Reverse engineering ComputerHardwareIds.exe with winedbg

In an ideal world vendors could use the same GUID value for hardware matching in Windows and Linux firmware. When installing firmware and drivers in Windows vendors can always use some generated HardwareID GUIDs that match useful things like the BIOS vendor and the product SKU. It would make sense to use the same scheme as Microsoft. There are a few issues in an otherwise simple plan.

The first, solved with a simple kernel patch I wrote (awaiting review by Jean Delvare), exposes a few more SMBIOS fields into /sys/class/dmi/id that are required for the GUID calculation.

The second problem is a little more tricky. We don’t actually know how Microsoft joins the strings, what encoding is used, or more importantly the secret namespace UUID used to seed the GUID. The only thing we have got is the closed source ComputerHardwareIds.exe program in the Windows DDK. This, luckily, runs in Wine although Wine isn’t able to get the system firmware data itself. This can be worked around, and actually makes testing easier.

So, some research. All we know from the MSDN page is that Each hardware ID string is converted into a GUID by using the SHA-1 hashing algorithm which actually tells us quite a bit. Generating a GUID from a SHA-1 hash means this has to be a type 5 UUID.

The reference code for a type-5 UUID is helpfully available in the IETF RFC document so it’s quite quick to get started with research. From a few minutes of searching online, the most likely symbols the program will be using are the BCrypt* set of functions. From the RFC code, we call the checksum generation update function with first the encoded namespace (aha!) and then the encoded joined string (ahaha!). For Win32 programs, BCryptHashData is the function we want to trace.

So, to check:

wine /home/hughsie/ComputerHardwareIds.exe /mfg "To be filled by O.E.M."

…matches the reference HardwareID-14 output from Microsoft. So onto debugging, using +relay shows all the calling values and return values from each Win32 exported symbol:

WINEDEBUG=+relay winedbg --gdb ~/ComputerHardwareIds.exe
Wine-gdb> b BCryptHashData
Wine-gdb> r ~/ComputerHardwareIds.exe /mfg "To be filled by O.E.M." /family "To be filled by O.E.M."
005b:Call bcrypt.BCryptHashData(0011bab8,0033fcf4,00000010,00000000) ret=0100699d
Breakpoint 1, 0x7ffd85f8 in BCryptHashData () from /lib/wine/bcrypt.dll.so
Wine-gdb> 

Great, so this is the secret namespace. The first parameter is the context, the second is the data address, the third is the length (0x10 as a length is indeed SHA-1) and the forth is the flags — so lets print out the data so we can see what it is:

Wine-gdb> x/16xb 0x0033fcf4
0x33fcf4:	0x70	0xff	0xd8	0x12	0x4c	0x7f	0x4c	0x7d
0x33fcfc:	0x00	0x00	0x00	0x00	0x00	0x00	0x00	0x00

Using either the uuid in python, or uuid_unparse in libuuid, we can format the namespace to 70ffd812-4c7f-4c7d-0000-000000000000 — now this doesn’t look like a randomly generated UUID to me! Onto the next thing, the encoding and joining policy:

Wine-gdb> c
005f:Call bcrypt.BCryptHashData(0011bb90,00341458,0000005a,00000000) ret=010069b3
Breakpoint 1, 0x7ffd85f8 in BCryptHashData () from /lib/wine/bcrypt.dll.so
Wine-gdb> x/90xb 0x00341458
0x341458:	0x54	0x00	0x6f	0x00	0x20	0x00	0x62	0x00
0x341460:	0x65	0x00	0x20	0x00	0x66	0x00	0x69	0x00
0x341468:	0x6c	0x00	0x6c	0x00	0x65	0x00	0x64	0x00
0x341470:	0x20	0x00	0x62	0x00	0x79	0x00	0x20	0x00
0x341478:	0x4f	0x00	0x2e	0x00	0x45	0x00	0x2e	0x00
0x341480:	0x4d	0x00	0x2e	0x00	0x26	0x00	0x54	0x00
0x341488:	0x6f	0x00	0x20	0x00	0x62	0x00	0x65	0x00
0x341490:	0x20	0x00	0x66	0x00	0x69	0x00	0x6c	0x00
0x341498:	0x6c	0x00	0x65	0x00	0x64	0x00	0x20	0x00
0x3414a0:	0x62	0x00	0x79	0x00	0x20	0x00	0x4f	0x00
0x3414a8:	0x2e	0x00	0x45	0x00	0x2e	0x00	0x4d	0x00
0x3414b0:	0x2e	0x00
Wine-gdb> q

So there we go. The encoding looks like UTF-16 (as expected, much of the Windows API is this way) and the joining character seems to be &.

