[PATCH 2/5 v2] efi_loader: Implement EFI variable handling via OP-TEE

[Ilias Apalodimas <ilias.apalodimas@linaro.org>]

On Fri, May 15, 2020 at 01:55:35PM +0200, Heinrich Schuchardt wrote:
> On 11.05.20 20:14, Ilias Apalodimas wrote:
> > In OP-TEE we can run EDK2's StandAloneMM on a secure partition.
> > StandAloneMM is responsible for the UEFI variable support. In
> > combination with OP-TEE and it's U-Boot supplicant, variables are
> > authenticated/validated in secure world and stored on an RPMB partition.
> >
> > So let's add a new config option in U-Boot implementing the necessary
> > calls to OP-TEE for the variable management.
> >
> > Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
> > Signed-off-by: Pipat Methavanitpong <pipat1010@gmail.com>
> > Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>
> > ---
> >  lib/efi_loader/Kconfig            |   9 +
> >  lib/efi_loader/Makefile           |   4 +
> >  lib/efi_loader/efi_variable_tee.c | 643 ++++++++++++++++++++++++++++++
> >  3 files changed, 656 insertions(+)
> >  create mode 100644 lib/efi_loader/efi_variable_tee.c
> >
> > diff --git a/lib/efi_loader/Kconfig b/lib/efi_loader/Kconfig
> > index 1cfa24ffcf72..e385cd0b9dae 100644
> > --- a/lib/efi_loader/Kconfig
> > +++ b/lib/efi_loader/Kconfig
> > @@ -164,4 +164,13 @@ config EFI_SECURE_BOOT
> >  	  it is signed with a trusted key. To do that, you need to install,
> >  	  at least, PK, KEK and db.
> >
> > +config EFI_MM_COMM_TEE
> > +	bool "UEFI variables storage service via OP-TEE"
> > +	depends on SUPPORT_EMMC_RPMB
> > +	default n
> > +	help
> > +	  If OP-TEE is present and running StandAloneMM dispatch all UEFI variable
> > +	  related operations to that. The application will verify, authenticate and
> > +	  store the variables on an RPMB
> > +
> >  endif
> 
> Dear Ilias,
> 
> at least CONFIG_TEE=y is needed as dependency. Otherwise compiling fails.

Ok I'll add that

> 
> If OP-TEE is not found:
> 
> => bootefi hello
> Unable to open OP-TEE session (err=-19)
> mm_communicate failed!
> Error: Cannot initialize UEFI sub-system, r = 3
> 
> I think it could be allowable to boot without variable support unless we
> are in secure boot audit mode. So if CONFIG_EFI_SECURE_BOOT=n, maybe we
> should be less strict. I guess it will end up in weighing user
> friendliness against complexity. What are your ideas?

I don't have any strong opinions on that tbh. But I think i'd choose the
stricter approach. If it's a UEFI boot/whatever, variables must be initialized
and accessible.

Regards
/Ilias
> 
> Best regards
> 
> Heinrich