Re: Security Random Number Generator support

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

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.