Messages in this thread |  | | From | Will Deacon <> | Subject | Re: [PATCH] random: avoid arch_get_random_seed_long() when collecting IRQ randomness | Date | Thu, 21 Jan 2021 17:53:18 +0000 |
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On Thu, 5 Nov 2020 16:29:44 +0100, Ard Biesheuvel wrote: > When reseeding the CRNG periodically, arch_get_random_seed_long() is > called to obtain entropy from an architecture specific source if one > is implemented. In most cases, these are special instructions, but in > some cases, such as on ARM, we may want to back this using firmware > calls, which are considerably more expensive. > > Another call to arch_get_random_seed_long() exists in the CRNG driver, > in add_interrupt_randomness(), which collects entropy by capturing > inter-interrupt timing and relying on interrupt jitter to provide > random bits. This is done by keeping a per-CPU state, and mixing in > the IRQ number, the cycle counter and the return address every time an > interrupt is taken, and mixing this per-CPU state into the entropy pool > every 64 invocations, or at least once per second. The entropy that is > gathered this way is credited as 1 bit of entropy. Every time this > happens, arch_get_random_seed_long() is invoked, and the result is > mixed in as well, and also credited with 1 bit of entropy. > > [...]
Applied to arm64 (for-next/random), thanks!
[1/1] random: avoid arch_get_random_seed_long() when collecting IRQ randomness https://git.kernel.org/arm64/c/390596c9959c
Ted -- please shout if you would prefer me not to carry this in the arm64 tree. I've haven't seen a response from you on this thread, but this patch is currently blocking support for the TRNG firmware call on arm64 [1], so I've pulled it in as a dependency. The branch above is stable, so you can pull it in as well if necessary.
[1] https://lore.kernel.org/r/20210106103453.152275-1-andre.przywara@arm.com
Cheers, -- Will
https://fixes.arm64.dev https://next.arm64.dev https://will.arm64.dev
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