1. UEFI The Great Satan and you Adam Williamson Presented by
Fedora QA Community Monkey (Red Hat)
Licensed as CC-BY-SA

2. Today's Topics What is UEFI? How does UEFI booting work?
How do I deal with UEFI boot in practice?

3. What is UEFI?

4. What is UEFI? Industry-defined system firmware standard
For PCs, replaces ad-hoc BIOS 'standard'
Required for Microsoft-approved Windows 8+
Used by Macs as well
Explain “firmware” - code baked into the system which handles initialization and hand-off to operating system. Mention that UEFI != Secure Boot, but we'll go into details later.

5. How does UEFI boot work?

6. Background: BIOS boot Very 'simple': run the boot block from a disk
Consequences of simplicity: chaotic complexity
Embedding areas!
Chainloading!
Who the hell owns the boot process anyway?
No configuration from OS layer
Lots of voodoo in actually implementing BIOS- style boot (mostly hidden from users)
Probably best not to ramble on too much here, though there's all sorts of juicy detail to go into – MBR history, different styles of MBR-type boot loading, blah blah. Point is, to a user, BIOS booting experience is more or less “pick a disk and boot from it”. The multiboot mess is perceived to exist at OS level, even though it's really somewhat more complex than that.

7. UEFI boot: concepts EFI executable format
GPT: improved partition table format
UEFI FAT: standard filesystem
UEFI boot manager: subsystem for accessing and executing UEFI boot loaders
Fallback path: convention for locating boot loader on a device (in the EFI system partition) without explicit configuration
BIOS compatibility mode (CSM)
Explain that BIOS compat mode is “locked in”: once you boot that way, as far as the system is concerned, the firmware's a BIOS.
Explain ESP as a part of the fallback path, as that's really what it is. 'Explicit' EFI boot loaders tend to reuse the ESP simply for convenience / efficiency.

8. UEFI boot: in action Firmware has a 'boot menu' of:
Full pointers directly to executables on UEFI FAT partitions on GPT-labeled disks
Pointers to devices for fallback path loading
Pointers to devices for BIOS compatibility boot
“Advanced class” options we'll ignore
Firmware UI may offer direct override of boot menu
Boot menu and behaviour can be overridden from user space
Internally, to a UEFI firmware, any boot action is handled as a part of the UEFI boot manager subsystem. Even if the firmware interface doesn't exactly represent it this way.
Note consequences of complexity: we don't need embedding areas any more. Stuff like network boot is supported at firmware level (though we're not discussing that today). UEFI boot loaders are just pretty normal files on pretty normal partitions in a fairly sensible modern format that can easily be manipulated from OS layer. Firmware layer's boot behaviour can be configured from OS layer. At least in theory, layering confusion is removed: firmware layer is capable of handling all aspects of multiboot.

9. How do I deal with UEFI boot in practice?

10. Is it UEFI? Did it come with Windows 8 pre-installed? Yes!
Did it come with Windows XP or earlier?
No!
Does it mention UEFI anywhere during boot or in firmware interface?
Is firmware interface at all graphical and/or mouse-able?
Check the manual, call for help
Does the interface mention Secure Boot or CSM?
Mention the wiki page

11. Single booting Easy – you can do pretty much anything
UEFI-native is fine
BIOS-native is fine
Secure Boot on or off is fine (if your distro supports it)
If you have trouble booting from your install media, keep paying attention

12. Multi booting Golden Rule of UEFI:
Install the same way your current OS is installed
Windows: 8 is UEFI, Vista pre-SP1 is BIOS. Later Vista and 7 could be either: check Disk Management for an EFI System Partition
Linux: check output of 'efibootmgr', or if /sys/firmware/efi exists
UEFI boot of installer will give UEFI install, BIOS boot of installer will give BIOS install: get this right

13. Writing install media
Direct write (dd) or optical media: will be UEFI bootable
Livecd-iso-to-disk: pass –efi –format –reset-mbr
Liveusb-creator: well...it might work
Unetbootin etc etc: probably won't

14. Using the firmware
Different firmwares present boot configuration options in different ways
Secure Boot will usually be a toggle: disabling Secure Boot is NOT “disabling UEFI”!
BIOS compatibility may be a simple toggle, or firmware may let you manipulate boot menu and choose to boot external media directly

15. What mode am I in?
Drop to a terminal in the installer (ctrl-alt-f4 in Fedora) and run 'efibootmgr', or check /sys/firmware/efi
Don't use noefi!
Can also look at the initial bootloader

16. Example UEFI firmwares
Show these from outside slide deck, for copyright reasons...

17. References http://www.uefi.org/specs/download
Windows hardware certification requirements
Adam's blog post
Fedora wiki page
Rod's Books
Matthew Garrett

18. Questions? adamw@happyassassin.net Contact:
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