src/cmd/internal/codesign/codesign.go - go - Git at Google

 // 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[:])
 	}
 }
	// 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 = 134 + 4 + 48

	// 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[:])
	}
	}