scripts/signrom.py

   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()