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ebfe66e494
What should have been only cosmetic changes, ended up in breaking the
script. Rename UIMAGE_CRC_SLICE back to (the original) UIMAGE_CRC_OFF.
Fixes issue #10204 "cameo-tag.py broken"
Reported-by: Markus Stockhausen <markus.stockhausen@gmx.de>
Fixes: f9e840b657 ("scripts: add CAMEO tag generator")
Signed-off-by: Sander Vanheule <sander@svanheule.net>
118 lines
5.0 KiB
Python
Executable File
118 lines
5.0 KiB
Python
Executable File
#!/usr/bin/python3
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# SPDX-License-Identifier: GPL-2.0-or-later
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#
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# Copyright (C) 2022 OpenWrt.org
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#
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# ./cameo-tag.py <uImageFileName> <OffsetOfRootFS>
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#
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# CAMEO tag generator used for the D-Link DGS-1210 switches. Their U-Boot
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# loader checks for the string CAMEOTAG and a checksum in the kernel and
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# rootfs partitions. If not found it complains about the boot image.
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# Nevertheless it will boot if the tags are available in the secondary
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# boot partitions. If some day we want to overwrite the original vendor
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# partition we must have the tags in place. To solve this we insert the
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# tag two times into the kernel image.
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#
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# To understand what we do here it is helpful to explain how the original
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# CAMEO tag generation/checking works. The firmware consists of two parts.
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# A kernel uImage (<1.5MB) and a rootfs image (<12MB) that are written to
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# their respective mtd partitions. The default generator simply checksums
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# both parts and appends 16 bytes [<CAMEOTAG><0001><checksum>] to each part.
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# The checksum is only an addition of all preceding bytes (b0+b1+b2+...).
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# A tag does not interfere with any data in the images itself. During boot
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# the loader will scan all primary/secondary partitions (2*kernel, 2*rootfs)
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# until it finds the CAMEO tag. If checksums match everything is fine.
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# If all 4 fail we are lost. Luckily the loader does not care about where
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# the tags are located and ignores any data beyond a tag.
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#
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# The OpenWrt image consists of a kernel (>1.5MB) and a rootfs. There is
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# no chance to add CAMEO tags at the default locations, since the kernel spans
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# both the original kernel partition and the start of the rootfs partition.
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# This would leave the kernel partition without a tag. So we must find suitable
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# space.
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#
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# Location for original kernel partition is at the end of the uImage header.
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# We will reuse the last bytes of the IH_NAME field. This is the tricky part
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# because we have the header CRC and the CAMEO checksum that must match the
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# whole header. uImage header CRC checksums all data except the CRC itself. The
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# for CAMEO checksum in turn, checksums all preceding data except itself.
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# Changing one of both results in a change of the other, but data trailing the
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# CAMEO checksum only influences the CRC.
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#
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# Location for original rootfs partition is very simple. It is behind the
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# OpenWrt compressed kernel image file that spans into the rootfs. So
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# the tag will be written somewhere to the following rootfs partition and
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# can be found by U-Boot. The CAMEO checksum calculation must start at the
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# offset of the original rootfs partition and includes the "second" half of the
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# "split" kernel uImage.
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import argparse
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import os
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import zlib
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READ_UNTIL_EOF = -1
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UIMAGE_HEADER_SIZE = 64
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UIMAGE_CRC_OFF = 4
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UIMAGE_CRC_END = 8
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UIMAGE_NAME_OFF = 32
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UIMAGE_NAME_END = 56
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UIMAGE_SUM_OFF = 56
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UIMAGE_SUM_END = 60
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UIMAGE_INV_OFF = 60
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UIMAGE_INV_END = 64
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CAMEO_TAG = bytes([0x43, 0x41, 0x4d, 0x45, 0x4f, 0x54, 0x41, 0x47, 0x00, 0x00, 0x00, 0x01])
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IMAGE_NAME = bytes([0x4f, 0x70, 0x65, 0x6e, 0x57, 0x72, 0x74, 0x00, 0x00, 0x00, 0x00, 0x00])
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CRC_00 = bytes([0x00] * 4)
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CRC_FF = bytes([0xff] * 4)
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def read_buffer(offset, count):
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args.uimage_file.seek(offset)
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return bytearray(args.uimage_file.read(count))
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def write_buffer(whence, buf):
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args.uimage_file.seek(0, whence)
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args.uimage_file.write(buf)
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def cameosum(buf):
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return (sum(buf) & 0xffffffff).to_bytes(4, 'big')
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def invertcrc(buf):
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return (zlib.crc32(buf) ^ 0xffffffff).to_bytes(4, 'little')
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def checksum_header(buf):
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# To efficently get a combination, we will make use of the following fact:
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# crc32(data + littleendian(crc32(data) ^ 0xffffffff)) = 0xffffffff
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#
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# After manipulation the uImage header looks like this:
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# [...<ffffffff>...<OpenWrt><000000><CAMEOTAG><0001><checksum><InvCRC>]
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buf[UIMAGE_NAME_OFF:UIMAGE_NAME_END] = IMAGE_NAME + CAMEO_TAG
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buf[UIMAGE_CRC_OFF:UIMAGE_CRC_END] = CRC_FF
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buf[UIMAGE_SUM_OFF:UIMAGE_SUM_END] = cameosum(buf[0:UIMAGE_NAME_END])
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buf[UIMAGE_CRC_OFF:UIMAGE_CRC_END] = CRC_00
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buf[UIMAGE_INV_OFF:UIMAGE_INV_END] = invertcrc(buf[0:UIMAGE_SUM_END])
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buf[UIMAGE_CRC_OFF:UIMAGE_CRC_END] = CRC_FF
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return buf
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parser = argparse.ArgumentParser(description='Insert CAMEO firmware tags.')
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parser.add_argument('uimage_file', type=argparse.FileType('r+b'))
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parser.add_argument('rootfs_start', type=int)
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args = parser.parse_args()
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args.uimage_file.seek(0, os.SEEK_END)
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if args.uimage_file.tell() <= args.rootfs_start:
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raise ValueError(f"uImage must be larger than {args.rootfs_start} bytes")
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# tag for the uImage Header of 64 bytes inside the kernel
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# partition. Read and mangle it so it contains a valid CAMEO tag
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# and checksum that matches perfectly to the uImage header CRC.
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buf = checksum_header(read_buffer(0, UIMAGE_HEADER_SIZE))
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write_buffer(os.SEEK_SET, buf)
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# tag for the second part of the kernel that resides in the
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# vendor rootfs partition. For this we will add the CAMEO tag
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# and the checksum to the end of the image.
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buf = read_buffer(args.rootfs_start, READ_UNTIL_EOF)
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write_buffer(os.SEEK_END, CAMEO_TAG + cameosum(buf + CAMEO_TAG))
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