[personal profile] mjg59
Since there are probably going to be some questions about this in the near future:

The UEFI secure boot protocol is part of recent UEFI specification releases. It permits one or more signing keys to be installed into a system firmware. Once enabled, secure boot prevents executables or drivers from being loaded unless they're signed by one of these keys. Another set of keys (Pkek) permits communication between an OS and the firmware. An OS with a Pkek matching that installed in the firmware may add additional keys to the whitelist. Alternatively, it may add keys to a blacklist. Binaries signed with a blacklisted key will not load.

There is no centralised signing authority for these UEFI keys. If a vendor key is installed on a machine, the only way to get code signed with that key is to get the vendor to perform the signing. A machine may have several keys installed, but if you are unable to get any of them to sign your binary then it won't be installable.

This impacts both software and hardware vendors. An OS vendor cannot boot their software on a system unless it's signed with a key that's included in the system firmware. A hardware vendor cannot run their hardware inside the EFI environment unless their drivers are signed with a key that's included in the system firmware. If you install a new graphics card that either has unsigned drivers, or drivers that are signed with a key that's not in your system firmware, you'll get no graphics support in the firmware.

Microsoft requires that machines conforming to the Windows 8 logo program and running a client version of Windows 8 ship with secure boot enabled. The two alternatives here are for Windows to be signed with a Microsoft key and for the public part of that key to be included with all systems, or alternatively for each OEM to include their own key and sign the pre-installed versions of Windows. The second approach would make it impossible to run boxed copies of Windows on Windows logo hardware, and also impossible to install new versions of Windows unless your OEM provided a new signed copy. The former seems more likely.

A system that ships with only OEM and Microsoft keys will not boot a generic copy of Linux.

Now, obviously, we could provide signed versions of Linux. This poses several problems. Firstly, we'd need a non-GPL bootloader. Grub 2 is released under the GPLv3, which explicitly requires that we provide the signing keys. Grub is under GPLv2 which lacks the explicit requirement for keys, but it could be argued that the requirement for the scripts used to control compilation includes that. It's a grey area, and exploiting it would be a pretty good show of bad faith. Secondly, in the near future the design of the kernel will mean that the kernel itself is part of the bootloader. This means that kernels will also have to be signed. Making it impossible for users or developers to build their own kernels is not practical. Finally, if we self-sign, it's still necessary to get our keys included by ever OEM.

There's no indication that Microsoft will prevent vendors from providing firmware support for disabling this feature and running unsigned code. However, experience indicates that many firmware vendors and OEMs are interested in providing only the minimum of firmware functionality required for their market. It's almost certainly the case that some systems will ship with the option of disabling this. Equally, it's almost certainly the case that some systems won't.

It's probably not worth panicking yet. But it is worth being concerned.

not just Linux

Date: 2011-09-20 10:00 pm (UTC)
From: (Anonymous)
Why single out Linux? Secure boot will not let you load Windows 7 either.

There is an explicit provision for disabling secure boot in firmware, but it can't be automated, so as not to be exploited by malware.

Re: not just Linux

Date: 2011-09-20 10:44 pm (UTC)
From: (Anonymous)
Oh yeah? How does this disable work, then?

Re: not just Linux

Date: 2011-09-20 10:59 pm (UTC)
From: (Anonymous)
That will be implementation-specific, but you should expect a Setup menu item.

Re: not just Linux

Date: 2011-09-21 03:36 am (UTC)
From: (Anonymous)
Even after knowing this, you're telling us to not panic. :-/

Re: not just Linux

Date: 2011-09-21 01:37 am (UTC)
From: (Anonymous)
Probably a jumper on the motherboard, as is common for password locked BIOS now.

Re: not just Linux

Date: 2011-09-21 02:29 pm (UTC)
From: (Anonymous)
Microsoft wants to kill off all old versions of their own OS as well because they want to take a 1/3 royalty for the new 'Metro' apps on Windows 8.

That by itself would be great for free software so Microsoft & Apple want to lock down all computers like cellphones and then charge perpetual monopolistic rents and hold your data hostage.

Just like RMS warned people they would.

Re: not just Linux

Date: 2011-09-21 07:54 pm (UTC)
From: (Anonymous)
It could lock out any OS the OEM either doesn't like or does not explicitly grant you the permission to use - FreeBSD, Linux, Hackintosh OS X, Haiku, &tc.. To me, this is an unfortunate continuation of the tendency of companies to try to control the use of their products after they are sold. This does not make me a happy camper.

Re: not just Linux

Date: 2011-09-22 09:53 pm (UTC)
From: [personal profile] fxchip
Microsoft can (and probably will) sign Windows 7. They probably will not sign anything else.

Re: not just Linux

Date: 2011-09-23 01:11 am (UTC)
From: (Anonymous)
They will and they did.

There was a video showing a tablet dual booting windows 8 and 7 by microsoft.
I'm starting to think microsoft did this to kill off it's competitors.


Matthew Garrett

About Matthew

Power management, mobile and firmware developer on Linux. Security developer at Google. Ex-biologist. @mjg59 on Twitter. Content here should not be interpreted as the opinion of my employer.

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