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// Copyright 2018 Google Inc. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package symbol_inject
import (
"debug/macho"
"encoding/binary"
"fmt"
"io"
"os"
"os/exec"
"path/filepath"
"sort"
"strings"
)
func machoSymbolsFromFile(r io.ReaderAt) (*File, error) {
machoFile, err := macho.NewFile(r)
if err != nil {
return nil, cantParseError{err}
}
return extractMachoSymbols(machoFile)
}
func extractMachoSymbols(machoFile *macho.File) (*File, error) {
symbols := machoFile.Symtab.Syms
sort.SliceStable(symbols, func(i, j int) bool {
if symbols[i].Sect != symbols[j].Sect {
return symbols[i].Sect < symbols[j].Sect
}
return symbols[i].Value < symbols[j].Value
})
file := &File{IsMachoFile: true}
for _, section := range machoFile.Sections {
file.Sections = append(file.Sections, &Section{
Name: section.Name,
Addr: section.Addr,
Offset: uint64(section.Offset),
Size: section.Size,
})
}
for _, symbol := range symbols {
if symbol.Sect > 0 {
section := file.Sections[symbol.Sect-1]
file.Symbols = append(file.Symbols, &Symbol{
// symbols in macho files seem to be prefixed with an underscore
Name: strings.TrimPrefix(symbol.Name, "_"),
// MachO symbol value is virtual address of the symbol, convert it to offset into the section.
Addr: symbol.Value - section.Addr,
// MachO symbols don't have size information.
Size: 0,
Section: section,
})
}
}
return file, nil
}
func dumpMachoSymbols(r io.ReaderAt) error {
machoFile, err := macho.NewFile(r)
if err != nil {
return cantParseError{err}
}
fmt.Println("&macho.File{")
fmt.Println("\tSections: []*macho.Section{")
for _, section := range machoFile.Sections {
fmt.Printf("\t\t&macho.Section{SectionHeader: %#v},\n", section.SectionHeader)
}
fmt.Println("\t},")
fmt.Println("\tSymtab: &macho.Symtab{")
fmt.Println("\t\tSyms: []macho.Symbol{")
for _, symbol := range machoFile.Symtab.Syms {
fmt.Printf("\t\t\t%#v,\n", symbol)
}
fmt.Println("\t\t},")
fmt.Println("\t},")
fmt.Println("}")
return nil
}
func CodeSignMachoFile(path string) error {
filename := filepath.Base(path)
cmd := exec.Command("/usr/bin/codesign", "--force", "-s", "-", "-i", filename, path)
if err := cmd.Run(); err != nil {
return err
}
return modifyCodeSignFlags(path)
}
const LC_CODE_SIGNATURE = 0x1d
const CSSLOT_CODEDIRECTORY = 0
// To make codesign not invalidated by stripping, modify codesign flags to 0x20002
// (adhoc | linkerSigned).
func modifyCodeSignFlags(path string) error {
f, err := os.OpenFile(path, os.O_RDWR, 0)
if err != nil {
return err
}
defer f.Close()
// Step 1: find code signature section.
machoFile, err := macho.NewFile(f)
if err != nil {
return err
}
var codeSignSectionOffset uint32 = 0
var codeSignSectionSize uint32 = 0
for _, l := range machoFile.Loads {
data := l.Raw()
cmd := machoFile.ByteOrder.Uint32(data)
if cmd == LC_CODE_SIGNATURE {
codeSignSectionOffset = machoFile.ByteOrder.Uint32(data[8:])
codeSignSectionSize = machoFile.ByteOrder.Uint32(data[12:])
}
}
if codeSignSectionOffset == 0 {
return fmt.Errorf("code signature section not found")
}
data := make([]byte, codeSignSectionSize)
_, err = f.ReadAt(data, int64(codeSignSectionOffset))
if err != nil {
return err
}
// Step 2: get flags offset.
blobCount := binary.BigEndian.Uint32(data[8:])
off := 12
var codeDirectoryOff uint32 = 0
for blobCount > 0 {
blobType := binary.BigEndian.Uint32(data[off:])
if blobType == CSSLOT_CODEDIRECTORY {
codeDirectoryOff = binary.BigEndian.Uint32(data[off+4:])
break
}
blobCount--
off += 8
}
if codeDirectoryOff == 0 {
return fmt.Errorf("no code directory in code signature section")
}
flagsOff := codeSignSectionOffset + codeDirectoryOff + 12
// Step 3: modify flags.
flagsData := make([]byte, 4)
_, err = f.ReadAt(flagsData, int64(flagsOff))
if err != nil {
return err
}
oldFlags := binary.BigEndian.Uint32(flagsData)
if oldFlags != 0x2 {
return fmt.Errorf("unexpected flags in code signature section: 0x%x", oldFlags)
}
binary.BigEndian.PutUint32(flagsData, 0x20002)
_, err = f.WriteAt(flagsData, int64(flagsOff))
return err
}
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