Re: [PATCH v9 0/6] introduce tee-based EFI Runtime Variable Service

[Ilias Apalodimas]

Kojima-san,

I found some time to do some extended testing here's what I found

Switching the permissions from RO->RW when the supplicant is started works
correctly
# mount | grep efiv
efivarfs on /sys/firmware/efi/efivars type efivarfs (ro,nosuid,nodev,noexec,relatime)
# tee-supplicant -d
[   77.374878] efivars: Unregistered efivars operations
[   77.381604] Use tee-based EFI runtime variable services
[   77.386862] efivars: Registered efivars operations
# mount | grep efiv
efivarfs on /sys/firmware/efi/efivars type efivarfs (rw,nosuid,nodev,noexec,relatime)
I didn't test unbinding yet, but I assume it's going to work fine and
remove the efivar ops.

Reading an writing non-authenticated EFI variables seems to work fine.
I verified this with U-Boot and the BootOrder changed correctly.
# efibootmgr -o 0001,0002,0000
BootCurrent: 0002
BootOrder: 0001,0002,0000
Boot0000* nvme 0:1
Boot0001* nvme 0:2
Boot0002* debian
# efibootmgr -o 0002,0000,0001
BootCurrent: 0002
BootOrder: 0002,0000,0001
Boot0000* nvme 0:1
Boot0001* nvme 0:2
Boot0002* debian

Writing authenticated EFI variables works the first time.
I also dumped those variables from both Linux and U-Boot and they matched
# efi-updatevar -f PK.auth PK
# efi-updatevar -f KEK.auth KEK
# efi-updatevar -f db.auth db

But removing the PK at runtime fails.
# efi-updatevar -f noPK.auth PK
# Failed to update PK: Operation not permitted
My guess is that the EDK2 code prohibits that, but we need to check why
this is happening.  I also got similar failures trying to update KEK and db.

But the most worrying thing is this. From Linux program KEK and db
# efi-updatevar -f KEK.auth KEK
# efi-updatevar -f db.auth db

Reboot the machine and U-Boot complains when it tries to populate the
runtime vars with:
Loading Linux 6.6.0-rc2-00654-g82a013b37495 ...
Loading initial ramdisk ...
EFI stub: Booting Linux Kernel...
EFI stub: Using DTB from configuration table
EFI stub: Exiting boot services...
Can't populate EFI variables. No runtime variables will be available <-- This

If you rewrite those vars from the U-Boot shell everything seems to come
back to normal
=> tftp  $loadaddr 192.168.49.5:noKEK.auth && setenv -e -nv -bs -rt -at -i $loadaddr:$filesize KEK
=> tftp  $loadaddr 192.168.49.5:nodb.auth && setenv -e -nv -bs -rt -at -i $loadaddr:$filesize db
=> tftp  $loadaddr 192.168.49.5:KEK.auth && setenv -e -nv -bs -rt -at -i $loadaddr:$filesize KEK
=> tftp  $loadaddr 192.168.49.5:db.auth && setenv -e -nv -bs -rt -at -i $loadaddr:$filesize db

Loading Linux 6.6.0-rc2-00654-g82a013b37495 ...
Loading initial ramdisk ...
EFI stub: Booting Linux Kernel...
EFI stub: Using DTB from configuration table
EFI stub: Exiting boot services...

