Documentation/admin-guide/LSM/ipe.rst

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Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

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.. SPDX-License-Identifier: GPL-2.0

Integrity Policy Enforcement (IPE)
==================================

.. NOTE::

   This is the documentation for admins, system builders, or individuals
   attempting to use IPE. If you're looking for more developer-focused
   documentation about IPE please see :doc:`the design docs </security/ipe>`.

Overview
--------

Integrity Policy Enforcement (IPE) is a Linux Security Module that takes a
complementary approach to access control. Unlike traditional access control
mechanisms that rely on labels and paths for decision-making, IPE focuses
on the immutable security properties inherent to system components. These
properties are fundamental attributes or features of a system component
that cannot be altered, ensuring a consistent and reliable basis for
security decisions.

To elaborate, in the context of IPE, system components primarily refer to
files or the devices these files reside on. However, this is just a
starting point. The concept of system components is flexible and can be
extended to include new elements as the system evolves. The immutable
properties include the origin of a file, which remains constant and
unchangeable over time. For example, IPE policies can be crafted to trust
files originating from the initramfs. Since initramfs is typically verified
by the bootloader, its files are deemed trustworthy; "file is from
initramfs" becomes an immutable property under IPE's consideration.

The immutable property concept extends to the security features enabled on
a file's origin, such as dm-verity or fs-verity, which provide a layer of
integrity and trust. For example, IPE allows the definition of policies
that trust files from a dm-verity protected device. dm-verity ensures the
integrity of an entire device by providing a verifiable and immutable state
of its contents. Similarly, fs-verity offers filesystem-level integrity
checks, allowing IPE to enforce policies that trust files protected by
fs-verity. These two features cannot be turned off once established, so
they are considered immutable properties. These examples demonstrate how
IPE leverages immutable properties, such as a file's origin and its
integrity protection mechanisms, to make access control decisions.

For the IPE policy, specifically, it grants the ability to enforce
stringent access controls by assessing security properties against
reference values defined within the policy. This assessment can be based on
the existence of a security property (e.g., verifying if a file originates
from initramfs) or evaluating the internal state of an immutable security
property. The latter includes checking the roothash of a dm-verity
protected device, determining whether dm-verity possesses a valid
signature, assessing the digest of a fs-verity protected file, or
determining whether fs-verity possesses a valid built-in signature. This
nuanced approach to policy enforcement enables a highly secure and
customizable system defense mechanism, tailored to specific security
requirements and trust models.

To enable IPE, ensure that ``CONFIG_SECURITY_IPE`` (under
:menuselection:`Security -> Integrity Policy Enforcement (IPE)`) config
option is enabled.

Use Cases
---------

IPE works best in fixed-function devices: devices in which their purpose
is clearly defined and not supposed to be changed (e.g. network firewall
device in a data center, an IoT device, etcetera), where all software and
configuration is built and provisioned by the system owner.

IPE is a long-way off for use in general-purpose computing: the Linux

Annotation

Implementation Notes