Class: ASMREPL::REPL

Inherits:
Object
  • Object
show all
Includes:
Fiddle
Defined in:
lib/asmrepl/repl.rb

Constant Summary collapse

CFuncs = 
Linux

Constants included from Fiddle

Fiddle::SIZEOF_INT64_T

Instance Method Summary collapse

Constructor Details

#initialize ⇒ REPL

Returns a new instance of REPL.



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# File 'lib/asmrepl/repl.rb', line 23

def initialize
  size = 1024 * 16 # 16k is enough for anyone!
  @buffer = CFuncs.jitbuffer(size)
  CFuncs.memset(@buffer.memory, 0xCC, size)
  @parser    = ASMREPL::Parser.new
  @assembler = ASMREPL::Assembler.new
end

Instance Method Details

#bold(string) ⇒ Object 



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# File 'lib/asmrepl/repl.rb', line 62

def bold string
  "\e[1m#{string}\e[0m"
end

#display_state(state) ⇒ Object 



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# File 'lib/asmrepl/repl.rb', line 31

def display_state state
  puts bold(" CPU STATE ".center(48, "="))
  puts state
  puts
  puts "FLAGS: #{state.flags.inspect}"
  puts
end

#display_state_change(last_state, state) ⇒ Object 



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# File 'lib/asmrepl/repl.rb', line 39

def display_state_change last_state, state
  puts bold(" REGISTER CHANGES ".center(48, "="))
  show_flags = false

  state.fields.each do |field|
    next if field == "rip"

    if last_state[field] != state[field]
      print "#{field.ljust(6)}  "
      print sprintf("%#018x", last_state[field] & MAXINT)
      print " => "
      puts bold(sprintf("%#018x", state[field] & MAXINT))
    end
  end

  if last_state.flags != state.flags
    puts
    puts "FLAGS: #{state.flags.inspect}"
  end

  puts
end

#start ⇒ Object 



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# File 'lib/asmrepl/repl.rb', line 66

def start
  pid = fork {
    CFuncs.traceme
    @buffer.to_function([], TYPE_INT).call
  }

  tracer = CFuncs::Tracer.new pid
  should_cpu = true
  last_state = nil

  while tracer.wait
    state = tracer.state

    # Show CPU state once on boot
    if last_state.nil?
      display_state state
      last_state = state
    else
      display_state_change last_state, state
      last_state = state
    end

    use_history = true
    begin
      loop do
        cmd = nil
        prompt = sprintf("(rip %#018x)> ", state.rip)
        text = Reline.readmultiline(prompt, use_history) do |multiline_input|
          case multiline_input
          when /\Adisasm\Z/
            cmd = :disasm
          when /\A\s*(\w+)\s*\Z/
            register = $1
            cmd = [:read, register]
          when /\A\s*(\w+)\s*=\s*(\d+)\Z/
            register = $1
            cmd = [:write, register, $2.to_i]
          else
            cmd = :run
          end
          true
        end

        case cmd
        in :disasm
          # disassembles the JIT buffer.  This is just for development,
          # I don't want to make a hard dependency on crabstone right now.
          # If you want to use this, install crabstone
          begin
            require "asmrepl/disasm"
            ASMREPL::Disasm.disasm @buffer
          rescue
          end
        in :run
          break if text.chomp.empty?
          begin
            parser_result = @parser.parse text.chomp
          rescue
            puts "Invalid intruction"
            next
          end

          begin
            binary = @assembler.assemble parser_result

            # Move the JIT buffer to the current instruction pointer, but
            # rewind RIP so that we write over the int3
            pos = (state.rip - @buffer.memory.to_i - 1)
            @buffer.seek pos
            binary.bytes.each { |byte| @buffer.putc byte }
            state.rip -= 1
            tracer.state = state
          rescue Fisk::Errors::InvalidInstructionError => e
            # Print an error message when the instruction is invalid
            puts e.message
            next
          end
          break
        in [:write, reg, val]
          state[reg] = val
          tracer.state = state
        in [:read, "cpu"]
          display_state state
        in [:read, reg]
          val = state[reg]
          if val
            puts sprintf("%#018x", state[reg])
          else
            puts "Unknown command: "
            puts "  " + text
          end
        else
        end
      end
    rescue Interrupt
      puts ""
      exit 0
    end
    tracer.continue
  end
end