scripts/signrom.py

   1 #
   2 # Option ROM signing utility
   3 #
   4 # Authors:
   5 #  Jan Kiszka <jan.kiszka@siemens.com>
   6 #
   7 # This work is licensed under the terms of the GNU GPL, version 2 or later.
   8 # See the COPYING file in the top-level directory.
   9
  10 import sys
  11 import struct
  12
  13 if len(sys.argv) < 3:
  14     print('usage: signrom.py input output')
  15     sys.exit(1)
  16
  17 fin = open(sys.argv[1], 'rb')
  18 fout = open(sys.argv[2], 'wb')
  19
  20 magic = fin.read(2)
  21 if magic != b'\x55\xaa':
  22     sys.exit("%s: option ROM does not begin with magic 55 aa" % sys.argv[1])
  23
  24 size_byte = ord(fin.read(1))
  25 fin.seek(0)
  26 data = fin.read()
  27
  28 size = size_byte * 512
  29 if len(data) > size:
  30     sys.stderr.write('error: ROM is too large (%d > %d)\n' % (len(data), size))
  31     sys.exit(1)
  32 elif len(data) < size:
  33     # Add padding if necessary, rounding the whole input to a multiple of
  34     # 512 bytes according to the third byte of the input.
  35     # size-1 because a final byte is added below to store the checksum.
  36     data = data.ljust(size-1, b'\0')
  37 else:
  38     if ord(data[-1:]) != 0:
  39         sys.stderr.write('WARNING: ROM includes nonzero checksum\n')
  40     data = data[:size-1]
  41
  42 fout.write(data)
  43
  44 checksum = 0
  45 for b in data:
  46     # catch Python 2 vs. 3 differences
  47     if isinstance(b, int):
  48         checksum += b
  49     else:
  50         checksum += ord(b)
  51 checksum = (256 - checksum) % 256
  52
  53 # Python 3 no longer allows chr(checksum)
  54 fout.write(struct.pack('B', checksum))
  55
  56 fin.close()
  57 fout.close()