Linux 4.18 Lands Random Patch To Fix Slow Boot Times For Some Systemd-Based Boxes
Last week I wrote about a change for the Linux kernel would better protect entropy sent in from user-space as a change driven as a result of some Linux distributions (such as Fedora) using a CPU jitter random number generator to resolve the lack of entropy at boot time and that on systemd-enabled Linux systems sometimes leading to slow boot times. That change has now ended up being queued into Linux 4.18 rather than having to wait for 4.19.
That protection is by mixing entropy sent in from user-space with RdRand. While not everyone trusts Intel's RdRand hardware, the CPU jitter RNG isn't necessarily the safest either but this is basically mixing the two together to create a bit more randomness than relying upon a single source. See the aforelinked article for more background information on the situation and how the lack of entropy was leading to stalled boot processes for some Linux systems -- particularly VMs -- over the lack of entropy following a recent CVE change.
As of this weekend in Linux 4.18 Git, the change has landed after originally being queued for the "-next" cycle (Linux 4.19) but then Ted Ts'o deciding to get this change into 4.18.