Secure boot is a feature of the UEFI, the Unified Extensible Firmware Interface, a replacement for the BIOS.
Microsoft has implemented this feature on hardware certified for Windows 8 in a way that requires the exchange of cryptographic keys; since the company controls the key-signing authority, anyone who wants to create a bootable medium has to necessarily obtain a key from Redmond.
Misinformation is rife about secure boot, simply because people confuse UEFI with secure boot and think that support for the former means support for the latter. Many so-called technical types are as guilty as others of spreading wrong information.
Linux kernel developer Matthew Garrett had a post on his personal blog a few days ago where this was the case. Garrett, it must be noted, has been involved in contributing code towards a solution for secure boot.
This post began gratuitously: "It's after Christmas, and some number of people doubtless ended up with Windows 8 PCs and may want to install Linux on them. If you'd like to do that without fiddling with firmware settings, here are your options."
All the information in this post was either old, or else gleaned from third parties. No verification was done before posting.
Garrett mentioned that Sabayon Linux, a distribution based on Gentoo, would now support booting out of the box on machines that have secure boot enabled. He said he could not speak for the current CD images - but then how would someone who wants to install Linux operate, except via these images?
Unfortunately, given his role in the response from Linux developers to secure boot, this half-baked information is spreading around the web.
I tested out a recent Sabayon image yesterday and while it does offer a menu that leads one to believe that it will boot after a key is installed, none of the keys provided work.
Garrett mentioned that Ubuntu 64-bit will boot on secure boot-enabled devices; this is well-known, but he did not make it clear whether his statement was not based on any personal testing. He now claims he has tested this version on a secure boot-enabled machine. I tested it out sometime back and verified it; I also pointed out that it would not install on the same disk as Windows 8. One had to use a second disk.
Garrett also mentioned that the recent test builds of Fedora 18 would support secure boot; while this is correct, the distribution cannot yet be installed on such systems, no matter if one has a single disk or two. Once again, this is from my own testing. The fact that Garrett provided is worthless in the light of his statement "...some number of people doubtless ended up with Windows 8 PCs and may want to install Linux on them".
There was some speculation about SUSE too, with Garrett saying, "Suse will be using a version of Shim signed by Microsoft, but I don't think it's in any pre-release versions yet." I tested out an openSUSE 12.3 Milestone 2 release a few days back. It does not support secure boot yet - no ifs, or buts or shoulds.
The latest Debian test releases cannot boot on secure boot-enabled hardware either. Garrett's statement that these releases support UEFI is correct but this is misleading because many people will take it to mean that secure boot is supported as well. Linux has been able to boot on machines with UEFI for a long time. It is only the secure boot hurdle that has to be overcome.