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feature/tpm: protect all TPM handle operations with a mutex (#17708)

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In particular on Windows, the `transport.TPMCloser` we get is not safe
for concurrent use. This is especially noticeable because
`tpm.attestationKey.Clone` uses the same open handle as the original
key. So wrap the operations on ak.tpm with a mutex and make a deep copy
with a new connection in Clone.

Updates #15830
Updates #17662
Updates #17644

Signed-off-by: Andrew Lytvynov <awly@tailscale.com>
This commit is contained in:
Andrew Lytvynov
2025-10-30 10:32:30 -07:00
committed by GitHub
parent b6c6960e40
commit f522b9dbb7
2 changed files with 100 additions and 6 deletions
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feature/tpm/attestation.go
+34 -6
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@@ -10,6 +10,7 @@ import (
"fmt"
"io"
"log"
"sync"
"github.com/google/go-tpm/tpm2"
"github.com/google/go-tpm/tpm2/transport"
@@ -19,7 +20,8 @@ import (
)
type attestationKey struct {
tpm transport.TPMCloser
tpmMu sync.Mutex
tpm transport.TPMCloser
// private and public parts of the TPM key as returned from tpm2.Create.
// These are used for serialization.
tpmPrivate tpm2.TPM2BPrivate
@@ -144,7 +146,7 @@ type attestationKeySerialized struct {
// MarshalJSON implements json.Marshaler.
func (ak *attestationKey) MarshalJSON() ([]byte, error) {
if ak == nil || ak.IsZero() {
if ak == nil || len(ak.tpmPublic.Bytes()) == 0 || len(ak.tpmPrivate.Buffer) == 0 {
return []byte("null"), nil
}
return json.Marshal(attestationKeySerialized{
@@ -163,6 +165,13 @@ func (ak *attestationKey) UnmarshalJSON(data []byte) (retErr error) {
ak.tpmPrivate = tpm2.TPM2BPrivate{Buffer: aks.TPMPrivate}
ak.tpmPublic = tpm2.BytesAs2B[tpm2.TPMTPublic, *tpm2.TPMTPublic](aks.TPMPublic)
ak.tpmMu.Lock()
defer ak.tpmMu.Unlock()
if ak.tpm != nil {
ak.tpm.Close()
ak.tpm = nil
}
tpm, err := open()
if err != nil {
return key.ErrUnsupported
@@ -182,6 +191,9 @@ func (ak *attestationKey) Public() crypto.PublicKey {
}
func (ak *attestationKey) Sign(rand io.Reader, digest []byte, opts crypto.SignerOpts) (signature []byte, err error) {
ak.tpmMu.Lock()
defer ak.tpmMu.Unlock()
if !ak.loaded() {
return nil, errors.New("tpm2 attestation key is not loaded during Sign")
}
@@ -247,6 +259,9 @@ func addASN1IntBytes(b *cryptobyte.Builder, bytes []byte) {
}
func (ak *attestationKey) Close() error {
ak.tpmMu.Lock()
defer ak.tpmMu.Unlock()
var errs []error
if ak.handle != nil && ak.tpm != nil {
_, err := tpm2.FlushContext{FlushHandle: ak.handle.Handle}.Execute(ak.tpm)
@@ -262,18 +277,31 @@ func (ak *attestationKey) Clone() key.HardwareAttestationKey {
if ak == nil {
return nil
}
return &attestationKey{
tpm: ak.tpm,
tpm, err := open()
if err != nil {
log.Printf("[unexpected] failed to open a TPM connection in feature/tpm.attestationKey.Clone: %v", err)
return nil
}
akc := &attestationKey{
tpm: tpm,
tpmPrivate: ak.tpmPrivate,
tpmPublic: ak.tpmPublic,
handle: ak.handle,
pub: ak.pub,
}
if err := akc.load(); err != nil {
log.Printf("[unexpected] failed to load TPM key in feature/tpm.attestationKey.Clone: %v", err)
tpm.Close()
return nil
}
return akc
}
func (ak *attestationKey) IsZero() bool {
if ak == nil {
return true
}
ak.tpmMu.Lock()
defer ak.tpmMu.Unlock()
return !ak.loaded()
}