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. IIUC, this also means that the efivar ops are updated while there is already a client. This seems less than ideal as well
