Re: Security Random Number Generator support

[Marc Zyngier]

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@xxxxxxxxxxxx> 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.
--
Jazz is not dead. It just smells funny...