3 files changed, 22 insertions, 7 deletions
diff --git a/pkg/sentry/arch/arch.go b/pkg/sentry/arch/arch.go
index 021789e4b..0189e958d 100644
--- a/pkg/sentry/arch/arch.go
+++ b/pkg/sentry/arch/arch.go
@@ -158,7 +158,7 @@ type Context interface {
 	// rt is true if SignalRestore is being entered from rt_sigreturn and
 	// false if SignalRestore is being entered from sigreturn.
 	// SignalRestore returns the thread's new signal mask.
-	SignalRestore(st *Stack, rt bool) (linux.SignalSet, error)
+	SignalRestore(st *Stack, rt bool) (linux.SignalSet, SignalStack, error)
 
 	// CPUIDEmulate emulates a CPUID instruction according to current register state.
 	CPUIDEmulate(l log.Logger)
diff --git a/pkg/sentry/arch/signal_amd64.go b/pkg/sentry/arch/signal_amd64.go
index 4040b530f..c1d743f38 100644
--- a/pkg/sentry/arch/signal_amd64.go
+++ b/pkg/sentry/arch/signal_amd64.go
@@ -377,6 +377,14 @@ func (c *context64) SignalSetup(st *Stack, act *SignalAct, info *SignalInfo, alt
 	sp = frameBottom + usermem.Addr(frameSize)
 	st.Bottom = sp
 
+	// Prior to proceeding, figure out if the frame will exhaust the range
+	// for the signal stack. This is not allowed, and should immediately
+	// force signal delivery (reverting to the default handler).
+	if act.IsOnStack() && alt.IsEnabled() && !alt.Contains(frameBottom) {
+		return syscall.EFAULT
+	}
+
+	// Adjust the code.
 	info.FixSignalCodeForUser()
 
 	// Set up the stack frame.
@@ -422,15 +430,15 @@ func (c *context64) SignalSetup(st *Stack, act *SignalAct, info *SignalInfo, alt
 
 // SignalRestore implements Context.SignalRestore. (Compare to Linux's
 // arch/x86/kernel/signal.c:sys_rt_sigreturn().)
-func (c *context64) SignalRestore(st *Stack, rt bool) (linux.SignalSet, error) {
+func (c *context64) SignalRestore(st *Stack, rt bool) (linux.SignalSet, SignalStack, error) {
 	// Copy out the stack frame.
 	var uc UContext64
 	if _, err := st.Pop(&uc); err != nil {
-		return 0, err
+		return 0, SignalStack{}, err
 	}
 	var info SignalInfo
 	if _, err := st.Pop(&info); err != nil {
-		return 0, err
+		return 0, SignalStack{}, err
 	}
 
 	// Restore registers.
@@ -472,5 +480,5 @@ func (c *context64) SignalRestore(st *Stack, rt bool) (linux.SignalSet, error) {
 		log.Infof("sigreturn unable to restore application fpstate")
 	}
 
-	return uc.Sigset, nil
+	return uc.Sigset, uc.Stack, nil
 }
diff --git a/pkg/sentry/arch/signal_stack.go b/pkg/sentry/arch/signal_stack.go
index 7c6531d79..ba43dd1d4 100644
--- a/pkg/sentry/arch/signal_stack.go
+++ b/pkg/sentry/arch/signal_stack.go
@@ -39,12 +39,19 @@ func (s SignalStack) Top() usermem.Addr {
 	return usermem.Addr(s.Addr + s.Size)
 }
 
-// SetOnStack marks this signal stack as in use. (This is only called on copies
-// sent to user applications, so there's no corresponding ClearOnStack.)
+// SetOnStack marks this signal stack as in use.
+//
+// Note that there is no corresponding ClearOnStack, and that this should only
+// be called on copies that are serialized to userspace.
 func (s *SignalStack) SetOnStack() {
 	s.Flags |= SignalStackFlagOnStack
 }
 
+// Contains checks if the stack pointer is within this stack.
+func (s *SignalStack) Contains(sp usermem.Addr) bool {
+	return usermem.Addr(s.Addr) < sp && sp <= usermem.Addr(s.Addr+s.Size)
+}
+
 // NativeSignalStack is a type that is equivalent to stack_t in the guest
 // architecture.
 type NativeSignalStack interface {