metasploit-framework/lib/rex/elfscan/scanner.rb

# -*- coding: binary -*-

# $Id$

module Rex
module ElfScan
module Scanner
class Generic

	attr_accessor :elf, :regex

	def initialize(elf)
		self.elf = elf
	end

	def config(param)
	end

	def scan(param)
		config(param)

		$stdout.puts "[#{param['file']}]"
		elf.program_header.each do |program_header|

			# Scan only loadable segment entries in the program header table
			if program_header.p_type == Rex::ElfParsey::ElfBase::PT_LOAD
				hits = scan_segment(program_header, param)
				hits.each do |hit|
					rva  = hit[0]
					message  = hit[1].is_a?(Array) ? hit[1].join(" ") : hit[1]
					$stdout.puts elf.ptr_s(rva) + " " + message
				end
			end

		end
	end

	def scan_segment(program_header, param={})
		[]
	end
end

class JmpRegScanner < Generic

	def config(param)
		regnums = param['args']

		# build a list of the call bytes
		calls  = _build_byte_list(0xd0, regnums - [4]) # note call esp's don't work..
		jmps   = _build_byte_list(0xe0, regnums)
		pushs1 = _build_byte_list(0x50, regnums)
		pushs2 = _build_byte_list(0xf0, regnums)

		regexstr = '('
		if !calls.empty?
			regexstr += "\xff[#{calls}]|"
		end

		regexstr += "\xff[#{jmps}]|([#{pushs1}]|\xff[#{pushs2}])(\xc3|\xc2..))"

		self.regex = Regexp.new(regexstr, nil, 'n')
	end

	# build a list for regex of the possible bytes, based on a base
	# byte and a list of register numbers..
	def _build_byte_list(base, regnums)
		regnums.collect { |regnum| Regexp.escape((base | regnum).chr) }.join('')
	end

	def _ret_size(offset)
		case elf.read(offset, 1)
			when "\xc3"
				return 1
			when "\xc2"
				return 3
		end

		raise "wtf"
	end

	def _parse_ret(data)
		if data.length == 1
			return "ret"
		else
			return "retn 0x%04x" % data[1, 2].unpack('v')[0]
		end
	end


	def scan_segment(program_header, param={})
		offset = program_header.p_offset

		hits = []

		while (offset = elf.index(regex, offset)) != nil

			rva     = elf.offset_to_rva(offset)
			message = ''

			parse_ret = false

			byte1 = elf.read(offset, 1).unpack('C')[0]

			if byte1 == 0xff
				byte2   = elf.read(offset+1, 1).unpack('C')[0]
				regname = Rex::Arch::X86.reg_name32(byte2 & 0x7)

				case byte2 & 0xf8
				when 0xd0
					message = "call #{regname}"
					offset += 2
				when 0xe0
					message = "jmp #{regname}"
					offset += 2
				when 0xf0
					retsize = _ret_size(offset+2)
					message = "push #{regname}; " + _parse_ret(elf.read(offset+2, retsize))
					offset += 2 + retsize
				else
					raise "wtf"
				end
			else
				regname = Rex::Arch::X86.reg_name32(byte1 & 0x7)
				retsize = _ret_size(offset+1)
				message = "push #{regname}; " + _parse_ret(elf.read(offset+1, retsize))
				offset += 1 + retsize
			end

			hits << [ rva, message ]
		end

		return hits
	end
end

class PopPopRetScanner < JmpRegScanner

	def config(param)
		pops = _build_byte_list(0x58, (0 .. 7).to_a - [4]) # we don't want pop esp's...
		self.regex = Regexp.new("[#{pops}][#{pops}](\xc3|\xc2..)", nil, 'n')
	end

	def scan_segment(program_header, param={})
		offset = program_header.p_offset

		hits = []

		while offset < program_header.p_offset + program_header.p_filesz &&
		(offset = elf.index(regex, offset)) != nil

			rva     = elf.offset_to_rva(offset)
			message = ''

			pops = elf.read(offset, 2)
			reg1 = Rex::Arch::X86.reg_name32(pops[0,1].unpack('C*')[0] & 0x7)
			reg2 = Rex::Arch::X86.reg_name32(pops[1,1].unpack('C*')[0] & 0x7)

			message = "pop #{reg1}; pop #{reg2}; "

			retsize = _ret_size(offset+2)
			message += _parse_ret(elf.read(offset+2, retsize))

			offset += 2 + retsize

			hits << [ rva, message ]
		end

		return hits
	end
end

class RegexScanner < JmpRegScanner

	def config(param)
		self.regex = Regexp.new(param['args'], nil, 'n')
	end

	def scan_segment(program_header, param={})
		offset = program_header.p_offset

		hits = []

		while offset < program_header.p_offset + program_header.p_filesz &&
		(offset = elf.index(regex, offset)) != nil

			idx = offset
			buf = ''
			mat = nil

			while (! (mat = buf.match(regex)))
				buf << elf.read(idx, 1)
				idx += 1
			end

			rva = elf.offset_to_rva(offset)

			hits << [ rva, buf.unpack("H*") ]
			offset += buf.length
		end

		return hits
	end
end

end
end
end