fuzz update/node/lib/metasm/metasm/cpu/bpf/decode.rb
#    This file is part of Metasm, the Ruby assembly manipulation suite
#    Copyright (C) 2006-2009 Yoann GUILLOT
#
#    Licence is LGPL, see LICENCE in the top-level directory


require 'metasm/cpu/bpf/opcodes'
require 'metasm/decode'

module Metasm
class BPF
	def build_bin_lookaside
		opcode_list.inject({}) { |h, op| h.update op.bin => op }
	end

	# tries to find the opcode encoded at edata.ptr
	def decode_findopcode(edata)
		return if edata.ptr > edata.data.length-8
		di = DecodedInstruction.new self
		code = edata.data[edata.ptr, 2].unpack('v')[0]
		return di if di.opcode = @bin_lookaside[code]
	end

	def decode_instr_op(edata, di)
		op = di.opcode
		di.instruction.opname = op.name
		di.bin_length = 8
		code, jt, jf, k = edata.read(8).unpack('vCCV')

		op.args.each { |a|
			di.instruction.args << case a
			when :k;    Expression[k]
			when :x;    Reg.new(:x)
			when :a;    Reg.new(:a)
			when :len;  Reg.new(:len)
			when :p_k;  PktRef.new(nil, Expression[k], op.props[:msz])
			when :p_xk; PktRef.new(Reg.new(:x), Expression[k], op.props[:msz])
			when :m_k;  MemRef.new(nil, Expression[4*k], 4)
			when :jt;   Expression[jt]
			when :jf;   Expression[jf]
			else raise "unhandled arg #{a}"
			end
		}

		# je a, x, 0, 12 -> jne a, x, 12
		# je a, x, 12, 0 -> je a, x, 12
		if op.args[2] == :jt and di.instruction.args[2] == Expression[0]
			di.opcode = op.dup
			di.opcode.props.delete :stopexec
			di.instruction.opname = { 'jg' => 'jle', 'jge' => 'jl', 'je' => 'jne', 'jtest' => 'jntest' }[di.instruction.opname]
			di.instruction.args.delete_at(2)
		elsif op.args[3] == :jf and di.instruction.args[3] == Expression[0]
			di.opcode = op.dup
			di.opcode.props.delete :stopexec
			di.instruction.args.delete_at(3)
		end

		di
	end

	def decode_instr_interpret(di, addr)
		if di.opcode.props[:setip]
			delta = di.instruction.args[-1].reduce + 1
			arg = Expression[addr, :+, 8*delta].reduce
			di.instruction.args[-1] = Expression[arg]

			if di.instruction.args.length == 4
				delta = di.instruction.args[2].reduce + 1
				arg = Expression[addr, :+, 8*delta].reduce
				di.instruction.args[2] = Expression[arg]
			end
		end

		di
	end

	# hash opcode_name => lambda { |dasm, di, *symbolic_args| instr_binding }
	def backtrace_binding
		@backtrace_binding ||= init_backtrace_binding
	end
	def backtrace_binding=(b) @backtrace_binding = b end

	# populate the @backtrace_binding hash with default values
	def init_backtrace_binding
		@backtrace_binding ||= {}

		opcode_list.map { |ol| ol.basename }.uniq.sort.each { |op|
			binding = case op
			when 'mov'; lambda { |di, a0, a1| { a0 => Expression[a1] } }
			when 'add'; lambda { |di, a0, a1| { a0 => Expression[a0, :+, a1] } }
			when 'sub'; lambda { |di, a0, a1| { a0 => Expression[a0, :-, a1] } }
			when 'mul'; lambda { |di, a0, a1| { a0 => Expression[a0, :*, a1] } }
			when 'div'; lambda { |di, a0, a1| { a0 => Expression[a0, :/, a1] } }
			when 'shl'; lambda { |di, a0, a1| { a0 => Expression[a0, :<<, a1] } }
			when 'shr'; lambda { |di, a0, a1| { a0 => Expression[a0, :>>, a1] } }
			when 'neg'; lambda { |di, a0| { a0 => Expression[:-, a0] } }
			when 'msh'; lambda { |di, a0, a1| { a0 => Expression[[a1, :&, 0xf], :<<, 2] } }
			when 'jmp', 'jg', 'jge', 'je', 'jtest', 'ret'; lambda { |di, *a| { } }
			end
			@backtrace_binding[op] ||= binding if binding
		}

		@backtrace_binding
	end

	def get_backtrace_binding(di)
		a = di.instruction.args.map { |arg|
			case arg
			when PktRef, MemRef, Reg; arg.symbolic(di)
			else arg
			end
		}

		if binding = backtrace_binding[di.opcode.name]
			binding[di, *a]
		else
			puts "unhandled instruction to backtrace: #{di}" if $VERBOSE
			{:incomplete_binding => Expression[1]}
		end
	end

	def get_xrefs_x(dasm, di)
		return [] if not di.opcode.props[:setip]

		if di.instruction.args.length == 4
			di.instruction.args[-2, 2]
		else
			di.instruction.args[-1, 1]
		end
	end

	# updates an instruction's argument replacing an expression with another (eg label renamed)
	def replace_instr_arg_immediate(i, old, new)
		i.args.map! { |a|
			case a
			when Expression; a == old ? new : Expression[a.bind(old => new).reduce]
			else a
			end
		}
	end
end
end
