fwts: RuntimeServicesSupported variable

[Heinrich Schuchardt]

On 14.10.20 19:58, Ard Biesheuvel wrote:
> On Wed, 14 Oct 2020 at 19:45, Heinrich Schuchardt <xypron.glpk at gmx.de> wrote:
>>
>> On 14.10.20 19:31, Heinrich Schuchardt wrote:
>>> Dear all,
>>>
>>> the fwts fails on U-Boot due to testing for a non-existent
>>> RuntimeServicesSupported variable.
>>>
>>> If you look at the UEFI specification 2.8 (Errata B) [1] you will
>>> discover in the change log:
>>>
>>> 2.8 A2049
>>> RuntimeServicesSupported EFI variable should be a config table
>>> February 2020
>>>
>>> Please, read the configuration table to determine if a runtime service
>>> is available on UEFI 2.8 systems.
>>>
>>> On lower UEFI firmware version neither the variable nor the table exists.
>>>
>>> Best regards
>>>
>>> Heinrich
>>>
>>> [1] UEFI Specification Version 2.8 (Errata B) (released June 2020),
>>> https://uefi.org/sites/default/files/resources/UEFI%20Spec%202.8B%20May%202020.pdf
>>>
>>
>> Hello Ard,
>>
>> what is your idea how the EFI_RT_PROPERTIES_TABLE shall be exposed to
>> the efi_test driver?
>>
>> Will the EFI runtime wrapper simply return EFI_UNSUPPORTED if the
>> function is not marked as supported in the table? Or will the
>> configuration table itself be make available?
>>
>
> The UEFI spec permits that runtime services return EFI_UNSUPPORTED at
> runtime, but requires that they are marked as such in the
> EFI_RT_PROPERTIES_TABLE.
>
> So assuming that the purpose of efi_test is compliance with the spec,
> it should only allow EFI_UNSUPPORTED as a return value for each of the
> tested runtime services if it is omitted from
> efi.runtime_supported_mask.
>
> Since the efi_test ioctl returns both an error code and the actual EFI
> status code, we should only fail the call on a EFI_UNSUPPORTED status
> code if the RTPROP mask does not allow that.
>
> E.g.,
>
> --- a/drivers/firmware/efi/test/efi_test.c
> +++ b/drivers/firmware/efi/test/efi_test.c
> @@ -265,7 +265,12 @@ static long efi_runtime_set_variable(unsigned long arg)
>                 goto out;
>         }
>
> -       rv = status == EFI_SUCCESS ? 0 : -EINVAL;
> +       if (status == EFI_SUCCESS ||
> +           (status == EFI_UNSUPPORTED &&
> +            !efi_rt_services_supported(EFI_RT_SUPPORTED_SET_VARIABLE)))
> +               rv = 0;
> +       else
> +               rv = -EINVAL;
>
>  out:
>         kfree(data);
>
>
> Do you think that could work?
>

The current fwts implementation assumes that EFI_UNSUPPORTED leads to
ioctl() returning -1. This value should not be changed. It would be
preferable to use another error code than -EINVAL, e.g. -EDOM if there
is a mismatch with the EFI_RT_PROPERTIES_TABLE configuration table. Then
a future verision of fwts can evaluate errno to discover the problem.

Do I read you correctly: the EFI runtime wrapper does not fend of calls
to runtime services marked as disallowed in EFI_RT_PROPERTIES_TABLE?
Directly returning an error code might help to avoid crashes on
non-compliant firmware.

Best regards

Heinrich