Implemented and Tested pcrReset. (#295)

* Implemented and Tested pcrReset.

* Fixed nits and rewrote TestPCRReset.

* Changed zero check in test to be more clear.

Co-authored-by: Matthew Tsai <matthewtsai@google.com>

direct/tpm2/pcr_test.go

@@ -0,0 +1,128 @@
+package tpm2
+
+import (
+	"bytes"
+	"crypto/sha1"
+	"crypto/sha256"
+	"crypto/sha512"
+	"testing"
+
+	"github.com/google/go-tpm/direct/structures/tpm"
+	"github.com/google/go-tpm/direct/structures/tpml"
+	"github.com/google/go-tpm/direct/structures/tpms"
+	"github.com/google/go-tpm/direct/structures/tpmt"
+	"github.com/google/go-tpm/direct/transport/simulator"
+)
+
+var extendsDirect = map[tpm.AlgID][]struct {
+	digest []byte
+}{
+	tpm.AlgSHA1: {
+		{bytes.Repeat([]byte{0x00}, sha1.Size)},
+		{bytes.Repeat([]byte{0x01}, sha1.Size)},
+		{bytes.Repeat([]byte{0x02}, sha1.Size)}},
+	tpm.AlgSHA256: {
+		{bytes.Repeat([]byte{0x00}, sha256.Size)},
+		{bytes.Repeat([]byte{0x01}, sha256.Size)},
+		{bytes.Repeat([]byte{0x02}, sha256.Size)}},
+	tpm.AlgSHA384: {
+		{bytes.Repeat([]byte{0x00}, sha512.Size384)},
+		{bytes.Repeat([]byte{0x01}, sha512.Size384)},
+		{bytes.Repeat([]byte{0x02}, sha512.Size384)}},
+}
+
+func allZero(s []byte) bool {
+    for _, v := range s {
+        if v != 0 {
+            return false
+        }
+    }
+    return true
+}
+
+func TestPCRReset(t *testing.T) {
+	thetpm, err := simulator.OpenSimulator()
+	if err != nil {
+		t.Fatalf("could not connect to TPM simulator: %v", err)
+	}
+	defer thetpm.Close()
+
+	DebugPCR := 16
+
+	cases := []struct {
+		name    string
+		hashalg tpm.AlgID
+	}{
+		{"SHA1", tpm.AlgSHA1},
+		{"SHA256", tpm.AlgSHA256},
+		{"SHA384", tpm.AlgSHA384},
+	}
+
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			PCRs, err := CreatePCRSelection([]int{DebugPCR})
+			if err != nil {
+				t.Fatalf("Failed to create PCRSelection")
+			}
+
+			authHandle := AuthHandle{
+				Handle: tpm.Handle(DebugPCR),
+				Auth:   PasswordAuth(nil),
+			}
+
+			pcrRead := PCRRead{
+				PCRSelectionIn: tpml.PCRSelection{
+					PCRSelections: []tpms.PCRSelection{
+						{
+							Hash:      c.hashalg,
+							PCRSelect: PCRs,
+						},
+					},
+				},
+			}
+
+			// Extending PCR 16
+			for _, d := range extendsDirect[c.hashalg] {
+				pcrExtend := PCRExtend{
+					PCRHandle: authHandle,
+					Digests: tpml.DigestValues{
+						Digests: []tpmt.HA{
+							{
+								HashAlg: c.hashalg,
+								Digest:  d.digest,
+							},
+						},
+					},
+				}
+				if err := pcrExtend.Execute(thetpm); err != nil {
+					t.Fatalf("failed to extend pcr for test %v", err)
+				}
+			}
+
+			pcrReadRsp, err := pcrRead.Execute(thetpm)
+			if err != nil {
+				t.Fatalf("failed to read PCRs")
+			}
+			postExtendPCR16 := pcrReadRsp.PCRValues.Digests[0].Buffer
+			if allZero(postExtendPCR16) {
+				t.Errorf("postExtendPCR16 not expected to be all Zero: %v", postExtendPCR16)
+			}
+
+			// Resetting PCR 16
+			pcrReset := PCRReset{
+				PCRHandle: authHandle,
+			}
+			if _, err := pcrReset.Execute(thetpm); err != nil {
+				t.Fatalf("pcrReset failed: %v", err)
+			}
+			if pcrReadRsp, err = pcrRead.Execute(thetpm); err != nil {
+				t.Fatalf("failed to read PCRs")
+			}
+			postResetPCR16 := pcrReadRsp.PCRValues.Digests[0].Buffer
+
+			if !allZero(postResetPCR16) {
+				t.Errorf("postResetPCR16 expected to be all Zero: %v", postExtendPCR16)
+			}
+		})
+	}
+}

direct/tpm2/tpm2.go

@@ -841,6 +841,31 @@ type PCRReadResponse struct {
 // Response implements the Response interface.
 func (*PCRReadResponse) Response() tpm.CC { return tpm.CCPCRRead }
 
+// PCRReset is the input to TPM2_PCRReset.
+// See definition in Part 3, Commands, section 22.8.
+type PCRReset struct {
+	// the PCR to reset
+	PCRHandle handle `gotpm:"handle,auth"`
+}
+
+// Command implements the Command interface.
+func (*PCRReset) Command() tpm.CC { return tpm.CCPCRReset }
+
+// Execute executes the command and returns the response.
+func (cmd *PCRReset) Execute(t transport.TPM, s ...Session) (*PCRResetResponse, error) {
+	var rsp PCRResetResponse
+	if err := execute(t, cmd, &rsp, s...); err != nil {
+		return nil, err
+	}
+	return &rsp, nil
+}
+
+// PCRResetResponse is the response from TPM2_PCRReset.
+type PCRResetResponse struct{}
+
+// Response implements the Response interface.
+func (*PCRResetResponse) Response() tpm.CC { return tpm.CCPCRReset }
+
 // PolicySigned is the input to TPM2_PolicySigned.
 // See definition in Part 3, Commands, section 23.3.
 type PolicySigned struct {