Messages in this thread | | | Date | Tue, 7 Jun 2022 14:16:24 +0200 | From | "Jason A. Donenfeld" <> | Subject | Re: [PATCH] random: do not use jump labels before they are initialized |
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Hi Ard,
On Tue, Jun 07, 2022 at 02:03:28PM +0200, Ard Biesheuvel wrote: > On Tue, 7 Jun 2022 at 13:35, Jason A. Donenfeld <Jason@zx2c4.com> wrote: > > > > Hi Ard, > > > > On Tue, Jun 07, 2022 at 01:10:52PM +0200, Ard Biesheuvel wrote: > > > Fair enough. What I would like is to remove the need to play around > > > with the placement of jump_label_init() across architectures. Jump > > > labels are fundamentally a performance optimization, so unless you can > > > explain how setting it as early as possible makes a material > > > difference, performance or otherwise, I really think we should pursue > > > a solution that does the static key manipulation at some later time. > > > > Alright. It sounds like Catalin also prefers the same. This seems simple > > enough with minimal downsides: https://lore.kernel.org/lkml/20220607113238.769088-1-Jason@zx2c4.com/ > > > > That looks simple enough. Do we risk causing any boot stalls due to > the crediting being deferred? Or new warnings about randomness being > used before CRNG is ready?
We don't risk boot stalls. But there will be warnings for developers who have enabled the CONFIG_WARN_ALL_UNSEEDED_RANDOM debug option.
> > So maybe we should just go that route. > > > > It is not my preferred approach, but I can live with it.
I'm not sure what your preferred approach is at this point in time actually. I'll summarize all the approaches discussed so far:
1) Fix archs to initialize jump labels earlier: https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git/commit/?id=73e2d827a501 https://lore.kernel.org/lkml/20220603121543.360283-1-Jason@zx2c4.com/
2) Defer mixing & crediting until random_init(): https://lore.kernel.org/lkml/20220607111514.755009-1-Jason@zx2c4.com/
3) Defer crediting (but not mixing) until random_init(): https://lore.kernel.org/lkml/20220607113238.769088-1-Jason@zx2c4.com/
4) Defer changing the static branch (but neither mixing nor crediting) until random_init(): https://lore.kernel.org/lkml/20220607100210.683136-1-Jason@zx2c4.com/
My first choice is (1) if it's feasible.
(2) is not possible without introducing a copy, so that's out.
What's your preferred approach? Or is there a number 5 you have in mind?
Jason
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