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Date:   Fri, 22 Nov 2019 18:42:59 +0800
From:   Herbert Xu <herbert@gondor.apana.org.au>
To:     Harald Freudenberger <freude@linux.ibm.com>
Cc:     linux-crypto@vger.kernel.org, ebiggers@kernel.org,
        heiko.carstens@de.ibm.com, gor@linux.ibm.com
Subject: Re: [PATCH 2/3] s390/crypto: Rework on paes implementation
Message-ID: <20191122104259.ofodwadrgszdxuto@gondor.apana.org.au>
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On Fri, Nov 22, 2019 at 10:54:50AM +0100, Harald Freudenberger wrote:
> The setkey() sets the base key material (usually a secure key) to an
> tfm instance. From this key a 'protected key' (pkey) is derived which
> may get invalid at any time and may need to get re-derived from the
> base key material.
> An tfm instance may be shared, so the context where the pkey is
> stored into is also shared. So when a pkey gets invalid there is a need
> to update the pkey value within the context struct. This update needs
> to be done atomic as another thread may concurrently use this pkey
> value. That's all what this spinlock does. Make sure read and write
> operations on the pkey within the context are atomic.
> It is still possible that two threads copy the pkey, try to use it, find out
> that it is invalid and needs refresh, re-derive and both update the pkey
> memory serialized by the spinlock. But this is no issue. The spinlock
> makes sure the stored pkey is always a consistent pkey (which may
> be valid or invalid but not corrupted).

OK.  Can you give me a bit more background info on how often
this is likely to happen? I mean it happened every time you
might as well not store the protected key in the tfm at all.

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