xref: /openbmc/qemu/scripts/signrom.py (revision 7f709ce7)
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
10import sys
11import struct
12
13if len(sys.argv) < 3:
14    print('usage: signrom.py input output')
15    sys.exit(1)
16
17fin = open(sys.argv[1], 'rb')
18fout = open(sys.argv[2], 'wb')
19
20magic = fin.read(2)
21if magic != '\x55\xaa':
22    sys.exit("%s: option ROM does not begin with magic 55 aa" % sys.argv[1])
23
24size_byte = ord(fin.read(1))
25fin.seek(0)
26data = fin.read()
27
28size = size_byte * 512
29if len(data) > size:
30    sys.stderr.write('error: ROM is too large (%d > %d)\n' % (len(data), size))
31    sys.exit(1)
32elif 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, '\0')
37else:
38    if ord(data[-1:]) != 0:
39        sys.stderr.write('WARNING: ROM includes nonzero checksum\n')
40    data = data[:size-1]
41
42fout.write(data)
43
44checksum = 0
45for b in data:
46    # catch Python 2 vs. 3 differences
47    if isinstance(b, int):
48        checksum += b
49    else:
50        checksum += ord(b)
51checksum = (256 - checksum) % 256
52
53# Python 3 no longer allows chr(checksum)
54fout.write(struct.pack('B', checksum))
55
56fin.close()
57fout.close()
58