ME 7.x parser

Based on the amazing me_cleaner, parses the required signed partition from an ME update file to generate a valid flashable ME binary.

This was written for Heads ROM to allow continuous integration reproducible builds for Lenovo xx20 models (X220, T420, T520, etc).

Usage

usage: me7_update_parser.py [-h] [-O output_file] file

positional arguments:
  file                  ME/TXE image or full dump

optional arguments:
  -h, --help            show this help message and exit
  -O output_file, --output output_file
                        save save file name other than the default
                        'flashregion_2_intel_me.bin'

How to use

1. Download an intel ME update from Lenovo, the latest version as of November 2020 is 7.1.91.3272 contained in 83rf46ww.exe:

wget https://download.lenovo.com/ibmdl/pub/pc/pccbbs/mobiles/83rf46ww.exe

2. Using innoextract, unpack 83rf46ww.exe

innoextract -I app/ME7_5M_UPD_Production.bin 83RF46WW.exe

3. Run the script:

python me7_update_parser.py app/ME7_5M_UPD_Production.bin

The result is a file flashregion_2_intel_me.bin

Resources

• me_cleaner
• Igor Skochinsky - Rootkit in your laptop - Breakpoint 2012
• Igor Skochinsky - Intel ME Secrets - RECON 2014
• MEAnalyzer
• dump_me
• me.bios.io ME_blob_format (Wayback Machine link)

Why not use me_cleaner.py

me_cleaner.py works by using the partition table to determine what information exists and what can be removed. Unfortunately, the ME 7.x update file only contains the data required to update; which does not include a partition table. Additionally, it modified the file directly. The locations of the partitions in the update file do not correspond to the stock file so add a partition table will not be enough.

We must work backwards. Using a valid ME partition from a stock BIOS, me_cleaner.py outputs a minified cleaned blob. Inspecting this blob, we see there is only one remaining partition, FTPR or "Factory Partition". In the update binary, this partition is found at offset 0x00000 and has the same length as the FTPR in the ME partition from a stock BIOS, 0x76000. While the offset in the update file is 0x00000, the offsets within this are relative to the location in the stock file. The same functions that me_cleaner.py uses to strip the unnecessary parts and relocate required remainder from a full ME blob have been copied and modified to work with an in memory copy of the FTPR partition and hard coded offsets to mimic a full ME.

Only the partitions are signed.The partition table is not signed and can be generated. Between information found on me.bios.io ME_blob_format (Wayback Machine link), MEAnalyzer source code and Igor Skochinsky's presentations (Rootkit in your laptop - Breakpoint 2012 and Intel ME Secrets - RECON 2014) the values of the me_cleaner.py output are associated with fields. The values of fields, in combination with the output from the modified me_cleaner functions, are written to a file. The value at address 0x00039is set to 0x00, at which point the file now can pass the verification function that was copied from me_cleaner.

Structure of output

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$FPT Partition table header

Offset	0	1	2	3	4	5	6	7	8	9	A	B	C	D	E	F
0x00	ROM BYPASS INSTR 0				ROM BYPASS INSTR 1				ROM BYPASS INSTR 2				ROM BYPASS INSTR 3
0x10	"$FPT"				# of partitions				Version	Entry Type	Length	Checksum	Flash Cycle Life		Flash Cycle Limit
0x20	UMA size		Flags						FIT Minor		FIT Major		FIT Hotfix		FIT build

Partition table entry

Offset	0	1	2	3	4	5	6	7	8	9	A	B	C	D	E	F
0x30	Entry Name				Entry Owner				Entry Offset				Entry Length
0x40	Start tokens				Max tokens				Scratch sectors				Entry Flags
0x50 - 0x400	(blank filled with 0xFF)

The remainder of the file is the cleaned signed and minified FTPR partition.

Things to investigate

• ROM BYPASS INSTR 0-ROM BYPASS INSTR 4: unsure what these values do or if they are required. May try replacing with 0x00 or 0xFF.
• Header flags: unsure of what the correspond to.
• Entry Flags: correlate to ExclBlockUse, Execute, Write, Read, DirectAccess. Not sure if any of these can be changed/disabled.
• Why does the value at 0x00039 need to be changed to 0x00? That has been tested with multiple ME update versions.