Current File : //usr/local/go/src/cmd/internal/codesign/codesign.go
// Copyright 2020 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package codesign provides basic functionalities for
// ad-hoc code signing of Mach-O files.
//
// This is not a general tool for code-signing. It is made
// specifically for the Go toolchain. It uses the same
// ad-hoc signing algorithm as the Darwin linker.
package codesign
import (
"crypto/sha256"
"debug/macho"
"encoding/binary"
"io"
)
// Code signature layout.
//
// The code signature is a block of bytes that contains
// a SuperBlob, which contains one or more Blobs. For ad-hoc
// signing, a single CodeDirectory Blob suffices.
//
// A SuperBlob starts with its header (the binary representation
// of the SuperBlob struct), followed by a list of (in our case,
// one) Blobs (offset and size). A CodeDirectory Blob starts
// with its head (the binary representation of CodeDirectory struct),
// followed by the identifier (as a C string) and the hashes, at
// the corresponding offsets.
//
// The signature data must be included in the __LINKEDIT segment.
// In the Mach-O file header, an LC_CODE_SIGNATURE load command
// points to the data.
const (
pageSizeBits = 12
pageSize = 1 << pageSizeBits
)
const LC_CODE_SIGNATURE = 0x1d
// Constants and struct layouts are from
// https://opensource.apple.com/source/xnu/xnu-4903.270.47/osfmk/kern/cs_blobs.h
const (
CSMAGIC_REQUIREMENT = 0xfade0c00 // single Requirement blob
CSMAGIC_REQUIREMENTS = 0xfade0c01 // Requirements vector (internal requirements)
CSMAGIC_CODEDIRECTORY = 0xfade0c02 // CodeDirectory blob
CSMAGIC_EMBEDDED_SIGNATURE = 0xfade0cc0 // embedded form of signature data
CSMAGIC_DETACHED_SIGNATURE = 0xfade0cc1 // multi-arch collection of embedded signatures
CSSLOT_CODEDIRECTORY = 0 // slot index for CodeDirectory
)
const (
CS_HASHTYPE_SHA1 = 1
CS_HASHTYPE_SHA256 = 2
CS_HASHTYPE_SHA256_TRUNCATED = 3
CS_HASHTYPE_SHA384 = 4
)
const (
CS_EXECSEG_MAIN_BINARY = 0x1 // executable segment denotes main binary
CS_EXECSEG_ALLOW_UNSIGNED = 0x10 // allow unsigned pages (for debugging)
CS_EXECSEG_DEBUGGER = 0x20 // main binary is debugger
CS_EXECSEG_JIT = 0x40 // JIT enabled
CS_EXECSEG_SKIP_LV = 0x80 // skip library validation
CS_EXECSEG_CAN_LOAD_CDHASH = 0x100 // can bless cdhash for execution
CS_EXECSEG_CAN_EXEC_CDHASH = 0x200 // can execute blessed cdhash
)
type Blob struct {
typ uint32 // type of entry
offset uint32 // offset of entry
// data follows
}
func (b *Blob) put(out []byte) []byte {
out = put32be(out, b.typ)
out = put32be(out, b.offset)
return out
}
const blobSize = 2 * 4
type SuperBlob struct {
magic uint32 // magic number
length uint32 // total length of SuperBlob
count uint32 // number of index entries following
// blobs []Blob
}
func (s *SuperBlob) put(out []byte) []byte {
out = put32be(out, s.magic)
out = put32be(out, s.length)
out = put32be(out, s.count)
return out
}
const superBlobSize = 3 * 4
type CodeDirectory struct {
magic uint32 // magic number (CSMAGIC_CODEDIRECTORY)
length uint32 // total length of CodeDirectory blob
version uint32 // compatibility version
flags uint32 // setup and mode flags
hashOffset uint32 // offset of hash slot element at index zero
identOffset uint32 // offset of identifier string
nSpecialSlots uint32 // number of special hash slots
nCodeSlots uint32 // number of ordinary (code) hash slots
codeLimit uint32 // limit to main image signature range
hashSize uint8 // size of each hash in bytes
hashType uint8 // type of hash (cdHashType* constants)
_pad1 uint8 // unused (must be zero)
pageSize uint8 // log2(page size in bytes); 0 => infinite
_pad2 uint32 // unused (must be zero)
scatterOffset uint32
teamOffset uint32
_pad3 uint32
codeLimit64 uint64
execSegBase uint64
execSegLimit uint64
execSegFlags uint64
// data follows
}
func (c *CodeDirectory) put(out []byte) []byte {
out = put32be(out, c.magic)
out = put32be(out, c.length)
out = put32be(out, c.version)
out = put32be(out, c.flags)
out = put32be(out, c.hashOffset)
out = put32be(out, c.identOffset)
out = put32be(out, c.nSpecialSlots)
out = put32be(out, c.nCodeSlots)
out = put32be(out, c.codeLimit)
out = put8(out, c.hashSize)
out = put8(out, c.hashType)
out = put8(out, c._pad1)
out = put8(out, c.pageSize)
out = put32be(out, c._pad2)
out = put32be(out, c.scatterOffset)
out = put32be(out, c.teamOffset)
out = put32be(out, c._pad3)
out = put64be(out, c.codeLimit64)
out = put64be(out, c.execSegBase)
out = put64be(out, c.execSegLimit)
out = put64be(out, c.execSegFlags)
return out
}
const codeDirectorySize = 13*4 + 4 + 4*8
// CodeSigCmd is Mach-O LC_CODE_SIGNATURE load command.
