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68 lines
2.3 KiB
Plaintext
68 lines
2.3 KiB
Plaintext
There are several common structures to the layout of all the firmwares
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that have been examined.
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For this description, the firmwares that were examined are:
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* x220 - Checked the major structures compared to x230
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* x230 - intense disassembly, with lesser checks on the rest of the
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xx30 series confirming the same details
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* x250 and x260 EC firmware - cursory checks
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Encryption:
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-----------
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Two parts of the firmware are encrypted - the interrupt vector table at the
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start of the image and area that has the encryption keys.
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See zmatt's blog post[1] for more details.
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[1] http://www.zmatt.net/unlocking-my-lenovo-laptop-part-3/
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Outer Checksum:
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---------------
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The firmware has a simple whole-file checksum at 0x2fffc
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Inner Checksums:
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----------------
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There is a table of checksum regions located at 0x2154, this table
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contains pairs of start-at/stop-before addresses and is terminated with
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a single 0xffffffff entry.
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The firmware uses this table to checksum the whole firmware image, comparing
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the results with the results table. If there is a failed checksum, the
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firmware will hang.
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The results table is located at 0x2048 and is a table of 32-bit checksums.
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Stable Addresses:
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-----------------
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These addresses have been seen to be stable in all the checked firmwares.
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0x00000: Interrupt vector table
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0x001ff: End of first encrypted region
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0x00240: EC version string
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0x00268: Copyright notice string
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0x00ff0: Start of second encrypted region
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0x02048: List of 32-bit checksum results ("inner checksum")
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0x02154: List of start/stop address pairs for checksum regions
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0x02fff: End of second encrypted region
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0x2fffc: Outer checksum
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Notes:
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* The x220 firmware starts the copyright string at 0x00264, which
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might just be because the default variable size on the H8S is 16bits,
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instead of the 32bit default on the ARC cpu - and that there are two
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default-sized variables before this string.
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* I did not actually try to decrypt the x250 firmware - it is a different
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layout to the xx30 series, but might use the same decryption process
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* The x260 was not encrypted at all, and did not have an outer checksum.
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However, the firmware file was 90112 bytes longer and the last 256 bytes
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are suspicious - perhaps they are a MAC for authenticating the firmware.
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