runtime: fix crash during VDSO calls on arm

As discussed in #32912, a crash occurs when go runtime calls a VDSO function (say
__vdso_clock_gettime) and a signal arrives to that thread.
Since VDSO functions temporarily destroy the G register (R10),
Go functions asynchronously executed in that thread (i.e. Go's signal
handler) can try to load data from the destroyed G, which causes
segmentation fault.

To fix the issue a guard is inserted in front of sigtrampgo, so that the control escapes from
signal handlers without touching G in case the signal occurred in the VDSO context.
The test case included in the patch is take from discussion in a relevant thread on github:
https://github.com/golang/go/issues/32912#issuecomment-517874531.
This patch not only fixes the issue on AArch64 but also that on 32bit ARM.

Fixes #32912

Change-Id: I657472e54b7aa3c617fabc5019ce63aa4105624a
GitHub-Last-Rev: 28ce42c4a02a060f08c1b0dd1c9a392123fd2ee9
GitHub-Pull-Request: golang/go#34030
Reviewed-on: https://go-review.googlesource.com/c/go/+/192937
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

1 files changed, 55 insertions, 0 deletions

diff --git a/src/runtime/testdata/testprog/vdso.go b/src/runtime/testdata/testprog/vdso.go
new file mode 100644
index 0000000000..6036f45bc8
--- /dev/null
+++ b/src/runtime/testdata/testprog/vdso.go
@@ -0,0 +1,55 @@
+// Copyright 2019 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.
+
+// Invoke signal hander in the VDSO context (see issue 32912).
+
+package main
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"runtime/pprof"
+	"time"
+)
+
+func init() {
+	register("SignalInVDSO", signalInVDSO)
+}
+
+func signalInVDSO() {
+        f, err := ioutil.TempFile("", "timeprofnow")
+        if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(2)
+        }
+
+        if err := pprof.StartCPUProfile(f); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(2)
+        }
+
+        t0 := time.Now()
+        t1 := t0
+        // We should get a profiling signal 100 times a second,
+        // so running for 1 second should be sufficient.
+        for t1.Sub(t0) < time.Second {
+                t1 = time.Now()
+        }
+
+        pprof.StopCPUProfile()
+
+        name := f.Name()
+        if err := f.Close(); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(2)
+        }
+
+        if err := os.Remove(name); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(2)
+        }
+
+	fmt.Println("success");
+}