metasploit-framework/lib/rex/assembly/nasm.rb

#!/usr/bin/env ruby
# -*- coding: binary -*-

require 'tempfile'
require 'rex/file'
require 'rex/text'

module Rex
module Assembly

###
#
# This class uses nasm to assemble and disassemble stuff.
#
###
class Nasm

  @@nasm_path    = 'nasm'
  @@ndisasm_path = 'ndisasm'

  #
  # Ensures that the nasm environment is sane.
  #
  def self.check
    @@nasm_path =
      Rex::FileUtils.find_full_path('nasm')      ||
      Rex::FileUtils.find_full_path('nasm.exe')  ||
      Rex::FileUtils.find_full_path('nasmw.exe') ||
      raise(RuntimeError, "No nasm installation was found.")

    @@ndisasm_path =
      Rex::FileUtils.find_full_path('ndisasm')      ||
      Rex::FileUtils.find_full_path('ndisasm.exe')  ||
      Rex::FileUtils.find_full_path('ndisasmw.exe') ||
      raise(RuntimeError, "No ndisasm installation was found.")
  end

  #
  # Assembles the supplied assembly and returns the raw opcodes.
  #
  def self.assemble(assembly, bits=32)
    check

    # Open the temporary file
    tmp = Tempfile.new('nasmXXXX')
    tmp.binmode

    tpath = tmp.path
    opath = tmp.path + '.out'

    # Write the assembly data to a file
    tmp.write("BITS #{bits}\n" + assembly)
    tmp.flush()
    tmp.seek(0)

    # Run nasm
    if (system(@@nasm_path, '-f', 'bin', '-o', opath, tpath) == false)
      raise RuntimeError, "Assembler did not complete successfully: #{$?.exitstatus}"
    end

    # Read the assembled text
    rv = ::IO.read(opath)

    # Remove temporary files
    File.unlink(opath)
    tmp.close(true)

    rv
  end

  #
  # Disassembles the supplied raw opcodes
  #
  def self.disassemble(raw, bits=32)
    check

    tmp = Tempfile.new('nasmout')
    tmp.binmode

    tfd = File.open(tmp.path, "wb")

    tfd.write(raw)
    tfd.flush()
    tfd.close

    p = ::IO.popen("\"#{@@ndisasm_path}\" -b #{bits} \"#{tmp.path}\"")
    o = ''

    begin
      until p.eof?
        o += p.read
      end
    ensure
      p.close
    end

    tmp.close(true)

    o
  end

end

end
end