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

[Ard Biesheuvel]

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

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