96 lines
2.7 KiB
Ruby
96 lines
2.7 KiB
Ruby
# This file is part of Metasm, the Ruby assembly manipulation suite
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# Copyright (C) 2006-2009 Yoann GUILLOT
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# Original script and idea by Alexandre GAZET
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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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# this script will load an upx-packed windows executable, find its
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# original entrypoint by disassembling the UPX stub, set breakpoint on it,
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# run the program, and dump the loaded image to an executable PE.
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#
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# usage: dump_upx.rb <packed.exe> [<dumped.exe>] [<rva iat>]
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#
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require 'metasm'
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include Metasm
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class UPXUnpacker
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# loads the file
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# find the oep by disassembling
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# run it until the oep
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# dump the memory image
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def initialize(file, dumpfile, iat_rva=nil)
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@dumpfile = dumpfile || 'upx-dumped.exe'
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@iat = iat_rva
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puts 'disassembling UPX loader...'
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pe = PE.decode_file(file)
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@oep = find_oep(pe)
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raise 'cant find oep...' if not @oep
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puts "oep found at #{Expression[@oep]}"
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@baseaddr = pe.optheader.image_base
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@iat -= @baseaddr if @iat > @baseaddr # va => rva
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@dbg = OS.current.create_process(file).debugger
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puts 'running...'
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debugloop
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end
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# disassemble the upx stub to find a cross-section jump (to the real entrypoint)
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def find_oep(pe)
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dasm = pe.disassemble_fast 'entrypoint'
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return if not jmp = dasm.decoded.find { |addr, di|
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# check only once per basic block
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next if not di.block_head?
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b = di.block
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# our target has only one follower
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next if b.to_subfuncret.to_a.length != 0 or b.to_normal.to_a.length != 1
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to = b.to_normal.first
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# ignore jump to unmmaped address
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next if not s = dasm.get_section_at(to)
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# ignore jump to same section
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next if dasm.get_section_at(di.address) == s
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# gotcha !
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true
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}
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# now jmp is a couple [addr, di], we extract and normalize the oep from there
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dasm.normalize(jmp[1].block.to_normal.first)
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end
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def debugloop
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# set up a oneshot breakpoint on oep
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@dbg.hwbp(@oep, :x, 1, true) { breakpoint_callback }
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@dbg.run_forever
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puts 'done'
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end
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def breakpoint_callback
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puts 'breakpoint hit !'
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# dump the process
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# create a genuine PE object from the memory image
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dump = LoadedPE.memdump @dbg.memory, @baseaddr, @oep, @iat
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# the UPX loader unpacks everything in sections marked read-only in the PE header, make them writeable
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dump.sections.each { |s| s.characteristics |= ['MEM_WRITE'] }
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# write the PE file to disk
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dump.encode_file @dumpfile
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puts 'dump complete'
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ensure
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# kill the process
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@dbg.kill
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end
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end
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if __FILE__ == $0
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# args: packed [unpacked] [iat rva]
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UPXUnpacker.new(ARGV.shift, ARGV.shift, (Integer(ARGV.shift) rescue nil))
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end
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