Re: [PATCH v5 3/8] crypto: AF_ALG: add AEAD support

[Stephan Mueller <smueller-T9tCv8IpfcWELgA04lAiVw@public.gmane.org>]

Am Mittwoch, 24. Dezember 2014, 09:54:33 schrieb Stephan Mueller:

Hi Stephan,

> Am Mittwoch, 24. Dezember 2014, 07:24:01 schrieb Herbert Xu:
> 
> Hi Herbert,
> 
> > On Tue, Dec 23, 2014 at 03:52:27PM +0100, Stephan Mueller wrote:
> > > Am Dienstag, 23. Dezember 2014, 22:56:26 schrieb Herbert Xu:
> > > > In fact AEAD is rather awkward because you need to do everything
> > > > in one go.  Perhaps we could adapt our kernel interface to allow
> > > > partial AEAD operations?
> > > 
> > > I am not sure what you are referring to. The invocation does not need to
> > > be in one go. You can have arbitrary number of sendmsg calls. But all
> > > input data needs to be supplied before you call recvmsg.
> > 
> > What I mean is that unlike skcipher we cannot precede until we
> > have the complete input.  So you cannot begin recvmsg until all
> > input has been sent.
> 
> That is right, but isn't that the nature of AEAD ciphers in general? Even if
> you are in the kernel, you need to have all scatter lists together for one
> invocation of the AEAD cipher.
> 
> In case of a threaded application, the recvmsg does not start until all data
> is in, marked with the missing MSG_MORE -- see aead_readable.
> 
> All we can do is allow the user to use multiple system calls to collect all
> data before the AEAD operation takes place.
> 
> Or do you see another way on how to invoke the AEAD operation in a different
> manner?
> 
> The only item that I see that could be made better is the output side:
> currently the code allows only one and exactly one iovec to point to the
> output buffer. I would like to allow multiple iovec buffers that are filled
> with the output of one invocation of the AEAD operation. However, to avoid
> making a kernel-internal scratch buffer, I would need to somehow link the
> kernel-internal scatter lists with the iovec buffers. That only works when
> walking the iovec lists first and call af_alg_make_sg with every iovec entry
> and create the kernel-internal scatterlist representation. That is followed
> by the AEAD operation on the scatterlist.
> 
> If we agree on walking the iovec list first, then the question arises how
> many iovec list entries we allow at max. Is 16 entries a sensible value?

I would be now ready with a new release of the AEAD and RNG interface patches 
against the current code base (including the iov_iter update). Though, I would 
like to get your answer regarding your concerns.

Thanks.

-- 
Ciao
Stephan