signrom.py (1272B)
1 #!/usr/bin/env python3 2 3 # 4 # Option ROM signing utility 5 # 6 # Authors: 7 # Jan Kiszka <jan.kiszka@siemens.com> 8 # 9 # This work is licensed under the terms of the GNU GPL, version 2 or later. 10 # See the COPYING file in the top-level directory. 11 12 import sys 13 import struct 14 15 if len(sys.argv) < 3: 16 print('usage: signrom.py input output') 17 sys.exit(1) 18 19 fin = open(sys.argv[1], 'rb') 20 fout = open(sys.argv[2], 'wb') 21 22 magic = fin.read(2) 23 if magic != b'\x55\xaa': 24 sys.exit("%s: option ROM does not begin with magic 55 aa" % sys.argv[1]) 25 26 size_byte = ord(fin.read(1)) 27 fin.seek(0) 28 data = fin.read() 29 30 size = size_byte * 512 31 if len(data) > size: 32 sys.stderr.write('error: ROM is too large (%d > %d)\n' % (len(data), size)) 33 sys.exit(1) 34 elif len(data) < size: 35 # Add padding if necessary, rounding the whole input to a multiple of 36 # 512 bytes according to the third byte of the input. 37 # size-1 because a final byte is added below to store the checksum. 38 data = data.ljust(size-1, b'\0') 39 else: 40 if ord(data[-1:]) != 0: 41 sys.stderr.write('WARNING: ROM includes nonzero checksum\n') 42 data = data[:size-1] 43 44 fout.write(data) 45 46 checksum = 0 47 for b in data: 48 checksum = (checksum - b) & 255 49 50 fout.write(struct.pack('B', checksum)) 51 52 fin.close() 53 fout.close()