Re: [PATCH v25 10/12] LRNG - add TRNG support

Stephan Müller
2019-11-20T09:00:13Z

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