[RFC][PATCH v2 01/12] diglim: Overview

[Roberto Sassu <roberto.sassu@huawei.com>]

Add an overview of DIGLIM to Documentation/security/diglim/introduction.rst
and the architecture to Documentation/security/diglim/architecture.rst

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 .../security/diglim/architecture.rst          |  45 ++
 Documentation/security/diglim/index.rst       |  11 +
 .../security/diglim/introduction.rst          | 631 ++++++++++++++++++
 Documentation/security/index.rst              |   1 +
 MAINTAINERS                                   |   9 +
 5 files changed, 697 insertions(+)
 create mode 100644 Documentation/security/diglim/architecture.rst
 create mode 100644 Documentation/security/diglim/index.rst
 create mode 100644 Documentation/security/diglim/introduction.rst

diff --git a/Documentation/security/diglim/architecture.rst b/Documentation/security/diglim/architecture.rst
new file mode 100644
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+.. SPDX-License-Identifier: GPL-2.0
+
+Architecture
+============
+
+This section introduces the high level architecture of DIGLIM.
+
+::
+
+ 5. add/delete from hash table and add refs to digest list
+        +---------------------------------------------+
+        |                            +-----+   +-------------+         +--+
+        |                            | key |-->| digest refs |-->...-->|  |
+        V                            +-----+   +-------------+         +--+
+ +-------------+                     +-----+   +-------------+
+ | digest list |                     | key |-->| digest refs |
+ |  (compact)  |                     +-----+   +-------------+
+ +-------------+                     +-----+   +-------------+
+        ^ 4. copy to                 | key |-->| digest refs |
+        |    kernel memory           +-----+   +-------------+ kernel space
+ --------------------------------------------------------------------------
+        ^                                          ^             user space
+        |<----------------+       3b. upload       |
+ +-------------+   +------------+                  | 6. query digest
+ | digest list |   | user space | 2b. convert
+ |  (compact)  |   |   parser   |
+ +-------------+   +------------+
+ 1a. upload               ^       1b. read
+                          |
+                   +------------+
+                   | RPM header |
+                   +------------+
+
+
+As mentioned before, digest lists can be uploaded directly if they are in
+the compact format (step 1a) or can be uploaded indirectly by the user
+space parser if they are in an alternative format (steps 1b-3b).
+
+During upload, the kernel makes a copy of the digest list to the kernel
+memory (step 4), and creates the necessary structures to index the digests
+(hash table and a linked list of digest list references to locate the
+digests in the digest list) (step 5).
+
+Finally, digests can be searched from user space through a securityfs file
+(step 6) or by the kernel itself.
diff --git a/Documentation/security/diglim/index.rst b/Documentation/security/diglim/index.rst
new file mode 100644
index 000000000000..0fc5ab019bc0
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+.. SPDX-License-Identifier: GPL-2.0
+
+======================================
+Digest Lists Integrity Module (DIGLIM)
+======================================
+
+.. toctree::
+   :maxdepth: 1
+
+   introduction
+   architecture
diff --git a/Documentation/security/diglim/introduction.rst b/Documentation/security/diglim/introduction.rst
new file mode 100644
index 000000000000..d8d8b2a17222
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+.. SPDX-License-Identifier: GPL-2.0
+
+Introduction
+============
+
+Digest Lists Integrity Module (DIGLIM) is a new component added to the
+integrity subsystem in the kernel, primarily aiming to aid Integrity
+Measurement Architecture (IMA) in the process of checking the integrity of
+file content and metadata. It accomplishes this task by storing reference
+values coming from software vendors and by reporting whether or not the
+digest of file content or metadata calculated by IMA (or EVM) is found
+among those values. In this way, IMA can decide, depending on the result of
+a query, if a measurement should be taken or access to the file should be
+granted. The `Security Assumptions`_ section explains more in detail why
+this component has been placed in the kernel.
+
+The main benefits of using IMA in conjunction with DIGLIM are the ability
+to implement advanced remote attestation schemes based on the usage of a
+TPM key for establishing a TLS secure channel [1][2], and to reduce the
+burden on Linux distribution vendors to extend secure boot at OS level to
+applications.
