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#!/usr/bin/env ruby
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##
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# This module requires Metasploit: https://metasploit.com/download
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# Current source: https://github.com/rapid7/metasploit-framework
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##
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#
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# This tool provides an easy way to see what opcodes are associated with
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# certain x86 instructions by making use of Metasm! Also allows to get
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# friendly output from a GAS assembler source code file.
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#
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#
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#    This file is part of Metasm, the Ruby assembly manipulation suite
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#    Copyright (C) 2007 Yoann GUILLOT
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#
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#    Licence is LGPL, see LICENCE in the top-level directory
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#
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begin
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msfbase = __FILE__
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while File.symlink?(msfbase)
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  msfbase = File.expand_path(File.readlink(msfbase), File.dirname(msfbase))
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end
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gem 'rex-text'
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$:.unshift(File.expand_path(File.join(File.dirname(msfbase), '..', '..', 'lib')))
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require 'msfenv'
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$:.unshift(ENV['MSF_LOCAL_LIB']) if ENV['MSF_LOCAL_LIB']
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require 'rex'
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require 'reline'
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require 'metasm'
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#PowerPC, seems broken for now in metasm
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#@Arch = ['Ia32','MIPS','PowerPC','ARM','X86_64']
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@Arch = ['Ia32','MIPS','ARM','X86_64']
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@Endian = ['little','big']
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@architecture = ""
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@endianness = ""
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def usage
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  $stderr.puts("\nUsage: #{$0} <options>\n" + $args.usage)
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  exit
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end
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$args = Rex::Parser::Arguments.new(
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  "-a" => [ true, "The architecture to encode as (#{@Arch.sort.collect{|a| a + ', ' }.join.gsub(/\, $/,'')})"],
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  "-e" => [ true, "The endianness to encode as (#{@Endian.sort.collect{|a| a + ', ' }.join.gsub(/\, $/,'')})" ],
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  "-h" => [ false, "Display this help information" ])
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$args.parse(ARGV) { |opt, idx, val|
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  case opt
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  when "-a"
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    found = nil
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    @Arch.each { |a|
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      if val.downcase == a.downcase
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        @architecture = a
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        found = true
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      end
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    }
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    usage if not found
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  when "-e"
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    found = nil
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    @Endian.each { |e|
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      if val.downcase == e.downcase
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        @endianness = e
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        found = true
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      end
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    }
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    usage if not found
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  when "-h"
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    usage
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  else
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    usage
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  end
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}
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unless @architecture.empty?
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  if @endianness.empty?
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    String.class_eval("@@cpu = Metasm::#{@architecture}.new")
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  else
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    String.class_eval("@@cpu = Metasm::#{@architecture}.new(:#{@endianness})")
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  end
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end
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class String
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  @@cpu ||= Metasm::Ia32.new
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  class << self
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    def cpu()   @@cpu   end
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    def cpu=(c) @@cpu=c end
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  end
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  # encodes the current string as a Shellcode, returns the resulting EncodedData
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  def metasm_encode_edata
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    s = Metasm::Shellcode.assemble @@cpu, self
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    s.encoded
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  end
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  # encodes the current string as a Shellcode, returns the resulting binary String
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  # outputs warnings on unresolved relocations
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  def metasm_encode
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    ed = metasm_encode_edata
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    if not ed.reloc.empty?
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      puts 'W: encoded string has unresolved relocations: ' + ed.reloc.map { |o, r| r.target.inspect }.join(', ')
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    end
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    ed.fill
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    ed.data
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  end
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  # decodes the current string as a Shellcode, with specified base address
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  # returns the resulting Disassembler
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  def metasm_decode_blocks(base_addr=0, eip=base_addr)
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    sc = Metasm::Shellcode.metasm_decode(self, @@cpu)
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    sc.base_addr = base_addr
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    sc.metasm_disassemble(eip)
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  end
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  # decodes the current string as a Shellcode, with specified base address
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  # returns the asm source equivallent
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  def metasm_decode(base_addr=0, eip=base_addr)
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    metasm_decode_blocks(base_addr, eip).to_s
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  end
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  def metasm_disassemble(str, eip=0)
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    Metasm::Shellcode.metasm_disassemble(@@cpu, str, eip)
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  end
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end
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def parse_gas_file(filename)
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  filename = File.expand_path(filename)
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  unless ::File.exist?(filename)
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    puts "File #{filename} not found"
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    return
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  end
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  shellcode = ""
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  puts "Reading file #{filename}"
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  ::File.open(filename, "rb") do |f|
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    f.each_line do |l|
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      l.gsub!(/#.*$/, "")    # Delete comments
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      l.gsub!(/@.*$/, "")    # Delete comments
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      l.gsub!(/\..*$/, "")   # Delete directives
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      l.gsub!(/(\r|\n)/, '') # Delete newlines... just in case...
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      next if l.strip.empty?
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      shellcode << "#{l}\n"
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    end
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  end
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  begin
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    encoded = shellcode.metasm_encode
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    puts Rex::Text.to_ruby(encoded)
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    puts encoded.metasm_disassemble(shellcode.metasm_encode)
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  rescue Metasm::Exception => e
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    puts "Error: #{e.class} #{e.message}"
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  end
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end
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# Start a pseudo shell and dispatch lines to be assembled and then
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# disassembled.
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history_file = File.join(Msf::Config.config_directory, 'metasm_history')
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shell = Rex::Ui::Text::PseudoShell.new("%bldmetasm%clr", '>', history_file)
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shell.init_ui(Rex::Ui::Text::Input::Stdio.new, Rex::Ui::Text::Output::Stdio.new)
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shell.history_manager = Rex::Ui::Text::Shell::HistoryManager.new
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puts [
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  'type "exit" or "quit" to quit',
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  'use ";" or "\\n" for newline',
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  'type "file <file>" to parse a GAS assembler source file',
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  '']
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shell.run { |l|
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  l.gsub!(/(\r|\n)/, '')
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  l.gsub!(/\\n/, "\n")
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  l.gsub!(';', "\n")
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  break if %w[quit exit].include? l.chomp
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  if l.chomp.index(/^file (.*)/)
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    parse_gas_file($1)
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    next
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  end
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  next if l.strip.empty?
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  begin
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    l = l.metasm_encode
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    puts '"' + l.unpack('C*').map { |c| '\\x%02x' % c }.join + '"'
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  rescue Metasm::Exception => e
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    puts "Error: #{e.class} #{e.message}"
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  end
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}
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rescue SignalException => e
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  puts("Aborted! #{e}")
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end
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