The 5.3 kernel is out [LWN.net]

The 5.3 kernel is out

Posted Sep 16, 2019 22:43 UTC (Mon) by Cyberax (✭ supporter ✭, #52523)
Parent article: The 5.3 kernel is out

Can the kernel artificially create some disk activity if it detects blocking?

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The 5.3 kernel is out

Posted Sep 17, 2019 7:22 UTC (Tue) by njs (subscriber, #40338) [Link]

Or systemd could do the same in userspace – from the discussion, apparently the reason systemd originally got blamed was because systemd does have a process that calls getrandom(), which it only does to figure out when enough entropy has been generated. So systemd already has the infrastructure to detect when entropy generation is being slow. When that happens, systemd could do things like issue some disk reads, print a message on the console telling the user to wiggle their mouse, and print a link to instructions on how to set up entropy preservation across boots.

The 5.3 kernel is out

Posted Sep 17, 2019 9:07 UTC (Tue) by patrakov (subscriber, #97174) [Link] (2 responses)

We already have jitterentropy_rng - unfortunately and by mistake, as a cryptoalg rng, not as hwrng. It extracts random bits from variations of timing of some CPU and memory operations, i.e. essentially from unsycnhronized clocks in different parts of the system. I will look at its conversion to something (e.g. hwrng) that can actually provide the entropy that Linux accounts for.

The 5.3 kernel is out

Posted Sep 17, 2019 9:41 UTC (Tue) by njs (subscriber, #40338) [Link] (1 responses)

IIRC Ted T'so has a longstanding veto on using jitterentropy to increment the random pool entropy counter in the past, on the grounds that we don't actually know where the apparent randomness comes from and whether it's actually unpredictable or not, esp. against an active attacker who can manipulate microarchitectural state.

The 5.3 kernel is out

Posted Sep 17, 2019 9:44 UTC (Tue) by patrakov (subscriber, #97174) [Link]

Thanks, that's useful to know. But he surely knows that Debian installs haveged by default on systems lacking rdrand, thus circumventing his veto.