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Diffstat (limited to 'src/cmd/internal/codesign/codesign.go')
| -rw-r--r-- | src/cmd/internal/codesign/codesign.go | 276 |
1 files changed, 276 insertions, 0 deletions
diff --git a/src/cmd/internal/codesign/codesign.go b/src/cmd/internal/codesign/codesign.go new file mode 100644 index 0000000..1116393 --- /dev/null +++ b/src/cmd/internal/codesign/codesign.go @@ -0,0 +1,276 @@ +// 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 ( + "debug/macho" + "encoding/binary" + "io" + + "cmd/internal/notsha256" +) + +// 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*notsha256.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: notsha256.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 + // NOTE(rsc): These must be SHA256, but for cgo bootstrap reasons + // we cannot import crypto/sha256 when GOEXPERIMENT=boringcrypto + // and the host is linux/amd64. So we use NOT-SHA256 + // and then apply a NOT ourselves to get SHA256. Sigh. + var buf [pageSize]byte + h := notsha256.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) + for i := range b { + b[i] ^= 0xFF // convert notsha256 to sha256 + } + outp = puts(outp, b[:]) + } +} |