[personal profile] mjg59
(Edit: It's been suggested that the title of this could give the wrong impression. "Don't like Secure Boot? That's not a reason to buy a Chromebook" may have been better)

People are, unsurprisingly, upset that Microsoft have imposed UEFI Secure Boot on the x86 market. A situation in which one company gets to determine which software will boot on systems by default is obviously open to abuse. What's more surprising is that many of the people who are upset about this are completely fine with encouraging people to buy Chromebooks.

Out of the box, Chromebooks are even more locked down than Windows 8 machines. The Chromebook firmware validates the kernel, and the kernel verifies the filesystem. Want to run a version of Chrome you've built yourself? Denied. Thankfully, Google have provided a way around this - you can (depending on the machine) either flip a physical switch or perform a special keystroke in the firmware to disable the validation. Doing so deletes all your data in the process, in order to avoid the situation where a physically present attacker wants to steal your data or backdoor your system unnoticed, but after that it'll boot any OS you want. The downside is that you've lost the security that you previously had. If a remote attacker manages to replace your kernel with a backdoored one, the firmware will boot it anyway. Want the same level of security as the stock firmware? You can't. There's no way for you to install your own signing keys, and Google won't sign third party binaries. Chromebooks are either secure and running Google's software, or insecure and running your software.

Much like Chromebooks, Windows 8 certified systems are required to permit the user to disable Secure Boot. In contrast to Chromebooks, Windows 8 certified systems are required to permit the user to install their own keys. And, unlike Google, Microsoft will sign alternative operating systems. Windows 8 certified systems provide greater user freedom than Chromebooks.

Some people don't like Secure Boot because they don't trust Microsoft. If you trust Google more, then a Chromebook is a reasonable choice. But some people don't like Secure Boot because they see it as an attack on user freedom, and those people should be willing to criticise Google's stance. Unlike Microsoft, Chromebooks force the user to choose between security and freedom. Nobody should be forced to make that choice.

(Updated to add that some Chromebooks have a software interface for disabling validation)

Re: Lot of chromebooks could be secured.

Date: 2013-02-05 08:03 am (UTC)
From: (Anonymous)
I missed one method write protect Bits in the CSD register of the sdcard.

This is also not a suggestion. The permanent write protect option burns the epproms fuseable link that allows writing clean out. Once done there is no reverse.

The switch is a suggestion or phsycal depending on the card. The CSD register if not set temp but permanent read only is a one way operation that can never be reversed. You need to change the bootloader dump the card start with another card if CSD register has been used since it will never allow changig.

This is the reality the level of brute force required is slightly different between all chromebooks. You prefer to have one with a controler that works or a SD with a working write protect switch. But all else fails blow te fuseable links and this will be write protected in every SD taking device forever more.

This is knowning the hardware. SD card can alway be set read only. SD card cannot always be set read write. Combine that with the fixed boot order of most chromebooks you have have to secure them.



Matthew Garrett

About Matthew

Power management, mobile and firmware developer on Linux. Security developer at CoreOS. Member of the Free Software Foundation board of directors. Ex-biologist. @mjg59 on Twitter. Content here should not be interpreted as the opinion of my employer.

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