xref: /openbmc/qemu/scripts/signrom.py (revision 988717b46b6424907618cb845ace9d69062703af)
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()
54