efi: Add EFI_SECURE_BOOT bit

UEFI machines can be booted in Secure Boot mode.  Add a EFI_SECURE_BOOT bit
that can be passed to efi_enabled() to find out whether secure boot is
enabled.

This will be used by the SysRq+x handler, registered by the x86 arch, to find
out whether secure boot mode is enabled so that it can be disabled.
Signed-off-by: Josh Boyer <jwboyer@fedoraproject.org>
Signed-off-by: David Howells <dhowells@redhat.com>

arch/x86/kernel/setup.c

@@ -1160,6 +1160,11 @@ void __init setup_arch(char **cmdline_p)
 
 	io_delay_init();
 
+	if (IS_ENABLED(CONFIG_EFI) && boot_params.secure_boot) {
+		set_bit(EFI_SECURE_BOOT, &efi.flags);
+		pr_info("Secure boot enabled\n");
+	}
+
 	/*
 	 * Parse the ACPI tables for possible boot-time SMP configuration.
 	 */

include/linux/efi.h

@@ -1066,6 +1066,7 @@ extern int __init efi_setup_pcdp_console(char *);
 #define EFI_ARCH_1		7	/* First arch-specific bit */
 #define EFI_DBG			8	/* Print additional debug info at runtime */
 #define EFI_NX_PE_DATA		9	/* Can runtime data regions be mapped non-executable? */
+#define EFI_SECURE_BOOT		10	/* Are we in Secure Boot mode? */
 
 #ifdef CONFIG_EFI
 /*