Date: 2013-02-26 06:25 pm (UTC)
I have a query related to using a linux distro on a Samsung laptop with this UEFI bug, while still using Secure boot/UEFI for Linux.

Should the proper solution to using Linux in UEFI/Secure boot mode in such a samsung laptop be to use a Linux kernel with the below Bug fix i.e

commit 266c43c175a51002b04c18a453a39708d1775ced
Author: Satoru Takeuchi
Date: Thu Feb 14 09:12:52 2013 +0900

efi: Clear EFI_RUNTIME_SERVICES rather than EFI_BOOT by "noefi" boot parameter

And in turn pass the noefi boot param to the kernel while booting into Linux.

The reason for my above assumption being that passing noefi to linux kernel as a boot param will I assume disable the use of efi runtime services by the kernel and its modules. And thus in no circumstance (including kernel crash) the Linux kernel will use the efi runtime service to write to the efi storage (I am also assuming that it will not allow any other logic to use efi service, by telling efi that it is relinquishing use of efi runtime service for this instance of the boot) And that is the 100% sure way of ensuring that under linux one cann't trigger this bug in the normal sense (Still is it 100% safe from a security perspective I am not sure if Samsung efi logic doesn't have any loop holes which allows one to call efi services even if one has already relinquished it - I am talking logically here, because I haven't looked into efi in detail so am making some/many assumptions).

So if one wants to dual boot a system with win8 already installed in Secure boot UEFI mode and Linux (in Secureboot/UEFI mode) THEN one should use a distro of linux which is using linux kernels later than Feb 15 with the above mentioned noefi bug fix included and in turn one should boot such a linux distro with noefi boot param to ensure that the Samsung laptops with this efi bug cann't be triggered from Linux during that boot.

Is my above understanding correct.

NOTE: I am not sure the linux kernel handles the transition from efi to no efi runtime mode gracefully if noefi is passed as a argument and the system is already in uefi boot mode. But I am assuming for now that the kernel handles this situation properly as well as that it is required to handle this in a specific manner, which it does. This is my assumption currently because I haven't looked into EFI specs at any level currently.

NOTE: A related query I have posted in the ubuntu launchpad tracked Bug related to this.

Also does anyone know when Samsung will release a fixed efi firmware.
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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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