148 lines
4.0 KiB
Go
148 lines
4.0 KiB
Go
// Copyright (c) 2017, Google Inc.
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//
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// Permission to use, copy, modify, and/or distribute this software for any
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// purpose with or without fee is hereby granted, provided that the above
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// copyright notice and this permission notice appear in all copies.
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//
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// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
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// SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
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// OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
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// CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
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// break-hash parses an ELF binary containing the FIPS module and corrupts the
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// first byte of the module. This should cause the integrity check to fail.
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package main
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import (
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"bytes"
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"crypto/hmac"
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"crypto/sha512"
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"debug/elf"
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"encoding/hex"
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"errors"
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"fmt"
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"io/ioutil"
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"os"
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)
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func do(outPath, inPath string) error {
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objectBytes, err := ioutil.ReadFile(inPath)
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if err != nil {
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return err
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}
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object, err := elf.NewFile(bytes.NewReader(objectBytes))
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if err != nil {
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return errors.New("failed to parse object: " + err.Error())
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}
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// Find the .text section.
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var textSection *elf.Section
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var textSectionIndex elf.SectionIndex
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for i, section := range object.Sections {
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if section.Name == ".text" {
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textSectionIndex = elf.SectionIndex(i)
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textSection = section
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break
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}
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}
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if textSection == nil {
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return errors.New("failed to find .text section in object")
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}
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symbols, err := object.Symbols()
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if err != nil {
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return errors.New("failed to parse symbols: " + err.Error())
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}
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// Find the start and end markers of the module.
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var startSeen, endSeen bool
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var start, end uint64
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for _, symbol := range symbols {
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if symbol.Section != textSectionIndex {
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continue
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}
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switch symbol.Name {
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case "BORINGSSL_bcm_text_start":
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if startSeen {
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return errors.New("duplicate start symbol found")
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}
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startSeen = true
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start = symbol.Value
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case "BORINGSSL_bcm_text_end":
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if endSeen {
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return errors.New("duplicate end symbol found")
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}
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endSeen = true
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end = symbol.Value
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default:
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continue
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}
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}
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if !startSeen || !endSeen {
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return errors.New("could not find module in object")
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}
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moduleText := make([]byte, end-start)
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if n, err := textSection.ReadAt(moduleText, int64(start-textSection.Addr)); err != nil {
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return fmt.Errorf("failed to read from module start (at %d of %d) in .text: %s", start, textSection.Size, err)
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} else if n != len(moduleText) {
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return fmt.Errorf("short read from .text: wanted %d, got %d", len(moduleText), n)
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}
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// In order to match up the module start with the raw ELF contents,
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// search for the first 256 bytes and assume that will be unique.
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offset := bytes.Index(objectBytes, moduleText[:256])
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if offset < 0 {
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return errors.New("did not find module prefix in object file")
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}
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if bytes.Index(objectBytes[offset+1:], moduleText[:256]) >= 0 {
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return errors.New("found two occurrences of prefix in object file")
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}
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// Corrupt the module in the ELF.
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objectBytes[offset] ^= 1
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// Calculate the before and after hash of the module.
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var zeroKey [64]byte
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mac := hmac.New(sha512.New, zeroKey[:])
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mac.Write(moduleText)
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hashWas := mac.Sum(nil)
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moduleText[0] ^= 1
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mac.Reset()
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mac.Write(moduleText)
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newHash := mac.Sum(nil)
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fmt.Printf("Found start of module at offset 0x%x (VMA 0x%x):\n", start-textSection.Addr, start)
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fmt.Printf(hex.Dump(moduleText[:128]))
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fmt.Printf("\nHash of module was: %x\n", hashWas)
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fmt.Printf("Hash of corrupted module is: %x\n", newHash)
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return ioutil.WriteFile(outPath, objectBytes, 0755)
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}
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func main() {
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if len(os.Args) != 3 {
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usage()
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os.Exit(1)
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}
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if err := do(os.Args[2], os.Args[1]); err != nil {
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fmt.Fprintf(os.Stderr, "%s\n", err)
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os.Exit(1)
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}
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}
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func usage() {
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fmt.Fprintf(os.Stderr, "Usage: %s <input binary> <output path>\n", os.Args[0])
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}
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