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#!/usr/bin/env ruby
# Deactivates any embedded code signatures in a Mach-O binary.
module MachO
class Unsign
def self.unsign(filename)
File.open(filename, "r+") do |f|
Unsign.new(f).headers
end
end
attr_accessor :headers
protected
FatHeader = Struct.new(:cpu_type, :cpu_subtype, :offset, :size, :align, :mach)
MachHeader = Struct.new(:cpu_type, :cpu_subtype, :filetype, :ncmds, :sizeofcmds, :flags, :reserved, :cmds)
LoadCommand = Struct.new(:cmd, :cmdsize)
def initialize(f)
@f = f
@headers = process
end
def debug(message)
puts message if ENV["DEBUG"]
end
def word_type
@big_endian ? 'N' : 'V'
end
def patch_code_signature(lc)
# just change LC_CODE_SIGNATURE to a high value that will be ignored by the loader
debug "PATCHING LC_CODE_SIGNATURE"
@f.seek(-8, IO::SEEK_CUR)
@f.write([0xff, lc.cmdsize].pack("#{word_type}2"))
lc
end
def process_mach
len = @x86_64 ? 7 : 6
header = MachHeader.new(*@f.read(len*4).unpack("#{word_type}#{len}"))
debug "MACH HEADER: #{header.inspect}"
header.cmds = (1..(header.ncmds)).collect do
lc = LoadCommand.new(*@f.read(8).unpack("#{word_type}2"))
debug "LOAD COMMAND: #{lc.inspect}"
lc = case lc.cmd
when 0x1d then patch_code_signature(lc)
else lc
end
@f.seek(lc.cmdsize - 8, IO::SEEK_CUR)
lc
end
header
end
def process_fat
num_arches, = @f.read(4).unpack("N")
arches = (1..num_arches).collect do
FatHeader.new(*@f.read(20).unpack("N5"))
end
debug "FAT HEADER: #{arches.inspect}"
arches.each do |arch|
@f.seek(arch.offset)
arch.mach = process
end
arches
end
def process
magic, = @f.read(4).unpack("N")
debug "MAGIC: 0x%08x" % magic
case magic
when 0xcafebabe then @big_endian, @x86_64 = false, false; process_fat
when 0xfeedface then @big_endian, @x86_64 = true, false; process_mach
when 0xcffaedfe then @big_endian, @x86_64 = false, true; process_mach
when 0xcefaedfe then @big_endian, @x86_64 = false, false; process_mach
else raise "unknown magic: 0x%08x" % magic
end
end
end
end
# command line driver
if __FILE__ == $0
if ARGV.empty?
$stderr.puts "usage: #{$0} filename ..."
exit 1
end
ARGV.each do |filename|
puts "removing signatures from: #{filename}"
MachO::Unsign::unsign(filename)
end
end