LSM: LoadPin: provide enablement CONFIG

Instead of being enabled by default when SECURITY_LOADPIN is selected,
provide an additional (default off) config to determine the boot time
behavior. As before, the "loadpin.enabled=0/1" kernel parameter remains
available.

Suggested-by: James Morris <jmorris@namei.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: James Morris <james.l.morris@oracle.com>

2 files changed, 15 insertions, 6 deletions

diff --git a/security/loadpin/Kconfig b/security/loadpin/Kconfig
index c668ac4eda65..dd01aa91e521 100644
--- a/security/loadpin/Kconfig
+++ b/security/loadpin/Kconfig
@@ -3,8 +3,17 @@ config SECURITY_LOADPIN
         depends on SECURITY && BLOCK
         help
           Any files read through the kernel file reading interface
-          (kernel modules, firmware, kexec images, security policy) will
-          be pinned to the first filesystem used for loading. Any files
-          that come from other filesystems will be rejected. This is best
-          used on systems without an initrd that have a root filesystem
-          backed by a read-only device such as dm-verity or a CDROM.
+          (kernel modules, firmware, kexec images, security policy)
+          can be pinned to the first filesystem used for loading. When
+          enabled, any files that come from other filesystems will be
+          rejected. This is best used on systems without an initrd that
+          have a root filesystem backed by a read-only device such as
+          dm-verity or a CDROM.
+
+config SECURITY_LOADPIN_ENABLED
+        bool "Enforce LoadPin at boot"
+        depends on SECURITY_LOADPIN
+        help
+          If selected, LoadPin will enforce pinning at boot. If not
+          selected, it can be enabled at boot with the kernel parameter
+          "loadpin.enabled=1".
diff --git a/security/loadpin/loadpin.c b/security/loadpin/loadpin.c
index e4debae3c4d6..89a46f10b8a7 100644
--- a/security/loadpin/loadpin.c
+++ b/security/loadpin/loadpin.c
@@ -45,7 +45,7 @@ static void report_load(const char *origin, struct file *file, char *operation)
         kfree(pathname);
 }
 
-static int enabled = 1;
+static int enabled = IS_ENABLED(CONFIG_SECURITY_LOADPIN_ENABLED);
 static struct super_block *pinned_root;
 static DEFINE_SPINLOCK(pinned_root_spinlock);