Merge tag 'random-5.18-rc1-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/crng/random

Pull random number generator updates from Jason Donenfeld:
 "There have been a few important changes to the RNG's crypto, but the
  intent for 5.18 has been to shore up the existing design as much as
  possible with modern cryptographic functions and proven constructions,
  rather than actually changing up anything fundamental to the RNG's
  design.

  So it's still the same old RNG at its core as before: it still counts
  entropy bits, and collects from the various sources with the same
  heuristics as before, and so forth. However, the cryptographic
  algorithms that transform that entropic data into safe random numbers
  have been modernized.

  Just as important, if not more, is that the code has been cleaned up
  and re-documented. As one of the first drivers in Linux, going back to
  1.3.30, its general style and organization was showing its age and
  becoming both a maintenance burden and an auditability impediment.

  Hopefully this provides a more solid foundation to build on for the
  future. I encourage you to open up the file in full, and maybe you'll
  remark, "oh, that's what it's doing," and enjoy reading it. That, at
  least, is the eventual goal, which this pull begins working toward.

  Here's a summary of the various patches in this pull:

   - /dev/urandom and /dev/random now do the same thing, per the patch
     we discussed on the list. I think this is worth trying out. If it
     does appear problematic, I've made sure to keep it standalone and
     revertible without any conflicts.

   - Fixes and cleanups for numerous integer type problems, locking
     issues, and general code quality concerns.

   - The input pool's LFSR has been replaced with a cryptographically
     secure hash function, which has security and performance benefits
     alike, and consequently allows us to count entropy bits linearly.

   - The pre-init injection now uses a real hash function too, instead
     of an LFSR or vanilla xor.

   - The interrupt handler's fast_mix() function now uses one round of
     SipHash, rather than the fake crypto that was there before.

   - All additions of RDRAND and RDSEED now go through the input pool's
     hash function, in part to mitigate ridiculous hypothetical CPU
     backdoors, but more so to have a consistent interface for ingesting
     entropy that's easy to analyze, making everything happen one way,
     instead of a potpourri of different ways.

   - The crng now works on per-cpu data, while also being in accordance
     with the actual "fast key erasure RNG" design. This allows us to
     fix several boot-time race complications associated with the prior
     dynamically allocated model, eliminates much locking, and makes our
     backtrack protection more robust.

   - Batched entropy now erases doled out values so that it's backtrack
     resistant.

   - Working closely with Sebastian, the interrupt handler no longer
     needs to take any locks at all, as we punt the
     synchronized/expensive operations to a workqueue. This is
     especially nice for PREEMPT_RT, where taking spinlocks in irq
     context is problematic. It also makes the handler faster for the
     rest of us.

   - Also working with Sebastian, we now do the right thing on CPU
     hotplug, so that we don't use stale entropy or fail to accumulate
     new entropy when CPUs come back online.

   - We handle virtual machines that fork / clone / snapshot, using the
     "vmgenid" ACPI specification for retrieving a unique new RNG seed,
     which we can use to also make WireGuard (and in the future, other
     things) safe across VM forks.

   - Around boot time, we now try to reseed more often if enough entropy
     is available, before settling on the usual 5 minute schedule.

   - Last, but certainly not least, the documentation in the file has
     been updated considerably"

* tag 'random-5.18-rc1-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/crng/random: (60 commits)
  random: check for signal and try earlier when generating entropy
  random: reseed more often immediately after booting
  random: make consistent usage of crng_ready()
  random: use SipHash as interrupt entropy accumulator
  wireguard: device: clear keys on VM fork
  random: provide notifier for VM fork
  random: replace custom notifier chain with standard one
  random: do not export add_vmfork_randomness() unless needed
  virt: vmgenid: notify RNG of VM fork and supply generation ID
  ACPI: allow longer device IDs
  random: add mechanism for VM forks to reinitialize crng
  random: don't let 644 read-only sysctls be written to
  random: give sysctl_random_min_urandom_seed a more sensible value
  random: block in /dev/urandom
  random: do crng pre-init loading in worker rather than irq
  random: unify cycles_t and jiffies usage and types
  random: cleanup UUID handling
  random: only wake up writers after zap if threshold was passed
  random: round-robin registers as ulong, not u32
  random: clear fast pool, crng, and batches in cpuhp bring up
  ...

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