linux-kernel - Re: Remaining crypto API regressions with CONFIG_VMAP

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Date:   Wed, 14 Dec 2016 12:56:14 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Eric Biggers <ebiggers3@...il.com>, linux-crypto@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        Andrew Lutomirski <luto@...nel.org>,
        Stephan Mueller <smueller@...onox.de>
Subject: Re: Remaining crypto API regressions with CONFIG_VMAP_STACK

On Tue, Dec 13, 2016 at 09:06:31AM -0800, Andy Lutomirski wrote:
>
> > Having 0 as type and CRYPTO_ALG_ASYNC as mask in general means
> > that we're requesting a sync algorithm (i.e., ASYNC bit off).
> >
> > However, it is completely unnecessary for shash as they can never
> > be async.  So this could be changed to just ("michael_mic", 0, 0).
> 
> I'm confused by a bunch of this.
> 
> 1. Is it really the case that crypto_alloc_xyz(..., CRYPTO_ALG_ASYNC)
> means to allocate a *synchronous* transform?  That's not what I
> expected.

crypto_alloc_xyz(name, 0, CRYPTO_ALG_ASYNC) allocates a sync tfm
and crypto_alloc_xyz(name, CRYPTO_ALG_ASYNC, CRYPTO_ALG_ASYNC)
allocates an async tfm while crypto_alloc_xyz(name, 0, 0) does
not care whether the allocated tfm is sync or asnc.

> 2. What guarantees that an async request is never allocated on the
> stack?  If it's just convention, could an assertion be added
> somewhere?

Sure we can add an assertion.

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt