runtime: don't crash if signal delivered on g0 stack

Also, if we changed the gsignal stack to match the stack we are
executing on, restore it when returning from the signal handler, for
safety.

Fixes #18255.

Change-Id: Ic289b36e4e38a56f8a6d4b5d74f68121c242e81a
Reviewed-on: https://go-review.googlesource.com/34239
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
Reviewed-by: David Crawshaw <crawshaw@golang.org>

misc/cgo/testsanitizers/test.bash

@@ -145,6 +145,7 @@ if test "$tsan" = "yes"; then
     testtsan tsan3.go
     testtsan tsan4.go
     testtsan tsan8.go
+    testtsan tsan9.go
 
     # These tests are only reliable using clang or GCC version 7 or later.
     # Otherwise runtime/cgo/libcgo.h can't tell whether TSAN is in use.

misc/cgo/testsanitizers/tsan9.go

+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+// This program failed when run under the C/C++ ThreadSanitizer. The
+// TSAN library was not keeping track of whether signals should be
+// delivered on the alternate signal stack.
+
+/*
+#cgo CFLAGS: -g -fsanitize=thread
+#cgo LDFLAGS: -g -fsanitize=thread
+
+#include <stdlib.h>
+#include <sys/time.h>
+
+void spin() {
+	size_t n;
+	struct timeval tvstart, tvnow;
+	int diff;
+
+	gettimeofday(&tvstart, NULL);
+	for (n = 0; n < 1<<20; n++) {
+		free(malloc(n));
+		gettimeofday(&tvnow, NULL);
+		diff = (tvnow.tv_sec - tvstart.tv_sec) * 1000 * 1000 + (tvnow.tv_usec - tvstart.tv_usec);
+
+		// Profile frequency is 100Hz so we should definitely
+		// get a signal in 50 milliseconds.
+		if (diff > 50 * 1000) {
+			break;
+		}
+	}
+}
+*/
+import "C"
+
+import (
+	"io/ioutil"
+	"runtime/pprof"
+	"time"
+)
+
+func goSpin() {
+	start := time.Now()
+	for n := 0; n < 1<<20; n++ {
+		_ = make([]byte, n)
+		if time.Since(start) > 50*time.Millisecond {
+			break
+		}
+	}
+}
+
+func main() {
+	pprof.StartCPUProfile(ioutil.Discard)
+	go C.spin()
+	goSpin()
+	pprof.StopCPUProfile()
+}

src/runtime/signal_unix.go

@@ -212,8 +212,24 @@ func sigtrampgo(sig uint32, info *siginfo, ctx unsafe.Pointer) {
 	}
 
 	// If some non-Go code called sigaltstack, adjust.
+	setStack := false
+	var gsignalStack gsignalStack
 	sp := uintptr(unsafe.Pointer(&sig))
 	if sp < g.m.gsignal.stack.lo || sp >= g.m.gsignal.stack.hi {
+		if sp >= g.m.g0.stack.lo && sp < g.m.g0.stack.hi {
+			// The signal was delivered on the g0 stack.
+			// This can happen when linked with C code
+			// using the thread sanitizer, which collects
+			// signals then delivers them itself by calling
+			// the signal handler directly when C code,
+			// including C code called via cgo, calls a
+			// TSAN-intercepted function such as malloc.
+			st := stackt{ss_size: g.m.g0.stack.hi - g.m.g0.stack.lo}
+			setSignalstackSP(&st, g.m.g0.stack.lo)
+			setGsignalStack(&st, &gsignalStack)
+			g.m.gsignal.stktopsp = getcallersp(unsafe.Pointer(&sig))
+			setStack = true
+		} else {
 			var st stackt
 			sigaltstack(nil, &st)
 			if st.ss_flags&_SS_DISABLE != 0 {
@@ -229,8 +245,10 @@ func sigtrampgo(sig uint32, info *siginfo, ctx unsafe.Pointer) {
 				sigNotOnStack(sig)
 				dropm()
 			}
-		setGsignalStack(&st)
+			setGsignalStack(&st, &gsignalStack)
 			g.m.gsignal.stktopsp = getcallersp(unsafe.Pointer(&sig))
+			setStack = true
+		}
 	}
 
 	setg(g.m.gsignal)
@@ -238,6 +256,9 @@ func sigtrampgo(sig uint32, info *siginfo, ctx unsafe.Pointer) {
 	c.fixsigcode(sig)
 	sighandler(sig, info, ctx, g)
 	setg(g)
+	if setStack {
+		restoreGsignalStack(&gsignalStack)
+	}
 }
 
 // sigpanic turns a synchronous signal into a run-time panic.
@@ -585,7 +606,7 @@ func minitSignalStack() {
 		signalstack(&_g_.m.gsignal.stack)
 		_g_.m.newSigstack = true
 	} else {
-		setGsignalStack(&st)
+		setGsignalStack(&st, nil)
 		_g_.m.newSigstack = false
 	}
 }
@@ -618,14 +639,32 @@ func unminitSignals() {
 	}
 }
 
+// gsignalStack saves the fields of the gsignal stack changed by
+// setGsignalStack.
+type gsignalStack struct {
+	stack       stack
+	stackguard0 uintptr
+	stackguard1 uintptr
+	stackAlloc  uintptr
+	stktopsp    uintptr
+}
+
 // setGsignalStack sets the gsignal stack of the current m to an
 // alternate signal stack returned from the sigaltstack system call.
+// It saves the old values in *old for use by restoreGsignalStack.
 // This is used when handling a signal if non-Go code has set the
 // alternate signal stack.
 //go:nosplit
 //go:nowritebarrierrec
-func setGsignalStack(st *stackt) {
+func setGsignalStack(st *stackt, old *gsignalStack) {
 	g := getg()
+	if old != nil {
+		old.stack = g.m.gsignal.stack
+		old.stackguard0 = g.m.gsignal.stackguard0
+		old.stackguard1 = g.m.gsignal.stackguard1
+		old.stackAlloc = g.m.gsignal.stackAlloc
+		old.stktopsp = g.m.gsignal.stktopsp
+	}
 	stsp := uintptr(unsafe.Pointer(st.ss_sp))
 	g.m.gsignal.stack.lo = stsp
 	g.m.gsignal.stack.hi = stsp + st.ss_size
@@ -634,6 +673,19 @@ func setGsignalStack(st *stackt) {
 	g.m.gsignal.stackAlloc = st.ss_size
 }
 
+// restoreGsignalStack restores the gsignal stack to the value it had
+// before entering the signal handler.
+//go:nosplit
+//go:nowritebarrierrec
+func restoreGsignalStack(st *gsignalStack) {
+	gp := getg().m.gsignal
+	gp.stack = st.stack
+	gp.stackguard0 = st.stackguard0
+	gp.stackguard1 = st.stackguard1
+	gp.stackAlloc = st.stackAlloc
+	gp.stktopsp = st.stktopsp
+}
+
 // signalstack sets the current thread's alternate signal stack to s.
 //go:nosplit
 func signalstack(s *stack) {