linux-kernel - Re: [PATCH v25 10/12] LRNG

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Date:   Wed, 20 Nov 2019 09:58:35 +0100
From:   Stephan Müller <smueller@...onox.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Andy Lutomirski <luto@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "Alexander E. Patrakov" <patrakov@...il.com>,
        "Ahmed S. Darwish" <darwish.07@...il.com>,
        "Theodore Y. Ts'o" <tytso@....edu>, Willy Tarreau <w@....eu>,
        Matthew Garrett <mjg59@...f.ucam.org>,
        Vito Caputo <vcaputo@...garu.com>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Jan Kara <jack@...e.cz>, Ray Strode <rstrode@...hat.com>,
        William Jon McCann <mccann@....edu>,
        zhangjs <zachary@...shancloud.com>,
        Florian Weimer <fweimer@...hat.com>,
        Lennart Poettering <mzxreary@...inter.de>,
        Nicolai Stange <nstange@...e.de>,
        "Peter, Matthias" <matthias.peter@....bund.de>,
        Marcelo Henrique Cerri <marcelo.cerri@...onical.com>,
        Roman Drahtmueller <draht@...altsekun.de>,
        Neil Horman <nhorman@...hat.com>
Subject: Re: [PATCH v25 10/12] LRNG - add TRNG support

Am Dienstag, 19. November 2019, 13:41:50 CET schrieb Greg Kroah-Hartman:

Hi Greg,

> On Tue, Nov 19, 2019 at 02:07:40AM -0800, Andy Lutomirski wrote:
> > > As this would introduce a new device file now, is there a special
> > > process that I need to follow or do I need to copy? Which major/minor
> > > number should I use?
> > > 
> > > Looking into static const struct memdev devlist[] I see
> > > 
> > >          [8] = { "random", 0666, &random_fops, 0 },
> > >          [9] = { "urandom", 0666, &urandom_fops, 0 },
> > > 
> > > Shall a true_random be added here with [10]?
> > 
> > I am not at all an expert on chardevs, but this sounds generally
> > reasonable.  gregkh is probably the real authority here.
> 
> [10] is the aio char device node, so you better not try to overlap it or
> bad things will happen :(

Thanks for your insights.

Which device minor number could we use?

Or another idea and apologies if I restart this conversation as there was 
already a discussion around it: what about extending the getrandom(2) call 
instead of adding a device file?

What about adding yet another flag to getrandom: GRND_TRUERANDOM and process 
it as follows:

        if (flags & ~(GRND_NONBLOCK|GRND_RANDOM|GRND_INSECURE|
GRND_TRUERANDOM))
                return -EINVAL;

        //From Andy's tree
        /*
         * Requesting insecure and blocking randomness at the same time makes
         * no sense.
         */
        if ((flags & (GRND_INSECURE|GRND_RANDOM)) == (GRND_INSECURE|
GRND_RANDOM))
                return -EINVAL;

	  /* We only allow GRND_TRUERANDOM by itself or with NONBLOCK */
	  if (! ((flags & GRND_TRUERANDOM) &&
               ((flags == GRND_TRUERANDOM) ||
                (flags == GRND_TRUERANDOM | GRND_NONBLOCK))))
		return -EINVAL;

	if (flags & GRND_TRUERANDOM) {
		... do the TRNG processing ...
		... may return -ENOPNOTSUPP if no TRNG available ...
	}

Thanks a lot.


Ciao
Stephan