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#!/usr/bin/env python
# Copyright (c) 2013 The Chromium OS Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.
# A script to pack EC binary into SPI flash image for MEC1322
# TODO(crosbug.com/p/24107): Add reference to document on image format.
import hashlib
import os
import struct
import subprocess
import tempfile
# TODO(crosbug.com/p/24188): Make these options available as command line
# arguments.
SPI_SIZE = 4 * 1024 * 1024
HEADER_PEM_FILE = 'rsakey_sign_header.pem'
PAYLOAD_PEM_FILE = 'rsakey_sign_payload.pem'
PAYLOAD_FILE = 'ec.bin' # Set to 'ec.RO.flat' for RO-only image
HEADER_LOCATION = 0x170000
HEADER_FLAG1 = 0x00
HEADER_FLAG2 = 0x01
SPI_READ_CMD = 0x01
LOAD_ADDR = 0x100000
SPI_CHIP_SELECT = 0
HEADER_SIZE = 0x140
PAYLOAD_OFFSET = 0x240
OUTPUT_FILE = 'ec.4mb.bin'
CRC_TABLE = [0x00, 0x07, 0x0e, 0x09, 0x1c, 0x1b, 0x12, 0x15,
0x38, 0x3f, 0x36, 0x31, 0x24, 0x23, 0x2a, 0x2d]
def Crc8(crc, data):
"""Update CRC8 value."""
data_bytes = map(lambda b: ord(b) if isinstance(b, str) else b, data)
for v in data_bytes:
crc = ((crc << 4) & 0xff) ^ (CRC_TABLE[(crc >> 4) ^ (v >> 4)]);
crc = ((crc << 4) & 0xff) ^ (CRC_TABLE[(crc >> 4) ^ (v & 0xf)]);
return crc ^ 0x55
def GetEntryPoint(payload_file):
"""Read entry point from payload EC image."""
with open(payload_file, 'rb') as f:
f.seek(4)
s = f.read(4)
return struct.unpack('<I', s)[0]
def GetPayload(payload_file):
"""Read payload and pad it to 64-byte aligned."""
with open(payload_file, 'rb') as f:
payload = bytearray(f.read())
rem_len = len(payload) % 64
if rem_len:
payload += '\0' * (64 - rem_len)
return payload
def GetPublicKey(pem_file):
"""Extract public exponent and modulus from PEM file."""
s = subprocess.check_output(['openssl', 'rsa', '-in', pem_file,
'-text', '-noout'])
modulus_raw = []
in_modulus = False
for line in s.split('\n'):
if line.startswith('modulus'):
in_modulus = True
elif not line.startswith(' '):
in_modulus = False
elif in_modulus:
modulus_raw.extend(line.strip().strip(':').split(':'))
if line.startswith('publicExponent'):
exp = int(line.split(' ')[1], 10)
modulus_raw.reverse()
modulus = bytearray(''.join(map(lambda x: chr(int(x, 16)),
modulus_raw[0:256])))
return struct.pack('<Q', exp), modulus
def PadZeroTo(data, size):
data.extend('\0' * (size - len(data)))
def BuildHeader(payload_len):
header = bytearray(['C', 'S', 'M', 'S', '\0'])
header.extend([HEADER_FLAG1, HEADER_FLAG2, SPI_READ_CMD])
header.extend(struct.pack('<I', LOAD_ADDR))
header.extend(struct.pack('<I', GetEntryPoint(PAYLOAD_FILE)))
header.append((payload_len >> 6) & 0xff)
header.append((payload_len >> 14) & 0xff)
PadZeroTo(header, 0x14)
header.extend(struct.pack('<I', PAYLOAD_OFFSET))
exp, modulus = GetPublicKey(PAYLOAD_PEM_FILE)
PadZeroTo(header, 0x20)
header.extend(exp)
PadZeroTo(header, 0x30)
header.extend(modulus)
PadZeroTo(header, HEADER_SIZE)
return header
def SignByteArray(data, pem_file):
hash_file = tempfile.mkstemp()[1]
sign_file = tempfile.mkstemp()[1]
with open(hash_file, 'wb') as f:
hasher = hashlib.sha256()
hasher.update(data)
f.write(hasher.digest())
subprocess.check_call(['openssl', 'rsautl', '-sign', '-inkey', pem_file,
'-keyform', 'PEM', '-in', hash_file,
'-out', sign_file])
with open(sign_file, 'rb') as f:
signed = list(f.read())
signed.reverse()
return bytearray(''.join(signed))
def BuildTag(header_loc):
tag = bytearray([(header_loc >> 8) & 0xff,
(header_loc >> 16) & 0xff,
(header_loc >> 24) & 0xff])
if SPI_CHIP_SELECT != 0:
tag[2] |= 0x80
tag.append(Crc8(0, tag))
return tag
def main():
spi_list = []
payload = GetPayload(PAYLOAD_FILE)
payload_len = len(payload)
payload_signature = SignByteArray(payload, PAYLOAD_PEM_FILE)
header = BuildHeader(payload_len)
header_signature = SignByteArray(header, HEADER_PEM_FILE)
tag = BuildTag(HEADER_LOCATION)
spi_list.append((HEADER_LOCATION, header))
spi_list.append((HEADER_LOCATION + HEADER_SIZE, header_signature))
spi_list.append((HEADER_LOCATION + PAYLOAD_OFFSET, payload))
spi_list.append((HEADER_LOCATION + PAYLOAD_OFFSET + payload_len,
payload_signature))
spi_list.append((SPI_SIZE - 256, tag))
spi_list = sorted(spi_list)
with open(OUTPUT_FILE, 'wb') as f:
addr = 0
for s in spi_list:
assert addr <= s[0]
if addr < s[0]:
f.write('\xff' * (s[0] - addr))
addr = s[0]
f.write(s[1])
addr += len(s[1])
if addr < SPI_SIZE:
f.write('\xff' * (SPI_SIZE - addr))
if __name__ == '__main__':
main()
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