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From:   Stephan =?ISO-8859-1?Q?M=FCller?= <smueller@chronox.de>
To:     Stefan Wahren <stefan.wahren@i2se.com>,
        Lukasz Stelmach <l.stelmach@samsung.com>
Cc:     Matt Mackall <mpm@selenic.com>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        Arnd Bergmann <arnd@arndb.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Ray Jui <rjui@broadcom.com>,
        Scott Branden <sbranden@broadcom.com>,
        bcm-kernel-feedback-list@broadcom.com,
        Kukjin Kim <kgene@kernel.org>,
        Krzysztof Kozlowski <krzk@kernel.org>,
        Florian Fainelli <f.fainelli@gmail.com>,
        Markus Elfring <elfring@users.sourceforge.net>,
        Matthias Brugger <mbrugger@suse.com>,
        linux-crypto@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org, linux-samsung-soc@vger.kernel.org,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Subject: Re: [PATCH v2 1/2] hwrng: iproc-rng200 - Set the quality value
Date:   Sat, 23 May 2020 20:46:26 +0200
Message-ID: <3080190.aeNJFYEL58@positron.chronox.de>
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Am Donnerstag, 21. Mai 2020, 21:14:02 CEST schrieb Lukasz Stelmach:

Hi Lukasz,

> It was <2020-05-21 czw 13:00>, when Stefan Wahren wrote:
> > Hi Lukasz,
> >=20
> > Am 19.05.20 um 23:25 schrieb =C5=81ukasz Stelmach:
> >> The value was estimaded with ea_iid[1] using on 10485760 bytes read fr=
om
> >> the RNG via /dev/hwrng. The min-entropy value calculated using the most
> >> common value estimate (NIST SP 800-90P[2], section 6.3.1) was 7.964464.
> >=20
> > could you please mention in the commit the used hardware
> > implementation(s) of iproc-rng200 to get this quality?
> >=20
> > AFAIK there is still no public register description at least for the
> > bcm2711. So is it safe to assume that the suggested quality applies to
> > all possible configurations?
>=20
> I've learnt that there is a post-processing unit in RNG200 that tests
> the output of the noise generator and fills FIFO only with data that
> passes FIPS tests. Unlike simmilar unit in Exynos, it cannot be disabled
> or bypassed. Therefore, after Stephan Mueller's thorough explanations I
> am considering dropping this patch in v3.

If you would be more clear what that FIPS test is all about, we may be able=
 to=20
identify whether it affects the entropy behavior or not. E.g. if it is the=
=20
SP800-90B health test following SP880-90B section 4.4, this does not affect=
=20
entropy and you could apply your calculation.
>=20
> However, I stil am still not 100% convinced that it is impossible to
> assign the quality a reasonable non-zero value in such case.
>=20
> > Thanks
> > Stefan
> >=20
> >> [1]
> >> https://protect2.fireeye.com/url?k=3Dda4735b2-87d99b28-da46befd-0cc47a=
336f
> >> ae-e1c21080bc6ab1e4&q=3D1&u=3Dhttps%3A%2F%2Fgithub.com%2Fusnistgov%2FS=
P800-90
> >> B_EntropyAssessment [2]
> >> https://csrc.nist.gov/publications/detail/sp/800-90b/final
> >>=20
> >> Signed-off-by: =C5=81ukasz Stelmach <l.stelmach@samsung.com>
> >> ---
> >>=20
> >>  drivers/char/hw_random/iproc-rng200.c | 1 +
> >>  1 file changed, 1 insertion(+)
> >>=20
> >> diff --git a/drivers/char/hw_random/iproc-rng200.c
> >> b/drivers/char/hw_random/iproc-rng200.c index 32d9fe61a225..95669ece05=
0f
> >> 100644
> >> --- a/drivers/char/hw_random/iproc-rng200.c
> >> +++ b/drivers/char/hw_random/iproc-rng200.c
> >> @@ -199,6 +199,7 @@ static int iproc_rng200_probe(struct platform_devi=
ce
> >> *pdev)>>=20
> >>  	priv->rng.read =3D iproc_rng200_read,
> >>  	priv->rng.init =3D iproc_rng200_init,
> >>  	priv->rng.cleanup =3D iproc_rng200_cleanup,
> >>=20
> >> +	priv->rng.quality =3D 1000,
> >>=20
> >>  	/* Register driver */
> >>  	ret =3D devm_hwrng_register(dev, &priv->rng);


Ciao
Stephan