[PATCH v4 2/5] security: Count the LSMs enabled at compile time

[KP Singh]

These macros are a clever trick to determine a count of the number of
LSMs that are enabled in the config to ascertain the maximum number of
static calls that need to be configured per LSM hook.

Without this one would need to generate static calls for the total
number of LSMs in the kernel (even if they are not compiled) times the
number of LSM hooks which ends up being quite wasteful.

Suggested-by: Kui-Feng Lee <sinquersw at gmail.com>
Suggested-by: Andrii Nakryiko <andrii at kernel.org>
Acked-by: Song Liu <song at kernel.org>
Signed-off-by: KP Singh <kpsingh at kernel.org>
---
 include/linux/lsm_count.h | 107 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 107 insertions(+)
 create mode 100644 include/linux/lsm_count.h

diff --git a/include/linux/lsm_count.h b/include/linux/lsm_count.h
new file mode 100644
index 000000000000..4d6dac6efb75
--- /dev/null
+++ b/include/linux/lsm_count.h
@@ -0,0 +1,107 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/*
+ * Copyright (C) 2023 Google LLC.
+ */
+
+#ifndef __LINUX_LSM_COUNT_H
+#define __LINUX_LSM_COUNT_H
+
+#include <linux/args.h>
+
+#ifdef CONFIG_SECURITY
+
+/*
+ * Macros to count the number of LSMs enabled in the kernel at compile time.
+ */
+
+/*
+ * Capabilities is enabled when CONFIG_SECURITY is enabled.
+ */
+#if IS_ENABLED(CONFIG_SECURITY)
+#define CAPABILITIES_ENABLED 1,
+#else
+#define CAPABILITIES_ENABLED
+#endif
+
+#if IS_ENABLED(CONFIG_SECURITY_SELINUX)
+#define SELINUX_ENABLED 1,
+#else
+#define SELINUX_ENABLED
+#endif
+
+#if IS_ENABLED(CONFIG_SECURITY_SMACK)
+#define SMACK_ENABLED 1,
+#else
+#define SMACK_ENABLED
+#endif
+
+#if IS_ENABLED(CONFIG_SECURITY_APPARMOR)
+#define APPARMOR_ENABLED 1,
+#else
+#define APPARMOR_ENABLED
+#endif
+
+#if IS_ENABLED(CONFIG_SECURITY_TOMOYO)
+#define TOMOYO_ENABLED 1,
+#else
+#define TOMOYO_ENABLED
+#endif
+
+#if IS_ENABLED(CONFIG_SECURITY_YAMA)
+#define YAMA_ENABLED 1,
+#else
+#define YAMA_ENABLED
+#endif
+
+#if IS_ENABLED(CONFIG_SECURITY_LOADPIN)
+#define LOADPIN_ENABLED 1,
+#else
+#define LOADPIN_ENABLED
+#endif
+
+#if IS_ENABLED(CONFIG_SECURITY_LOCKDOWN_LSM)
+#define LOCKDOWN_ENABLED 1,
+#else
+#define LOCKDOWN_ENABLED
+#endif
+
+#if IS_ENABLED(CONFIG_BPF_LSM)
+#define BPF_LSM_ENABLED 1,
+#else
+#define BPF_LSM_ENABLED
+#endif
+
+#if IS_ENABLED(CONFIG_SECURITY_LANDLOCK)
+#define LANDLOCK_ENABLED 1,
+#else
+#define LANDLOCK_ENABLED
+#endif
+
+/*
+ *  There is a trailing comma that we need to be accounted for. This is done by
+ *  using a skipped argument in __COUNT_LSMS
+ */
+#define __COUNT_LSMS(skipped_arg, args...) COUNT_ARGS(args)
+#define COUNT_LSMS(args...) __COUNT_LSMS(args)
+
+#define MAX_LSM_COUNT			\
+	COUNT_LSMS(			\
+		CAPABILITIES_ENABLED	\
+		SELINUX_ENABLED		\
+		SMACK_ENABLED		\
+		APPARMOR_ENABLED	\
+		TOMOYO_ENABLED		\
+		YAMA_ENABLED		\
+		LOADPIN_ENABLED		\
+		LOCKDOWN_ENABLED	\
+		BPF_LSM_ENABLED		\
+		LANDLOCK_ENABLED)
+
+#else
+
+#define MAX_LSM_COUNT 0
+
+#endif /* CONFIG_SECURITY */
+
+#endif  /* __LINUX_LSM_COUNT_H */
-- 
2.42.0.515.g380fc7ccd1-goog