Re: Security Random Number Generator support

[Neal Liu <neal.liu@mediatek.com>]

On Wed, 2020-06-03 at 08:40 +0100, Marc Zyngier wrote:
> On 2020-06-03 08:29, Neal Liu wrote:
> > On Tue, 2020-06-02 at 21:02 +0800, Marc Zyngier wrote:
> >> On 2020-06-02 13:14, Ard Biesheuvel wrote:
> >> > On Tue, 2 Jun 2020 at 10:15, Neal Liu <neal.liu@mediatek.com> wrote:
> >> >>
> >> >> These patch series introduce a security random number generator
> >> >> which provides a generic interface to get hardware rnd from Secure
> >> >> state. The Secure state can be Arm Trusted Firmware(ATF), Trusted
> >> >> Execution Environment(TEE), or even EL2 hypervisor.
> >> >>
> >> >> Patch #1..2 adds sec-rng kernel driver for Trustzone based SoCs.
> >> >> For security awareness SoCs on ARMv8 with TrustZone enabled,
> >> >> peripherals like entropy sources is not accessible from normal world
> >> >> (linux) and rather accessible from secure world (HYP/ATF/TEE) only.
> >> >> This driver aims to provide a generic interface to Arm Trusted
> >> >> Firmware or Hypervisor rng service.
> >> >>
> >> >>
> >> >> changes since v1:
> >> >> - rename mt67xx-rng to mtk-sec-rng since all MediaTek ARMv8 SoCs can
> >> >> reuse
> >> >>   this driver.
> >> >>   - refine coding style and unnecessary check.
> >> >>
> >> >>   changes since v2:
> >> >>   - remove unused comments.
> >> >>   - remove redundant variable.
> >> >>
> >> >>   changes since v3:
> >> >>   - add dt-bindings for MediaTek rng with TrustZone enabled.
> >> >>   - revise HWRNG SMC call fid.
> >> >>
> >> >>   changes since v4:
> >> >>   - move bindings to the arm/firmware directory.
> >> >>   - revise driver init flow to check more property.
> >> >>
> >> >>   changes since v5:
> >> >>   - refactor to more generic security rng driver which
> >> >>     is not platform specific.
> >> >>
> >> >> *** BLURB HERE ***
> >> >>
> >> >> Neal Liu (2):
> >> >>   dt-bindings: rng: add bindings for sec-rng
> >> >>   hwrng: add sec-rng driver
> >> >>
> >> >
> >> > There is no reason to model a SMC call as a driver, and represent it
> >> > via a DT node like this.
> >> 
> >> +1.
> >> 
> >> > It would be much better if this SMC interface is made truly generic,
> >> > and wired into the arch_get_random() interface, which can be used much
> >> > earlier.
> >> 
> >> Wasn't there a plan to standardize a SMC call to rule them all?
> >> 
> >>          M.
> > 
> > Could you give us a hint how to make this SMC interface more generic in
> > addition to my approach?
> > There is no (easy) way to get platform-independent SMC function ID,
> > which is why we encode it into device tree, and provide a generic
> > driver. In this way, different devices can be mapped and then get
> > different function ID internally.
> 
> The idea is simply to have *one* single ID that caters for all
> implementations, just like we did for PSCI at the time. This
> requires ARM to edict a standard, which is what I was referring
> to above.
> 
> There is zero benefit in having a platform-dependent ID. It just
> pointlessly increases complexity, and means we cannot use the RNG
> before the firmware tables are available (yes, we need it that
> early).
> 
>          M.

Do you know which ARM expert could edict this standard?
Or is there any chance that we can make one? And be reviewed by
maintainers?