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Merge "Add a tool to inject data into an elf, macho, or PE symbol"

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Treehugger Robot 2018-02-06 22:51:05 +00:00 committed by Gerrit Code Review
parent 750e557011 5498f8548b
commit deda6efac4
5 changed files with 407 additions and 0 deletions
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23
cmd/symbol_inject/Android.bp Normal file
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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",
],
}

76
cmd/symbol_inject/elf.go Normal file
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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)
}
}

65
cmd/symbol_inject/macho.go Normal file
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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
}

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cmd/symbol_inject/pe.go Normal file
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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
}

176
cmd/symbol_inject/symbol_inject.go Normal file
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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
}