On 06.06.23 08:57, Ard Biesheuvel wrote: > On Tue, 6 Jun 2023 at 08:52, Sumit Garg <sumit.garg@xxxxxxxxxx> wrote: >> >> Hi Jan, >> >> On Tue, 6 Jun 2023 at 12:09, Jan Kiszka <jan.kiszka@xxxxxxxxxxx> wrote: >>> >>> On 26.05.23 03:07, Masahisa Kojima wrote: >>>> When the flash is not owned by the non-secure world, accessing the EFI >>>> variables is straightforward and done via EFI Runtime Variable Services. >>>> In this case, critical variables for system integrity and security >>>> are normally stored in the dedicated secure storage and only accessible >>>> from the secure world. >>>> >>>> On the other hand, the small embedded devices don't have the special >>>> dedicated secure storage. The eMMC device with an RPMB partition is >>>> becoming more common, we can use an RPMB partition to store the >>>> EFI Variables. >>>> >>>> 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 >>>> TEE(OP-TEE in this case), 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 TEE and StandaloneMM. >>>> >>>> So let's add the kernel functions needed. >>>> >>>> This feature is implemented as a kernel module. >>>> StMM PTA has TA_FLAG_DEVICE_ENUM_SUPP flag when registered to OP-TEE >>>> so that this tee_stmm_efi module is probed after tee-supplicant starts, >>>> since "SetVariable" EFI Runtime Variable Service requires to >>>> interact with tee-supplicant. >>>> >>>> Acked-by: Sumit Garg <sumit.garg@xxxxxxxxxx> >>>> Co-developed-by: Ilias Apalodimas <ilias.apalodimas@xxxxxxxxxx> >>>> Signed-off-by: Ilias Apalodimas <ilias.apalodimas@xxxxxxxxxx> >>>> Signed-off-by: Masahisa Kojima <masahisa.kojima@xxxxxxxxxx> >>>> --- >>>> drivers/firmware/efi/Kconfig | 15 + >>>> drivers/firmware/efi/Makefile | 1 + >>>> drivers/firmware/efi/stmm/mm_communication.h | 236 +++++++ >>>> drivers/firmware/efi/stmm/tee_stmm_efi.c | 638 +++++++++++++++++++ >>>> 4 files changed, 890 insertions(+) >>>> create mode 100644 drivers/firmware/efi/stmm/mm_communication.h >>>> create mode 100644 drivers/firmware/efi/stmm/tee_stmm_efi.c >>>> > ... >>> >>> I think we have a probe ordering issue with this driver: >>> efivarfs_fill_super() may be called before the TEE bus was probed, thus >>> with the default efivar ops still registered. And that means >>> efivar_supports_writes() will return false, and the fs declares itself >>> as readonly. I've seen systemd mounting it r/o initialling, and you need >>> to remount the fs to enable writability. >>> >>> Is there anything that could be done to re-order things reliably, probe >>> the tee bus earlier etc.? >> >> This driver has a dependency on user-space daemon: tee-supplicant to >> be running for RPMB access. So once you start that daemon the >> corresponding device will be enumerated on the TEE bus and this driver >> probe will be invoked. So I would suggest you to load this daemon very >> early in the boot process or better to make it a part of initramfs. >> > > That is not the point, really. > > If this dependency exists, the code should be aware of that, and made > to work correctly in spite of it. Requiring a module to be part of > initramfs is not a reasonable fix. In fact, I've tested a non-modularized build as well, just to exclude that issue. The daemon dependency is more likely the problem here. > > IIUC, this also means that the efivar ops are updated while there is > already a client. This seems less than ideal as well Jan -- Siemens AG, Technology Competence Center Embedded Linux
