Re: [PATCH v4] mac80211: move extra crypto data off the stack

On 17 October 2016 at 14:16, Johannes Berg [off-list ref] wrote:

On Mon, 2016-10-17 at 14:06 +0100, Ard Biesheuvel wrote:

quoted

Actually, while I think it will be worthwhile going forward to
implement such an 'auxiliary data' feature in a generic way, I still
think we should address the issue at hand without too much
complication.

If we pedal back to the version of 'mac80211: move struct aead_req
off the stack' that uses kzalloc() instead of aead_request_alloc(),
we can simply add some space for aad[] and/or zero[], and get rid of
the kmem cache entirely.

If you're past this point already, i won't bother but otherwise I can
rework 'mac80211: move struct aead_req off the stack' so that the
other patch is no longer required (and IIRC, this is actually
something you proposed yourself a couple of iterations ago?)

Yes, I did consider that.

It makes some sense, and I guess the extra memcpy() would be cheaper
than the extra alloc?

I'd happily use that instead of the combination of my two patches. The
aead_request_alloc() is just a simple inline anyway, so no real problem
not using it.

Indeed. And it keeps the clutter inside the aes_xxx.c files, which
could easily be updated in the future to use some auxdata feature if
it ever materializes.

I think it would help this code, but also the ESP code you pointed
out, to have some kind of 'ordered synchronous' CRYPTO_xxx flag, where
the crypto API could manage the kmem cache and percpu pointers to
allocations. This goes well beyond what we can do as a fix, though, so
we need an intermediate solution in any case.

Shall I propose the patch?