linux-kernel - Re: [PATCH v6 0/7] enable CAAM's HWRNG as default

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Date:   Wed, 22 Jan 2020 15:11:51 +0000
From:   Horia Geanta <horia.geanta@....com>
To:     Andrey Smirnov <andrew.smirnov@...il.com>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>
CC:     Chris Healy <cphealy@...il.com>,
        Lucas Stach <l.stach@...gutronix.de>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Iuliana Prodan <iuliana.prodan@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>,
        Andrei Botila <andrei.botila@....com>,
        Laurentiu Tudor <laurentiu.tudor@....com>
Subject: Re: [PATCH v6 0/7] enable CAAM's HWRNG as default

On 1/8/2020 5:41 PM, Andrey Smirnov wrote:
> Everyone:
> 
> This series is a continuation of original [discussion]. I don't know
> if what's in the series is enough to use CAAMs HWRNG system wide, but
> I am hoping that with enough iterations and feedback it will be.
> 
Testing on DPAA2-based Layerscape platforms, for e.g. LS1088A:
[...]
[   12.379136] caam_jr 8010000.jr: 20000256: CCB: desc idx 2: RNG: Prediction resistance
[   12.387036] hwrng: no data available
[...]

caamrng driver fails, because RNG initialization is skipped
in ctrl.c - caam_probe():
	[...]
	np = of_find_compatible_node(NULL, NULL, "fsl,qoriq-mc");
	ctrlpriv->mc_en = !!np;
	[...]
	/*
	 * If SEC has RNG version >= 4 and RNG state handle has not been
	 * already instantiated, do RNG instantiation
	 * In case of SoCs with Management Complex, RNG is managed by MC f/w.
	 */
	if (!ctrlpriv->mc_en && rng_vid >= 4) {
	[...]

NXP is working at adding RNG Prediction Resistance support in MC f/w
(will be available in v10.20.1).

However, there's a backwards-compatibility requirement: kernel should work
with older MC f/w versions.
To fix this, my suggestion is to force RNG (re)initialization in case
MC f/w is present and its version is < 10.20.1, i.e.:
	if ((!ctrlpriv->mc_en || (fsl_mc_get_version() < "10.20.1")) &&
	    rng_vid >= 4) {
	[...]

fsl_mc_get_version() - I've made this up, it currently doesn't exist,
it should be added in fsl-mc bus driver (drivers/bus/fsl-mc).
We will provide this shortly, the plan being to integrate this change
as part of this series.

Thanks,
Horia