/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.
With negative numbers we wouldn't account for the minus sign, thus
returning a string with one character too short, triggering buffer
overflows in certain situations.
This makes a bunch of closely related changes:
1. The "entry-token" concept already introduced in kernel-install is now
made use of. i.e. specifically there's a new option --entry-token=
that can be used to explicitly select by which ID to identify boot
loader entries: the machine ID, or some OS ID (ID= or IMAGE_ID= from
/etc/os-release, or even some completely different string. The
selected string is then persisted to /etc/kernel/entry-token, so that
kernel-install can find it there.
2. The --make-machine-id-directory= switch is renamed to
--make-entry-directory= since after all it's not necessarily the
machine ID the dir is named after, but can be any other string as
selected by the entry token.
3. This drops all code to make automatic changes to /etc/machine-info.
Specifically, the KERNEL_INSTALL_MACHINE_ID= field is now more
generically implemented in /etc/kernel/entry-token described above,
hence no need to place it at two locations. And the
KERNEL_INSTALL_LAYOUT= field is not configurable by user switch or
similar anyway in bootctl, but only read from
/etc/kernel/install.conf, and hence copying it from one configuration
file to another appears unnecessary, the second copy is fully
redundant. Note that this just drops writing these fields, they'll
still be honoured when already set.
This drops documentation of KERNEL_INSTALL_MACHINE_ID as machine-info
field (though we'll still read it for compat).
This updates the kernel-install man page to always say "ENTRY-TOKEN"
instead of "MACHINE-ID" where appropriate, to clear the confusion up
between the two.
This also tries to fix how we denote env vars (always prefix with $ and
without = suffix), and other vars (without $ but with = suffix)
Other fixes.
If not explicitly configured, let's search a bit harder for the
ENTRY_TOKEN, and let's try the machine ID, the IMAGE_ID and ID fields of
/etc/os-release and finally "Default", all below potential $XBOOTLDR.
Now that we can distinguish the naming of the boot loader spec
dirs/files and the machine ID let's tweak the logic for suffixing the
kernel cmdline with systemd.boot_id=: let's only do that when we
actually need the boot ID for naming these dirs/files. If we don't,
let's not bother.
This should be beneficial for "golden" images that shall not carry any
machine IDs at all, i.e acquire their identity only once the final
userspace is actually reached.