+
+DIGLIM does not have the complexity of feature-rich databases. In fact, its
+main functionality comes from the hash table primitives already in the
+kernel. It does not have an ad-hoc storage module, it just indexes data in
+a fixed format (digest lists, a set of concatenated digests preceded by a
+header), copied to kernel memory as they are. Lastly, it does not support
+database-oriented languages such as SQL, but only accepts a digest and its
+algorithm as a query.
+
+The only digest list format supported by DIGLIM is called ``compact``.
+However, Linux distribution vendors don't have to generate new digest lists
+in this format for the packages they release, as already available
+information, such as RPM headers and DEB package metadata, can be already
+used as a source for reference values (they already include file digests),
+with a user space parser taking care of the conversion to the compact
+format.
+
+Although one might perceive that storing file or metadata digests for a
+Linux distribution would significantly increase the memory usage, this does
+not seem to be the case. As an anticipation of the evaluation done in the
+`Preliminary Performance Evaluation`_ section, protecting binaries and
+shared libraries of a minimal Fedora 33 installation requires 208K of
+memory for the digest lists plus 556K for indexing.
+
+In exchange for a slightly increased memory usage, DIGLIM improves the
+performance of the integrity subsystem. In the considered scenario, IMA
+measurement and appraisal with digest lists requires respectively less than
+one quarter and less than half the time, compared to the current solution.
+
+DIGLIM also keeps track of whether digest lists have been processed in some
+way (e.g. measured or appraised by IMA). This is important for example for
+remote attestation, so that remote verifiers understand what has been
+uploaded to the kernel.
+
+DIGLIM behaves like a transactional database, i.e. it has the ability to
+roll back to the beginning of the transaction if an error occurred during
+the addition of a digest list (the deletion operation always succeeds).
+This capability has been tested with an ad-hoc fault injection mechanism
+capable of simulating failures during the operations.
+
+Finally, DIGLIM exposes to user space, through securityfs, the digest lists
+currently loaded, the number of digests added, a query interface and an
+interface to set digest list labels.
+
+[1] LSS EU 2019
+
+-   slides:
+    https://static.sched.com/hosted_files/lsseu2019/bd/secure_attested_communication_channels_lss_eu_2019.pdf
+-   video: https://youtu.be/mffdQgkvDNY
+
+[2] FutureTPM EU project, final review meeting demo
+
+-   slides:
+    https://futuretpm.eu/images/07-3-FutureTPM-Final-Review-Slides-WP6-Device-Management-Use-Case-HWDU.pdf
+-   video: https://vimeo.com/528251864/4c1d55abcd
+
+
+Binary Integrity
+----------------
+
+Integrity is a fundamental security property in information systems.
+Integrity could be described as the condition in which a generic
+component is just after it has been released by the entity that created it.
+
+One way to check whether a component is in this condition (called binary
+integrity) is to calculate its digest and to compare it with a reference
+value (i.e. the digest calculated in controlled conditions, when the
+component is released).
+
+IMA, a software part of the integrity subsystem, can perform such
+evaluation and execute different actions:
+
+- store the digest in an integrity-protected measurement list, so that it
+  can be sent to a remote verifier for analysis;
+- compare the calculated digest with a reference value (usually protected
+  with a signature) and deny operations if the file is found corrupted;
+- store the digest in the system log.
+
+
+Contribution
+------------
+
+DIGLIM further enhances the capabilities offered by IMA-based solutions
+and, at the same time, makes them more practical to adopt by reusing
+existing sources as reference values for integrity decisions.
+
+Possible sources for digest lists are:
+
+- RPM headers;
+- Debian repository metadata.
+
+
+Benefits for IMA Measurement
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+One of the issues that arises when files are measured by the OS is that,
+due to parallel execution, the order in which file accesses happen cannot
+be predicted. Since the TPM Platform Configuration Register (PCR) extend
+operation, executed after each file measurement, cryptographically binds
+the current measurement to the previous ones, the PCR value at the end of a
+workload cannot be predicted too.
+
+Thus, even if the usage of a TPM key, bound to a PCR value, should be
+allowed when only good files were accessed, the TPM could unexpectedly deny
+an operation on that key if files accesses did not happen as stated by the
+key policy (which allows only one of the possible sequences).
