Saturday, September 28, 2013

Where do I 'sign' up?

This post spends a little time discussing how to get pre-OS independent software vendor (ISV) content ‘signed’/’enrolled’ onto a UEFI Secure Boot protected platform.

As a quick background:
Intel (R) Boot Guard binds the OEM low level boot firmware (PI code as exemplified by SEC/PEI/DXE) with the hardware, so the Boot guard trust anchors would not directly interface with the trust anchors for 3rd party UEFI content.  Details on Intel Boot Guard can be found on page 4 of http://www.intel.com/content/dam/www/public/us/en/documents/product-briefs/4th-gen-core-family-mobile-brief.pdf.  

People often ask about the relationship of something like Intel (R) Boot Guard and its "Verified Boot" versus UEFI Secure Boot, as defined in chapter 26 of the UEFI 2.4 specification. We talked a little about this earlier, too, at http://uefidk.intel.com/sites/default/files/resources/Platform_Security_Review_Intel_Cisco_White_Paper.pdf, page 16.  The “Reset Time Verified Launch” in Figure 5 logically maps to something like Intel(R) Boot Guard. The verification happens 'before' UEFI PI code and vets the provenance of that code, typically if the code was created and updated under the authority of the system board manufacturer. UEFI, on the other hand, is on the right hand side of that flow.

In other words, the underlying PI-code update key, say for validating a capsule update (install time verification) or the embedded signature of the PI code (load time verification) should not be the PK but some other system board vendor-managed key store.  Recall that on certain x86 systems the end user could even edit the PK via a physically-present setup page.  In that latter case, having the end user control the PI update key (and associated system firmware updates) is often not desired.  In the PI specification there are definitions of signed firmware files and volumes, but there is no defined policy store and trust anchors for 'Secure Boot' of PEI and DXE elements. 

In the end, users want end-to-end integrity, though, so both protection of the underlying firmware and the run time are important.  This was discussed a bit in the Intel Developer Forum presentation earlier in the month with the system architecture picture updated to the revised below.

Note in this picture above that Intel (R) Device Protection Technology with Boot Guard surfaces from the system hardware and precedes execution of the PI SEC/PEI/DXE codes.

UEFI Secure Boot, on the other hand, is intended for 3rd party UEFI content, such as UEFI drivers or applications on the UEFI system partition.  Intel(R) Boot Guard and PI code verification keys should have their own manifest and storage structure.  For the 3rd party trust anchors, the place where this enrollment would happen is with the UEFI Secure Boot key hierarchy.  The hierarchy for UEFI Secure boot includes the PK, KEK, DB, DBX.  The factory-default configuration typically entails a PK that is owned by the OEM, and the PK authorizes updates to the KEK.  The KEK is OS Vendor1 + OEM + other OS vendors, and the KEK entries authorize updates to the DB/DBX.  DB is the ‘allowed’ list of code that can execute, and for a Microsoft (R) Windows8 machine contains a Microsoft OS certificate, the Microsoft UEFI CA cert, and possibly other OSV/ISV entries. 

Now for going from theory-to-practice-

Given a population of UEFI Secure Boot capable machines in the field, how is a pre-OS Independent Software Vendor (ISV) able to deploy content (i.e., the action item from above)?   The short answer is that the ISV has 2 options:

-          1. Sign up w/ Winqual and get the UEFI driver/application signed by the UEFI CA

and/or
-          2. Create own verification certificate and

o   Have end user enroll manually

and/or
o   Have OEM preinstall (or update in field via firmware update)


An ISV can do 1+2 above since UEFI Authenticode-based executables support ‘multisigning’ so that they can be signed by BOTH the UEFI CA and the ISV’s own key (see more on the final links below w/ SUSE example).

