Messages in this thread | | | Date | Fri, 3 Feb 2023 11:55:44 +0100 | From | Jens Wiklander <> | Subject | Re: [RFC PATCH 0/2] introduce op-tee based EFI Runtime Variable Service |
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On Fri, Feb 03, 2023 at 03:03:34PM +0530, Sumit Garg wrote: > Hi Jens, > > On Fri, 3 Feb 2023 at 13:59, Jens Wiklander <jens.wiklander@linaro.org> wrote: > > > > Hi Sumit, > > > > On Thu, Feb 02, 2023 at 05:35:49PM +0530, Sumit Garg wrote: > > > Hi Masahisa, > > > > > > On Thu, 26 Jan 2023 at 18:52, Masahisa Kojima > > > <masahisa.kojima@linaro.org> wrote: > > > > > > > > This RFC series introduces the op-tee based EFI Runtime Variable > > > > Service. > > > > > > > > The eMMC device is typically owned by the non-secure world(linux in > > > > this case). There is an existing solution utilizing eMMC RPMB partition > > > > for EFI Variables, it is implemented by interacting with > > > > OP-TEE, StandaloneMM(as EFI Variable Service Pseudo TA), eMMC driver > > > > and tee-supplicant. The last piece is the tee-based variable access > > > > driver to interact with OP-TEE and StandaloneMM. > > > > > > > > > > After an overall look at the APIs, following are some initial comments: > > > - Is there any reason to have the edk2 specific StandaloneMM stack in > > > Linux to communicate with OP-TEE pseudo TA? > > > - I think the OP-TEE pseudo TA should be able to expose a rather > > > generic invoke commands such as: > > > TEE_EFI_GET_VARIABLE > > > TEE_EFI_GET_NEXT_VARIABLE > > > TEE_EFI_SET_VARIABLE > > > So it should no longer be tied to StMM stack and other TEE > > > implementations can re-use the abstracted interface to communicate > > > with its corresponding secure storage TA. > > > > In the current setup we have the following layers in the kernel: > > 1. efivar_operations > > 2. MM > > 3. PTA_STMM > > 4. OP-TEE MSG > > > > and in the secure world: > > S1. internal to StMM > > S2. MM interface to StMM > > S3. PTA_STMM > > S4. OP-TEE MSG > > > > If I understand you correctly you'd like to see this instead: > > Kernel: > > 1. efivar_operations > > 2. PTA_EFIVAR > > 4. OP-TEE MSG > > > > Since we still have the MM interface with StMM we'd have this in the secure > > world: > > S1. internal to StMM > > S2. MM interface to StMM > > S3. PTA_EFIVAR > > S4. OP-TEE MSG > > > > At S3 we'd have to convert between EFIVAR and MM messages. The > > difference is that we're moving the EFIVAR <-> MM conversion from the > > non-secure world into the secure world. We're still using OP-TEE > > specific communication at the fourth layer. So we're only moving problem > > around, I'd rather avoid growing the OP-TEE part in the secure world. > > > > If you look carefully, we are essentially defining an ABI towards the > secure world. The approach in this patch-set adds the MM interface as > a redundant ABI layer which makes it complex to maintain. Now think > about if every TEE implementation would propose such a complex ABI. It > looks like a maintenance nightmare to me. > > The concerns you are highlighting about OP-TEE size, I think those are > implementation details which can be simplified later but once you have > defined an ABI then you are stuck with its maintainability.
You have a point, but keep in mind that it's StMM that matters here. StMM uses the MM protocol. It was originially using raw SMCs as a conduit, but with the need for OP-TEE accessing RPMB that's not usable. So instead we use OP-TEE MSG as a conduit. Seen from that perspective we're only resuing something established instead of inventing something new.
Cheers, Jens
> > -Sumit > > > Cheers, > > Jens > > > > > > > > -Sumit > > > > > > > Masahisa Kojima (2): > > > > efi: expose efivar generic ops register function > > > > tee: Add op-tee helper functions for variable access > > > > > > > > drivers/firmware/efi/efi.c | 12 + > > > > drivers/tee/optee/Kconfig | 10 + > > > > drivers/tee/optee/Makefile | 1 + > > > > drivers/tee/optee/mm_communication.h | 249 +++++++++++ > > > > drivers/tee/optee/optee_private.h | 5 +- > > > > drivers/tee/optee/optee_stmm_efi.c | 598 +++++++++++++++++++++++++++ > > > > drivers/tee/tee_core.c | 23 ++ > > > > include/linux/efi.h | 4 + > > > > include/linux/tee_drv.h | 23 ++ > > > > 9 files changed, 924 insertions(+), 1 deletion(-) > > > > create mode 100644 drivers/tee/optee/mm_communication.h > > > > create mode 100644 drivers/tee/optee/optee_stmm_efi.c > > > > > > > > -- > > > > 2.30.2 > > > >
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