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. Thanks -Neal
