[EXT] Re: [PATCH v18 3/7] firmware: imx: add driver for NXP EdgeLock Enclave

[Marco Felsch]

Hi Frieder,

On 25-06-30, Frieder Schrempf wrote:
> Hi Marco,
> 
> Am 27.06.25 um 10:46 schrieb Marco Felsch:
> > Hi,
> > 
> > your e-mail configuration mixed my e-mail with your answer, which makes
> > it hard to read. Can you please check the quoting next time :)
> > 
> > On 25-06-27, Pankaj Gupta wrote:
> >>>> Add driver for enabling MU based communication interface to
> >> secure-enclave.
> >>>>
> >>>> NXP hardware IP(s) for secure-enclaves like Edgelock Enclave(ELE), are 
> >>>> embedded in the SoC to support the features like HSM, SHE & V2X, using 
> >>>> message based communication interface.
> >>>>
> >>>> The secure enclave FW communicates with Linux over single or multiple 
> >>>> dedicated messaging unit(MU) based interface(s).
> >>>> Exists on i.MX SoC(s) like i.MX8ULP, i.MX93, i.MX95 etc.
> >>
> >>> You write single or multiple MUs are possible. I'm aware that the i.MX93
> >>> has two MUs one for the secure and one for the non-secure world. But I'm
> >>> really concerned about the fact that both MUs can't be used at the same time
> >>> from both world:
> >>
> >> Yes, you are correct.
> >>
> >> Fix is still work in progress.
> > 
> > So after ~6 months no fix is available :(
> > 
> >>> Also how is the secure and non-secure world talking to the ELE if there is
> >>> only one MU as you have written?
> >>
> >> Till the fix is WIP, either Linux or OPTEE can use the ELE, at one point in
> >> time.
> > 
> > That has nothing to do with the fix. The fix is for platforms/SoCs which
> > do have 2-MUs, but you also have written that there are platforms with
> > only 1-MU.
> > 
> > This MU can't be shared between secure and non-secure world.
> > 
> >>> IMHO it makes much more sense to put the complete ELE communication into
> >>> (OP-)TEE and let the secure OS taking care of it. All non-secure world
> >>> requests are passed via (OP-)TEE to the ELE. This involves:
> >>> - eFuse access (done via OP-TEE i.MX specific PTA)
> >>> - ELE 23h59m ping (kernel SMC WDG driver, requires OP-TEE watchdog driver)
> >>> - HW-RNG (kernel OP-TEE HWRNG driver + OP-TEE HWRNG PTA)
> >>
> >> There is a dedicated MU "trusted-MU" for OPTEE-OS. The idea to converge to a
> > 
> > Yes for systems with 2-MUs there is a "trusted-MU" and a
> > "non-trusted-MU". As of now, there is no fix available for using both
> > MUs at the same time. Furhtermore there are platforms/SoCs with only
> > 1-MU, as you have written in your commit message. This 1-MU system can
> > have the MU either trusted or non-trusted.
> > 
> >> single path via OPTEE-OS, is good. But it will impact the performance of the
> >> features at Linux side.
> > 
> > Performance? We are talking about a ping every 23h59m (I still don't
> > know if this is a feature or bug), eFuse write/read, and the HW-RNG
> > which can seed the Linux PRNG.
> > 
> >> Since the fix is still WIP. Let's wait till then.
> > 
> > The fix is for the 2-MUs SoCs but not the 1-MU case.
> > 
> > I would like to have a system design which doesn't differ too much
> > between SoCs which are equipped with the ELE engine.
> 
> Do we really want to depend on OP-TEE to be available for having things
> like OTP fuse access and HWRNG? Personally I'd like to be able to build
> systems with OTP access and HWRNG but without OP-TEE. Requiring OP-TEE
> only to make the ELE available to the kernel in cases where the secure
> world isn't used for anything else seems to be unnecessarily complex.

I understand your point. I don't like pulling in more FW neither but we
need to the face the following facts:

 - OTP eFuse R/W access after doing the LOCK_DOWN fuse is no longer
   possible without OP-TEE. This involves general purpose (GP) eFuses
   too. We faced this limitation in a current project.

 - With new regulations like the EU CRA I think we need some sort of
   secure-enclave anyway.

 - Making it optional cause more paths of potential errors e.g. by not
   including the correct "secure.dtsi". Multiple paths also require more
   maintain- and testing effort. IMHO I do think that one of the paths
   get unmaintened at some point but we would need to keep it for
   backward compatibility.

   Having one implementation eliminates this since.

 - All above points assume that the ELE-FW and -HW is capable of talking
   to both world, which is not the case. As we learned NXP doesn't have
   a fix for the 2-MUs ELE yet and even more important there are 1-MU
   ELE-IPs.

I do see the (minimal) drawback of having +1 FW but I think this is more
an integration problem.
Speaking of FW files, for the new i.MX9* you already have plenty fo
them: bootloader, TF-A, ele-fw, scu-fw (i.MX95). So your integation
needs to handle multiple firmware files already.

> Anyway, I see your point of having a single implementation for the ELE
> API in the "right" place. But as far as I know other platforms like
> STM32MP1 also implement both ways for the HWRNG, secure access via OPTEE
> and non-secure access via kernel directly.

I'm not a STM32MP1 expert but here you have this setup with the
*-scmi.dtsi. So you have two code paths which needs to be maintained and
tested. Also if one customer of yours want to use OP-TEE you need the
integration anyway, so you (Kontron) needs to maintain multiple
configuration as well. I don't see the added value.

I think for STM32MP1 the *-scmi.dtsi support was added later because it
required a lot effort to support it. This is not the case for the i.MX9*
series.

Regards,
  Marco

> Thanks
> Frieder
>