63 lines
1.6 KiB
Python
63 lines
1.6 KiB
Python
#
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# Option ROM signing utility
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#
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# Authors:
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# Jan Kiszka <jan.kiszka@siemens.com>
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#
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# This work is licensed under the terms of the GNU GPL, version 2 or later.
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# See the COPYING file in the top-level directory.
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import sys
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import struct
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if len(sys.argv) < 3:
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print('usage: signrom.py input output')
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sys.exit(1)
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fin = open(sys.argv[1], 'rb')
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fout = open(sys.argv[2], 'wb')
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magic = fin.read(2)
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if magic != '\x55\xaa':
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sys.exit("%s: option ROM does not begin with magic 55 aa" % sys.argv[1])
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size_byte = ord(fin.read(1))
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fin.seek(0)
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if size_byte == 0:
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# If the caller left the size field blank then we will fill it in,
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# also rounding the whole input to a multiple of 512 bytes.
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data = fin.read()
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# +1 because we need a byte to store the checksum.
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size = len(data) + 1
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# Round up to next multiple of 512.
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size += 511
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size -= size % 512
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if size >= 65536:
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sys.exit("%s: option ROM size too large" % sys.argv[1])
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# size-1 because a final byte is added below to store the checksum.
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data = data.ljust(size-1, '\0')
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data = data[:2] + chr(size/512) + data[3:]
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else:
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# Otherwise the input file specifies the size so use it.
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# -1 because we overwrite the last byte of the file with the checksum.
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size = size_byte * 512 - 1
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data = fin.read(size)
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fout.write(data)
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checksum = 0
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for b in data:
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# catch Python 2 vs. 3 differences
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if isinstance(b, int):
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checksum += b
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else:
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checksum += ord(b)
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checksum = (256 - checksum) % 256
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# Python 3 no longer allows chr(checksum)
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fout.write(struct.pack('B', checksum))
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fin.close()
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fout.close()
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