feature/tpm: check TPM family data for compatibility (#17624)

Check that the TPM we have opened is advertised as a 2.0 family device
before using it for state sealing / hardware attestation.

Updates #17622

Signed-off-by: Patrick O'Doherty <patrick@tailscale.com>

feature/tpm/tpm.go

@@ -55,12 +55,11 @@ func init() {
 }
 
 func tpmSupported() bool {
-	tpm, err := open()
-	if err != nil {
+	hi := infoOnce()
+	if hi == nil {
 		return false
 	}
-	tpm.Close()
-	return true
+	return hi.FamilyIndicator == "2.0"
 }
 
 var verboseTPM = envknob.RegisterBool("TS_DEBUG_TPM")
@@ -104,6 +103,7 @@ func info() *tailcfg.TPMInfo {
 		{tpm2.TPMPTVendorTPMType, func(info *tailcfg.TPMInfo, value uint32) { info.Model = int(value) }},
 		{tpm2.TPMPTFirmwareVersion1, func(info *tailcfg.TPMInfo, value uint32) { info.FirmwareVersion += uint64(value) << 32 }},
 		{tpm2.TPMPTFirmwareVersion2, func(info *tailcfg.TPMInfo, value uint32) { info.FirmwareVersion += uint64(value) }},
+		{tpm2.TPMPTFamilyIndicator, toStr(&info.FamilyIndicator)},
 	} {
 		resp, err := tpm2.GetCapability{
 			Capability:    tpm2.TPMCapTPMProperties,

feature/tpm/tpm_test.go

@@ -133,6 +133,19 @@ func TestStore(t *testing.T) {
 	})
 }
 
+func BenchmarkInfo(b *testing.B) {
+	b.StopTimer()
+	skipWithoutTPM(b)
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		hi := info()
+		if hi == nil {
+			b.Fatalf("tpm info error")
+		}
+	}
+	b.StopTimer()
+}
+
 func BenchmarkStore(b *testing.B) {
 	skipWithoutTPM(b)
 	b.StopTimer()

ipn/ipnlocal/c2n_test.go

@@ -384,6 +384,7 @@ func TestRedactNetmapPrivateKeys(t *testing.T) {
 		f(tailcfg.Service{}, "Port"):                       false,
 		f(tailcfg.Service{}, "Proto"):                      false,
 		f(tailcfg.Service{}, "_"):                          false,
+		f(tailcfg.TPMInfo{}, "FamilyIndicator"):            false,
 		f(tailcfg.TPMInfo{}, "FirmwareVersion"):            false,
 		f(tailcfg.TPMInfo{}, "Manufacturer"):               false,
 		f(tailcfg.TPMInfo{}, "Model"):                      false,

tailcfg/tailcfg.go

@@ -928,6 +928,10 @@ type TPMInfo struct {
 	// https://trustedcomputinggroup.org/resource/tpm-library-specification/.
 	// Before revision 184, TCG used the "01.83" format for revision 183.
 	SpecRevision int `json:",omitempty"`
+
+	// FamilyIndicator is the TPM spec family, like "2.0".
+	// Read from TPM_PT_FAMILY_INDICATOR.
+	FamilyIndicator string `json:",omitempty"`
 }
 
 // Present reports whether a TPM device is present on this machine.