Re: [PATCH 0/4] firmware: Add support for Qualcomm UEFI Secure Application

Srinivas Kandagatla
2022-08-02T11:51:49Z

Hi Maximilian,

On 23/07/2022 23:49, Maximilian Luz wrote:
> On modern Qualcomm platforms, access to EFI variables is restricted to
> the secure world / TrustZone, i.e. the Trusted Execution Environment
> (TrEE or TEE) as Qualcomm seems to call it. To access EFI variables, we
> therefore need to talk to the UEFI Secure Application (uefisecapp),
> residing in the TrEE.
>
> This series adds support for accessing EFI variables on those platforms.
>
> To do this, we first need to add some SCM call functions used to manage
> and talk to Secure Applications. A very small subset of this interface
> is added in the second patch (whereas the first one exports the required
> functions for that). Interface specifications are extracted from [1].
> While this does not (yet) support re-entrant SCM calls (including
> callbacks and listeners), this is enough to talk to the aforementioned
> uefisecapp on a couple of platforms (I've tested this on a Surface Pro X
> and heard reports from Lenovo Flex 5G, Lenovo Thinkpad x13s, and Lenovo
> Yoga C630 devices).
>
> The third patch adds a client driver for uefisecapp, installing the
> respective efivar operations. The application interface has been reverse
> engineered from the Windows QcTrEE8180.sys driver.
>
> Apart from uefisecapp, there are more Secure Applications running that
> we might want to support in the future. For example, on the Surface Pro
> X (sc8180x-based), the TPM is also managed via one.
>
> I'm not sure whether this should go to drivers/firmware or to
> drivers/soc/qcom. I've put this into firmware as all of this is
> essentially an interface to the secure firmware running in the TrustZone
> (and SCM stuff is handled here already), but please let me know if I
> should move this.

From what I see so far is that this is adapted from downstream qseecom
driver, this approach could work for a limited usecases but not
scalable, as we cannot add drivers for each Qualcomm specific TA in kernel.
This has to be handled in much generic way using Linux TEE framework,
and let the userspace side deal with TA specific bits.

AFAIU, Qualcomm is moving away from qseecom interface to new smc-invoke
interface, most of Qualcomm SoCs starting from SDM660 already have
support to this.

This interface provides a better abstracted IPC mechanism to talk to TA.
Most of these TA specific interfaces are packed in closed userspace source.
Having said that QTEE smcinvoke driver can be modeled as a proper TEE
driver with Userspace driving the TA specific bits using existing tee uapis.
This also brings in other features like loading, Listeners aka
callbacks, secure memory allocations..etc.

In the past, I have tried to do a prototype of this smcinvoke driver as
a proper tee driver, incase you are interested patches are at
https://git.linaro.org/landing-teams/working/qualcomm/kernel.git/log/?h=tracking-qcomlt-qcomtee
Plan is to discuss with Qualcomm and send it for upstream review.

I think its worth exploring if uefisecapp can talk smcinvoke.
I can ping Qualcomm engineers to see if that is doable.

thanks,
Srini

>
> Regards,
> Max
>
> [1]: https://git.codelinaro.org/clo/la/kernel/msm-4.14/-/blob/auto-kernel.lnx.4.14.c34/drivers/misc/qseecom.c
>
> Maximilian Luz (4):
> firmware: qcom_scm: Export SCM call functions
> firmware: Add support for Qualcomm Trusted Execution Environment SCM
> calls
> firmware: Add support for Qualcomm UEFI Secure Application
> dt-bindings: firmware: Add Qualcomm UEFI Secure Application client
>
> .../firmware/qcom,tee-uefisecapp.yaml | 38 +
> MAINTAINERS | 14 +
> drivers/firmware/Kconfig | 20 +
> drivers/firmware/Makefile | 2 +
> drivers/firmware/qcom_scm.c | 118 ++-
> drivers/firmware/qcom_scm.h | 47 --
> drivers/firmware/qcom_tee.c | 213 +++++
> drivers/firmware/qcom_tee_uefisecapp.c | 761 ++++++++++++++++++
> include/linux/qcom_scm.h | 49 ++
> include/linux/qcom_tee.h | 179 ++++
> 10 files changed, 1355 insertions(+), 86 deletions(-)
> create mode 100644 Documentation/devicetree/bindings/firmware/qcom,tee-uefisecapp.yaml
> create mode 100644 drivers/firmware/qcom_tee.c
> create mode 100644 drivers/firmware/qcom_tee_uefisecapp.c
> create mode 100644 include/linux/qcom_tee.h
>