Let me know if you need any more information

Regards
/Ilias
On Fri, Oct 13, 2023 at 04:45:33PM +0900, Masahisa Kojima wrote:
> This series introduces the 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.
>
> Changelog:
> v8 -> v9
> - patch #6 "tee: optee: restore efivars ops when tee-supplicant stops"
>   is newly added
> - remove !EFI_VARS_PSTORE Kconfig dependency, we have added a non-blocking
>   set_variable and it just returns EFI_UNSUPPORTED.
> - remove obvious comments
>
> v7 -> v8
> Only patch #3 "efi: Add tee-based EFI variable driver" is updated.
> - fix typos
> - refactor error handling, direct return if applicable
> - use devm_add_action_or_reset() for closing of tee context/session
> - remove obvious comment
>
> v6 -> v7
> Patch #1-#4 are not updated.
> Patch #5 is added into this series, original patch is here:
> https://lore.kernel.org/all/20230609094532.562934-1-ilias.apalodimas@xxxxxxxxxx/
>
> There are two issues in the v6 series and v7 series addresses those.
>
> 1) efivar ops is not restored when the tee-supplicant daemon terminates.
>  -> As the following patch says, user must remove the device before
>     terminating tee-supplicant daemon.
>     https://lore.kernel.org/all/20230728134832.326467-1-sumit.garg@xxxxxxxxxx/
>
> 2) cause panic when someone remounts the efivarfs as RW even if
> SetVariable is not supported
>  -> The fifth patch addresses this issue.
>    "[PATCH v7 5/5] efivarfs: force RO when remounting if SetVariable is
>     not supported"
>
> v5 -> v6
> - new patch #4 is added in this series, #1-#3 patches are unchanged.
>   automatically update super block flag when the efivarops support
>   SetVariable runtime service, so that user does not need to manually
>   remount the efivarfs as RW.
>
> v4 -> v5
> - rebase to efi-next based on v6.4-rc1
> - set generic_ops.query_variable_info, it works as expected as follows.
> $ df -h /sys/firmware/efi/efivars/
> Filesystem      Size  Used Avail Use% Mounted on
> efivarfs         16K  1.3K   15K   8% /sys/firmware/efi/efivars
>
> v3 -> v4:
> - replace the reference from EDK2 to PI Specification
> - remove EDK2 source code reference comments
> - prepare nonblocking variant of set_variable, it just returns
>   EFI_UNSUPPORTED
> - remove redundant buffer size check
> - argument name change in mm_communicate
> - function interface changes in setup_mm_hdr to remove (void **) cast
>
> v2 -> v3:
> - add CONFIG_EFI dependency to TEE_STMM_EFI
> - add missing return code check for tee_client_invoke_func()
> - directly call efivars_register/unregister from tee_stmm_efi.c
>
> rfc v1 -> v2:
> - split patch into three patches, one for drivers/tee,
>   one for include/linux/efi.h, and one for the driver/firmware/efi/stmm
> - context/session management into probe() and remove() same as other tee
> client driver
> - StMM variable driver is moved from driver/tee/optee to driver/firmware/efi
> - use "tee" prefix instead of "optee" in driver/firmware/efi/stmm/tee_stmm_efi.c,
>   this file does not contain op-tee specific code, abstracted by tee layer and
>   StMM variable driver will work on other tee implementation.
> - PTA_STMM_CMD_COMMUNICATE -> PTA_STMM_CMD_COMMUNICATE
> - implement query_variable_store() but currently not used
> - no use of TEEC_SUCCESS, it is defined in driver/tee/optee/optee_private.h.
>   Other tee client drivers use 0 instead of using TEEC_SUCCESS
> - remove TEEC_ERROR_EXCESS_DATA status, it is referred just to output
> error message
>
> Ilias Apalodimas (1):
>   efivarfs: force RO when remounting if SetVariable is not supported
>
> Masahisa Kojima (5):
>   efi: expose efivar generic ops register function
>   efi: Add EFI_ACCESS_DENIED status code
>   efi: Add tee-based EFI variable driver
>   efivarfs: automatically update super block flag
>   tee: optee: restore efivars ops when tee-supplicant stops
>
>  drivers/firmware/efi/Kconfig                 |  15 +
>  drivers/firmware/efi/Makefile                |   1 +
>  drivers/firmware/efi/efi.c                   |  18 +
>  drivers/firmware/efi/stmm/mm_communication.h | 236 +++++++
>  drivers/firmware/efi/stmm/tee_stmm_efi.c     | 617 +++++++++++++++++++
>  drivers/firmware/efi/vars.c                  |   8 +
>  drivers/tee/optee/supp.c                     |   4 +
>  fs/efivarfs/super.c                          |  45 ++
>  include/linux/efi.h                          |  13 +
>  9 files changed, 957 insertions(+)
>  create mode 100644 drivers/firmware/efi/stmm/mm_communication.h
>  create mode 100644 drivers/firmware/efi/stmm/tee_stmm_efi.c
>
>
> base-commit: b691118f2c44d16b84fc65b8147b33620eb18cac
> --
> 2.30.2
>