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Date: Wed, 14 Dec 2016 12:56:14 +0800
From: Herbert Xu <>
To: Andy Lutomirski <>
Cc: Eric Biggers <>,,
	"" <>,
	"" <>,
	"" <>,
	Andrew Lutomirski <>,
	Stephan Mueller <>
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.

Email: Herbert Xu <>
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