vm/qemu, vm/gce: dump LOCKDEP state in Diagnose

For context see the discussion at:
https://groups.google.com/g/syzkaller/c/ruwaYUvwHTw/m/E9Cg9OfvAgAJ

3 files changed, 60 insertions, 10 deletions

diff --git a/vm/gce/gce.go b/vm/gce/gce.go
index b5565aff0..c4cd9f184 100644
--- a/vm/gce/gce.go
+++ b/vm/gce/gce.go
@@ -20,6 +20,7 @@ import (
 	"io/ioutil"
 	"os"
 	"path/filepath"
+	"strings"
 	"time"
 
 	"github.com/google/syzkaller/pkg/config"
@@ -266,13 +267,7 @@ func (inst *instance) Run(timeout time.Duration, stop <-chan bool, command strin
 		sshRpipe.Close()
 		return nil, nil, err
 	}
-	if inst.env.OS == targets.Linux {
-		if inst.sshUser != "root" {
-			command = fmt.Sprintf("sudo bash -c '%v'", command)
-		}
-	}
-	args := append(vmimpl.SSHArgs(inst.debug, inst.sshKey, 22), inst.sshUser+"@"+inst.ip, command)
-	ssh := osutil.Command("ssh", args...)
+	ssh := osutil.Command("ssh", inst.sshArgs(command)...)
 	ssh.Stdout = sshWpipe
 	ssh.Stderr = sshWpipe
 	if err := ssh.Start(); err != nil {
@@ -371,15 +366,30 @@ func waitForConsoleConnect(merger *vmimpl.OutputMerger) error {
 }
 
 func (inst *instance) Diagnose(rep *report.Report) ([]byte, bool) {
-	if inst.env.OS == targets.FreeBSD {
+	switch inst.env.OS {
+	case targets.Linux:
+		output, wait, _ := vmimpl.DiagnoseLinux(rep, inst.ssh)
+		return output, wait
+	case targets.FreeBSD:
 		return vmimpl.DiagnoseFreeBSD(inst.consolew)
-	}
-	if inst.env.OS == targets.OpenBSD {
+	case targets.OpenBSD:
 		return vmimpl.DiagnoseOpenBSD(inst.consolew)
 	}
 	return nil, false
 }
 
+func (inst *instance) ssh(args ...string) ([]byte, error) {
+	return osutil.RunCmd(time.Minute, "", "ssh", inst.sshArgs(args...)...)
+}
+
+func (inst *instance) sshArgs(args ...string) []string {
+	sshArgs := append(vmimpl.SSHArgs(inst.debug, inst.sshKey, 22), inst.sshUser+"@"+inst.ip)
+	if inst.env.OS == targets.Linux && inst.sshUser != "root" {
+		args = []string{"sudo", "bash", "-c", "'" + strings.Join(args, " ") + "'"}
+	}
+	return append(sshArgs, args...)
+}
+
 func (pool *Pool) getSerialPortOutput(name, gceKey string) ([]byte, error) {
 	conRpipe, conWpipe, err := osutil.LongPipe()
 	if err != nil {
diff --git a/vm/qemu/qemu.go b/vm/qemu/qemu.go
index d0689fa1d..eaa82cbb2 100644
--- a/vm/qemu/qemu.go
+++ b/vm/qemu/qemu.go
@@ -621,6 +621,11 @@ func (inst *instance) Run(timeout time.Duration, stop <-chan bool, command strin
 }
 
 func (inst *instance) Diagnose(rep *report.Report) ([]byte, bool) {
+	if inst.target.OS == targets.Linux {
+		if output, wait, handled := vmimpl.DiagnoseLinux(rep, inst.ssh); handled {
+			return output, wait
+		}
+	}
 	// TODO: we don't need registers on all reports. Probably only relevant for "crashes"
 	// (NULL derefs, paging faults, etc), but is not useful for WARNING/BUG/HANG (?).
 	ret := []byte(fmt.Sprintf("%s Registers:\n", time.Now().Format("15:04:05 ")))
@@ -637,6 +642,15 @@ func (inst *instance) Diagnose(rep *report.Report) ([]byte, bool) {
 	return ret, false
 }
 
+func (inst *instance) ssh(args ...string) ([]byte, error) {
+	return osutil.RunCmd(time.Minute, "", "ssh", inst.sshArgs(args...)...)
+}
+
+func (inst *instance) sshArgs(args ...string) []string {
+	sshArgs := append(vmimpl.SSHArgs(inst.debug, inst.sshkey, inst.port), inst.sshuser+"@localhost")
+	return append(sshArgs, args...)
+}
+
 // nolint: lll
 const initScript = `#! /bin/bash
 set -eux
diff --git a/vm/vmimpl/linux.go b/vm/vmimpl/linux.go
new file mode 100644
index 000000000..0406035f6
--- /dev/null
+++ b/vm/vmimpl/linux.go
@@ -0,0 +1,26 @@
+// Copyright 2020 syzkaller project authors. All rights reserved.
+// Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.
+
+package vmimpl
+
+import (
+	"regexp"
+	"strings"
+
+	"github.com/google/syzkaller/pkg/report"
+)
+
+// DiagnoseLinux diagnoses some Linux kernel bugs over the provided ssh callback.
+func DiagnoseLinux(rep *report.Report, ssh func(args ...string) ([]byte, error)) (output []byte, wait, handled bool) {
+	if !strings.Contains(rep.Title, "MAX_LOCKDEP") {
+		return nil, false, false
+	}
+	// Dump /proc/lockdep* files on BUG: MAX_LOCKDEP_{KEYS,ENTRIES,CHAINS,CHAIN_HLOCKS} too low!
+	output, err := ssh("cat", "/proc/lockdep_stats", "/proc/lockdep", "/proc/lockdep_chains")
+	if err != nil {
+		output = append(output, err.Error()...)
+	}
+	// Remove mangled pointer values, they take lots of space but don't add any value.
+	output = regexp.MustCompile(` *\[?[0-9a-f]{8,}\]?\s*`).ReplaceAll(output, nil)
+	return output, false, true
+}