Add a tool to inject data into an elf, macho, or PE symbol
Test: symbol_inject -i a.out -o a.out2 -s symbol -v value
Change-Id: I16cd8facbae754f679bef07ab0ba23638286e1d7
diff --git a/cmd/symbol_inject/Android.bp b/cmd/symbol_inject/Android.bp
new file mode 100644
index 0000000..5f9c4a4
--- /dev/null
+++ b/cmd/symbol_inject/Android.bp
@@ -0,0 +1,23 @@
+// 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",
+ ],
+}
diff --git a/cmd/symbol_inject/elf.go b/cmd/symbol_inject/elf.go
new file mode 100644
index 0000000..1741a5b
--- /dev/null
+++ b/cmd/symbol_inject/elf.go
@@ -0,0 +1,76 @@
+// 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)
+ }
+}
diff --git a/cmd/symbol_inject/macho.go b/cmd/symbol_inject/macho.go
new file mode 100644
index 0000000..0945293
--- /dev/null
+++ b/cmd/symbol_inject/macho.go
@@ -0,0 +1,65 @@
+// 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
+}
diff --git a/cmd/symbol_inject/pe.go b/cmd/symbol_inject/pe.go
new file mode 100644
index 0000000..86f6162
--- /dev/null
+++ b/cmd/symbol_inject/pe.go
@@ -0,0 +1,67 @@
+// 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
+}
diff --git a/cmd/symbol_inject/symbol_inject.go b/cmd/symbol_inject/symbol_inject.go
new file mode 100644
index 0000000..75f8a1a
--- /dev/null
+++ b/cmd/symbol_inject/symbol_inject.go
@@ -0,0 +1,176 @@
+// 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
+}