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encodingexec.go
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encodingexec.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.
// This file does serialization of programs for executor binary.
// The format aims at simple parsing: binary and irreversible.
// Exec format is an sequence of uint64's which encodes a sequence of calls.
// The sequence is terminated by a speciall call execInstrEOF.
// Each call is (call ID, copyout index, number of arguments, arguments...).
// Each argument is (type, size, value).
// There are 4 types of arguments:
// - execArgConst: value is const value
// - execArgResult: value is copyout index we want to reference
// - execArgData: value is a binary blob (represented as ]size/8[ uint64's)
// - execArgCsum: runtime checksum calculation
// There are 2 other special calls:
// - execInstrCopyin: copies its second argument into address specified by first argument
// - execInstrCopyout: reads value at address specified by first argument (result can be referenced by execArgResult)
package prog
import (
"fmt"
"sort"
)
const (
execInstrEOF = ^uint64(iota)
execInstrCopyin
execInstrCopyout
)
const (
execArgConst = uint64(iota)
execArgResult
execArgData
execArgCsum
execArgDataReadable = uint64(1 << 63)
)
const (
ExecArgCsumInet = uint64(iota)
)
const (
ExecArgCsumChunkData = uint64(iota)
ExecArgCsumChunkConst
)
const (
ExecBufferSize = 4 << 20 // keep in sync with kMaxInput in executor.cc
ExecNoCopyout = ^uint64(0)
)
// SerializeForExec serializes program p for execution by process pid into the provided buffer.
// Returns number of bytes written to the buffer.
// If the provided buffer is too small for the program an error is returned.
func (p *Prog) SerializeForExec(buffer []byte) (int, error) {
p.debugValidate()
w := &execContext{
target: p.Target,
buf: buffer,
eof: false,
args: make(map[Arg]argInfo),
}
for _, c := range p.Calls {
w.csumMap, w.csumUses = calcChecksumsCall(c)
w.serializeCall(c)
}
w.write(execInstrEOF)
if w.eof {
return 0, fmt.Errorf("provided buffer is too small")
}
return len(buffer) - len(w.buf), nil
}
func (w *execContext) serializeCall(c *Call) {
// Calculate arg offsets within structs.
// Generate copyin instructions that fill in data into pointer arguments.
w.writeCopyin(c)
// Generate checksum calculation instructions starting from the last one,
// since checksum values can depend on values of the latter ones
w.writeChecksums()
// Generate the call itself.
w.write(uint64(c.Meta.ID))
if c.Ret != nil && len(c.Ret.uses) != 0 {
if _, ok := w.args[c.Ret]; ok {
panic("argInfo is already created for return value")
}
w.args[c.Ret] = argInfo{Idx: w.copyoutSeq, Ret: true}
w.write(w.copyoutSeq)
w.copyoutSeq++
} else {
w.write(ExecNoCopyout)
}
w.write(uint64(len(c.Args)))
for _, arg := range c.Args {
w.writeArg(arg)
}
// Generate copyout instructions that persist interesting return values.
w.writeCopyout(c)
}
type execContext struct {
target *Target
buf []byte
eof bool
args map[Arg]argInfo
copyoutSeq uint64
// Per-call state cached here to not pass it through all functions.
