efivars: respect EFI_UNSUPPORTED return from firmware

As per UEFI spec 2.8B section 8.2, EFI_UNSUPPORTED may be returned by
EFI variable runtime services if no variable storage is supported by
firmware.  In this case, there is no point for kernel to continue
efivars initialization.  That said, efivar_init() should fail by
returning an error code, so that efivarfs will not be mounted on
/sys/firmware/efi/efivars at all.  Otherwise, user space like efibootmgr
will be confused by the EFIVARFS_MAGIC seen there, while EFI variable
calls cannot be made successfully.

Cc: <stable@vger.kernel.org> # v5.10+
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

diff --git a/drivers/firmware/efi/vars.c b/drivers/firmware/efi/vars.c
index 41c1d00bf933c682d45144880c0ba1099057603b..abdc8a6a396318a915455dd73e26439b88c1b003 100644 (file)
--- a/drivers/firmware/efi/vars.c
+++ b/drivers/firmware/efi/vars.c
@@ -484,6 +484,10 @@ int efivar_init(int (*func)(efi_char16_t *, efi_guid_t, unsigned long, void *),
                                }
                        }
 
+                       break;
+               case EFI_UNSUPPORTED:
+                       err = -EOPNOTSUPP;
+                       status = EFI_NOT_FOUND;
                        break;
                case EFI_NOT_FOUND:
                        break;