/
syscalls_linux.go
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/
syscalls_linux.go
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// Copyright 2015 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 host
import (
"bytes"
"fmt"
"io/ioutil"
"os"
"regexp"
"runtime"
"strconv"
"strings"
"sync"
"syscall"
"time"
"github.com/google/syzkaller/pkg/log"
"github.com/google/syzkaller/pkg/osutil"
"github.com/google/syzkaller/prog"
)
func isSupported(c *prog.Syscall, target *prog.Target, sandbox string) (bool, string) {
log.Logf(2, "checking support for %v", c.Name)
if strings.HasPrefix(c.CallName, "syz_") {
return isSupportedSyzkall(sandbox, c)
}
if reason := isSupportedLSM(c); reason != "" {
return false, reason
}
if strings.HasPrefix(c.Name, "socket$") ||
strings.HasPrefix(c.Name, "socketpair$") {
return isSupportedSocket(c)
}
if strings.HasPrefix(c.Name, "openat$") {
return isSupportedOpenAt(c)
}
if strings.HasPrefix(c.Name, "mount$") {
return isSupportedMount(c, sandbox)
}
if c.Name == "ioctl$EXT4_IOC_SHUTDOWN" && sandbox == "none" {
// Don't shutdown root filesystem.
return false, "unsafe with sandbox=none"
}
// There are 3 possible strategies for detecting supported syscalls:
// 1. Executes all syscalls with presumably invalid arguments and check for ENOprog.
// But not all syscalls are safe to execute. For example, pause will hang,
// while setpgrp will push the process into own process group.
// 2. Check presence of /sys/kernel/debug/tracing/events/syscalls/sys_enter_* files.
// This requires root and CONFIG_FTRACE_SYSCALLS. Also it lies for some syscalls.
// For example, on x86_64 it says that sendfile is not present (only sendfile64).
// 3. Check sys_syscallname in /proc/kallsyms.
// Requires CONFIG_KALLSYMS.
// Kallsyms seems to be the most reliable and fast. That's what we use first.
// If kallsyms is not present, we fallback to execution of syscalls.
kallsymsOnce.Do(func() {
kallsyms, _ := ioutil.ReadFile("/proc/kallsyms")
if len(kallsyms) == 0 {
return
}
kallsymsSyscallSet = parseKallsyms(kallsyms, target.Arch)
})
if !testFallback && len(kallsymsSyscallSet) != 0 {
r, v := isSupportedKallsyms(c)
return r, v
}
return isSupportedTrial(c)
}
func parseKallsyms(kallsyms []byte, arch string) map[string]bool {
set := make(map[string]bool)
var re *regexp.Regexp
switch arch {
case "386", "amd64":
re = regexp.MustCompile(` T (__ia32_|__x64_)?sys_([^\n]+)\n`)
case "arm", "arm64":
re = regexp.MustCompile(` T (__arm64_)?sys_([^\n]+)\n`)
case "ppc64le":
re = regexp.MustCompile(` T ()?sys_([^\n]+)\n`)
case "mips64le":
re = regexp.MustCompile(` T sys_(mips_)?([^\n]+)\n`)
default:
panic("unsupported arch for kallsyms parsing")
}
matches := re.FindAllSubmatch(kallsyms, -1)
for _, m := range matches {
name := string(m[2])
log.Logf(2, "found in kallsyms: %v", name)
set[name] = true
}
return set
}
func isSupportedKallsyms(c *prog.Syscall) (bool, string) {
name := c.CallName
if newname := kallsymsRenameMap[name]; newname != "" {
name = newname
}
if !kallsymsSyscallSet[name] {
return false, fmt.Sprintf("sys_%v is not present in /proc/kallsyms", name)
}
return true, ""
}
func isSupportedTrial(c *prog.Syscall) (bool, string) {
switch c.CallName {
// These known to cause hangs.
case "exit", "pause":
return true, ""
}
trialMu.Lock()
defer trialMu.Unlock()
if res, ok := trialSupported[c.NR]; ok {
return res, "ENOSYS"
}
cmd := osutil.Command(os.Args[0])
cmd.Env = []string{fmt.Sprintf("SYZ_TRIAL_TEST=%v", c.NR)}
_, err := osutil.Run(10*time.Second, cmd)
res := err != nil
trialSupported[c.NR] = res
return res, "ENOSYS"
}
func init() {
str := os.Getenv("SYZ_TRIAL_TEST")
if str == "" {
return
}
nr, err := strconv.Atoi(str)
if err != nil {
panic(err)
}
arg := ^uintptr(0) - 1e4 // something as invalid as possible
_, _, err = syscall.Syscall6(uintptr(nr), arg, arg, arg, arg, arg, arg)
if err == syscall.ENOSYS {
os.Exit(0)
}
os.Exit(1)
}
// Some syscall names diverge in __NR_* consts and kallsyms.
