+ TEE ML

On Fri, 2 Sept 2022 at 18:48, Maximilian Luz luzmaximilian@gmail.com wrote:

Hi,

On 9/2/22 09:26, Sumit Garg wrote:

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Hi Maximilian,

On 02/08/22 18:52, Maximilian Luz wrote:

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Thanks for this information! So as far as I understand it, this is currently an interface to user-space only, i.e. does not allow in-kernel drivers for apps?

The Linux TEE framework already provides an in-kernel interface to TEE as well via TEE bus [1]. There are already multiple kernel drivers [2] [3] [4] [5] [6] [7] using it. So an EFI driver can be an addition to that.

Now coming on to TEE implementations, the drivers I mentioned are based on OP-TEE where devices are queried/enumerated during OP-TEE probe here [8]. So in similar manner QTEE smcinvoke driver should be able to register devices on the TEE bus.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Docu...

[2] drivers/char/tpm/tpm_ftpm_tee.c

[3] drivers/char/hw_random/optee-rng.c

[4] drivers/firmware/arm_scmi/optee.c

[5] security/keys/trusted-keys/trusted_tee.c

[6] drivers/firmware/broadcom/tee_bnxt_fw.c

[7] drivers/rtc/rtc-optee.c

[8] drivers/tee/optee/device.c

Thanks for those links!

I think it would indeed be good if we could make it work via that interface and I guess that should generally be possible. As far as I can see, the biggest problem might be that the current firmware doesn't seem to use UUIDs, so I guess we might need to emulate them somehow.

Okay, so I had a brief look at your driver to get an idea how QTEE identifies its trusted/secure applications. AFAIU, it uses constant strings as follows:

#define QCTEE_UEFISEC_APP_NAME "qcom.tz.uefisecapp"

I think we should be able to extend the TEE bus concept to accept constant strings as device IDs as well. So if a driver wants to support both OP-TEE and QTEE based apps then it can put corresponding identifiers (UUID or a constant string) in the TEE device match ID table. This way we should be able to support other TEE implementations as I think any other identifier apart from UUID can be represented as a constant string.

If anyone else has any better then feel free to discuss.

-Sumit

It would be great if someone with some actual knowledge of the firmware used on those devices could have a look at this and provide some insights.

My plan for now is to hold off on the UEFI variable driver until we have a (proper) TEE driver, which unfortunately might be a bit out of my depth. I'm happy to help out in any way I can though.

Regards, Max