[PATCH bpf-next 2/4] security: Generate a header with the count of enabled LSMs

[KP Singh <kpsingh@kernel.org>]

The header defines a MAX_LSM_COUNT constant which is used in a
subsequent patch to generate the static calls for each LSM hook which
are named using preprocessor token pasting. Since token pasting does not
work with arithmetic expressions, generate a simple lsm_count.h header
which represents the subset of LSMs that can be enabled on a given
kernel based on the config.

While one can generate static calls for all the possible LSMs that the
kernel has, this is actually wasteful as most kernels only enable a
handful of LSMs.

Signed-off-by: KP Singh <kpsingh@kernel.org>
---
 scripts/Makefile                 |  1 +
 scripts/security/.gitignore      |  1 +
 scripts/security/Makefile        |  4 +++
 scripts/security/gen_lsm_count.c | 57 ++++++++++++++++++++++++++++++++
 security/Makefile                | 11 ++++++
 5 files changed, 74 insertions(+)
 create mode 100644 scripts/security/.gitignore
 create mode 100644 scripts/security/Makefile
 create mode 100644 scripts/security/gen_lsm_count.c

diff --git a/scripts/Makefile b/scripts/Makefile
index 1575af84d557..9712249c0fb3 100644
--- a/scripts/Makefile
+++ b/scripts/Makefile
@@ -41,6 +41,7 @@ targets += module.lds
 subdir-$(CONFIG_GCC_PLUGINS) += gcc-plugins
 subdir-$(CONFIG_MODVERSIONS) += genksyms
 subdir-$(CONFIG_SECURITY_SELINUX) += selinux
+subdir-$(CONFIG_SECURITY) += security
 
 # Let clean descend into subdirs
 subdir-	+= basic dtc gdb kconfig mod
diff --git a/scripts/security/.gitignore b/scripts/security/.gitignore
new file mode 100644
index 000000000000..684af16735f1
--- /dev/null
+++ b/scripts/security/.gitignore
@@ -0,0 +1 @@
+gen_lsm_count
diff --git a/scripts/security/Makefile b/scripts/security/Makefile
new file mode 100644
index 000000000000..05f7e4109052
--- /dev/null
+++ b/scripts/security/Makefile
@@ -0,0 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0
+hostprogs-always-y += gen_lsm_count
+HOST_EXTRACFLAGS += \
+	-I$(srctree)/include/uapi -I$(srctree)/include
diff --git a/scripts/security/gen_lsm_count.c b/scripts/security/gen_lsm_count.c
new file mode 100644
index 000000000000..a9a227724d84
--- /dev/null
+++ b/scripts/security/gen_lsm_count.c
@@ -0,0 +1,57 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/* NOTE: we really do want to use the kernel headers here */
+#define __EXPORTED_HEADERS__
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+#include <errno.h>
+#include <ctype.h>
+
+#include <linux/kconfig.h>
+
+#define GEN_MAX_LSM_COUNT (				\
+	/* Capabilities */				\
+	IS_ENABLED(CONFIG_SECURITY) +			\
+	IS_ENABLED(CONFIG_SECURITY_SELINUX) +		\
+	IS_ENABLED(CONFIG_SECURITY_SMACK) +		\
+	IS_ENABLED(CONFIG_SECURITY_TOMOYO) +		\
+	IS_ENABLED(CONFIG_SECURITY_APPARMOR) +		\
+	IS_ENABLED(CONFIG_SECURITY_YAMA) +		\
+	IS_ENABLED(CONFIG_SECURITY_LOADPIN) +		\
+	IS_ENABLED(CONFIG_SECURITY_SAFESETID) +		\
+	IS_ENABLED(CONFIG_SECURITY_LOCKDOWN_LSM) + 	\
+	IS_ENABLED(CONFIG_BPF_LSM) + \
+	IS_ENABLED(CONFIG_SECURITY_LANDLOCK))
+
+const char *progname;
+
+static void usage(void)
+{
+	printf("usage: %s lsm_count.h\n", progname);
+	exit(1);
+}
+
+int main(int argc, char *argv[])
+{
+	FILE *fout;
+
+	progname = argv[0];
+
+	if (argc < 2)
+		usage();
+
+	fout = fopen(argv[1], "w");
+	if (!fout) {
+		fprintf(stderr, "Could not open %s for writing:  %s\n",
+			argv[1], strerror(errno));
+		exit(2);
+	}
+
+	fprintf(fout, "#ifndef _LSM_COUNT_H_\n#define _LSM_COUNT_H_\n\n");
+	fprintf(fout, "\n#define MAX_LSM_COUNT %d\n", GEN_MAX_LSM_COUNT);
+	fprintf(fout, "#endif /* _LSM_COUNT_H_ */\n");
+	exit(0);
+}
diff --git a/security/Makefile b/security/Makefile
index 18121f8f85cd..7a47174831f4 100644
--- a/security/Makefile
+++ b/security/Makefile
@@ -3,6 +3,7 @@
 # Makefile for the kernel security code
 #
 
+gen := include/generated
 obj-$(CONFIG_KEYS)			+= keys/
 
 # always enable default capabilities
@@ -27,3 +28,13 @@ obj-$(CONFIG_SECURITY_LANDLOCK)		+= landlock/
 
 # Object integrity file lists
 obj-$(CONFIG_INTEGRITY)			+= integrity/
+
+$(addprefix $(obj)/,$(obj-y)): $(gen)/lsm_count.h
+
+quiet_cmd_lsm_count = GEN     ${gen}/lsm_count.h
+      cmd_lsm_count = scripts/security/gen_lsm_count ${gen}/lsm_count.h
+
+targets += lsm_count.h
+
+${gen}/lsm_count.h: FORCE
+	$(call if_changed,lsm_count)
-- 
2.39.0.246.g2a6d74b583-goog