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

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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




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