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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.
// Verifies a host bionic executable with an embedded linker.
package main
import (
"debug/elf"
"flag"
"fmt"
"io"
"os"
)
func main() {
var inputFile, linkerFile string
flag.StringVar(&inputFile, "i", "", "Input file")
flag.StringVar(&linkerFile, "l", "", "Linker file")
flag.Parse()
if inputFile == "" || linkerFile == "" || flag.NArg() != 0 {
flag.Usage()
os.Exit(1)
}
r, err := os.Open(inputFile)
if err != nil {
fmt.Fprintln(os.Stderr, err.Error())
os.Exit(2)
}
defer r.Close()
linker, err := elf.Open(linkerFile)
if err != nil {
fmt.Fprintln(os.Stderr, err.Error())
os.Exit(4)
}
err = checkElf(r, linker)
if err != nil {
fmt.Fprintln(os.Stderr, err.Error())
os.Exit(5)
}
}
// Check the ELF file, and return the address to the _start function
func checkElf(r io.ReaderAt, linker *elf.File) error {
file, err := elf.NewFile(r)
if err != nil {
return err
}
symbols, err := file.Symbols()
if err != nil {
return err
}
for _, prog := range file.Progs {
if prog.Type == elf.PT_INTERP {
return fmt.Errorf("File should not have a PT_INTERP header")
}
}
if dlwrap_start, err := findSymbol(symbols, "__dlwrap__start"); err != nil {
return err
} else if dlwrap_start.Value != file.Entry {
return fmt.Errorf("Expected file entry(0x%x) to point to __dlwrap_start(0x%x)",
file.Entry, dlwrap_start.Value)
}
err = checkLinker(file, linker, symbols)
if err != nil {
return fmt.Errorf("Linker executable failed verification against app embedded linker: %s\n"+
"linker might not be in sync with crtbegin_dynamic.o.",
err)
}
return nil
}
func findSymbol(symbols []elf.Symbol, name string) (elf.Symbol, error) {
for _, sym := range symbols {
if sym.Name == name {
return sym, nil
}
}
return elf.Symbol{}, fmt.Errorf("Failed to find symbol %q", name)
}
// Check that all of the PT_LOAD segments have been embedded properly
func checkLinker(file, linker *elf.File, fileSyms []elf.Symbol) error {
dlwrapLinkerOffset, err := findSymbol(fileSyms, "__dlwrap_linker_offset")
if err != nil {
return err
}
for i, lprog := range linker.Progs {
if lprog.Type != elf.PT_LOAD {
continue
}
laddr := lprog.Vaddr + dlwrapLinkerOffset.Value
found := false
for _, prog := range file.Progs {
if prog.Type != elf.PT_LOAD {
continue
}
if laddr < prog.Vaddr || laddr > prog.Vaddr+prog.Memsz {
continue
}
found = true
if lprog.Flags != prog.Flags {
return fmt.Errorf("Linker prog %d (0x%x) flags (%s) do not match (%s)",
i, lprog.Vaddr, lprog.Flags, prog.Flags)
}
if laddr+lprog.Memsz > prog.Vaddr+prog.Filesz {
return fmt.Errorf("Linker prog %d (0x%x) not fully present (0x%x > 0x%x)",
i, lprog.Vaddr, laddr+lprog.Memsz, prog.Vaddr+prog.Filesz)
}
}
if !found {
return fmt.Errorf("Linker prog %d (0x%x) not found at offset 0x%x",
i, lprog.Vaddr, dlwrapLinkerOffset.Value)
}
}
return nil
}
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