com/google/go-tpm-tools/client"
+	"github.com/google/go-tpm/tpm2"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
@@ -47,3 +48,52 @@ func TestFailOpener(t *testing.T) {
 
 	assert.Error(MarkNodeAsInitialized(func() (io.ReadWriteCloser, error) { return nil, errors.New("failed") }, []byte{0x0, 0x1, 0x2, 0x3}, []byte{0x0, 0x1, 0x2, 0x3}))
 }
+
+func TestIsNodeInitialized(t *testing.T) {
+	testCases := map[string]struct {
+		pcrValueOwnerID   []byte
+		pcrValueClusterID []byte
+		expectInitialized bool
+		expectErr         bool
+	}{
+		"uninitialized PCRs results in uninitialized node": {},
+		"initializing PCRs result in initialized node": {
+			pcrValueOwnerID:   []byte{0x0, 0x1, 0x2, 0x3},
+			pcrValueClusterID: []byte{0x4, 0x5, 0x6, 0x7},
+			expectInitialized: true,
+		},
+		"initializing ownerID alone fails": {
+			pcrValueOwnerID: []byte{0x0, 0x1, 0x2, 0x3},
+			expectErr:       true,
+		},
+		"initializing clusterID alone fails": {
+			pcrValueClusterID: []byte{0x4, 0x5, 0x6, 0x7},
+			expectErr:         true,
+		},
+	}
+
+	for name, tc := range testCases {
+		t.Run(name, func(t *testing.T) {
+			assert := require.New(t)
+			require := require.New(t)
+			tpm, err := OpenSimulatedTPM()
+			require.NoError(err)
+			defer tpm.Close()
+			if tc.pcrValueOwnerID != nil {
+				require.NoError(tpm2.PCREvent(tpm, PCRIndexOwnerID, tc.pcrValueOwnerID))
+			}
+			if tc.pcrValueClusterID != nil {
+				require.NoError(tpm2.PCREvent(tpm, PCRIndexClusterID, tc.pcrValueClusterID))
+			}
+			initialized, err := IsNodeInitialized(func() (io.ReadWriteCloser, error) {
+				return &simTPMNOPCloser{tpm}, nil
+			})
+			if tc.expectErr {
+				assert.Error(err)
+				return
+			}
+			require.NoError(err)
+			require.Equal(tc.expectInitialized, initialized)
+		})
+	}
+}