Messages in this thread | | | Subject | Re: [PATCH v5 3/3] hwrng: add mtk-sec-rng driver | Date | Thu, 12 Dec 2019 14:30:38 +0000 | From | Marc Zyngier <> |
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On 2019-12-12 14:03, Ard Biesheuvel wrote: > On Thu, 12 Dec 2019 at 12:45, Marc Zyngier <maz@kernel.org> wrote: >> >> 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@linaro.org> wrote: >> >> >> >> >> >>> (adding some more arm64 folks) >> >> >>> >> >> >>> On Fri, 29 Nov 2019 at 11:30, Neal Liu >> <neal.liu@mediatek.com> >> >> >>> 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@mediatek.com> >> >> >>>>> 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. >> > > > Yeah, but I'm not sure it makes sense to model it as a device like > this. It would be nice if we could tie this into the ARM SMCCC > discovery, and use the SMC calls to back arch_get_random_seed_long()
Probably I wasn't clear enough, but that's really what I meant by a unified interface (implemented by the firmware or the hypervisor).
> [provided we fix the braindead way in which that is being used today > in the interrupt code]
Ah, I said I'd look into it. Thanks for the reminder...
Thanks,
M. -- Jazz is not dead. It just smells funny...
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