Add getCapability and GetManufacturer (#84)

These methods can be used to query the TPM for various information.
GetManufacturer specifically queries the Vendor ID.

tpm/commands.go

@@ -143,6 +143,21 @@ func getPubKey(rw io.ReadWriter, keyHandle tpmutil.Handle, ca *commandAuth) (*pu
 	return &pk, &ra, ret, nil
 }
 
+// getCapability reads the requested capability and sub-capability from NVRAM
+func getCapability(rw io.ReadWriter, cap, subcap uint32) ([]byte, error) {
+	subCapBytes, err := tpmutil.Pack(subcap)
+	if err != nil {
+		return nil, err
+	}
+	var b []byte
+	in := []interface{}{cap, subCapBytes}
+	out := []interface{}{&b}
+	if _, err := submitTPMRequest(rw, tagRQUCommand, ordGetCapability, in, out); err != nil {
+		return nil, err
+	}
+	return b, nil
+}
+
 func nvReadValue(rw io.ReadWriter, index, offset, len uint32, ca *commandAuth) ([]byte, *responseAuth, uint32, error) {
 	var b []byte
 	var ra responseAuth

tpm/constants.go

@@ -63,7 +63,13 @@ const (
 
 // Capability types.
 const (
-	capHandle uint32 = 0x00000014
+	capProperty uint32 = 0x00000005
+	capHandle   uint32 = 0x00000014
+)
+
+// SubCapabilities
+const (
+	tpmCapPropManufacturer uint32 = 0x00000103
 )
 
 // Entity types. The LSB gives the entity type, and the MSB (currently fixed to

tpm/tpm.go

@@ -39,16 +39,10 @@ var OpenTPM = tpmutil.OpenTPM
 
 // GetKeys gets the list of handles for currently-loaded TPM keys.
 func GetKeys(rw io.ReadWriter) ([]tpmutil.Handle, error) {
-	var b []byte
-	subCap, err := tpmutil.Pack(rtKey)
+	b, err := getCapability(rw, capHandle, rtKey)
 	if err != nil {
 		return nil, err
 	}
-	in := []interface{}{capHandle, subCap}
-	out := []interface{}{&b}
-	if _, err := submitTPMRequest(rw, tagRQUCommand, ordGetCapability, in, out); err != nil {
-		return nil, err
-	}
 	var handles []tpmutil.Handle
 	if _, err := tpmutil.Unpack(b, &handles); err != nil {
 		return nil, err
@@ -981,6 +975,11 @@ func ReadPubEK(rw io.ReadWriter) ([]byte, error) {
 	return tpmutil.Pack(pk)
 }
 
+// GetManufacturer returns the manufacturer ID
+func GetManufacturer(rw io.ReadWriter) ([]byte, error) {
+	return getCapability(rw, capProperty, tpmCapPropManufacturer)
+}
+
 // OwnerClear uses owner auth to clear the TPM. After this operation, the TPM
 // can change ownership.
 func OwnerClear(rw io.ReadWriter, ownerAuth digest) error {

tpm/tpm_test.go

@@ -58,6 +58,18 @@ func TestGetKeys(t *testing.T) {
 	t.Logf("Got %d keys: % d\n", len(handles), handles)
 }
 
+func TestGetManufacturer(t *testing.T) {
+	rwc := openTPMOrSkip(t)
+	defer rwc.Close()
+
+	vendorID, err := GetManufacturer(rwc)
+	if err != nil {
+		t.Fatal("Couldn't read VendorID from TPM:", err)
+	}
+
+	t.Logf("TPM VendorID: %v\n", vendorID)
+}
+
 func TestPcrExtend(t *testing.T) {
 	rwc := openTPMOrSkip(t)
 	defer rwc.Close()