doc: ReSTify LoadPin.txt

Adjusts for ReST markup and moves under LSM admin guide.

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/admin-guide/LSM/LoadPin.rst

@@ -0,0 +1,21 @@
+=======
+LoadPin
+=======
+
+LoadPin is a Linux Security Module that ensures all kernel-loaded files
+(modules, firmware, etc) all originate from the same filesystem, with
+the expectation that such a filesystem is backed by a read-only device
+such as dm-verity or CDROM. This allows systems that have a verified
+and/or unchangeable filesystem to enforce module and firmware loading
+restrictions without needing to sign the files individually.
+
+The LSM is selectable at build-time with ``CONFIG_SECURITY_LOADPIN``, and
+can be controlled at boot-time with the kernel command line option
+"``loadpin.enabled``". By default, it is enabled, but can be disabled at
+boot ("``loadpin.enabled=0``").
+
+LoadPin starts pinning when it sees the first file loaded. If the
+block device backing the filesystem is not read-only, a sysctl is
+created to toggle pinning: ``/proc/sys/kernel/loadpin/enabled``. (Having
+a mutable filesystem means pinning is mutable too, but having the
+sysctl allows for easy testing on systems with a mutable filesystem.)

Documentation/admin-guide/LSM/index.rst

@@ -34,6 +34,7 @@ the one "major" module (e.g. SELinux) if there is one configured.
    :maxdepth: 1
 
    apparmor
+   LoadPin
    SELinux
    tomoyo
    Yama