// umount2 is renamed to umount in arch/x86/entry/syscalls/syscall_64.tbl.
// Where umount is renamed to oldumount is unclear.
var (
kallsymsOnce sync.Once
kallsymsSyscallSet map[string]bool
kallsymsRenameMap = map[string]string{
"umount": "oldumount",
"umount2": "umount",
"stat": "newstat",
}
trialMu sync.Mutex
trialSupported = make(map[uint64]bool)
filesystems []byte
filesystemsOnce sync.Once
lsmOnce sync.Once
lsmError error
lsmDisabled map[string]bool
)
// The function is lengthy as it handles all pseudo-syscalls,
// but it does not seem to cause comprehension problems as there is no shared state.
// Splitting this per-syscall will only increase code size.
// nolint: gocyclo
func isSupportedSyzkall(sandbox string, c *prog.Syscall) (bool, string) {
switch c.CallName {
case "syz_open_dev":
if _, ok := c.Args[0].(*prog.ConstType); ok {
// This is for syz_open_dev$char/block.
// They are currently commented out, but in case one enables them.
return true, ""
}
fname, ok := extractStringConst(c.Args[0])
if !ok {
panic("first open arg is not a pointer to string const")
}
if checkUSBInjection() == "" {
// These entries might not be available at boot time,
// but will be created by connected USB devices.
USBDevicePrefixes := []string{
"/dev/hidraw", "/dev/usb/hiddev", "/dev/input/",
}
for _, prefix := range USBDevicePrefixes {
if strings.HasPrefix(fname, prefix) {
return true, ""
}
}
}
var check func(dev string) bool
check = func(dev string) bool {
if !strings.Contains(dev, "#") {
// Note: don't try to open them all, some can hang (e.g. /dev/snd/pcmC#D#p).
return osutil.IsExist(dev)
}
for i := 0; i < 10; i++ {
if check(strings.Replace(dev, "#", strconv.Itoa(i), 1)) {
return true
}
}
return false
}
if !check(fname) {
return false, fmt.Sprintf("file %v does not exist", fname)
}
return onlySandboxNoneOrNamespace(sandbox)
case "syz_open_procfs":
return true, ""
case "syz_open_pts":
return true, ""
case "syz_emit_ethernet", "syz_extract_tcp_res":
reason := checkNetInjection()
return reason == "", reason
case "syz_usb_connect", "syz_usb_disconnect", "syz_usb_control_io", "syz_usb_ep_write", "syz_usb_ep_read":
reason := checkUSBInjection()
return reason == "", reason
case "syz_kvm_setup_cpu":
switch c.Name {
case "syz_kvm_setup_cpu$x86":
if runtime.GOARCH == "amd64" || runtime.GOARCH == "386" {
return true, ""
}
case "syz_kvm_setup_cpu$arm64":
if runtime.GOARCH == "arm64" {
return true, ""
}
}
return false, "unsupported arch"
case "syz_init_net_socket":
// Unfortunately this only works with sandbox none at the moment.
// The problem is that setns of a network namespace requires CAP_SYS_ADMIN
// in the target namespace, and we've lost all privs in the init namespace
// during creation of a user namespace.
if ok, reason := onlySandboxNone(sandbox); !ok {
return false, reason
}
return isSupportedSocket(c)
case "syz_genetlink_get_family_id":
fd, err := syscall.Socket(syscall.AF_NETLINK, syscall.SOCK_RAW, syscall.NETLINK_GENERIC)
if fd == -1 {
return false, fmt.Sprintf("socket(AF_NETLINK, SOCK_RAW, NETLINK_GENERIC) failed: %v", err)
}
syscall.Close(fd)
return true, ""
case "syz_mount_image":
if ok, reason := onlySandboxNone(sandbox); !ok {
return ok, reason
}
fstype, ok := extractStringConst(c.Args[0])
if !ok {
panic("syz_mount_image arg is not string")
}
return isSupportedFilesystem(fstype)
case "syz_read_part_table":
return onlySandboxNone(sandbox)
case "syz_execute_func":
return true, ""
}
panic("unknown syzkall: " + c.Name)
}
func isSupportedLSM(c *prog.Syscall) string {
lsmOnce.Do(func() {
data, err := ioutil.ReadFile("/sys/kernel/security/lsm")
if err != nil {
// securityfs may not be mounted, but it does not mean
// that no LSMs are enabled.
if !os.IsNotExist(err) {
lsmError = err
}
return
}
lsmDisabled = make(map[string]bool)
for _, lsm := range []string{"selinux", "apparmor", "smack"} {
if !strings.Contains(string(data), lsm) {
lsmDisabled[lsm] = true
}
}
})
if lsmError != nil {
return lsmError.Error()
}
for lsm := range lsmDisabled {
if strings.Contains(strings.ToLower(c.Name), lsm) {
return fmt.Sprintf("LSM %v is not enabled", lsm)
}
}
return ""
}
func onlySandboxNone(sandbox string) (bool, string) {
if syscall.Getuid() != 0 || sandbox != "none" {
return false, "only supported under root with sandbox=none"
}
return true, ""
}
func onlySandboxNoneOrNamespace(sandbox string) (bool, string) {
if syscall.Getuid() != 0 || sandbox == "setuid" {
return false, "only supported under root with sandbox=none/namespace"
}
return true, ""
}
func isSupportedSocket(c *prog.Syscall) (bool, string) {
af, ok := c.Args[0].(*prog.ConstType)
if !ok {
panic("socket family is not const")
}
fd, err := syscall.Socket(int(af.Val), 0, 0)
if fd != -1 {
syscall.Close(fd)
}
if err == syscall.ENOSYS {
return false, "socket syscall returns ENOSYS"
}
if err == syscall.EAFNOSUPPORT {
return false, "socket family is not supported (EAFNOSUPPORT)"
}
proto, ok := c.Args[2].(*prog.ConstType)
if !ok {
return true, ""
}
var typ uint64
if arg, ok := c.Args[1].(*prog.ConstType); ok {
typ = arg.Val
} else if arg, ok := c.Args[1].(*prog.FlagsType); ok {
typ = arg.Vals[0]
} else {
return true, ""
}
fd, err = syscall.Socket(int(af.Val), int(typ), int(proto.Val))
if fd != -1 {
syscall.Close(fd)
return true, ""
}
return false, err.Error()
}
func isSupportedOpenAt(c *prog.Syscall) (bool, string) {
var fd int
var err error
fname, ok := extractStringConst(c.Args[1])
if !ok || len(fname) == 0 || fname[0] != '/' {
return true, ""
}
modes := []int{syscall.O_RDONLY, syscall.O_WRONLY, syscall.O_RDWR}
// Attempt to extract flags from the syscall description
if mode, ok := c.Args[2].(*prog.ConstType); ok {
modes = []int{int(mode.Val)}
}
for _, mode := range modes {
fd, err = syscall.Open(fname, mode, 0)
if fd != -1 {
syscall.Close(fd)
}
if err == nil {
return true, ""
}
}
return false, fmt.Sprintf("open(%v) failed: %v", fname, err)
}
func isSupportedMount(c *prog.Syscall, sandbox string) (bool, string) {
fstype, ok := extractStringConst(c.Args[2])
if !ok {
panic(fmt.Sprintf("%v: filesystem is not string const", c.Name))
}
if ok, reason := isSupportedFilesystem(fstype); !ok {
return ok, reason
}
switch fstype {
case "fuse", "fuseblk":
if err := osutil.IsAccessible("/dev/fuse"); err != nil {
return false, err.Error()
}
return onlySandboxNoneOrNamespace(sandbox)
default:
return onlySandboxNone(sandbox)
}
}
func isSupportedFilesystem(fstype string) (bool, string) {
filesystemsOnce.Do(func() {
filesystems, _ = ioutil.ReadFile("/proc/filesystems")
})
if !bytes.Contains(filesystems, []byte("\t"+fstype+"\n")) {
return false, fmt.Sprintf("/proc/filesystems does not contain %v", fstype)
}
return true, ""
}
func extractStringConst(typ prog.Type) (string, bool) {
ptr, ok := typ.(*prog.PtrType)
if !ok {
panic("first open arg is not a pointer to string const")
}
str, ok := ptr.Type.(*prog.BufferType)
if !ok || str.Kind != prog.BufferString || len(str.Values) == 0 {
return "", false
}
v := str.Values[0]
for len(v) != 0 && v[len(v)-1] == 0 {
v = v[:len(v)-1] // string terminating \x00
}
return v, true
}