systrap: don't fail if seccomp_unotify isn't supported

Fixes #10633

PiperOrigin-RevId: 652717946

pkg/sentry/platform/systrap/subprocess.go

@@ -178,6 +178,21 @@ type subprocess struct {
 	dead atomicbitops.Bool
 }
 
+var seccompNotifyIsSupported = false
+
+func initSeccompNotify() {
+	_, _, errno := unix.Syscall(seccomp.SYS_SECCOMP, linux.SECCOMP_SET_MODE_FILTER, linux.SECCOMP_FILTER_FLAG_NEW_LISTENER, 0)
+	switch errno {
+	case unix.EFAULT:
+		// seccomp unotify is supported.
+	case unix.EINVAL:
+		log.Warningf("Seccomp user-space notification mechanism isn't " +
+			"supported by the kernel (available since Linux 5.0).")
+	default:
+		panic(fmt.Sprintf("seccomp returns unexpected code: %d", errno))
+	}
+}
+
 func (s *subprocess) initSyscallThread(ptraceThread *thread, seccompNotify bool) error {
 	s.syscallThreadMu.Lock()
 	defer s.syscallThreadMu.Unlock()

pkg/sentry/platform/systrap/syscall_thread.go

@@ -97,8 +97,11 @@ func (t *syscallThread) init(seccompNotify bool) error {
 		return err
 	}
 
-	if seccompNotify {
-		t.seccompNotify = t.installSeccompNotify()
+	if seccompNotify && seccompNotifyIsSupported {
+		if t.seccompNotify, err = t.installSeccompNotify(); err != nil {
+			t.destroy()
+			return fmt.Errorf("failed to install seccomp notify rules: %w", err)
+		}
 	}
 
 	// Map the stack into the sentry.
@@ -142,19 +145,19 @@ func (t *syscallThread) destroy() {
 	t.subproc.sysmsgStackPool.Put(t.thread.sysmsgStackID)
 }
 
-func (t *syscallThread) installSeccompNotify() *os.File {
+func (t *syscallThread) installSeccompNotify() (*os.File, error) {
 	fd, err := t.thread.syscallIgnoreInterrupt(&t.thread.initRegs, seccomp.SYS_SECCOMP,
 		arch.SyscallArgument{Value: uintptr(linux.SECCOMP_SET_MODE_FILTER)},
 		arch.SyscallArgument{Value: uintptr(linux.SECCOMP_FILTER_FLAG_NEW_LISTENER)},
 		arch.SyscallArgument{Value: stubSyscallRules})
 	if err != nil {
-		panic(fmt.Sprintf("seccomp failed: %v", err))
+		return nil, err
 	}
 	_, _, errno := unix.RawSyscall(unix.SYS_IOCTL, fd, linux.SECCOMP_IOCTL_NOTIF_SET_FLAGS, linux.SECCOMP_USER_NOTIF_FD_SYNC_WAKE_UP)
 	if errno != 0 {
 		t.thread.Debugf("failed to set SECCOMP_USER_NOTIF_FD_SYNC_WAKE_UP")
 	}
-	return os.NewFile(fd, "seccomp_notify")
+	return os.NewFile(fd, "seccomp_notify"), nil
 }
 
 // mapMessageIntoStub maps the syscall message into the stub process address space.

pkg/sentry/platform/systrap/systrap.go

@@ -350,6 +350,8 @@ func New() (*Systrap, error) {
 		globalPool.source = source
 
 		initSysmsgThreadPriority()
+
+		initSeccompNotify()
 	})
 
 	latencyMonitoring.Do(func() {