Re: [Xen-devel] [PATCH v6 09/10] tools/arm: tee: add "tee" option for xl.cfg

[Julien Grall <julien.grall@arm.com>]

Hi Volodymyr,

On 6/11/19 7:46 PM, Volodymyr Babchuk wrote:
> This enumeration controls TEE type for a domain. Currently there is
> two possible options: either 'none' or 'optee'.
> 
> 'none' is the default value and it basically disables TEE support at
> all.
> 
> 'optee' enables access to the OP-TEE running on a host machine. This
> requires special OP-TEE build with virtualization support enabled.
> 
> Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@epam.com>
> 
> ---
>   All the patches to optee.c should be merged together. They were
>   split to ease up review. But they depend heavily on each other.
> 
>   Changes from v5:
>    - Replaced "native" with "optee" in the commit description.
>    - Updated and extended documentation based on Julien Grall's
>      and Ian Jackson's suggestions.
> 
>   Changes from v4:
>    - "native" option was replaced with "optee"
>    - "tee" property was moved from arch-specific section to the
>       global one. Documentation moved inside "Devices" section.
> 
>   Changes from v3:
>    - tee_enabled renamed to tee_type. Currently two types are supported
>      as described in the commit message
>    - Add LIBXL_HAVE_BUILDINFO_ARCH_ARM_TEE definition
> 
>   Changes from v2:
>    - Use arch.tee_enabled instead of separate domctl
> ---
>   docs/man/xl.cfg.5.pod.in    | 21 +++++++++++++++++++++
>   tools/libxl/libxl.h         |  5 +++++
>   tools/libxl/libxl_arm.c     | 13 +++++++++++++
>   tools/libxl/libxl_types.idl |  6 ++++++
>   tools/xl/xl_parse.c         |  9 +++++++++
>   5 files changed, 54 insertions(+)
> 
> diff --git a/docs/man/xl.cfg.5.pod.in b/docs/man/xl.cfg.5.pod.in
> index c99d40307e..e65ab6111f 100644
> --- a/docs/man/xl.cfg.5.pod.in
> +++ b/docs/man/xl.cfg.5.pod.in
> @@ -1544,6 +1544,27 @@ Set maximum height for pointer device.
>   
>   =back
>   
> +=item B<tee="STRING">
> +
> +B<Arm only.> Set TEE type for the guest. TEE is a Trusted Execution
> +Environment -- separate secure OS found on some platforms. B<STRING> can be one of the:
> +
> +=over 4
> +
> +=item B<none>
> +
> +Disable TEE support at all. This is the default value.
How about "Don't allow the guest to use TEE if present on the platform. 
This is the default value.".

> +
> +=item B<optee>
> +
> +Allow a guest to use OP-TEE. Note that a virtualization-aware OP-TEE
> +is required for this. If this option is selected, guest will be able

OOI, what happen if OP-TEE does not support virtualization. Will Xen 
forbid to use it?

> +to access to the real OP-TEE OS running on the host. Guest creation

s/real// it is redundant with the rest of the sentence. However, it does 
not really answer to the question regarding isolation.

> +will fail if OP-TEE have no resources for a new guest. Number of supported
> +guests depends on OP-TEE configuration.

How about the following description (correct me if my understanding is 
wrong):

"Allow a guest to access the host OP-TEE OS. Xen will mediate the access 
to OP-TEE and the resource isolation will be provided directly by 
OP-TEE. OP-TEE itself may limit the number of guests that can 
concurrently use it. This requires a virtualization-aware OP-TEE for 
this to work.

This feature is a B<technology preview>."

How can a user know whether OP-TEE supports virtualization? Is it 
configurable at build?

Cheers,

-- 
Julien Grall

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