linux-kernel - RE: [PATCH v5 2/3] hw_random: cctrng: introduce Arm CryptoCell driver

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Date:   Mon, 23 Mar 2020 19:50:54 +0000
From:   Hadar Gat <Hadar.Gat@....com>
To:     Rouven Czerwinski <r.czerwinski@...gutronix.de>,
        Matt Mackall <mpm@...enic.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <Mark.Rutland@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Alexander Sverdlin <alexander.sverdlin@...ia.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tomer Maimon <tmaimon77@...il.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Zaibo Xu <xuzaibo@...wei.com>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>
CC:     "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Gilad Ben-Yossef <gilad@...yossef.com>,
        Ofir Drang <Ofir.Drang@....com>, nd <nd@....com>
Subject: RE: [PATCH v5 2/3] hw_random: cctrng: introduce Arm CryptoCell driver

Hi Rouven,

> 
> Hello Hadar,
> 
> On Sun, 2020-03-22 at 17:31 +0200, Hadar Gat wrote:
> > Introduce low level Arm CryptoCell TRNG HW support.
> >
> > Signed-off-by: Hadar Gat <hadar.gat@....com>
> > ---
> >  drivers/char/hw_random/Kconfig  |  12 +
> >  drivers/char/hw_random/Makefile |   1 +
> >  drivers/char/hw_random/cctrng.c | 735
> > ++++++++++++++++++++++++++++++++++++++++
> >  drivers/char/hw_random/cctrng.h |  69 ++++
> >  4 files changed, 817 insertions(+)
> >  create mode 100644 drivers/char/hw_random/cctrng.c  create mode
> > 100644 drivers/char/hw_random/cctrng.h
> >
> > [...]
> > +static int cctrng_probe(struct platform_device *pdev) {
> > +	struct resource *req_mem_cc_regs = NULL;
> > +	struct cctrng_drvdata *drvdata;
> > +	struct device *dev = &pdev->dev;
> > +	int rc = 0;
> > +	u32 val;
> > +	int irq;
> > +
> > +	drvdata = devm_kzalloc(dev, sizeof(*drvdata), GFP_KERNEL);
> > +	if (!drvdata)
> > +		return -ENOMEM;
> > +
> > +	drvdata->rng.name = devm_kstrdup(dev, dev_name(dev),
> > GFP_KERNEL);
> > +	if (!drvdata->rng.name)
> > +		return -ENOMEM;
> > +
> > +	drvdata->rng.read = cctrng_read;
> > +	drvdata->rng.priv = (unsigned long)drvdata;
> 
> You are not initializing drvdata->rng.quality to a default value, which results in
> the TRNG not being used by the kernel by default. If its a perfect TRNG this
> should be set to 1024, i.e. 1024 bits of entropy per
> 1024 bits of input.

Thanks for noticing. I'll fix that.

> 
> Regards,
> Rouven Czerwinski

Thanks,
Hadar