[PATCH] efi: Override runtime supported mask from a EFI variable if present

[Ard Biesheuvel]

On Thu, 10 Nov 2022 at 15:37, Alexandru Elisei <alexandru.elisei at arm.com> wrote:
>
> Hi,
>
> On Wed, Nov 09, 2022 at 06:27:50PM +0100, Ard Biesheuvel wrote:
> > For debugging purposes, allow the runtime override mask to be set from a
> > EFI variable if one exists. For instance, the RT supported mask can be
> > set to 0xfffd to disable the SetTime() runtime service, and enable all
> > others:
> >
> >   echo -ne "\x7\0\0\0\xfd\xff" \
> >     > /sys/firmware/efi/efivars/LinuxRtMaskOverride-eb66918a-7eef-402a-842e-931d21c38ae9
>
> I'm really sorry, I applied this patch, but I couldn't find the file
> (LinuxRtMaskOverride*) under efivars, and couldn't find another way of
> setting the variable.
>

The variable will be created by writing to the file.

But no worries, I think we have enough context now. I've queued up the
patch that checks the SMBIOS record for Altra machines.


> >
> > Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
> > ---
> >  drivers/firmware/efi/efi.c | 12 +++++++++++-
> >  1 file changed, 11 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
> > index a46df5d1d0942751..faed1ef78c044924 100644
> > --- a/drivers/firmware/efi/efi.c
> > +++ b/drivers/firmware/efi/efi.c
> > @@ -367,7 +367,17 @@ static int __init efisubsys_init(void)
> >               }
> >       }
> >
> > -     if (efi_rt_services_supported(EFI_RT_SUPPORTED_TIME_SERVICES))
> > +     if (efi_rt_services_supported(EFI_RT_SUPPORTED_GET_VARIABLE)) {
> > +             unsigned long size = sizeof(efi.runtime_supported_mask);
> > +
> > +             if (efi.get_variable(L"LinuxRtMaskOverride",
> > +                                  &EFI_RT_PROPERTIES_TABLE_GUID, NULL, &size,
> > +                                  &efi.runtime_supported_mask) == EFI_SUCCESS)
> > +                     pr_info("Overriding runtime_supported_mask to 0x%x\n",
> > +                             efi.runtime_supported_mask);
> > +     }
> > +
> > +     if (efi_rt_services_supported(EFI_RT_SUPPORTED_GET_TIME))
> >               platform_device_register_simple("rtc-efi", 0, NULL, 0);
> >
> >       /* We register the efi directory at /sys/firmware/efi */
> > --
> > 2.35.1
> >