What is Secure boot?
Secure boot is a setup using UEFI firmware to check cryptographic signatures on the bootloader and associated OS kernel to ensure they have not been tampered with or bypassed in the boot process.
With the release of Windows 8, Microsoft has decided that all hardware that is marked "Windows 8 client ready" should:
- Have secure boot enabled by default.
- Allow a physically present user to disable secure boot in the firmware interface.
- Ship the Microsoft keys in firmware.
- Allow a physically present user to enroll their own keys in the firmware interface.
This means that Fedora releases prior to Fedora 18 will refuse to boot until the user disables secure boot in the firmware. The Fedora 18 release supports booting in Secure Boot mode.
How does it work?
Fedora and Secure Boot
Maintainers of the grub2, kernel and associated packages have proposed a plan where by Fedora will have Verisign (via Microsoft) sign a bootloader shim that will in turn boot grub2 (signed by a Fedora key) and the Fedora kernel (signed by a Fedora key) to allow out of the box booting on secure boot enabled hardware. Additionally, they will provide tools and information for users to create their own keys and sign their own copy of boot shim and grub2 and kernel (and whatever else they wish to sign). This plan has been approved by the Fedora Engineering Steering Committee as of 23-Jul-2012.
Questions and Answers
Q: I think it would be much better if "Microsoft or UEFI or All hardware OEMs or The Government" would just "do X"
A: Feel free to contact any of the above and ask them to change their plans. Sadly, we can only work with the plans as we know them.
Q: Are you sure secure boot will be possible to disable in the firmware?
A: Yes, the Microsoft Windows 8 ready requirements require that to be the case.
Q: Can I remove the Microsoft key and use my own?
A: YES. According to the UEFI and Microsoft Windows 8 ready requirements you can remove all the keys and enroll your own. You will need to sign and install the various components with your new keys.
Q: Whats this about a $99 fee?
A: There is a one time fee of $99 to access the Microsoft sysdev portal in order to get your binaries signed by the Microsoft key (shipped by default in all Windows 8 ready devices). The Fedora shim binary has been signed via the Microsoft service and the $99 fee has already been paid. Individual users do not need to pay $99 unless they wish to build their own UEFI applications and get them signed independently.
Q: What if I want to build a custom kernel or load 3rd party kernel modules?
A: You will need to disable Secure boot, or setup your own keys and sign everything with them.
Q: What if I want to make a Fedora remix or distro based on Fedora?
A: If you ship the Fedora boot shim, grub2 and kernel unchanged, your remix or distro will boot on secure boot enabled machines (if the proposed plan is approved).
Q: what about ARM?
A: On ARM Microsoft Windows 8 ready requirements say that Secure boot should be enabled by default and cannot be disabled. Fedora has no plans to support secure boot on that platform and suggests buying Non Windows 8 ready hardware.
Q: What about the Fedora ARM folks, if UEFI cannot be disabled ? What will the impact be, if we ever are able to install Fedora on to mobile phone units ? Does this not limit users choice ?
A: Fedora is not responsible for the Windows 8 ARM requirements. There is nothing we can do in this case. See the answer to the above question.
Q: Does this apply to servers too?
A: No. This is a Windows 8 client ready set of requirements. Servers will not have secure boot enabled by default.
Q: If I disable Secure boot, and I have a dual boot setup with Fedora and Windows 8, will Windows 8 boot ok?
A: Yes. Windows 8 will boot ok with Secure boot disabled.
Q: What are all these secure boot databases that are talked about?
A: There are a number of databases kept by Secure boot:
signature database (db) - signatures or image hashes of UEFI applications, operating system loaders, and UEFI drivers that can be loaded
revoked signatures database (dbx) - no longer trusted/loadable signers or image hashes.
Key Enrollment Key database (KEK) - database of keys that can be used to update the signature database and revoked signatures database.
platform key (PK) - Generated by OEM's, this database/key allows updating KEK or db's.
Machine Owner Keys (MoK) - A list similar to db above, but provided by shim itself. There is a userspace tool called 'mokutil' that allows for easier enrolment of keys from Linux userspace.
Q: What are the supposed benefits to us all, if Secure Boot is used ? what exactly are they ? (Elaborate a little please)
Free software Foundation on Secure boot:
Matthew Garret's post outlining the background and problems and possible Fedora plans:
Microsoft Windows 8 requirements:
Source code repo for signing tools:
Source code repo for bootloader shim:
Miscrosoft intro to Secure boot tech paper: