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

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Date:   Tue, 25 Feb 2020 18:32:50 -0800
From:   Eric Biggers <ebiggers@...nel.org>
To:     Gilad Ben-Yossef <gilad@...yossef.com>
Cc:     Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        Ofir Drang <ofir.drang@....com>, linux-crypto@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] crypto: testmgr - use generic algs making test vecs

On Tue, Feb 25, 2020 at 11:45:51AM -0800, Eric Biggers 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.
> 
> > @@ -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?".
> 
> > +		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().
> 
> We could also just move test_aead_inauthentic_inputs() to below
> test_aead_vs_generic_impl() so that it runs last.
> 

Also: if we did make the inauthentic input tests use the generic implementation,
then it would be better to move them into test_aead_vs_generic_impl() so that we
don't duplicate the code that allocates a tfm and request for the generic
implementation.

But to me it makes more sense to keep them separate, since a generic
implementation is not needed to run the inauthentic input tests.

- Eric