sentry: wait for restore clock instead of panicing in Timekeeper.

PiperOrigin-RevId: 204372296
Change-Id: If1ed9843b93039806e0c65521f30177dc8036979

pkg/sentry/kernel/timekeeper.go

@@ -44,14 +44,14 @@ type Timekeeper struct {
 	// It is set only once, by SetClocks.
 	monotonicOffset int64 `state:"nosave"`
 
-	// restored indicates that this Timekeeper was restored from a state
-	// file.
-	restored bool `state:"nosave"`
+	// restored, if non-nil, indicates that this Timekeeper was restored
+	// from a state file. The clocks are not set until restored is closed.
+	restored chan struct{} `state:"nosave"`
 
 	// saveMonotonic is the (offset) value of the monotonic clock at the
 	// time of save.
 	//
-	// It is only valid if restored is true.
+	// It is only valid if restored is non-nil.
 	//
 	// It is only used in SetClocks after restore to compute the new
 	// monotonicOffset.
@@ -59,7 +59,7 @@ type Timekeeper struct {
 
 	// saveRealtime is the value of the realtime clock at the time of save.
 	//
-	// It is only valid if restored is true.
+	// It is only valid if restored is non-nil.
 	//
 	// It is only used in SetClocks after restore to compute the new
 	// monotonicOffset.
@@ -98,7 +98,7 @@ func NewTimekeeper(platform platform.Platform, paramPage platform.FileRange) (*T
 func (t *Timekeeper) SetClocks(c sentrytime.Clocks) {
 	// Update the params, marking them "not ready", as we may need to
 	// restart calibration on this new machine.
-	if t.restored {
+	if t.restored != nil {
 		if err := t.params.Write(func() vdsoParams {
 			return vdsoParams{}
 		}); err != nil {
@@ -135,7 +135,7 @@ func (t *Timekeeper) SetClocks(c sentrytime.Clocks) {
 		panic("Unable to get current realtime: " + err.Error())
 	}
 
-	if t.restored {
+	if t.restored != nil {
 		wantMonotonic = t.saveMonotonic
 		elapsed := nowRealtime - t.saveRealtime
 		if elapsed > 0 {
@@ -145,7 +145,7 @@ func (t *Timekeeper) SetClocks(c sentrytime.Clocks) {
 
 	t.monotonicOffset = wantMonotonic - nowMonotonic
 
-	if !t.restored {
+	if t.restored == nil {
 		// Hold on to the initial "boot" time.
 		t.bootTime = ktime.FromNanoseconds(nowRealtime)
 	}
@@ -153,6 +153,10 @@ func (t *Timekeeper) SetClocks(c sentrytime.Clocks) {
 	t.mu.Lock()
 	defer t.mu.Unlock()
 	t.startUpdater()
+
+	if t.restored != nil {
+		close(t.restored)
+	}
 }
 
 // startUpdater starts an update goroutine that keeps the clocks updated.
@@ -255,7 +259,10 @@ func (t *Timekeeper) ResumeUpdates() {
 // GetTime returns the current time in nanoseconds.
 func (t *Timekeeper) GetTime(c sentrytime.ClockID) (int64, error) {
 	if t.clocks == nil {
-		panic("Timekeeper used before initialized with SetClocks")
+		if t.restored == nil {
+			panic("Timekeeper used before initialized with SetClocks")
+		}
+		<-t.restored
 	}
 	now, err := t.clocks.GetTime(c)
 	if err == nil && c == sentrytime.Monotonic {

pkg/sentry/kernel/timekeeper_state.go

@@ -37,5 +37,5 @@ func (t *Timekeeper) beforeSave() {
 
 // afterLoad is invoked by stateify.
 func (t *Timekeeper) afterLoad() {
-	t.restored = true
+	t.restored = make(chan struct{})
 }

pkg/sentry/kernel/timekeeper_test.go

@@ -107,7 +107,7 @@ func TestTimekeeperMonotonicForward(t *testing.T) {
 	}
 
 	tk := stateTestClocklessTimekeeper(t)
-	tk.restored = true
+	tk.restored = make(chan struct{})
 	tk.saveMonotonic = 100000
 	tk.saveRealtime = 400000
 	tk.SetClocks(c)
@@ -135,7 +135,7 @@ func TestTimekeeperMonotonicJumpBackwards(t *testing.T) {
 	}
 
 	tk := stateTestClocklessTimekeeper(t)
-	tk.restored = true
+	tk.restored = make(chan struct{})
 	tk.saveMonotonic = 100000
 	tk.saveRealtime = 600000
 	tk.SetClocks(c)