scripts/signrom.py

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