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From:   Ard Biesheuvel <ard.biesheuvel@linaro.org>
Date:   Wed, 17 Apr 2019 13:15:57 -0700
Message-ID: <CAKv+Gu8000sDAX89=cre2uZ07vJC86FVjcoKagyk_Qqyrkbytw@mail.gmail.com>
Subject: Re: Question regarding crypto scatterlists / testmgr
To:     Pascal Van Leeuwen <pvanleeuwen@insidesecure.com>
Cc:     "linux-crypto@vger.kernel.org" <linux-crypto@vger.kernel.org>,
        Eric Biggers <ebiggers@kernel.org>,
        Herbert Xu <herbert@gondor.apana.org.au>
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On Wed, 17 Apr 2019 at 12:51, Pascal Van Leeuwen
<pvanleeuwen@insidesecure.com> wrote:
>
> Hi,
>
> I'm trying to fix the inside-secure driver to pass all testmgr
> tests and I have one final issue remaining with the AEAD ciphers.
> As it was not clear at all what the exact problem was, I spent
> some time reverse engineering testmgr and I got the distinct
> impression that it is using scatter particles that cross page
> boundaries. On purpose, even.
>
> While the inside-secure driver is built on the premise that
> scatter particles are continuous in device space. As I can't
> think of any reason why you would want to scatter/gather other
> than to handle virtual-to-physical address translation ...
> In any case, this should affect all other other operations as
> well, but maybe those just got "lucky" by getting particles
> that were still contiguous in device space, despite the page
> crossing (to *really* verify this, you would have to fully
> randomize your page allocation!)
>
> Anyway, assuming that I *should* be able to handle particles
> that are *not* contiguous in device space, then there should
> probably already exist some function in the kernel API that
> converts a scatterlist with non-contiguous particles into a
> scatterlist with contiguous particles, taking into account the
> presence of an IOMMU? Considering pretty much every device
> driver would need to do that?
> Does anyone know which function(s) to use for that?
>

Hello Pascal,

Scatterlists are made up of struct page/offset tuples, and so they
should map transparently onto physical ranges.

It looks like the AEAD skcipher walk API lacks a *_async() variant
setting the SKCIPHER_WALK_PHYS bit, like we have for the ordinary
block ciphers. Plumbing that into crypto/skcipher.c should be rather
straight-forward.

-- 
Ard.