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d0620706f0
All NETGEAR EX6150v2 validate the rootfs for which OpenWrt places a
fakeheader at the position, where the bootloader expects it.
Some EX6150v2 bootloaders do however make a broken assumption about
where the rootfs starts. This is due to them calculating the rootfs
start not based upon the kernel-length but the string-offset of the
FIT-image.
We have to be compatible with both this broken as well as the valid
calculation. So we do relocate the FDT string section to a
block-boundary and enlarge the FIT image to end at this boundary +
BLOCKSIZE / 2. This way, both the broken as well as correct calculations
do expect the rootfs-header at the same position.
It is worth noting, that this is a rare edge-case in which only happens
if the image-length as well as the start of the string-section are not
placed in the same erase-block. This is an edge-case which happens very
rarely (thus it was not spotted prior).
Affected:
- U-Boot 2012.07 (Jun 16 2016 - 11:59:37)
Signed-off-by: David Bauer <mail@david-bauer.net>
(cherry picked from commit de59fc4540)
90 lines
3.2 KiB
Python
Executable File
90 lines
3.2 KiB
Python
Executable File
#!/usr/bin/env python3
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# SPDX-License-Identifier: MIT
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# -*- coding: utf-8 -*-
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# NETGEAR EX6150v2 padding tool
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# (c) 2024 David Bauer <mail@david-bauer.net>
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import math
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import sys
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FLASH_BLOCK_SIZE = 64 * 1024
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def read_field(data, offset):
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return data[offset + 3] | data[offset + 2] << 8 | data[offset + 1] << 16 | data[offset] << 24
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if __name__ == '__main__':
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if len(sys.argv) != 3:
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print('Usage: {} <input-image> <output-image>'.format(sys.argv[0]))
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sys.exit(1)
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with open(sys.argv[1], 'rb') as f:
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data = f.read()
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file_len = len(data)
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# File-len in fdt header at offset 0x4
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file_len_hdr = read_field(data, 0x4)
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# String offset in fdt header at offset 0xc
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str_off = read_field(data, 0xc)
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print("file_len={} hdr_file_len={} str_off={}".format(file_len, file_len_hdr, str_off))
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# Off to NETGEAR calculations - Taken from u-boot source (cmd_dni.c:2145)
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#
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# rootfs_addr = (ntohl(hdr->ih_size)/CONFIG_SYS_FLASH_SECTOR_SIZE+1) * CONFIG_SYS_FLASH_SECTOR_SIZE +
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# 2*sizeof(image_header_t)-sizeof(image_header_t);
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# rootfs_addr = rootfs_addr - (0x80 - mem_addr);
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# NETGEAR did fuck up badly. The image uses a FIT header, while the calculation is done on a legacy header
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# assumption. 'ih_size' matches 'off_dt_strings' of a fdt_header.
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# From my observations, this seems to be fixed on newer bootloader versions.
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# However, we need to be compatible with both.
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# This presents a challenge: FDT_STR might end short of a block boundary, colliding with the rootfs_addr
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#
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# Our dirty solution:
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# - Move the string_table to match a block_boundary.
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# - Update the total file_len to end on 50% of a block boundary.
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#
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# This ensures all netgear calculations will be correct, regardless whether they are done based on the
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# 'off_dt_strings' or 'totalsize' fields of a fdt header.
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new_dt_strings = int((math.floor(file_len / FLASH_BLOCK_SIZE) + 2) * FLASH_BLOCK_SIZE)
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new_image_len = int(new_dt_strings + (FLASH_BLOCK_SIZE / 2))
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new_file_len = int(new_dt_strings + FLASH_BLOCK_SIZE - 64)
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print(f"new_file_len={new_file_len} new_hdr_file_len={new_image_len} new_str_offset={new_dt_strings}")
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# Convert data to bytearray
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data = bytearray(data)
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# Enlarge byte-array to new size
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data.extend(bytearray(new_file_len - file_len))
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# Assert that the new and old string-tables are at least 256 bytes apart.
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# We pad by two blocks, but let's be extra sure.
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assert new_dt_strings - str_off >= 256
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# Move the string table to the new offset
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for i in range(0, 256):
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data[new_dt_strings + i] = data[str_off + i]
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data[str_off + i] = 0
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# Update the string offset in the header
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data[0xc] = (new_dt_strings >> 24) & 0xFF
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data[0xd] = (new_dt_strings >> 16) & 0xFF
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data[0xe] = (new_dt_strings >> 8) & 0xFF
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data[0xf] = new_dt_strings & 0xFF
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# Update the file length in the header
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data[0x4] = (new_image_len >> 24) & 0xFF
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data[0x5] = (new_image_len >> 16) & 0xFF
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data[0x6] = (new_image_len >> 8) & 0xFF
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data[0x7] = new_image_len & 0xFF
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# Write the new file
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with open(sys.argv[1] + '.new', 'wb') as f:
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f.write(data)
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