extract kernel builtin_fw

extract.py

#!/usr/bin/env python3

import argparse
import mmap
import os

parser = argparse.ArgumentParser(description='extract builtin_fw')
parser.add_argument('image', metavar='IMAGE', type=str,
                    help='kernel image file')
parser.add_argument('kallsyms', metavar='KALLSYMS', type=str,
                    help='kallsyms out file')
parser.add_argument('--start', dest='kstart', type=int, default=0xffffffc000000000,
                    help='kallsyms out file')


# kernel logical memory map
# <5>[    0.000000] Virtual kernel memory layout:
# <5>[    0.000000]     vmalloc : 0xffffff8000000000 - 0xffffffbbffff0000   (245759 MB)
# <5>[    0.000000]     vmemmap : 0xffffffbc02000000 - 0xffffffbc04000000   (    32 MB)
# <5>[    0.000000]     modules : 0xffffffbffc000000 - 0xffffffc000000000   (    64 MB)
# <5>[    0.000000]     memory  : 0xffffffc000000000 - 0xffffffc080000000   (  2048 MB) <-- look for this line
# <5>[    0.000000]       .init : 0xffffffc0010c9000 - 0xffffffc0011348c0   (   431 kB)
# <5>[    0.000000]       .text : 0xffffffc000080000 - 0xffffffc0010c8fd4   ( 16676 kB)
# <5>[    0.000000]       .data : 0xffffffc001135000 - 0xffffffc0012cded8   (  1636 kB)


def process_kallsyms(kallsyms):
    with open(kallsyms, 'r') as fd:
        fw = {}

        for e in fd.readlines():
            split = e.strip().split()
            if len(split) < 3:
                continue
            if split[2] == '__start_builtin_fw':
                fw['start'] = split[0]

            if split[2] == '__end_builtin_fw':
                fw['end'] = split[0]

        for k in ['start', 'end']:
            if k not in fw.keys():
                print('could not find __{}_builtin_fw; exit'.format(k))
                exit(1)

    return int(fw['start'], 16), int(fw['end'], 16)

def extract(kernel, start, fw_start, fw_end):
    # struct builtin_fw {
    #     char *name; // 8
    #     void *data; // 8
    #     unsigned long size; // 8
    # };

    offsetb = kernel[8:16]
    offset = int.from_bytes(offsetb, byteorder='little')

    for b_fw_a in range(fw_start, fw_end, 24):
        b_fw_a_f = b_fw_a - start - offset

        b_fw = kernel[b_fw_a_f:b_fw_a_f+24]

        na = int.from_bytes(b_fw[0:8], byteorder='little')
        da = int.from_bytes(b_fw[8:16], byteorder='little')
        sz = int.from_bytes(b_fw[16:24], byteorder='little')

        name = ''
        na_f = na - start - offset;
        while kernel[na_f] != 0:
            name += chr(kernel[na_f])
            na_f = na_f + 1

        da_f = da - start - offset
        with open(name, 'wb') as fw_fd:
            fw_fd.write(kernel[da_f:da_f+sz])
            fw_fd.close()

        print('{} : {} bytes'.format(name, sz))

def main(image, kallsyms, kstart):
    (fw_start, fw_end) = process_kallsyms(kallsyms)

    with open(image, "rb") as fd:
        map = mmap.mmap(fd.fileno(), 0, access=mmap.ACCESS_READ)
        extract(map, kstart, fw_start, fw_end)
        map.close()

if __name__ == '__main__':
    args = parser.parse_args()
    main(args.image, args.kallsyms, args.kstart)