[PATCH v1] landlock: Explain how to support Landlock

[Mickaël Salaün]

Let's help users by documenting how to enable and check for Landlock in
the kernel and the running system.  The userspace-api section may not be
the best place for this but it still makes sense to put all the user
documentation at the same place.

Cc: Paul Moore <paul at paul-moore.com>
Signed-off-by: Mickaël Salaün <mic at digikod.net>
Link: https://lore.kernel.org/r/20220512120847.124822-1-mic@digikod.net
---
 Documentation/userspace-api/landlock.rst | 26 ++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/Documentation/userspace-api/landlock.rst b/Documentation/userspace-api/landlock.rst
index 7b4fe6218132..e69dbddcc191 100644
--- a/Documentation/userspace-api/landlock.rst
+++ b/Documentation/userspace-api/landlock.rst
@@ -388,6 +388,32 @@ Starting with the Landlock ABI version 2, it is now possible to securely
 control renaming and linking thanks to the new `LANDLOCK_ACCESS_FS_REFER`
 access right.
 
+Landlock support
+================
+
+Kernel configuration
+--------------------
+
+Landlock can be supported since Linux 5.13 but it must be configured in the
+kernel with `CONFIG_SECURITY_LANDLOCK=y`, and it should be enabled at boot time
+with `CONFIG_LSM=landlock,[...]`.  The `[...]` must be replaced with the list
+of LSMs that may be useful for the running system (see the `CONFIG_LSM` help).
+
+Running system configuration
+----------------------------
+
+If the running kernel doesn't have `landlock` in `CONFIG_LSM`, then we can
+still enable it by adding `lsm=landlock,[...]` to
+Documentation/admin-guide/kernel-parameters.rst. The `[...]` must be replaced
+with the list of LSMs that may be useful for the running system (see the
+`CONFIG_LSM` help).
+
+Running system check
+--------------------
+
+We can check that Landlock is enabled by looking for "landlock: Up and running"
+in kernel logs: `dmesg | grep landlock`
+
 Questions and answers
 =====================
 

base-commit: 67761d8181f0fb9dbd264caa5b6408dbc0d8e86a
-- 
2.36.0