x86/ima: retry detecting secure boot mode

The secure boot mode may not be detected on boot for some reason (eg.
buggy firmware).  This patch attempts one more time to detect the
secure boot mode.
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

arch/x86/kernel/Makefile

@@ -151,4 +151,6 @@ ifeq ($(CONFIG_X86_64),y)
 	obj-y				+= vsmp_64.o
 endif
 
+ifdef CONFIG_EFI
 obj-$(CONFIG_IMA)			+= ima_arch.o
+endif

arch/x86/kernel/ima_arch.c

@@ -7,10 +7,52 @@
 
 extern struct boot_params boot_params;
 
+static enum efi_secureboot_mode get_sb_mode(void)
+{
+	efi_char16_t efi_SecureBoot_name[] = L"SecureBoot";
+	efi_guid_t efi_variable_guid = EFI_GLOBAL_VARIABLE_GUID;
+	efi_status_t status;
+	unsigned long size;
+	u8 secboot;
+
+	size = sizeof(secboot);
+
+	/* Get variable contents into buffer */
+	status = efi.get_variable(efi_SecureBoot_name, &efi_variable_guid,
+				  NULL, &size, &secboot);
+	if (status == EFI_NOT_FOUND) {
+		pr_info("ima: secureboot mode disabled\n");
+		return efi_secureboot_mode_disabled;
+	}
+
+	if (status != EFI_SUCCESS) {
+		pr_info("ima: secureboot mode unknown\n");
+		return efi_secureboot_mode_unknown;
+	}
+
+	if (secboot == 0) {
+		pr_info("ima: secureboot mode disabled\n");
+		return efi_secureboot_mode_disabled;
+	}
+
+	pr_info("ima: secureboot mode enabled\n");
+	return efi_secureboot_mode_enabled;
+}
+
 bool arch_ima_get_secureboot(void)
 {
-	if (efi_enabled(EFI_BOOT) &&
-		(boot_params.secure_boot == efi_secureboot_mode_enabled))
+	static enum efi_secureboot_mode sb_mode;
+	static bool initialized;
+
+	if (!initialized && efi_enabled(EFI_BOOT)) {
+		sb_mode = boot_params.secure_boot;
+
+		if (sb_mode == efi_secureboot_mode_unset)
+			sb_mode = get_sb_mode();
+		initialized = true;
+	}
+
+	if (sb_mode == efi_secureboot_mode_enabled)
 		return true;
 	else
 		return false;

include/linux/ima.h

@@ -30,7 +30,7 @@ extern void ima_post_path_mknod(struct dentry *dentry);
 extern void ima_add_kexec_buffer(struct kimage *image);
 #endif
 
-#ifdef CONFIG_X86
+#if defined(CONFIG_X86) && defined(CONFIG_EFI)
 extern bool arch_ima_get_secureboot(void);
 extern const char * const *arch_get_ima_policy(void);
 #else