Summary: Windows 10/11 increasingly enables Bitlocker (full disk encryption) 
out of the box with the encryption key sealed in the TPM. Two different issues 
result:

1. Fedora's installer, Anaconda, can't resize Bitlocker volumes. We could use 
better documentation to help the user perform the volume resize in Windows, 
before proceeding to booting our installation media. The documentation probably 
should be explicitly referenced by the Windows version of Fedora Media Writer.

2. The Bitlocker encryption key is unsealed only if the boot chain measurement 
by the TPM matches the expected values in a TPM PCR. When shim+GRUB are in the 
boot chain, as is the case in our default dual boot installation, the 
measurements are wrong, and this means the GRUB menu entry to boot Windows 
won't work. The user is dropped to a Windows Bitlocker recovery page. If they 
have their backup encryption key handy, it will work but to say the least this 
condition is unexpected and not  user friendly - not least of which is many 
users won't have this backup key handy since they didn't take the action to 
enable Bitlocker in the first place.

The bug report for this is https://bugzilla.redhat.com/show_bug.cgi?id=2049849

It was a Fedora 36 final release blocking bug, but considered a "difficult to 
fix" exceptional case, moving it to Fedora 37 final. Some of the options for 
consideration:

a. Fix GRUB by giving it the ability to modify UEFI NRAM "bootnext" value, so 
that instead of chainloading the Windows bootloader from GRUB, GRUB will modify 
the system NVRAM such that the next boot (only) will directly boot the Windows 
bootloader. Thus far there's no interest by GRUB upstream. Whereas systemd-boot 
has implemented it.

b. Add a user space utility modifies system NVRAM such that the next boot 
(only) will directly boot the Windows bootloader. And also remove the Windows 
boot entry in GRUB, on UEFI systems. (It would be retained on BIOS systems.)

c. Change the release criterion.
 
https://fedoraproject.org/wiki/Fedora_36_Final_Release_Criteria#Windows_dual_boot

Current: The installer must be able to install into free space alongside an 
existing clean Windows installation and install a bootloader which can boot 
into both Windows and Fedora.

Replacement: The installer must be able to install into free space alongside an 
existing clean Windows installation, install and configure a bootloader that 
will boot Fedora. 

d. Consider the problem sufficiently difficult to fix that we need an extension 
to the exceptional case allowance, and wave the bug for another release.

Thoughts?


--
Chris Murphy
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