Add a tool to inject data into an elf, macho, or PE symbol (5498f854) · Commits · e / os / android_build_soong

cmd/symbol_inject/Android.bp

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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.

		blueprint_go_binary {
		name: "symbol_inject",
		srcs: [
		"symbol_inject.go",
		"elf.go",
		"macho.go",
		"pe.go",
		],
		}

cmd/symbol_inject/elf.go

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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 main

		import (
		"debug/elf"
		"fmt"
		"io"
		)

		func findElfSymbol(r io.ReaderAt, symbol string) (uint64, uint64, error) {
		elfFile, err := elf.NewFile(r)
		if err != nil {
		return maxUint64, maxUint64, cantParseError{err}
		}

		symbols, err := elfFile.Symbols()
		if err != nil {
		return maxUint64, maxUint64, err
		}

		for _, s := range symbols {
		if elf.ST_TYPE(s.Info) != elf.STT_OBJECT {
		continue
		}
		if s.Name == symbol {
		offset, err := calculateElfSymbolOffset(elfFile, s)
		if err != nil {
		return maxUint64, maxUint64, err
		}
		return offset, s.Size, nil
		}
		}

		return maxUint64, maxUint64, fmt.Errorf("symbol not found")
		}

		func calculateElfSymbolOffset(file *elf.File, symbol elf.Symbol) (uint64, error) {
		if symbol.Section == elf.SHN_UNDEF \|\| int(symbol.Section) >= len(file.Sections) {
		return maxUint64, fmt.Errorf("invalid section index %d", symbol.Section)
		}
		section := file.Sections[symbol.Section]
		switch file.Type {
		case elf.ET_REL:
		// "In relocatable files, st_value holds a section offset for a defined symbol.
		// That is, st_value is an offset from the beginning of the section that st_shndx identifies."
		return file.Sections[symbol.Section].Addr + symbol.Value, nil
		case elf.ET_EXEC, elf.ET_DYN:
		// "In executable and shared object files, st_value holds a virtual address. To make these
		// files’ symbols more useful for the dynamic linker, the section offset (file interpretation)
		// gives way to a virtual address (memory interpretation) for which the section number is
		// irrelevant."
		if symbol.Value < section.Addr {
		return maxUint64, fmt.Errorf("symbol starts before the start of its section")
		}
		section_offset := symbol.Value - section.Addr
		if section_offset+symbol.Size > section.Size {
		return maxUint64, fmt.Errorf("symbol extends past the end of its section")
		}
		return section.Offset + section_offset, nil
		default:
		return maxUint64, fmt.Errorf("unsupported elf file type %d", file.Type)
		}
		}

cmd/symbol_inject/macho.go

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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 main

		import (
		"debug/macho"
		"fmt"
		"io"
		)

		func findMachoSymbol(r io.ReaderAt, symbolName string) (uint64, uint64, error) {
		machoFile, err := macho.NewFile(r)
		if err != nil {
		return maxUint64, maxUint64, cantParseError{err}
		}

		// TODO(ccross): why?
		symbolName = "_" + symbolName

		for i, symbol := range machoFile.Symtab.Syms {
		if symbol.Sect == 0 {
		continue
		}
		if symbol.Name == symbolName {
		var nextSymbol *macho.Symbol
		if i+1 < len(machoFile.Symtab.Syms) {
		nextSymbol = &machoFile.Symtab.Syms[i+1]
		}
		return calculateMachoSymbolOffset(machoFile, symbol, nextSymbol)
		}
		}

		return maxUint64, maxUint64, fmt.Errorf("symbol not found")
		}

		func calculateMachoSymbolOffset(file macho.File, symbol macho.Symbol, nextSymbol macho.Symbol) (uint64, uint64, error) {
		section := file.Sections[symbol.Sect-1]

		var end uint64
		if nextSymbol != nil && nextSymbol.Sect != symbol.Sect {
		nextSymbol = nil
		}
		if nextSymbol != nil {
		end = nextSymbol.Value
		} else {
		end = section.Addr + section.Size
		}

		size := end - symbol.Value - 1
		offset := uint64(section.Offset) + (symbol.Value - section.Addr)

		return offset, size, nil
		}

cmd/symbol_inject/pe.go

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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 main

		import (
		"debug/pe"
		"fmt"
		"io"
		"sort"
		)

		func findPESymbol(r io.ReaderAt, symbolName string) (uint64, uint64, error) {
		peFile, err := pe.NewFile(r)
		if err != nil {
		return maxUint64, maxUint64, cantParseError{err}
		}

		sort.Slice(peFile.Symbols, func(i, j int) bool {
		if peFile.Symbols[i].SectionNumber != peFile.Symbols[j].SectionNumber {
		return peFile.Symbols[i].SectionNumber < peFile.Symbols[j].SectionNumber
		}
		return peFile.Symbols[i].Value < peFile.Symbols[j].Value
		})

		for i, symbol := range peFile.Symbols {
		if symbol.Name == symbolName {
		var nextSymbol *pe.Symbol
		if i+1 < len(peFile.Symbols) {
		nextSymbol = peFile.Symbols[i+1]
		}
		return calculatePESymbolOffset(peFile, symbol, nextSymbol)
		}
		}

		return maxUint64, maxUint64, fmt.Errorf("symbol not found")
		}

		func calculatePESymbolOffset(file pe.File, symbol pe.Symbol, nextSymbol *pe.Symbol) (uint64, uint64, error) {
		section := file.Sections[symbol.SectionNumber-1]

		var end uint32
		if nextSymbol != nil && nextSymbol.SectionNumber != symbol.SectionNumber {
		nextSymbol = nil
		}
		if nextSymbol != nil {
		end = nextSymbol.Value
		} else {
		end = section.Size
		}

		size := end - symbol.Value - 1
		offset := section.Offset + symbol.Value

		return uint64(offset), uint64(size), nil
		}

cmd/symbol_inject/symbol_inject.go

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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 main

		import (
		"bytes"
		"flag"
		"fmt"
		"io"
		"math"
		"os"
		)

		var (
		input = flag.String("i", "", "input file")
		output = flag.String("o", "", "output file")
		symbol = flag.String("s", "", "symbol to inject into")
		from = flag.String("from", "", "optional existing value of the symbol for verification")
		value = flag.String("v", "", "value to inject into symbol")
		)

		var maxUint64 uint64 = math.MaxUint64

		type cantParseError struct {
		error
		}

		func main() {
		flag.Parse()

		usageError := func(s string) {
		fmt.Fprintln(os.Stderr, s)
		flag.Usage()
		os.Exit(1)
		}

		if *input == "" {
		usageError("-i is required")
		}

		if *output == "" {
		usageError("-o is required")
		}

		if *symbol == "" {
		usageError("-s is required")
		}

		if *value == "" {
		usageError("-v is required")
		}

		r, err := os.Open(*input)
		if err != nil {
		fmt.Fprintln(os.Stderr, err.Error())
		os.Exit(2)
		}
		defer r.Close()

		w, err := os.OpenFile(*output, os.O_RDWR\|os.O_CREATE\|os.O_TRUNC, 0777)
		if err != nil {
		fmt.Fprintln(os.Stderr, err.Error())
		os.Exit(3)
		}
		defer w.Close()

		err = injectSymbol(r, w, symbol, value, *from)
		if err != nil {
		fmt.Fprintln(os.Stderr, err.Error())
		os.Remove(*output)
		os.Exit(2)
		}
		}

		type ReadSeekerAt interface {
		io.ReaderAt
		io.ReadSeeker
		}

		func injectSymbol(r ReadSeekerAt, w io.Writer, symbol, value, from string) error {
		var offset, size uint64
		var err error

		offset, size, err = findElfSymbol(r, symbol)
		if elfError, ok := err.(cantParseError); ok {
		// Try as a mach-o file
		offset, size, err = findMachoSymbol(r, symbol)
		if _, ok := err.(cantParseError); ok {
		// Try as a windows PE file
		offset, size, err = findPESymbol(r, symbol)
		if _, ok := err.(cantParseError); ok {
		// Can't parse as elf, macho, or PE, return the elf error
		return elfError
		}
		}
		}
		if err != nil {
		return err
		}

		if uint64(len(value))+1 > size {
		return fmt.Errorf("value length %d overflows symbol size %d", len(value), size)
		}

		if from != "" {
		// Read the exsting symbol contents and verify they match the expected value
		expected := make([]byte, size)
		existing := make([]byte, size)
		copy(expected, from)
		_, err := r.ReadAt(existing, int64(offset))
		if err != nil {
		return err
		}
		if bytes.Compare(existing, expected) != 0 {
		return fmt.Errorf("existing symbol contents %q did not match expected value %q",
		string(existing), string(expected))
		}
		}

		return copyAndInject(r, w, offset, size, value)
		}

		func copyAndInject(r io.ReadSeeker, w io.Writer, offset, size uint64, value string) (err error) {
		// helper that asserts a two-value function returning an int64 and an error has err != nil
		must := func(n int64, err error) {
		if err != nil {
		panic(err)
		}
		}

		// helper that asserts a two-value function returning an int and an error has err != nil
		must2 := func(n int, err error) {
		must(int64(n), err)
		}

		// convert a panic into returning an error
		defer func() {
		if r := recover(); r != nil {
		err, _ = r.(error)
		if err == io.EOF {
		err = io.ErrUnexpectedEOF
		}
		if err == nil {
		panic(r)
		}
		}
		}()

		buf := make([]byte, size)
		copy(buf, value)

		// Reset the input file
		must(r.Seek(0, io.SeekStart))
		// Copy the first bytes up to the symbol offset
		must(io.CopyN(w, r, int64(offset)))
		// Skip the symbol contents in the input file
		must(r.Seek(int64(size), io.SeekCurrent))
		// Write the injected value in the output file
		must2(w.Write(buf))
		// Write the remainder of the file
		must(io.Copy(w, r))

		return nil
		}