Add tool for corrupting the FIPS module in a binary.

This is for demonstrating an integrity check failure.

Change-Id: I4b52b1aa5450f5dec024f381863aeed92b5e9ce0
Reviewed-on: https://boringssl-review.googlesource.com/16465
Reviewed-by: Martin Kreichgauer <martinkr@google.com>
Reviewed-by: Adam Langley <alangley@gmail.com>

util/fipstools/break-hash.go

diff --git a/util/fipstools/break-hash.go b/util/fipstools/break-hash.go
new file mode 100644
index 0000000..53e1c5c
--- /dev/null
+++ b/util/fipstools/break-hash.go
@@ -0,0 +1,147 @@
+// Copyright (c) 2017, Google Inc.
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
+// SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
+// OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+// CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
+
+// break-hash parses an ELF binary containing the FIPS module and corrupts the
+// first byte of the module. This should cause the integrity check to fail.
+package main
+
+import (
+	"bytes"
+	"crypto/hmac"
+	"crypto/sha512"
+	"debug/elf"
+	"encoding/hex"
+	"errors"
+	"fmt"
+	"io/ioutil"
+	"os"
+)
+
+func do(outPath, inPath string) error {
+	objectBytes, err := ioutil.ReadFile(inPath)
+	if err != nil {
+		return err
+	}
+
+	object, err := elf.NewFile(bytes.NewReader(objectBytes))
+	if err != nil {
+		return errors.New("failed to parse object: " + err.Error())
+	}
+
+	// Find the .text section.
+	var textSection *elf.Section
+	var textSectionIndex elf.SectionIndex
+	for i, section := range object.Sections {
+		if section.Name == ".text" {
+			textSectionIndex = elf.SectionIndex(i)
+			textSection = section
+			break
+		}
+	}
+
+	if textSection == nil {
+		return errors.New("failed to find .text section in object")
+	}
+
+	symbols, err := object.Symbols()
+	if err != nil {
+		return errors.New("failed to parse symbols: " + err.Error())
+	}
+
+	// Find the start and end markers of the module.
+	var startSeen, endSeen bool
+	var start, end uint64
+
+	for _, symbol := range symbols {
+		if symbol.Section != textSectionIndex {
+			continue
+		}
+
+		switch symbol.Name {
+		case "BORINGSSL_bcm_text_start":
+			if startSeen {
+				return errors.New("duplicate start symbol found")
+			}
+			startSeen = true
+			start = symbol.Value
+		case "BORINGSSL_bcm_text_end":
+			if endSeen {
+				return errors.New("duplicate end symbol found")
+			}
+			endSeen = true
+			end = symbol.Value
+		default:
+			continue
+		}
+	}
+
+	if !startSeen || !endSeen {
+		return errors.New("could not find module in object")
+	}
+
+	moduleText := make([]byte, end-start)
+	if n, err := textSection.ReadAt(moduleText, int64(start-textSection.Addr)); err != nil {
+		return fmt.Errorf("failed to read from module start (at %d of %d) in .text: %s", start, textSection.Size, err)
+	} else if n != len(moduleText) {
+		return fmt.Errorf("short read from .text: wanted %d, got %d", len(moduleText), n)
+	}
+
+	// In order to match up the module start with the raw ELF contents,
+	// search for the first 256 bytes and assume that will be unique.
+	offset := bytes.Index(objectBytes, moduleText[:256])
+	if offset < 0 {
+		return errors.New("did not find module prefix in object file")
+	}
+
+	if bytes.Index(objectBytes[offset+1:], moduleText[:256]) >= 0 {
+		return errors.New("found two occurrences of prefix in object file")
+	}
+
+	// Corrupt the module in the ELF.
+	objectBytes[offset] ^= 1
+
+	// Calculate the before and after hash of the module.
+	var zeroKey [64]byte
+	mac := hmac.New(sha512.New, zeroKey[:])
+	mac.Write(moduleText)
+	hashWas := mac.Sum(nil)
+
+	moduleText[0] ^= 1
+	mac.Reset()
+	mac.Write(moduleText)
+	newHash := mac.Sum(nil)
+
+	fmt.Printf("Found start of module at offset 0x%x (VMA 0x%x):\n", start-textSection.Addr, start)
+	fmt.Printf(hex.Dump(moduleText[:128]))
+	fmt.Printf("\nHash of module was:          %x\n", hashWas)
+	fmt.Printf("Hash of corrupted module is: %x\n", newHash)
+
+	return ioutil.WriteFile(outPath, objectBytes, 0755)
+}
+
+func main() {
+	if len(os.Args) != 3 {
+		usage()
+		os.Exit(1)
+	}
+
+	if err := do(os.Args[2], os.Args[1]); err != nil {
+		fmt.Fprintf(os.Stderr, "%s\n", err)
+		os.Exit(1)
+	}
+}
+
+func usage() {
+	fmt.Fprintf(os.Stderr, "Usage: %s <input binary> <output path>\n", os.Args[0])
+}