Re: [PATCH v5 3/3] hwrng: add mtk-sec-rng driver

[Marc Zyngier]

On 2019-12-12 05:13, Neal Liu wrote:
> On Tue, 2019-12-03 at 11:17 +0000, Marc Zyngier wrote:
> > On 2019-12-03 04:16, Florian Fainelli wrote:
> > > On 12/2/2019 11:11 AM, Marc Zyngier wrote:
> > >> On Mon, 2 Dec 2019 16:12:09 +0000
> > >> Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> wrote:
> > >>
> > >>> (adding some more arm64 folks)
> > >>>
> > >>> On Fri, 29 Nov 2019 at 11:30, Neal Liu <neal.liu@xxxxxxxxxxxx>
> > >>> wrote:
> > >>>>
> > >>>> On Fri, 2019-11-29 at 18:02 +0800, Lars Persson wrote:
> > >>>>> Hi Neal,
> > >>>>>
> > >>>>> On Wed, Nov 27, 2019 at 3:23 PM Neal Liu 
> > <neal.liu@xxxxxxxxxxxx>
> > >>>>> wrote:
> > >>>>>>
> > >>>>>> For MediaTek SoCs on ARMv8 with TrustZone enabled, 
> > peripherals
> > >>>>>> like
> > >>>>>> entropy sources is not accessible from normal world (linux) 
> > and
> > >>>>>> rather accessible from secure world (ATF/TEE) only. This 
> > driver
> > >>>>>> aims
> > >>>>>> to provide a generic interface to ATF rng service.
> > >>>>>>
> > >>>>>
> > >>>>> I am working on several SoCs that also will need this kind of
> > >>>>> driver
> > >>>>> to get entropy from Arm trusted firmware.
> > >>>>> If you intend to make this a generic interface, please clean 
> > up
> > >>>>> the
> > >>>>> references to MediaTek and give it a more generic name. For
> > >>>>> example
> > >>>>> "Arm Trusted Firmware random number driver".
> > >>>>>
> > >>>>> It will also be helpful if the SMC call number is 
> > configurable.
> > >>>>>
> > >>>>> - Lars
> > >>>>
> > >>>> Yes, I'm trying to make this to a generic interface. I'll try 
> > to
> > >>>> make
> > >>>> HW/platform related dependency to be configurable and let it 
> > more
> > >>>> generic.
> > >>>> Thanks for your suggestion.
> > >>>>
> > >>>
> > >>> I don't think it makes sense for each arm64 platform to expose 
> > an
> > >>> entropy source via SMC calls in a slightly different way, and 
> > model
> > >>> it
> > >>> as a h/w driver. Instead, we should try to standardize this, and
> > >>> perhaps expose it via the architectural helpers that already 
> > exist
> > >>> (get_random_seed_long() and friends), so they get plugged into 
> > the
> > >>> kernel random pool driver directly.
> > >>
> > >> Absolutely. I'd love to see a standard, ARM-specified, 
> > virtualizable
> > >> RNG that is abstracted from the HW.
> > >
> > > Do you think we could use virtio-rng on top of a modified 
> > virtio-mmio
> > > which instead of being backed by a hardware mailbox, could use
> > > hvc/smc
> > > calls to signal writes to shared memory and get notifications via 
> > an
> > > interrupt? This would also open up the doors to other virtio uses
> > > cases
> > > beyond just RNG (e.g.: console, block devices?). If this is
> > > completely
> > > stupid, then please disregard this comment.
> >
> > The problem with a virtio device is that it is a ... device. What we
> > want
> > is to be able to have access to an entropy source extremely early in
> > the
> > kernel life, and devices tend to be available pretty late in the 
> > game.
> > This means we cannot plug them in the architectural helpers that Ard
> > mentions above.
> >
> > What you're suggesting looks more like a new kind of virtio 
> > transport,
> > which is interesting, in a remarkably twisted way... ;-)
> >
> > Thanks,
> >
> >          M.
>
> In conclusion, is it helpful that hw_random has a generic interface 
> to
> add device randomness by talking to hwrng which is implemented in the
> firmware or the hypervisor?
> For most chip vendors, I think the answer is yes. We already prepared 
> a
> new patchset and need you agree with this idea.

As long as it is a *unified* interface, I'm all for that.

Thanks,

        M.
--
Jazz is not dead. It just smells funny...