I’ve written some code in fwupd so that this happens:

$ fwupdmgr hwids
Computer Information
--------------------
BiosVendor: LENOVO
BiosVersion: GJET75WW (2.25 )
Manufacturer: LENOVO
Family: ThinkPad T440s
ProductName: 20ARS19C0C
ProductSku: LENOVO_MT_20AR_BU_Think_FM_ThinkPad T440s
EnclosureKind: 10
BaseboardManufacturer: LENOVO
BaseboardProduct: 20ARS19C0C

Hardware IDs
------------
{c4159f74-3d2c-526f-b6d1-fe24a2fbc881}   <- Manufacturer + Family + ProductName + ProductSku + BiosVendor + BiosVersion + BiosMajorRelease + BiosMinorRelease
{ff66cb74-5f5d-5669-875a-8a8f97be22c1}   <- Manufacturer + Family + ProductName + BiosVendor + BiosVersion + BiosMajorRelease + BiosMinorRelease
{2e4dad4e-27a0-5de0-8e92-f395fc3fa5ba}   <- Manufacturer + ProductName + BiosVendor + BiosVersion + BiosMajorRelease + BiosMinorRelease
{3faec92a-3ae3-5744-be88-495e90a7d541}   <- Manufacturer + Family + ProductName + ProductSku + BaseboardManufacturer + BaseboardProduct
{660ccba8-1b78-5a33-80e6-9fb8354ee873}   <- Manufacturer + Family + ProductName + ProductSku
{8dc9b7c5-f5d5-5850-9ab3-bd6f0549d814}   <- Manufacturer + Family + ProductName
{178cd22d-ad9f-562d-ae0a-34009822cdbe}   <- Manufacturer + ProductSku + BaseboardManufacturer + BaseboardProduct
{da1da9b6-62f5-5f22-8aaa-14db7eeda2a4}   <- Manufacturer + ProductSku
{059eb22d-6dc7-59af-abd3-94bbe017f67c}   <- Manufacturer + ProductName + BaseboardManufacturer + BaseboardProduct
{0cf8618d-9eff-537c-9f35-46861406eb9c}   <- Manufacturer + ProductName
{f4275c1f-6130-5191-845c-3426247eb6a1}   <- Manufacturer + Family + BaseboardManufacturer + BaseboardProduct
{db73af4c-4612-50f7-b8a7-787cf4871847}   <- Manufacturer + Family
{5e820764-888e-529d-a6f9-dfd12bacb160}   <- Manufacturer + EnclosureKind
{f8e1de5f-b68c-5f52-9d1a-f1ba52f1f773}   <- Manufacturer + BaseboardManufacturer + BaseboardProduct
{6de5d951-d755-576b-bd09-c5cf66b27234}   <- Manufacturer

Which basically matches the output of ComputerHardwareIds.exe on the same hardware. If the kernel patch gets into the next release I’ll merge the fwupd branch to master and allow vendors to start using the Microsoft HardwareID GUID values.

Published by

hughsie

Richard has over 10 years of experience developing open source software. He is the maintainer of GNOME Software, PackageKit, GNOME Packagekit, GNOME Power Manager, GNOME Color Manager, colord, and UPower and also contributes to many other projects and opensource standards. Richard has three main areas of interest on the free desktop, color management, package management, and power management.

Richard graduated a few years ago from the University of Surrey with a Masters in Electronics Engineering. He now works for Red Hat in the desktop group, and also manages a company selling open source calibration equipment. Richard’s outside interests include taking photos and eating good food.