efi: x86/xen: switch to efi_get_secureboot_mode helper

Now that we have a static inline helper to discover the platform's secure
boot mode that can be shared between the EFI stub and the kernel proper,
switch to it, and drop some comments about keeping them in sync manually.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

arch/x86/xen/efi.c

@@ -93,37 +93,22 @@ static efi_system_table_t __init *xen_efi_probe(void)
 
 /*
  * Determine whether we're in secure boot mode.
- *
- * Please keep the logic in sync with
- * drivers/firmware/efi/libstub/secureboot.c:efi_get_secureboot().
  */
 static enum efi_secureboot_mode xen_efi_get_secureboot(void)
 {
-	static efi_guid_t efi_variable_guid = EFI_GLOBAL_VARIABLE_GUID;
 	static efi_guid_t shim_guid = EFI_SHIM_LOCK_GUID;
+	enum efi_secureboot_mode mode;
 	efi_status_t status;
-	u8 moksbstate, secboot, setupmode;
+	u8 moksbstate;
 	unsigned long size;
 
-	size = sizeof(secboot);
-	status = efi.get_variable(L"SecureBoot", &efi_variable_guid,
-				  NULL, &size, &secboot);
-
-	if (status == EFI_NOT_FOUND)
-		return efi_secureboot_mode_disabled;
-
-	if (status != EFI_SUCCESS)
-		goto out_efi_err;
-
-	size = sizeof(setupmode);
-	status = efi.get_variable(L"SetupMode", &efi_variable_guid,
-				  NULL, &size, &setupmode);
-
-	if (status != EFI_SUCCESS)
-		goto out_efi_err;
-
-	if (secboot == 0 || setupmode == 1)
-		return efi_secureboot_mode_disabled;
+	mode = efi_get_secureboot_mode(efi.get_variable);
+	if (mode == efi_secureboot_mode_unknown) {
+		pr_err("Could not determine UEFI Secure Boot status.\n");
+		return efi_secureboot_mode_unknown;
+	}
+	if (mode != efi_secureboot_mode_enabled)
+		return mode;
 
 	/* See if a user has put the shim into insecure mode. */
 	size = sizeof(moksbstate);
@@ -140,10 +125,6 @@ static enum efi_secureboot_mode xen_efi_get_secureboot(void)
  secure_boot_enabled:
 	pr_info("UEFI Secure Boot is enabled.\n");
 	return efi_secureboot_mode_enabled;
-
- out_efi_err:
-	pr_err("Could not determine UEFI Secure Boot status.\n");
-	return efi_secureboot_mode_unknown;
 }
 
 void __init xen_efi_init(struct boot_params *boot_params)

drivers/firmware/efi/libstub/secureboot.c

@@ -24,9 +24,6 @@ static efi_status_t get_var(efi_char16_t *name, efi_guid_t *vendor, u32 *attr,
 
 /*
  * Determine whether we're in secure boot mode.
- *
- * Please keep the logic in sync with
- * arch/x86/xen/efi.c:xen_efi_get_secureboot().
  */
 enum efi_secureboot_mode efi_get_secureboot(void)
 {