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

[Masahisa Kojima]

Hi Ilias,

On Wed, 18 Oct 2023 at 20:35, Ilias Apalodimas
<ilias.apalodimas@xxxxxxxxxx> wrote:
>
> 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.

"# efi-updatevar -f noPK.auth PK" does not reach the kernel efivarfs code.
With strace, error occurs when efi-updatevar tries to open
/sys/firmware/efi/efivars/KEK-*** file.
I guess O_TRUNC option in open() is not required?

openat(AT_FDCWD,
"/sys/firmware/efi/efivars/KEK-8be4df61-93ca-11d2-aa0d-00e098032b8c",
O_RDWR|O_CREAT|O_TRUNC, 0644) = -1 EPERM (Operation not permitted)
write(2, "Failed to update KEK: ", 22Failed to update KEK: )  = 22
write(2, "Operation not permitted\n", 24Operation not permitted
) = 24
exit_group(1)                           = ?
+++ exited with 1 +++

We can use "efivar" instead to remove the keys. It also works for KEK and db.
# efi-updatevar -f PK.auth PK
# efi-updatevar -f noPK.auth PK     <--- it does not work
# efivar -w -n 8be4df61-93ca-11d2-aa0d-00e098032b8c-PK -f noPK.auth
<--- it works

>
> 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

I could not reproduce this issue.
I tried the following command then reboot the board. Linux boots fine.
 # efi-updatevar -f KEK.auth KEK
 # efi-updatevar -f db.auth db

I also enroll the PK, then UEFI secure boot works.
Signed grub and signed kernel boot in UEFI secure boot enabled.

Are there any additional steps to reproduce?

Thanks,
Masahisa Kojima

>
> 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
> >