type CodeSigCmd struct {
Cmd uint32 // LC_CODE_SIGNATURE
Cmdsize uint32 // sizeof this command (16)
Dataoff uint32 // file offset of data in __LINKEDIT segment
Datasize uint32 // file size of data in __LINKEDIT segment
}
func FindCodeSigCmd(f *macho.File) (CodeSigCmd, bool) {
get32 := f.ByteOrder.Uint32
for _, l := range f.Loads {
data := l.Raw()
cmd := get32(data)
if cmd == LC_CODE_SIGNATURE {
return CodeSigCmd{
cmd,
get32(data[4:]),
get32(data[8:]),
get32(data[12:]),
}, true
}
}
return CodeSigCmd{}, false
}
func put32be(b []byte, x uint32) []byte { binary.BigEndian.PutUint32(b, x); return b[4:] }
func put64be(b []byte, x uint64) []byte { binary.BigEndian.PutUint64(b, x); return b[8:] }
func put8(b []byte, x uint8) []byte { b[0] = x; return b[1:] }
func puts(b, s []byte) []byte { n := copy(b, s); return b[n:] }
// Size computes the size of the code signature.
// id is the identifier used for signing (a field in CodeDirectory blob, which
// has no significance in ad-hoc signing).
func Size(codeSize int64, id string) int64 {
nhashes := (codeSize + pageSize - 1) / pageSize
idOff := int64(codeDirectorySize)
hashOff := idOff + int64(len(id)+1)
cdirSz := hashOff + nhashes*sha256.Size
return int64(superBlobSize+blobSize) + cdirSz
}
// Sign generates an ad-hoc code signature and writes it to out.
// out must have length at least Size(codeSize, id).
// data is the file content without the signature, of size codeSize.
// textOff and textSize is the file offset and size of the text segment.
// isMain is true if this is a main executable.
// id is the identifier used for signing (a field in CodeDirectory blob, which
// has no significance in ad-hoc signing).
func Sign(out []byte, data io.Reader, id string, codeSize, textOff, textSize int64, isMain bool) {
nhashes := (codeSize + pageSize - 1) / pageSize
idOff := int64(codeDirectorySize)
hashOff := idOff + int64(len(id)+1)
sz := Size(codeSize, id)
// emit blob headers
sb := SuperBlob{
magic: CSMAGIC_EMBEDDED_SIGNATURE,
length: uint32(sz),
count: 1,
}
blob := Blob{
typ: CSSLOT_CODEDIRECTORY,
offset: superBlobSize + blobSize,
}
cdir := CodeDirectory{
magic: CSMAGIC_CODEDIRECTORY,
length: uint32(sz) - (superBlobSize + blobSize),
version: 0x20400,
flags: 0x20002, // adhoc | linkerSigned
hashOffset: uint32(hashOff),
identOffset: uint32(idOff),
nCodeSlots: uint32(nhashes),
codeLimit: uint32(codeSize),
hashSize: sha256.Size,
hashType: CS_HASHTYPE_SHA256,
pageSize: uint8(pageSizeBits),
execSegBase: uint64(textOff),
execSegLimit: uint64(textSize),
}
if isMain {
cdir.execSegFlags = CS_EXECSEG_MAIN_BINARY
}
outp := out
outp = sb.put(outp)
outp = blob.put(outp)
outp = cdir.put(outp)
// emit the identifier
outp = puts(outp, []byte(id+"\000"))
// emit hashes
var buf [pageSize]byte
h := sha256.New()
p := 0
for p < int(codeSize) {
n, err := io.ReadFull(data, buf[:])
if err == io.EOF {
break
}
if err != nil && err != io.ErrUnexpectedEOF {
panic(err)
}
if p+n > int(codeSize) {
n = int(codeSize) - p
}
p += n
h.Reset()
h.Write(buf[:n])
b := h.Sum(nil)
outp = puts(outp, b[:])
}
}
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