[PATCH v3 2/3] ima: replace arch-specific get_sb_mode() with a common helper ima_get_efi_secureboot()

[Chester Lin]

remove the get_sb_mode() from x86/kernel/ima_arch.c and create a common
helper ima_get_efi_secureboot() in IMA so that all EFI-based architectures
can refer to the same procedure.

Signed-off-by: Chester Lin <clin@xxxxxxxx>
---
 arch/x86/kernel/ima_arch.c       | 69 +++++++-------------------------
 include/linux/ima.h              | 10 +++++
 security/integrity/ima/Makefile  |  1 +
 security/integrity/ima/ima_efi.c | 26 ++++++++++++
 4 files changed, 51 insertions(+), 55 deletions(-)
 create mode 100644 security/integrity/ima/ima_efi.c

diff --git a/arch/x86/kernel/ima_arch.c b/arch/x86/kernel/ima_arch.c
index 7dfb1e808928..2c773532ff0a 100644
--- a/arch/x86/kernel/ima_arch.c
+++ b/arch/x86/kernel/ima_arch.c
@@ -8,69 +8,28 @@
 
 extern struct boot_params boot_params;
 
-static enum efi_secureboot_mode get_sb_mode(void)
-{
-	efi_guid_t efi_variable_guid = EFI_GLOBAL_VARIABLE_GUID;
-	efi_status_t status;
-	unsigned long size;
-	u8 secboot, setupmode;
-
-	size = sizeof(secboot);
-
-	if (!efi_rt_services_supported(EFI_RT_SUPPORTED_GET_VARIABLE)) {
-		pr_info("ima: secureboot mode unknown, no efi\n");
-		return efi_secureboot_mode_unknown;
-	}
-
-	/* Get variable contents into buffer */
-	status = efi.get_variable(L"SecureBoot", &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;
-	}
-
-	size = sizeof(setupmode);
-	status = efi.get_variable(L"SetupMode", &efi_variable_guid,
-				  NULL, &size, &setupmode);
-
-	if (status != EFI_SUCCESS)	/* ignore unknown SetupMode */
-		setupmode = 0;
-
-	if (secboot == 0 || setupmode == 1) {
-		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)
 {
-	static enum efi_secureboot_mode sb_mode;
-	static bool initialized;
-
-	if (!initialized && efi_enabled(EFI_BOOT)) {
-		sb_mode = boot_params.secure_boot;
+	static bool sb_enabled, initialized;
 
-		if (sb_mode == efi_secureboot_mode_unset)
-			sb_mode = get_sb_mode();
+	if (initialized) {
+		return sb_enabled;
+	} else if (efi_enabled(EFI_BOOT)) {
 		initialized = true;
+
+		if (boot_params.secure_boot == efi_secureboot_mode_unset) {
+			sb_enabled = ima_get_efi_secureboot();
+			return sb_enabled;
+		}
 	}
 
-	if (sb_mode == efi_secureboot_mode_enabled)
-		return true;
-	else
-		return false;
+	if (boot_params.secure_boot == efi_secureboot_mode_enabled)
+		sb_enabled = true;
+
+	return sb_enabled;
 }
 
-/* secureboot arch rules */
+/* secure and trusted boot arch rules */
 static const char * const sb_arch_rules[] = {
 #if !IS_ENABLED(CONFIG_KEXEC_SIG)
 	"appraise func=KEXEC_KERNEL_CHECK appraise_type=imasig",
diff --git a/include/linux/ima.h b/include/linux/ima.h
index 8fa7bcfb2da2..9f9699f017be 100644
--- a/include/linux/ima.h
+++ b/include/linux/ima.h
@@ -50,6 +50,16 @@ static inline const char * const *arch_get_ima_policy(void)
 }
 #endif
 
+#if defined(CONFIG_EFI) && defined(CONFIG_IMA_SECURE_AND_OR_TRUSTED_BOOT)
+extern bool ima_get_efi_secureboot(void);
+#else
+static inline bool ima_get_efi_secureboot(void)
+{
+	return false;
+}
+#endif
+
+
 #else
 static inline int ima_bprm_check(struct linux_binprm *bprm)
 {
diff --git a/security/integrity/ima/Makefile b/security/integrity/ima/Makefile
index 67dabca670e2..32076b3fd292 100644
--- a/security/integrity/ima/Makefile
+++ b/security/integrity/ima/Makefile
@@ -14,3 +14,4 @@ ima-$(CONFIG_HAVE_IMA_KEXEC) += ima_kexec.o
 ima-$(CONFIG_IMA_BLACKLIST_KEYRING) += ima_mok.o
 ima-$(CONFIG_IMA_MEASURE_ASYMMETRIC_KEYS) += ima_asymmetric_keys.o
 ima-$(CONFIG_IMA_QUEUE_EARLY_BOOT_KEYS) += ima_queue_keys.o
+ima-$(CONFIG_EFI) += ima_efi.o
diff --git a/security/integrity/ima/ima_efi.c b/security/integrity/ima/ima_efi.c
new file mode 100644
index 000000000000..a78f66e19689
--- /dev/null
+++ b/security/integrity/ima/ima_efi.c
@@ -0,0 +1,26 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2020 SUSE LLC
+ *
+ * Author:
+ * Chester Lin <clin@xxxxxxxx>
+ */
+
+#include <linux/efi.h>
+#include <linux/ima.h>
+
+#ifdef CONFIG_IMA_SECURE_AND_OR_TRUSTED_BOOT
+bool ima_get_efi_secureboot(void)
+{
+	enum efi_secureboot_mode sb_mode;
+
+	if (!efi_rt_services_supported(EFI_RT_SUPPORTED_GET_VARIABLE)) {
+		pr_info("ima: secureboot mode unknown, no efi\n");
+		return false;
+	}
+
+	sb_mode = efi_get_secureboot(efi.get_variable);
+
+	return (sb_mode == efi_secureboot_mode_enabled) ? true : false;
+}
+#endif
-- 
2.28.0