x86/ima: define arch_ima_get_secureboot

Distros are concerned about totally disabling the kexec_load syscall.
As a compromise, the kexec_load syscall will only be disabled when
CONFIG_KEXEC_VERIFY_SIG is configured and the system is booted with
secureboot enabled.

This patch defines the new arch specific function called
arch_ima_get_secureboot() to retrieve the secureboot state of the system.

Signed-off-by: Nayna Jain <nayna@linux.ibm.com>
Suggested-by: Seth Forshee <seth.forshee@canonical.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Peter Jones <pjones@redhat.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Dave Young <dyoung@redhat.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

arch/x86/kernel/Makefile

@@ -150,3 +150,5 @@ ifeq ($(CONFIG_X86_64),y)
 	obj-$(CONFIG_MMCONF_FAM10H)	+= mmconf-fam10h_64.o
 	obj-y				+= vsmp_64.o
 endif
+
+obj-$(CONFIG_IMA)			+= ima_arch.o

arch/x86/kernel/ima_arch.c

@@ -0,0 +1,17 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Copyright (C) 2018 IBM Corporation
+ */
+#include <linux/efi.h>
+#include <linux/ima.h>
+
+extern struct boot_params boot_params;
+
+bool arch_ima_get_secureboot(void)
+{
+	if (efi_enabled(EFI_BOOT) &&
+		(boot_params.secure_boot == efi_secureboot_mode_enabled))
+		return true;
+	else
+		return false;
+}

include/linux/ima.h

@@ -30,6 +30,15 @@ extern void ima_post_path_mknod(struct dentry *dentry);
 extern void ima_add_kexec_buffer(struct kimage *image);
 #endif
 
+#ifdef CONFIG_X86
+extern bool arch_ima_get_secureboot(void);
+#else
+static inline bool arch_ima_get_secureboot(void)
+{
+	return false;
+}
+#endif
+
 #else
 static inline int ima_bprm_check(struct linux_binprm *bprm)
 {