Conceptually the feature is great and should exist, but in its current
form should be worked to be generic (i.e. not specific to
Windows/Bitlocker, but appliable to any boot entry), not be global (but
be a per-entry thing), not require a BootXXXX entry to exist, and not
check for the BitLocker signature (as TPMs are not just used for
BitLocker).
Since we want to get 251 released, mark it in the documentation, in NEWS
and in code as experimental and make clear it will be reworked in a
future release. Also, make it opt-in to make it less likely people come
to rely on it without reading up on it, and understanding that it will
likely change sooner or later.
Follow-up for: #22043
See: #22390
/dev/urandom is seeded with RDRAND. Calling genuine_random_bytes(...,
..., 0) will use /dev/urandom as a last resort. Hence, we gain nothing
here by having our own RDRAND wrapper, because /dev/urandom already is
based on RDRAND output, even before /dev/urandom has fully initialized.
Furthermore, RDRAND is not actually fast! And on each successive
generation of new x86 CPUs, from both AMD and Intel, it just gets
slower.
This commit simplifies things by just using /dev/urandom in cases where
we before might use RDRAND, since /dev/urandom will always have RDRAND
mixed in as part of it.
And above where I say "/dev/urandom", what I actually mean is
GRND_INSECURE, which is the same thing but won't generate warnings in
dmesg.
All those pages contain a redirect at the top of the page, so it doesn't
make much sense to tell people to take the detour. Linking directly will
also increase the search rankings of the new pages.
If KERNEL_INSTALL_MACHINE_ID is defined in /etc/machine-info, prefer it
over the machine ID from /etc/machine-id. If a machine ID is defined in
neither /etc/machine-info nor in /etc/machine-id, generate a new UUID
and try to write it to /etc/machine-info as KERNEL_INSTALL_MACHINE_ID
and use it as the machine ID if writing it to /etc/machine-info succeeds.
In practice, this means we have a more robust fallback if there's no
machine ID in /etc/machine-id than just using "Default" and allows
image builders to force kernel-install to use KERNEL_INSTALL_MACHINE_ID
by simply writing it to /etc/machine-info themselves.
