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// Copyright 2017 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 openbsd
import (
"fmt"
"math"
"github.com/google/syzkaller/prog"
"github.com/google/syzkaller/sys/targets"
)
func InitTarget(target *prog.Target) {
arch := &arch{
unix: targets.MakeUnixNeutralizer(target),
CTL_KERN: target.GetConst("CTL_KERN"),
DIOCCLRSTATES: target.GetConst("DIOCCLRSTATES"),
DIOCKILLSTATES: target.GetConst("DIOCKILLSTATES"),
KERN_MAXCLUSTERS: target.GetConst("KERN_MAXCLUSTERS"),
S_IFCHR: target.GetConst("S_IFCHR"),
S_IFMT: target.GetConst("S_IFMT"),
MCL_FUTURE: target.GetConst("MCL_FUTURE"),
RLIMIT_DATA: target.GetConst("RLIMIT_DATA"),
RLIMIT_STACK: target.GetConst("RLIMIT_STACK"),
}
target.MakeDataMmap = targets.MakePosixMmap(target, false, false)
target.Neutralize = arch.neutralize
target.AnnotateCall = arch.annotateCall
}
type arch struct {
unix *targets.UnixNeutralizer
CTL_KERN uint64
DIOCCLRSTATES uint64
DIOCKILLSTATES uint64
KERN_MAXCLUSTERS uint64
S_IFCHR uint64
S_IFMT uint64
MCL_FUTURE uint64
RLIMIT_DATA uint64
RLIMIT_STACK uint64
}
const (
mknodMode = 0
mknodDev = 1
// openbsd:src/etc/etc.amd64/MAKEDEV
devFdMajor = 22
devNullDevT = 0x0202
// kCoverFd in executor/executor.cc
kcovFdMinorMin = 232
// kOutPipeFd in executor/executor.cc
kcovFdMinorMax = 248
// Mask covering all valid rlimit resources.
rlimitMask = 0xf
)
// openbsd:src/sys/sys/types.h
func devmajor(dev uint64) uint64 {
return (dev >> 8) & 0xff
}
// openbsd:src/sys/sys/types.h
func devminor(dev uint64) uint64 {
return (dev & 0xff) | ((dev & 0xffff0000) >> 8)
}
func isKcovFd(dev uint64) bool {
major := devmajor(dev)
minor := devminor(dev)
return major == devFdMajor && minor >= kcovFdMinorMin && minor < kcovFdMinorMax
}
func (arch *arch) neutralize(c *prog.Call) {
argStart := 1
switch c.Meta.CallName {
case "chflagsat":
argStart = 2
fallthrough
case "chflags", "fchflags":
// Prevent changing mutability flags on files. This is
// especially problematic for file descriptors referring to
// tty/pty devices since it can cause the SSH connection to the
// VM to die.
flags := c.Args[argStart].(*prog.ConstArg)
badflags := [...]uint64{
0x00000002, // UF_IMMUTABLE
0x00000004, // UF_APPEND
0x00020000, // SF_IMMUTABLE
0x00040000, // SF_APPEND
}
for _, f := range badflags {
flags.Val &= ^f
}
case "ioctl":
// Performing the following ioctl commands on a /dev/pf file
// descriptor causes the ssh VM connection to die. For now, just
// rewire them to an invalid command.
request := c.Args[1].(*prog.ConstArg)
if request.Val == arch.DIOCCLRSTATES || request.Val == arch.DIOCKILLSTATES {
request.Val = 0
}
case "mknodat":
argStart = 2
fallthrough
case "mknod":
// Prevent vnodes of type VBAD from being created. Such vnodes will
// likely trigger assertion errors by the kernel.
mode := c.Args[argStart+mknodMode].(*prog.ConstArg)
if mode.Val&arch.S_IFMT == arch.S_IFMT {
mode.Val &^= arch.S_IFMT
mode.Val |= arch.S_IFCHR
}
// Prevent /dev/fd/X devices from getting created where X maps
// to an open kcov fd. They interfere with kcov data collection
// and cause corpus explosion.
// https://groups.google.com/d/msg/syzkaller/_IRWeAjVoy4/Akl2XMZTDAAJ
dev := c.Args[argStart+mknodDev].(*prog.ConstArg)
if isKcovFd(dev.Val) {
dev.Val = devNullDevT
}
// Prevent /dev/sd0b (swap partition) and /dev/sd0c (raw disk)
// nodes from being created. Writing to such devices can corrupt
// the file system.
if devmajor(dev.Val) == 4 && (devminor(dev.Val) == 1 || devminor(dev.Val) == 2) {
dev.Val = devNullDevT
}
case "mlockall":
flags := c.Args[0].(*prog.ConstArg)
flags.Val &= ^arch.MCL_FUTURE
case "setrlimit":
arch.neutralizeRlimit(c)
case "sysctl":
arch.neutralizeSysctl(c)
default:
arch.unix.Neutralize(c)
}
}
func (arch *arch) neutralizeRlimit(c *prog.Call) {
rlimitMin := uint64(0)
rlimitMax := uint64(math.MaxUint64)
resource := c.Args[0].(*prog.ConstArg).Val & rlimitMask
if resource == arch.RLIMIT_DATA {
// OpenBSD performs a strict validation of the RLIMIT_DATA soft
// limit during memory allocation. Lowering the same limit could
// cause syz-executor to run out of memory quickly. Therefore
// make sure to not go lower than the default soft limit for the
// staff group.
rlimitMin = 1536 * 1024 * 1024
} else if resource == arch.RLIMIT_STACK {
// Do not allow the stack to grow beyond the initial soft limit
// chosen by syz-executor. Otherwise, syz-executor will most
// likely not be able to perform any more heap allocations since
// they majority of memory is reserved for the stack.
rlimitMax = 1 * 1024 * 1024
} else {
return
}
ptr := c.Args[1].(*prog.PointerArg)
if ptr.Res == nil {
return
}
args := ptr.Res.(*prog.GroupArg).Inner
for _, arg := range args {
switch v := arg.(type) {
case *prog.ConstArg:
if v.Val < rlimitMin {
v.Val = rlimitMin
}
if v.Val > rlimitMax {
v.Val = rlimitMax
}
}
}
}
func (arch *arch) neutralizeSysctl(c *prog.Call) {
ptr := c.Args[0].(*prog.PointerArg)
if ptr.Res == nil {
return
}
mib := ptr.Res.(*prog.GroupArg).Inner
if len(mib) < 2 {
return
}
n1 := mib[0].(*prog.ConstArg)
n2 := mib[1].(*prog.ConstArg)
// Do not fiddle with root only knob kern.maxclusters, one of the causes
// of "no output from test machine" reports.
if n1.Val == arch.CTL_KERN && n2.Val == arch.KERN_MAXCLUSTERS {
n1.Val = 0
n2.Val = 0
}
}
func (arch *arch) annotateCall(c prog.ExecCall) string {
devArg := 2
switch c.Meta.Name {
case "mknodat":
devArg = 3
fallthrough
case "mknod":
dev := c.Args[devArg].(prog.ExecArgConst).Value
return fmt.Sprintf("major = %v, minor = %v", devmajor(dev), devminor(dev))
}
return ""
}
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