[LTP] [PATCH] crypto: api - Fix generic algorithm self-test races

[Herbert Xu]

On Sat, Oct 05, 2024 at 03:24:48PM -0700, Eric Biggers wrote:
>
> The tests are still failing on upstream:
> 
> [    0.343845] alg: self-tests for rfc4106(gcm(aes)) using rfc4106(gcm_base(ctr(aes-generic),ghash-generic)) failed (rc=-2)

You're right.  I only disabled the warnings at the point of
allocation, the overall self-test warning is still there.  Let
me get rid of them too.

> Besides the test failures, it looks like there's no longer any guarantee that
> algorithms are actually available now that their module is loaded.

That would indeed be a bug.  But I haven't seen it in practice.
Although the s390 folks were reporting some weird errors with
dm-crypt, they have recently disappeared.

If you do see an actual failure please report it and then I'll
consider reverting it until it's fixed.

> E.g. consider if someone does 'modprobe aesni-intel' and then immediately
> creates a dm-crypt device.  Now it sounds like the AES-NI algorithms might not
> have finished being tested yet and the generic algorithms can be used instead,
> resulting in a performance regression.

That is not the case.  After modprobe returns, the algorithm is
guaranteed to have been registered.  Yes it is untested, but that
should not be a problem because a test larval will have been created
and all users looking for that algorithm will be waiting on that
test larval.

> I understand that you want to try to fix the edge cases in "fallback" ciphers.
> But "fallback" ciphers have always seemed like a bad design due to how they use
> the crypto API recursively.  I think the algorithms that use them should
> generally be migrated off of them, e.g. as I did in commit f235bc11cc95
> ("crypto: arm/aes-neonbs - go back to using aes-arm directly").  That fixed the
> problem in aes-neonbs that seems to have triggered this work in the first place.

Yes getting rid of fallbacks is nice, but this it not the reason why
we're making self-test asynchronous.  The primary issue with synchronous
self-tests is the modprobe dead-lock.

Cheers,
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
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