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@xxxxxxxxxxxxxx> Signed-off-by: Mickaël Salaün <mic@xxxxxxxxxxx> Link: https://lore.kernel.org/r/20220513112743.156414-1-mic@xxxxxxxxxxx --- Changes since v1: * Move the checking subsection at the beginning (suggested by Paul Moore) and merge the two configuration subsections. * Use both dmesg and journalctl to handle cases where journald is not installed or when the kernel log buffer is full. * Add reference to the syscall check (ABI section). * Improve explanations. * Update copyright date. --- Documentation/userspace-api/landlock.rst | 29 +++++++++++++++++++++++- 1 file changed, 28 insertions(+), 1 deletion(-) diff --git a/Documentation/userspace-api/landlock.rst b/Documentation/userspace-api/landlock.rst index 7b4fe6218132..b8ea59493964 100644 --- a/Documentation/userspace-api/landlock.rst +++ b/Documentation/userspace-api/landlock.rst @@ -1,7 +1,7 @@ .. SPDX-License-Identifier: GPL-2.0 .. Copyright © 2017-2020 Mickaël Salaün <mic@xxxxxxxxxxx> .. Copyright © 2019-2020 ANSSI -.. Copyright © 2021 Microsoft Corporation +.. Copyright © 2021-2022 Microsoft Corporation ===================================== Landlock: unprivileged access control @@ -18,6 +18,13 @@ is expected to help mitigate the security impact of bugs or unexpected/malicious behaviors in user space applications. Landlock empowers any process, including unprivileged ones, to securely restrict themselves. +We can quickly make sure that Landlock is enabled in the running system by +looking for "landlock: Up and running" in kernel logs (as root): ``dmesg | grep +landlock || journalctl -kg landlock`` . Developers can also easily check for +Landlock support with a :ref:`related system call <landlock_abi_versions>`. If +Landlock is not currently supported, we need to :ref:`configure the kernel +appropriately <kernel_support>`. + Landlock rules ============== @@ -264,6 +271,8 @@ users, and because they may use different kernel versions, it is strongly encouraged to follow a best-effort security approach by checking the Landlock ABI version at runtime and only enforcing the supported features. +.. _landlock_abi_versions: + Landlock ABI versions --------------------- @@ -388,6 +397,24 @@ 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. +.. _kernel_support: + +Kernel support +============== + +Landlock was first introduced in Linux 5.13 but it must be configured at build +time with `CONFIG_SECURITY_LANDLOCK=y`. Landlock must also be enabled at boot +time as the other security modules. The list of security modules enabled by +default is set with `CONFIG_LSM`. The kernel configuration should then +contains `CONFIG_LSM=landlock,[...]` with `[...]` as the list of other +potentially useful security modules for the running system (see the +`CONFIG_LSM` help). + +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 thanks to the bootloader +configuration. + Questions and answers ===================== base-commit: 67761d8181f0fb9dbd264caa5b6408dbc0d8e86a -- 2.36.0
