linux-kernel - Re: [PATCH 1/2] crypto: testmgr - use generic algs making test vecs

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Date:   Wed, 26 Feb 2020 16:42:45 +0200
From:   Gilad Ben-Yossef <gilad@...yossef.com>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        Ofir Drang <ofir.drang@....com>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        Linux kernel mailing list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] crypto: testmgr - use generic algs making test vecs

On Tue, Feb 25, 2020 at 9:45 PM Eric Biggers <ebiggers@...nel.org> wrote:
>
> On Tue, Feb 25, 2020 at 05:48:33PM +0200, Gilad Ben-Yossef wrote:
> > Use generic algs to produce inauthentic AEAD messages,
> > otherwise we are running the risk of using an untested
> > code to produce the test messages.
> >
> > As this code is only used in developer only extended tests
> > any cycles/runtime costs are negligible.
> >
> > Signed-off-by: Gilad Ben-Yossef <gilad@...yossef.com>
> > Cc: Eric Biggers <ebiggers@...nel.org>
>
> It's intentional to use the same implementation to generate the inauthentic AEAD
> messages, because it allows the inauthentic AEAD input tests to run even if the
> generic implementation is unavailable.

That is a good.
We can simply revert to the same implementation if the generic one is
not available.

>
> > @@ -2337,8 +2338,42 @@ static int test_aead_inauthentic_inputs(struct aead_extra_tests_ctx *ctx)
> >  {
> >       unsigned int i;
> >       int err;
> > +     struct crypto_aead *tfm = ctx->tfm;
> > +     const char *algname = crypto_aead_alg(tfm)->base.cra_name;
> > +     const char *driver = ctx->driver;
> > +     const char *generic_driver = ctx->test_desc->generic_driver;
> > +     char _generic_driver[CRYPTO_MAX_ALG_NAME];
> > +     struct crypto_aead *generic_tfm = NULL;
> > +     struct aead_request *generic_req = NULL;
> > +
> > +     if (!generic_driver) {
> > +             err = build_generic_driver_name(algname, _generic_driver);
> > +             if (err)
> > +                     return err;
> > +             generic_driver = _generic_driver;
> > +     }
> > +
> > +     if (!strcmp(generic_driver, driver) == 0) {
> > +             /* Already the generic impl? */
> > +
> > +             generic_tfm = crypto_alloc_aead(generic_driver, 0, 0);
>
> I think you meant the condition to be 'if (strcmp(generic_driver, driver) != 0)'
> and for the comment to be "Not already the generic impl?".

Yes, of course. Silly me,

>
> > +             if (IS_ERR(generic_tfm)) {
> > +                     err = PTR_ERR(generic_tfm);
> > +                     pr_err("alg: aead: error allocating %s (generic impl of %s): %d\n",
> > +                     generic_driver, algname, err);
> > +                     return err;
> > +             }
>
> This means the test won't run if the generic implementation is unavailable.
> Is there any particular reason to impose that requirement?
>
> You mentioned a concern about the implementation being "untested", but it
> actually already passed test_aead() before getting to test_aead_extra().
>

The impetus to write this patch came from my experience debugging a
test failure with the ccree driver.
At some point while tweaking around I got into a situation where the
test was succeeding (that is, declaring the message inauthentic) not
because the mutation was being detected but because the generation of
the origin was producing a bogus ICV.
At that point it seemed to me that it would be safer to "isolate" the
original AEAD messages generation from the code that was being teste.

> We could also just move test_aead_inauthentic_inputs() to below
> test_aead_vs_generic_impl() so that it runs last.

This would probably be better, although I think that this stage also
generates inauthentic messages from time to time, no?

At any rate, I don't have strong feelings about it either way. I defer
to your judgment whether it is worth it to add a fallback to use the
same implementation and fix what needs fixing or drop the patch
altogether if you think this isn't worth the trouble - just let me
know.

Thanks,
Gilad



-- 
Gilad Ben-Yossef
Chief Coffee Drinker

values of β will give rise to dom!