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

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Message-ID: <CALCETrVz4B2rthaKPJAOpiHm1kCh-mD2C5kKti0q8iBQ0QEzuA@mail.gmail.com>
Date:   Tue, 13 Dec 2016 09:06:31 -0800
From:   Andy Lutomirski <luto@...capital.net>
To:     Herbert Xu <herbert@...dor.apana.org.au>
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 Mon, Dec 12, 2016 at 7:39 PM, Herbert Xu <herbert@...dor.apana.org.au> wrote:
> On Mon, Dec 12, 2016 at 10:34:10AM -0800, Andy Lutomirski wrote:
>>
>> Here's my status.
>>
>> >         drivers/crypto/bfin_crc.c:351
>> >         drivers/crypto/qce/sha.c:299
>> >         drivers/crypto/sahara.c:973,988
>> >         drivers/crypto/talitos.c:1910
>> >         drivers/crypto/qce/sha.c:325
>>
>> I have a patch to make these depend on !VMAP_STACK.
>
> Why? They're all marked as ASYNC AFAIK.
>
>> I have a patch to convert this to, drumroll please:
>>
>>     priv->tx_tfm_mic = crypto_alloc_shash("michael_mic", 0,
>>                           CRYPTO_ALG_ASYNC);
>>
>> Herbert, I'm at a loss as what a "shash" that's "ASYNC" even means.
>
> 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.

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