platform/ptrace: return errors from switchToApp() rather than panicking

PiperOrigin-RevId: 820872406

Author: nixprime

pkg/sentry/platform/ptrace/ptrace.go

@@ -110,7 +110,10 @@ func (c *context) Switch(ctx pkgcontext.Context, mm platform.MemoryManager, ac *
 	as := mm.AddressSpace()
 	s := as.(*subprocess)
 restart:
-	isSyscall := s.switchToApp(c, ac)
+	isSyscall, err := s.switchToApp(c, ac)
+	if err != nil {
+		return nil, hostarch.NoAccess, err
+	}
 
 	var (
 		faultSP   *subprocess

pkg/sentry/platform/ptrace/subprocess.go

@@ -509,7 +509,7 @@ func (t *thread) NotifyInterrupt() {
 // switchToApp is called from the main SwitchToApp entrypoint.
 //
 // This function returns true on a system call, false on a signal.
-func (s *subprocess) switchToApp(c *context, ac *arch.Context64) bool {
+func (s *subprocess) switchToApp(c *context, ac *arch.Context64) (bool, error) {
 	// Lock the thread for ptrace operations.
 	runtime.LockOSThread()
 	defer runtime.UnlockOSThread()
@@ -532,19 +532,19 @@ func (s *subprocess) switchToApp(c *context, ac *arch.Context64) bool {
 	if !c.interrupt.Enable(t) {
 		// Pending interrupt; simulate.
 		c.signalInfo = linux.SignalInfo{Signo: int32(platform.SignalInterrupt)}
-		return false
+		return false, nil
 	}
 	defer c.interrupt.Disable()
 
 	// Set registers.
 	if err := t.setRegs(regs); err != nil {
-		panic(fmt.Sprintf("ptrace set regs (%+v) failed: %v", regs, err))
+		return false, fmt.Errorf("ptrace set regs (%+v) failed: %w", regs, err)
 	}
 	if err := t.setFPRegs(fpState, &c.archContext); err != nil {
-		panic(fmt.Sprintf("ptrace set fpregs (%+v) failed: %v", fpState, err))
+		return false, fmt.Errorf("ptrace set fpregs (%+v) failed: %w", fpState, err)
 	}
 	if err := t.setTLS(&tls); err != nil {
-		panic(fmt.Sprintf("ptrace set tls (%+v) failed: %v", tls, err))
+		return false, fmt.Errorf("ptrace set tls (%+v) failed: %w", tls, err)
 	}
 
 	for {
@@ -554,14 +554,14 @@ func (s *subprocess) switchToApp(c *context, ac *arch.Context64) bool {
 				unix.SYS_PTRACE,
 				unix.PTRACE_SYSEMU_SINGLESTEP,
 				uintptr(t.tid), 0, 0, 0, 0); errno != 0 {
-				panic(fmt.Sprintf("ptrace sysemu failed: %v", errno))
+				return false, fmt.Errorf("ptrace sysemu failed: %w", errno)
 			}
 		} else {
 			if _, _, errno := unix.RawSyscall6(
 				unix.SYS_PTRACE,
 				unix.PTRACE_SYSEMU,
 				uintptr(t.tid), 0, 0, 0, 0); errno != 0 {
-				panic(fmt.Sprintf("ptrace sysemu failed: %v", errno))
+				return false, fmt.Errorf("ptrace sysemu failed: %w", errno)
 			}
 		}
 
@@ -576,16 +576,16 @@ func (s *subprocess) switchToApp(c *context, ac *arch.Context64) bool {
 
 		// Refresh all registers.
 		if err := t.getRegs(regs); err != nil {
-			panic(fmt.Sprintf("ptrace get regs failed: %v", err))
+			return false, fmt.Errorf("ptrace get regs failed: %w", err)
 		}
 		if err := t.getFPRegs(fpState, &c.archContext); err != nil {
-			panic(fmt.Sprintf("ptrace get fpregs failed: %v", err))
+			return false, fmt.Errorf("ptrace get fpregs failed: %w", err)
 		}
 		if err := t.getTLS(&tls); err != nil {
-			panic(fmt.Sprintf("ptrace get tls failed: %v", err))
+			return false, fmt.Errorf("ptrace get tls failed: %w", err)
 		}
 		if !ac.SetTLS(uintptr(tls)) {
-			panic(fmt.Sprintf("tls value %v is invalid", tls))
+			return false, fmt.Errorf("tls value %v is invalid", tls)
 		}
 
 		// Is it a system call?
@@ -594,13 +594,12 @@ func (s *subprocess) switchToApp(c *context, ac *arch.Context64) bool {
 
 			// Ensure registers are sane.
 			updateSyscallRegs(regs)
-			return true
+			return true, nil
 		}
 
 		// Grab signal information.
 		if err := t.getSignalInfo(&c.signalInfo); err != nil {
-			// Should never happen.
-			panic(fmt.Sprintf("ptrace get signal info failed: %v", err))
+			return false, fmt.Errorf("ptrace get signal info failed: %w", err)
 		}
 
 		// We have a signal. We verify however, that the signal was
@@ -611,13 +610,13 @@ func (s *subprocess) switchToApp(c *context, ac *arch.Context64) bool {
 			// the signal information, and may patch it in order to
 			// facilitate vsyscall emulation. See patchSignalInfo.
 			patchSignalInfo(regs, &c.signalInfo)
-			return false
+			return false, nil
 		} else if c.signalInfo.Code <= 0 && c.signalInfo.PID() == int32(os.Getpid()) {
 			// The signal was generated by this process. That means
 			// that it was an interrupt or something else that we
 			// should bail for. Note that we ignore signals
 			// generated by other processes.
-			return false
+			return false, nil
 		}
 	}
 }