Merge "Add a tool to inject data into an elf, macho, or PE symbol"
This commit is contained in:
Treehugger Robot
Gerrit Code Review
commit
deda6efac4
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// Copyright 2018 Google Inc. All rights reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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blueprint_go_binary {
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name: "symbol_inject",
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srcs: [
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"symbol_inject.go",
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"elf.go",
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"macho.go",
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"pe.go",
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],
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}
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// Copyright 2018 Google Inc. All rights reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package main
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import (
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"debug/elf"
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"fmt"
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"io"
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)
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func findElfSymbol(r io.ReaderAt, symbol string) (uint64, uint64, error) {
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elfFile, err := elf.NewFile(r)
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if err != nil {
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return maxUint64, maxUint64, cantParseError{err}
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}
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symbols, err := elfFile.Symbols()
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if err != nil {
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return maxUint64, maxUint64, err
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}
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for _, s := range symbols {
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if elf.ST_TYPE(s.Info) != elf.STT_OBJECT {
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continue
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}
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if s.Name == symbol {
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offset, err := calculateElfSymbolOffset(elfFile, s)
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if err != nil {
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return maxUint64, maxUint64, err
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}
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return offset, s.Size, nil
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}
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}
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return maxUint64, maxUint64, fmt.Errorf("symbol not found")
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}
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func calculateElfSymbolOffset(file *elf.File, symbol elf.Symbol) (uint64, error) {
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if symbol.Section == elf.SHN_UNDEF || int(symbol.Section) >= len(file.Sections) {
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return maxUint64, fmt.Errorf("invalid section index %d", symbol.Section)
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}
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section := file.Sections[symbol.Section]
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switch file.Type {
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case elf.ET_REL:
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// "In relocatable files, st_value holds a section offset for a defined symbol.
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// That is, st_value is an offset from the beginning of the section that st_shndx identifies."
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return file.Sections[symbol.Section].Addr + symbol.Value, nil
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case elf.ET_EXEC, elf.ET_DYN:
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// "In executable and shared object files, st_value holds a virtual address. To make these
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// files’ symbols more useful for the dynamic linker, the section offset (file interpretation)
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// gives way to a virtual address (memory interpretation) for which the section number is
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// irrelevant."
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if symbol.Value < section.Addr {
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return maxUint64, fmt.Errorf("symbol starts before the start of its section")
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}
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section_offset := symbol.Value - section.Addr
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if section_offset+symbol.Size > section.Size {
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return maxUint64, fmt.Errorf("symbol extends past the end of its section")
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}
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return section.Offset + section_offset, nil
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default:
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return maxUint64, fmt.Errorf("unsupported elf file type %d", file.Type)
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}
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}
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// Copyright 2018 Google Inc. All rights reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package main
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import (
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"debug/macho"
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"fmt"
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"io"
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)
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func findMachoSymbol(r io.ReaderAt, symbolName string) (uint64, uint64, error) {
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machoFile, err := macho.NewFile(r)
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if err != nil {
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return maxUint64, maxUint64, cantParseError{err}
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}
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// TODO(ccross): why?
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symbolName = "_" + symbolName
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for i, symbol := range machoFile.Symtab.Syms {
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if symbol.Sect == 0 {
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continue
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}
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if symbol.Name == symbolName {
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var nextSymbol *macho.Symbol
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if i+1 < len(machoFile.Symtab.Syms) {
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nextSymbol = &machoFile.Symtab.Syms[i+1]
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}
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return calculateMachoSymbolOffset(machoFile, symbol, nextSymbol)
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}
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}
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return maxUint64, maxUint64, fmt.Errorf("symbol not found")
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}
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func calculateMachoSymbolOffset(file *macho.File, symbol macho.Symbol, nextSymbol *macho.Symbol) (uint64, uint64, error) {
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section := file.Sections[symbol.Sect-1]
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var end uint64
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if nextSymbol != nil && nextSymbol.Sect != symbol.Sect {
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nextSymbol = nil
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}
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if nextSymbol != nil {
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end = nextSymbol.Value
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} else {
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end = section.Addr + section.Size
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}
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size := end - symbol.Value - 1
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offset := uint64(section.Offset) + (symbol.Value - section.Addr)
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return offset, size, nil
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}
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// Copyright 2018 Google Inc. All rights reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package main
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import (
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"debug/pe"
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"fmt"
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"io"
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"sort"
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)
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func findPESymbol(r io.ReaderAt, symbolName string) (uint64, uint64, error) {
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peFile, err := pe.NewFile(r)
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if err != nil {
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return maxUint64, maxUint64, cantParseError{err}
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}
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sort.Slice(peFile.Symbols, func(i, j int) bool {
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if peFile.Symbols[i].SectionNumber != peFile.Symbols[j].SectionNumber {
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return peFile.Symbols[i].SectionNumber < peFile.Symbols[j].SectionNumber
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}
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return peFile.Symbols[i].Value < peFile.Symbols[j].Value
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})
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for i, symbol := range peFile.Symbols {
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if symbol.Name == symbolName {
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var nextSymbol *pe.Symbol
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if i+1 < len(peFile.Symbols) {
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nextSymbol = peFile.Symbols[i+1]
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}
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return calculatePESymbolOffset(peFile, symbol, nextSymbol)
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}
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}
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return maxUint64, maxUint64, fmt.Errorf("symbol not found")
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}
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func calculatePESymbolOffset(file *pe.File, symbol *pe.Symbol, nextSymbol *pe.Symbol) (uint64, uint64, error) {