csumMap map[Arg]CsumInfo
csumUses map[Arg]struct{}
}
type argInfo struct {
Addr uint64 // physical addr
Idx uint64 // copyout instruction index
Ret bool
}
func (w *execContext) writeCopyin(c *Call) {
ForeachArg(c, func(arg Arg, ctx *ArgCtx) {
if ctx.Base == nil {
return
}
addr := w.target.PhysicalAddr(ctx.Base) + ctx.Offset
addr -= arg.Type().UnitOffset()
if w.willBeUsed(arg) {
w.args[arg] = argInfo{Addr: addr}
}
switch arg.(type) {
case *GroupArg, *UnionArg:
return
}
typ := arg.Type()
if arg.Dir() == DirOut || IsPad(typ) || (arg.Size() == 0 && !typ.IsBitfield()) {
return
}
w.write(execInstrCopyin)
w.write(addr)
w.writeArg(arg)
})
}
func (w *execContext) willBeUsed(arg Arg) bool {
if res, ok := arg.(*ResultArg); ok && len(res.uses) != 0 {
return true
}
_, ok1 := w.csumMap[arg]
_, ok2 := w.csumUses[arg]
return ok1 || ok2
}
func (w *execContext) writeChecksums() {
if len(w.csumMap) == 0 {
return
}
csumArgs := make([]Arg, 0, len(w.csumMap))
for arg := range w.csumMap {
csumArgs = append(csumArgs, arg)
}
sort.Slice(csumArgs, func(i, j int) bool {
return w.args[csumArgs[i]].Addr < w.args[csumArgs[j]].Addr
})
for i := len(csumArgs) - 1; i >= 0; i-- {
arg := csumArgs[i]
info := w.csumMap[arg]
if _, ok := arg.Type().(*CsumType); !ok {
panic("csum arg is not csum type")
}
w.write(execInstrCopyin)
w.write(w.args[arg].Addr)
w.write(execArgCsum)
w.write(arg.Size())
switch info.Kind {
case CsumInet:
w.write(ExecArgCsumInet)
w.write(uint64(len(info.Chunks)))
for _, chunk := range info.Chunks {
switch chunk.Kind {
case CsumChunkArg:
w.write(ExecArgCsumChunkData)
w.write(w.args[chunk.Arg].Addr)
w.write(chunk.Arg.Size())
case CsumChunkConst:
w.write(ExecArgCsumChunkConst)
w.write(chunk.Value)
w.write(chunk.Size)
default:
panic(fmt.Sprintf("csum chunk has unknown kind %v", chunk.Kind))
}
}
default:
panic(fmt.Sprintf("csum arg has unknown kind %v", info.Kind))
}
}
}
func (w *execContext) writeCopyout(c *Call) {
ForeachArg(c, func(arg Arg, _ *ArgCtx) {
if res, ok := arg.(*ResultArg); ok && len(res.uses) != 0 {
// Create a separate copyout instruction that has own Idx.
info := w.args[arg]
if info.Ret {
return // Idx is already assigned above.
}
info.Idx = w.copyoutSeq
w.copyoutSeq++
w.args[arg] = info
w.write(execInstrCopyout)
w.write(info.Idx)
w.write(info.Addr)
w.write(arg.Size())
}
})
}
func (w *execContext) write(v uint64) {
if len(w.buf) < 8 {
w.eof = true
return
}
w.buf[0] = byte(v >> 0)
w.buf[1] = byte(v >> 8)
w.buf[2] = byte(v >> 16)
w.buf[3] = byte(v >> 24)
w.buf[4] = byte(v >> 32)
w.buf[5] = byte(v >> 40)
w.buf[6] = byte(v >> 48)
w.buf[7] = byte(v >> 56)
w.buf = w.buf[8:]
}
func (w *execContext) writeArg(arg Arg) {
switch a := arg.(type) {
case *ConstArg:
val, pidStride := a.Value()
typ := a.Type()
w.writeConstArg(typ.UnitSize(), val, typ.BitfieldOffset(), typ.BitfieldLength(), pidStride, typ.Format())
case *ResultArg:
if a.Res == nil {
w.writeConstArg(a.Size(), a.Val, 0, 0, 0, a.Type().Format())
} else {
info, ok := w.args[a.Res]
if !ok {
panic("no copyout index")
}
w.write(execArgResult)
meta := a.Size() | uint64(a.Type().Format())<<8
w.write(meta)
w.write(info.Idx)
w.write(a.OpDiv)
w.write(a.OpAdd)
w.write(a.Type().(*ResourceType).Default())
}
case *PointerArg:
w.writeConstArg(a.Size(), w.target.PhysicalAddr(a), 0, 0, 0, FormatNative)
case *DataArg:
data := a.Data()
if len(data) == 0 {
return
}
w.write(execArgData)
flags := uint64(len(data))
if isReadableDataType(a.Type().(*BufferType)) {
flags |= execArgDataReadable
}
w.write(flags)
padded := len(data)
if pad := 8 - len(data)%8; pad != 8 {
padded += pad
}
if len(w.buf) < padded {
w.eof = true
} else {
copy(w.buf, data)
w.buf = w.buf[padded:]
}
case *UnionArg:
w.writeArg(a.Option)
default:
panic("unknown arg type")
}
}
func (w *execContext) writeConstArg(size, val, bfOffset, bfLength, pidStride uint64, bf BinaryFormat) {
w.write(execArgConst)
meta := size | uint64(bf)<<8 | bfOffset<<16 | bfLength<<24 | pidStride<<32
w.write(meta)
w.write(val)
}