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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.
package prog
import (
"fmt"
"github.com/google/syzkaller/sys"
)
const (
ExecInstrEOF = ^uintptr(iota)
ExecInstrCopyin
ExecInstrCopyout
)
const (
ExecArgConst = uintptr(iota)
ExecArgResult
ExecArgData
)
const (
ExecBufferSize = 2 << 20
ptrSize = 8
pageSize = 4 << 10
dataOffset = 512 << 20
)
// SerializeForExec serializes program p for execution by process pid into the provided buffer.
// If the provided buffer is too small for the program an error is returned.
func (p *Prog) SerializeForExec(buffer []byte, pid int) error {
if err := p.validate(); err != nil {
panic(fmt.Errorf("serializing invalid program: %v", err))
}
var instrSeq uintptr
w := &execContext{
buf: buffer,
eof: false,
args: make(map[*Arg]argInfo),
}
for _, c := range p.Calls {
// Calculate arg offsets within structs.
// Generate copyin instructions that fill in data into pointer arguments.
foreachArg(c, func(arg, _ *Arg, _ *[]*Arg) {
if arg.Kind == ArgPointer && arg.Res != nil {
var rec func(*Arg, uintptr) uintptr
rec = func(arg1 *Arg, offset uintptr) uintptr {
if len(arg1.Uses) != 0 {
w.args[arg1] = argInfo{Offset: offset}
}
if arg1.Kind == ArgGroup {
var totalSize uintptr
for _, arg2 := range arg1.Inner {
size := rec(arg2, offset)
if arg2.Type.BitfieldLength() == 0 || arg2.Type.BitfieldLast() {
offset += size
totalSize += size
}
}
if totalSize > arg1.Size() {
panic(fmt.Sprintf("bad group arg size %v, should be <= %v for %+v", totalSize, arg1.Size(), arg1))
}
return arg1.Size()
}
if arg1.Kind == ArgUnion {
size := rec(arg1.Option, offset)
offset += size
if size > arg1.Size() {
panic(fmt.Sprintf("bad union arg size %v, should be <= %v for arg %+v with type %+v", size, arg1.Size(), arg1, arg1.Type))
}
return arg1.Size()
}
if !sys.IsPad(arg1.Type) &&
!(arg1.Kind == ArgData && len(arg1.Data) == 0) &&
arg1.Type.Dir() != sys.DirOut {
w.write(ExecInstrCopyin)
w.write(physicalAddr(arg) + offset)
w.writeArg(arg1, pid)
instrSeq++
}
return arg1.Size()
}
rec(arg.Res, 0)
}
})
// Generate the call itself.
w.write(uintptr(c.Meta.ID))
w.write(uintptr(len(c.Args)))
for _, arg := range c.Args {
w.writeArg(arg, pid)
}
if len(c.Ret.Uses) != 0 {
w.args[c.Ret] = argInfo{Idx: instrSeq}
}
instrSeq++
// Generate copyout instructions that persist interesting return values.
foreachArg(c, func(arg, base *Arg, _ *[]*Arg) {
if len(arg.Uses) == 0 {
return
}
switch arg.Kind {
case ArgReturn:
// Idx is already assigned above.
case ArgConst, ArgResult:
// Create a separate copyout instruction that has own Idx.
if base.Kind != ArgPointer {
panic("arg base is not a pointer")
}
info := w.args[arg]
info.Idx = instrSeq
instrSeq++
w.args[arg] = info
w.write(ExecInstrCopyout)
w.write(physicalAddr(base) + info.Offset)
w.write(arg.Size())
default:
panic("bad arg kind in copyout")
}
})
}
w.write(ExecInstrEOF)
if w.eof {
return fmt.Errorf("provided buffer is too small")
}
return nil
}
func physicalAddr(arg *Arg) uintptr {
if arg.Kind != ArgPointer {
panic("physicalAddr: bad arg kind")
}
addr := arg.AddrPage*pageSize + dataOffset
if arg.AddrOffset >= 0 {
addr += uintptr(arg.AddrOffset)
} else {
addr += pageSize - uintptr(-arg.AddrOffset)
}
return addr
}
type execContext struct {
buf []byte
eof bool
args map[*Arg]argInfo
}
type argInfo struct {
Offset uintptr // from base pointer
Idx uintptr // instruction index
}
func (w *execContext) write(v uintptr) {
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, pid int) {
switch arg.Kind {
case ArgConst:
w.write(ExecArgConst)
w.write(arg.Size())
w.write(arg.Value(pid))
w.write(arg.Type.BitfieldOffset())
w.write(arg.Type.BitfieldLength())
case ArgResult:
w.write(ExecArgResult)
w.write(arg.Size())
w.write(w.args[arg.Res].Idx)
w.write(arg.OpDiv)
w.write(arg.OpAdd)
case ArgPointer:
w.write(ExecArgConst)
w.write(arg.Size())
w.write(physicalAddr(arg))
w.write(0) // bit field offset
w.write(0) // bit field length
case ArgPageSize:
w.write(ExecArgConst)
w.write(arg.Size())
w.write(arg.AddrPage * pageSize)
w.write(0) // bit field offset
w.write(0) // bit field length
case ArgData:
w.write(ExecArgData)
w.write(uintptr(len(arg.Data)))
padded := len(arg.Data)
if pad := 8 - len(arg.Data)%8; pad != 8 {
padded += pad
}
if len(w.buf) < padded {
w.eof = true
} else {
copy(w.buf, arg.Data)
w.buf = w.buf[padded:]
}
default:
panic("unknown arg type")
}
}
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