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section := file.Sections[symbol.SectionNumber-1]
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var end uint32
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if nextSymbol != nil && nextSymbol.SectionNumber != symbol.SectionNumber {
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nextSymbol = nil
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}
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if nextSymbol != nil {
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end = nextSymbol.Value
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} else {
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end = section.Size
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}
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size := end - symbol.Value - 1
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offset := section.Offset + symbol.Value
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return uint64(offset), uint64(size), nil
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}
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// Copyright 2018 Google Inc. All rights reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package main
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import (
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"bytes"
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"flag"
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"fmt"
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"io"
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"math"
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"os"
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)
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var (
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input = flag.String("i", "", "input file")
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output = flag.String("o", "", "output file")
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symbol = flag.String("s", "", "symbol to inject into")
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from = flag.String("from", "", "optional existing value of the symbol for verification")
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value = flag.String("v", "", "value to inject into symbol")
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)
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var maxUint64 uint64 = math.MaxUint64
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type cantParseError struct {
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error
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}
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func main() {
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flag.Parse()
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usageError := func(s string) {
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fmt.Fprintln(os.Stderr, s)
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flag.Usage()
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os.Exit(1)
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}
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if *input == "" {
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usageError("-i is required")
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}
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if *output == "" {
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usageError("-o is required")
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}
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if *symbol == "" {
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usageError("-s is required")
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}
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if *value == "" {
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usageError("-v is required")
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}
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r, err := os.Open(*input)
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if err != nil {
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fmt.Fprintln(os.Stderr, err.Error())
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os.Exit(2)
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}
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defer r.Close()
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w, err := os.OpenFile(*output, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0777)
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if err != nil {
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fmt.Fprintln(os.Stderr, err.Error())
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os.Exit(3)
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}
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defer w.Close()
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err = injectSymbol(r, w, *symbol, *value, *from)
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if err != nil {
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fmt.Fprintln(os.Stderr, err.Error())
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os.Remove(*output)
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os.Exit(2)
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}
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}
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type ReadSeekerAt interface {
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io.ReaderAt
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io.ReadSeeker
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}
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func injectSymbol(r ReadSeekerAt, w io.Writer, symbol, value, from string) error {
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var offset, size uint64
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var err error
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offset, size, err = findElfSymbol(r, symbol)
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if elfError, ok := err.(cantParseError); ok {
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// Try as a mach-o file
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offset, size, err = findMachoSymbol(r, symbol)
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if _, ok := err.(cantParseError); ok {
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// Try as a windows PE file
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offset, size, err = findPESymbol(r, symbol)
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if _, ok := err.(cantParseError); ok {
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// Can't parse as elf, macho, or PE, return the elf error
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return elfError
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}
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}
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}
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if err != nil {
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return err
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}
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if uint64(len(value))+1 > size {
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return fmt.Errorf("value length %d overflows symbol size %d", len(value), size)
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}
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if from != "" {
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// Read the exsting symbol contents and verify they match the expected value
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expected := make([]byte, size)
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existing := make([]byte, size)
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copy(expected, from)
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_, err := r.ReadAt(existing, int64(offset))
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if err != nil {
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return err
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}
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if bytes.Compare(existing, expected) != 0 {
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return fmt.Errorf("existing symbol contents %q did not match expected value %q",
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string(existing), string(expected))
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}
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}
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return copyAndInject(r, w, offset, size, value)
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}
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func copyAndInject(r io.ReadSeeker, w io.Writer, offset, size uint64, value string) (err error) {
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// helper that asserts a two-value function returning an int64 and an error has err != nil
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must := func(n int64, err error) {
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if err != nil {
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panic(err)
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}
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}
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// helper that asserts a two-value function returning an int and an error has err != nil
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must2 := func(n int, err error) {
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must(int64(n), err)
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}
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// convert a panic into returning an error
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defer func() {
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if r := recover(); r != nil {
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err, _ = r.(error)
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if err == io.EOF {
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err = io.ErrUnexpectedEOF
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}
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if err == nil {
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panic(r)
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}
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}
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}()
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buf := make([]byte, size)
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copy(buf, value)
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// Reset the input file
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must(r.Seek(0, io.SeekStart))
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// Copy the first bytes up to the symbol offset
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must(io.CopyN(w, r, int64(offset)))
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// Skip the symbol contents in the input file
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must(r.Seek(int64(size), io.SeekCurrent))
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// Write the injected value in the output file
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must2(w.Write(buf))
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// Write the remainder of the file
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must(io.Copy(w, r))
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return nil
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}
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