Allow to return an error from PullFullState.

PiperOrigin-RevId: 504415294

pkg/sentry/kernel/task_clone.go

@@ -65,7 +65,12 @@ func (t *Task) Clone(args *linux.CloneArgs) (ThreadID, *SyscallControl, error) {
 
 	// Pull task registers and FPU state, a cloned task will inherit the
 	// state of the current task.
-	t.p.PullFullState(t.MemoryManager().AddressSpace(), t.Arch())
+	if err := t.p.PullFullState(t.MemoryManager().AddressSpace(), t.Arch()); err != nil {
+		t.Warningf("Unable to pull a full state: %v", err)
+		t.forceSignal(linux.SIGILL, true /* unconditional */)
+		t.SendSignal(SignalInfoPriv(linux.SIGILL))
+		return 0, nil, linuxerr.EFAULT
+	}
 
 	// "If CLONE_NEWUSER is specified along with other CLONE_NEW* flags in a
 	// single clone(2) or unshare(2) call, the user namespace is guaranteed to

pkg/sentry/kernel/task_run.go

@@ -247,7 +247,10 @@ func (app *runApp) execute(t *Task) taskRunState {
 		t.Arch().ClearSingleStep()
 	}
 	if t.hasTracer() {
-		t.p.PullFullState(t.MemoryManager().AddressSpace(), t.Arch())
+		if e := t.p.PullFullState(t.MemoryManager().AddressSpace(), t.Arch()); e != nil {
+			t.Warningf("Unable to pull a full state: %v", e)
+			err = e
+		}
 	}
 
 	switch err {

pkg/sentry/kernel/task_signals.go

@@ -644,8 +644,9 @@ func (t *Task) SetSavedSignalMask(mask linux.SignalSet) {
 }
 
 // SignalStack returns the task-private signal stack.
+//
+// By precondition, a full state has to be pulled.
 func (t *Task) SignalStack() linux.SignalStack {
-	t.p.PullFullState(t.MemoryManager().AddressSpace(), t.Arch())
 	alt := t.signalStack
 	if t.onSignalStack(alt) {
 		alt.Flags |= linux.SS_ONSTACK
@@ -653,6 +654,34 @@ func (t *Task) SignalStack() linux.SignalStack {
 	return alt
 }
 
+// SigaltStack implements the sigaltstack syscall.
+func (t *Task) SigaltStack(setaddr hostarch.Addr, oldaddr hostarch.Addr) (*SyscallControl, error) {
+	if err := t.p.PullFullState(t.MemoryManager().AddressSpace(), t.Arch()); err != nil {
+		t.PrepareGroupExit(linux.WaitStatusTerminationSignal(linux.SIGILL))
+		return CtrlDoExit, linuxerr.EFAULT
+	}
+
+	alt := t.SignalStack()
+	if oldaddr != 0 {
+		if _, err := alt.CopyOut(t, oldaddr); err != nil {
+			return nil, err
+		}
+	}
+	if setaddr != 0 {
+		if _, err := alt.CopyIn(t, setaddr); err != nil {
+			return nil, err
+		}
+		// The signal stack cannot be changed if the task is currently
+		// on the stack. This is enforced at the lowest level because
+		// these semantics apply to changing the signal stack via a
+		// ucontext during a signal handler.
+		if !t.SetSignalStack(alt) {
+			return nil, linuxerr.EPERM
+		}
+	}
+	return nil, nil
+}
+
 // onSignalStack returns true if the task is executing on the given signal stack.
 func (t *Task) onSignalStack(alt linux.SignalStack) bool {
 	sp := hostarch.Addr(t.Arch().Stack())
@@ -1018,7 +1047,10 @@ func (*runInterrupt) execute(t *Task) taskRunState {
 
 	// Are there signals pending?
 	if info := t.dequeueSignalLocked(linux.SignalSet(t.signalMask.RacyLoad())); info != nil {
-		t.p.PullFullState(t.MemoryManager().AddressSpace(), t.Arch())
+		if err := t.p.PullFullState(t.MemoryManager().AddressSpace(), t.Arch()); err != nil {
+			t.PrepareGroupExit(linux.WaitStatusTerminationSignal(linux.SIGILL))
+			return (*runExit)(nil)
+		}
 
 		if linux.SignalSetOf(linux.Signal(info.Signo))&StopSignals != 0 {
 			// Indicate that we've dequeued a stop signal before unlocking the

pkg/sentry/platform/kvm/context.go

@@ -125,7 +125,7 @@ func (c *context) Release() {}
 func (c *context) FullStateChanged() {}
 
 // PullFullState implements platform.Context.PullFullState.
-func (c *context) PullFullState(as platform.AddressSpace, ac *arch.Context64) {}
+func (c *context) PullFullState(as platform.AddressSpace, ac *arch.Context64) error { return nil }
 
 // PrepareSleep implements platform.Context.platform.Context.
 func (*context) PrepareSleep() {}

pkg/sentry/platform/platform.go

@@ -221,7 +221,7 @@ type Context interface {
 	// PullFullState() to load all registers and FPU state.
 	//
 	// Preconditions: The caller must be running on the task goroutine.
-	PullFullState(as AddressSpace, ac *arch.Context64)
+	PullFullState(as AddressSpace, ac *arch.Context64) error
 
 	// FullStateChanged() indicates that a thread state has been changed by
 	// the Sentry. This happens in case of the rt_sigreturn, execve, etc.

pkg/sentry/platform/ptrace/ptrace.go

@@ -197,7 +197,7 @@ func (c *context) Release() {}
 func (c *context) FullStateChanged() {}
 
 // PullFullState implements platform.Context.PullFullState.
-func (c *context) PullFullState(as platform.AddressSpace, ac *arch.Context64) {}
+func (c *context) PullFullState(as platform.AddressSpace, ac *arch.Context64) error { return nil }
 
 // PrepareSleep implements platform.Context.platform.PrepareSleep.
 func (*context) PrepareSleep() {}

pkg/sentry/syscalls/linux/sys_signal.go

@@ -323,26 +323,8 @@ func Sigaltstack(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.S
 	setaddr := args[0].Pointer()
 	oldaddr := args[1].Pointer()
 
-	alt := t.SignalStack()
-	if oldaddr != 0 {
-		if _, err := alt.CopyOut(t, oldaddr); err != nil {
-			return 0, nil, err
-		}
-	}
-	if setaddr != 0 {
-		if _, err := alt.CopyIn(t, setaddr); err != nil {
-			return 0, nil, err
-		}
-		// The signal stack cannot be changed if the task is currently
-		// on the stack. This is enforced at the lowest level because
-		// these semantics apply to changing the signal stack via a
-		// ucontext during a signal handler.
-		if !t.SetSignalStack(alt) {
-			return 0, nil, linuxerr.EPERM
-		}
-	}
-
-	return 0, nil, nil
+	ctrl, err := t.SigaltStack(setaddr, oldaddr)
+	return 0, ctrl, err
 }
 
 // Pause implements linux syscall pause(2).