During the last weeks, I spent several nights playing with UEFI and its extension called UEFI SecureBoot. I must admit that I have mixed feelings about UEFI in general; on one hand, you have a nice and modern “BIOS replacement” that can boot .efi files with no need for a bootloader like GRUB, on the other hand, some hardware, not even the most exotic one, is not yet glitch-free. But that’s what happens with new stuff in general. I cannot go much into detail without drifting away from the main topic, but surely enough, a simple google search about UEFI and Linux will point you to the problems I just mentioned above.

But hey, what does it all mean for our beloved Gentoo-based distro named Sabayon? Since DAILY ISO images dated 20121224, Sabayon can boot off UEFI systems, through DVD and USB (thanks to isohybrid –uefi) and, surprise surprise, with SecureBoot turned on!. I am almost sure that we’re the first Linux distro supporting SecureBoot out of the box (update: using shim!) and I am very proud of it. This is of course thanks to Matthew Garrett’s shim UEFI loader that is chainloading our signed UEFI GRUB2 image.

The process is simple and works like this: you boot an UEFI-compatible Sabayon ISO image off DVD or USB, if SecureBoot is turned on, shim will launch MokManager, that you can use to enroll our distro key, called sabayon.der and available on our image under the “SecureBoot” directory. Once you enrolled the key, on some systems, you’re forced to reboot (I had to on my shiny new Asus Zenbook UX32VD), but then, the magic happens.

There is a tricky part however. Due to the way GRUB2 .efi images are generated (at install time, with settings depending on your partition layout and platform details), I have been forced to implement a nasty way to ensure that SecureBoot can still accept such platform-dependent images: our installer, Anaconda, now generates a hardware-specific SecureBoot keypair (private and public key), then our modified grub2-install version, automatically signs every .efi image it generates with that key, which is placed into the EFI Boot Partition under EFI/boot/sabayon ready to be enrolled by shim at the next boot.
This is sub-optimal, but after several days of messing around, it turned out that it’s the most reliable, cleanest and easiest way to support SecureBoot after install without disclosing our private key we use to sign our install media. Another advantage is that our distro keypair, once enrolled, will allow any Sabayon image to boot, while we still allow full control over the installed system to our users (by generating a platform-specific private key at install time).

SecureBoot is not that evil after all, my laptop came with Windows 8 (which I just ripped off completely) and SecureBoot disabled by default and lets anyone sign their own .efi binaries from the “BIOS”. I don’t see how my freedom could be affected by this, though.

Similar Posts