Re: [PATCH] random: do not use jump labels before they are initialized

Hi Ard,

On Tue, Jun 07, 2022 at 12:56:20PM +0200, Ard Biesheuvel wrote:

Could we do this to defer the static key manipulation? That way, the
first call to crng_reseed() that occurs after the static keys API
becomes available will set the static key, and patch itself away at
the same time.

That's almost the same as the patch I just posted, except you
pushed the logic down into crng_reseed() instead of credit_init_bits().
(A previous mini-project aimed to remove as much logic as possible from
crng_reseed(), counting on those blocks in crng_init_bits() to only ever
run once.) What this means is that the static key won't get changed
until whenever the next reseeding is. I guess that's "fine" but I think
I'd prefer to keep the entropy counting stuff as separate from the init
bits stuff as possible.

quoted

As a third, I could just defer doing anything with the bootloader seed
until random_init(). This might actually be the simplest solution...
I'll sketch something out. A downside, which might be sort of
significant, is that a few odd things actually use randomness before
random_init() is called. So these would miss out on having that seed.
I'll have to look what exactly to see if we're actually getting anything
real out of that.

This is kind of the point of using a firmware provided seed, i.e.,
that it is available much earlier than anything else.

I'll send a patch for this anyway because I'm sort of curious now. Maybe
it'll be a dead end, for the reason you mentioned, but I think I'll
still try to evaluate it.

Jason

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