For the first option 1. above, the ISV can sign up w/ Microsoft Winqual and submit their content to be signed by the Microsoft UEFI CA.  Most ISV's, IHV's, and non-MSFT OSV's already has a Winqual account if they deliver signed Windows drivers today since Microsoft has been doing kernel mode driver signing since Vista SP1.  In addition, most IA machines that support UEFI2.3.1 Secure Boot carry a Microsoft UEFI CA DB certificate, so getting signed by the MSFT UEFI CA will mean that the ISV's .efi UEFI driver or application will simply work on a large class of PCs.  More info on the process can be found at:

For the second option 2. above, if the ISV wishes to generate its own roots and manually enroll in a PC (e.g., using PC setup screens) or distribute its keys for the OEM’s to pre-enroll, some details on the process can be found at http://sourceforge.net/apps/mediawiki/tianocore/index.php?title=SecurityPkg

Beyond this information, some of the practices of a Security ISV like McAfee for their pre-OS UEFI content can be found at

If you have a machine at home, you can use some of the flows described in the white paper above on running dmpstore and other commands at the UEFI shell to discover the configuration of UEFI Secure boot.  A more user friendly way is to run the Secure Boot Checkup Utility http://apps.insyde.com/sbutil.html from Insyde on your Microsoft (R) Windows 8 machine.  Thanks to Jeff Bobzin at Insyde for pointing this tool out to me.

This is the report from my Asus Windows 8 Intel (R) i3 touch laptop.  Well, my former laptop prior to my fourteen year old daughter commandeering it.  The output from the report proceeds below-

Secure Boot Status on this system:
System Status: MS Required KEK: MS Required OS Cert: 3rd Party (MS CA):
Secure Boot Enabled Present Present Present

UEFI Variables:
SetupMode: 
SecureBoot: 
OsIndicationsSupported: 

BootOrder Item List: 
BootCurrent: Boot00000 1 0000000000000001 0000 0000 Windows Boot Manager

Secure Boot Database Contents:

PK Variable Certificate (Platform Master Key):
X.509 Certificate:
CN=ASUSTeK Notebook PK Certificate

KEK Variable Certificates (Database Management):
X.509 Certificate: X.509 Certificate: X.509 Certificate:
CN=ASUSTeK Notebook KEK Certificate 
CN=Microsoft Corporation KEK CA 2011 
CN=Canonical Ltd. Master Certificate Authority

db Variable Certificates and Hashes (Allowed Signers):
X.509 Certificate: X.509 Certificate: X.509 Certificate: X.509 Certificate: X.509 Certificate:
CN=ASUSTeK Notebook SW Key Certificate 
CN=ASUSTeK MotherBoard SW Key Certificate 
CN=Microsoft Corporation UEFI CA 2011 
CN=Microsoft Windows Production PCA 2011 
CN=Canonical Ltd. Master Certificate Authority

dbx Variable Certificates and Hashes (Forbidden Signers):
X.509 Certificate:
CN=DO NOT TRUST - Lost Certificate

The interesting thing about this machine is that there is both a ASUSTeK KEK and Canonical KEK, along with the Microsoft KEK.  So this set of KEK entries includes one for the OEM and two alternative operating system vendors, namely Microsoft for Windows and Canonical for Ubuntu http://www.ubuntu.com/.

Below is a friendlier view of the tool in action.



Finally, back to closing thoughts on the Intel Developer Forum. 

Within that deck, one of the slides I enjoyed the most was the quote on slide 21 from SUSE that read:

"UEFI Secure Boot no longer an issue to the Linux* World"


Regarding IDF, it was great having the opportunity to meet with people from all across the industry.  I found the perspective of what I do from the different companies refreshing and helpful in informing customer and business-focused activities with my colleagues going forward.  Translation: I learned about a lot of things I need to get done quickly. 

This IDF talk marked ten years since my first IDF presentation in San Francisco.  I shuffled a bit less than the first talk, but I have to admit that I haven't evolved to the aplomb and sophistication of a Ted Talk http://www.ted.com.  The irony is that one of those talks I delivered in 2003 read on porting the Intel Framework (PEI/DXE) for different platforms, factoring silicon initialization code, etc. Since 2003 Framework 0.9x specifications became PI1.3, the EFI Developer Kit (EDK) became EDK2, and the preceding UEFI track talk at IDF 2013 discussed factoring all of the silicon initialization PEI modules as this new Firmware Support Package (FSP) http://www.intel.com/content/www/us/en/intelligent-systems/intel-firmware-support-package/intel-fsp-overview.html.  Oh yeah, Windows 8 shipped with UEFI as the default boot loader option recently, too.  Quite the decade indeed.

Speaking of getting things done, I had better end today's entry and get back to work.

Cheers

2/15/2015 update -
My friend's book http://www.apress.com/9781430265719 has a good description of Boot Guard in chapter 6.  Take a look.
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