fuzz update/node/lib/metasm/samples/dasm-plugins/patch_file.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


# metasm dasm plugin: allow patching the file from the dasm interface
# use P to assemble a new instruction at the current address

# backup the executable file
def backup_program_file
	f = @program.filename
	if File.exist?(f) and not File.exist?(f + '.bak')
		File.open(f + '.bak', 'wb') { |wfd|
			File.open(f, 'rb') { |rfd|
				while buf = rfd.read(1024*1024)
					wfd.write buf
				end
			}
		}
	end
end

# create a backup and reopen the backend VirtualFile RW
def reopen_rw(addr=nil, edata=nil)
	if not edata
		sections.each { |k, v| reopen_rw(k, v) }
		return true
	end

	return if not File.writable?(@program.filename)
	backup_program_file
	if not edata.data.kind_of? VirtualFile
		# section too small, loaded as real String
		# force reopen as VFile (allow hexediting in gui)
		return if not off = addr_to_fileoff(addr)
		len = edata.data.length
		edata.data = VirtualFile.read(@program.filename, 'rb+').dup(off, len)
	else
		edata.data.fd.reopen @program.filename, 'rb+'
	end
end

raise "cant find original file" if not @program.filename or not File.exist? @program.filename

reopen_rw

def patch_instrs(addr, asmsrc)
	sc = Metasm::Shellcode.new(cpu, addr)	# pfx needed for autorequire
	sc.assemble(asmsrc, cpu)
	sc.encoded.fixup! prog_binding	# allow references to dasm labels in the shellcode
	raw = sc.encode_string

	if s = get_section_at(addr) and s[0].data.kind_of? VirtualFile
		s[0][s[0].ptr, raw.length] = raw
	elsif o = addr_to_fileoff(addr)	# section too small, not loaded as a VirtFile
		backup_program_file
		File.open(@program.filename, 'rb+') { |fd|
			fd.pos = o
			fd.write raw
		}
		s[0][s[0].ptr, raw.length] = raw if s
	else
		return
	end

	b = split_block(addr)

	# clear what we had in the rewritten space
	raw.length.times { |rawoff|
		next if not di = di_at(addr+rawoff)
		di.block.list.each { |ldi| @decoded.delete ldi.address }
	}

	disassemble_fast(addr) if b
	if b and @decoded[addr]
		nb = @decoded[addr].block
		nb.from_normal = b.from_normal
		nb.from_subfuncret = b.from_subfuncret
		nb.from_indirect = b.from_indirect
	end
	true
end

if gui
	gui.keyboard_callback[?P] = lambda { |k|
		addr = gui.curaddr
		gui.inputbox('new instructions') { |src|
			src = src.gsub(/;\s+/, "\n")
			patch_instrs(addr, src)
			gui.gui_update
		}
		true
	}
end