+
+DIGLIM solves this issue by making the PCR value stable over the time and
+not dependent on file accesses. The following figure depicts the current
+and the new approaches:
+
+::
+
+ IMA measurement list (current)
+
+ entry#        1st boot               2nd boot               3rd boot
+       +----+---------------+ +----+---------------+ +----+---------------+
+ 1:    | 10 | file1 measur. | | 10 | file3 measur. | | 10 | file2 measur. |
+       +----+---------------+ +----+---------------+ +----+---------------+
+ 2:    | 10 | file2 measur. | | 10 | file2 measur. | | 10 | file3 measur. |
+       +----+---------------+ +----+---------------+ +----+---------------+
+ 3:    | 10 | file3 measur. | | 10 | file1 measur. | | 10 | file4 measur. |
+       +----+---------------+ +----+---------------+ +----+---------------+
+
+ PCR:  Extend              != Extend              != Extend
+       file1, file2, file3    file3, file2, file1    file2, file3, file4
+
+
+ PCR Extend definition:
+
+       PCR(new value) = Hash(Hash(meas. entry), PCR(previous value))
+
+A new entry in the measurement list is created by IMA for each file access.
+Assuming that ``file1``, ``file2`` and ``file3`` are files provided by the
+software vendor, ``file4`` is an unknown file, the first two PCR values
+above represent a good system state, the third a bad system state. The PCR
+values are the result of the PCR extend operation performed for each
+measurement entry with the digest of the measurement entry as an input.
+
+::
+
+ IMA measurement list (with DIGLIM)
+
+ dlist
+ +--------------+
+ |    header    |
+ +--------------+
+ | file1 digest |
+ | file2 digest |
+ | file3 digest |
+ +--------------+
+
+``dlist`` is a digest list containing the digest of ``file1``, ``file2``
+and ``file3``. In the intended scenario, it is generated by a software
+vendor at the end of the building process, and retrieved by the
+administrator of the system where the digest list is loaded.
+
+::
+
+ entry#        1st boot               2nd boot               3rd boot
+       +----+---------------+ +----+---------------+ +----+---------------+
+ 0:    | 11 | dlist measur. | | 11 | dlist measur. | | 11 | dlist measur. |
+       +----+---------------+ +----+---------------+ +----+---------------+
+ 1:    < file1 measur. skip > < file3 measur. skip > < file2 measur. skip >
+
+ 2:    < file2 measur. skip > < file2 measur. skip > < file3 measur. skip >
+                                                     +----+---------------+
+ 3:    < file3 measur. skip > < file1 measur. skip > | 11 | file4 measur. |
+                                                     +----+---------------+
+
+ PCR:  Extend               = Extend              != Extend
+       dlist                  dlist                  dlist, file4
+
+
+The first entry in the measurement list contains the digest of the digest
+list uploaded to the kernel at kernel initialization time.
+
+When a file is accessed, IMA queries DIGLIM with the calculated file digest
+and, if it is found, IMA skips the measurement.
+
+Thus, the only information sent to remote verifiers are: the list of
+files that could possibly be accessed (from the digest list), but not if
+they were accessed and when; the measurement of unknown files.
+
+Despite providing less information, this solution has the advantage that
+the good system state (i.e. when only ``file1``, ``file2`` and ``file3``
+are accessed) now can be represented with a deterministic PCR value (the
+PCR is extended only with the measurement of the digest list). Also, the
+bad system state can still be distinguished from the good state (the PCR is
+extended also with the measurement of ``file4``).
+
+If a TPM key is bound to the good PCR value, the TPM would allow the key to
+be used if ``file1``, ``file2`` or ``file3`` are accessed, regardless of
+the sequence in which they are accessed (the PCR value does not change),
+and would revoke the permission when the unknown ``file4`` is accessed (the
+PCR value changes). If a system is able to establish a TLS connection with
+a peer, this implicitly means that the system was in a good state (i.e.
+``file4`` was not accessed, otherwise the TPM would have denied the usage
+of the TPM key due to the key policy).
+
+
+Benefits for IMA Appraisal
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Extending secure boot to applications means being able to verify the
+provenance of files accessed. IMA does it by verifying file signatures with
+a key that it trusts, which requires Linux distribution vendors to
+additionally include in the package header a signature for each file that
+must be verified (there is the dedicated ``RPMTAG_FILESIGNATURES`` section
+in the RPM header).
+
+The proposed approach would be instead to verify data provenance from
+already available metadata (file digests) in existing packages. IMA would
+verify the signature of package metadata and search file digests extracted
+from package metadata and added to the hash table in the kernel.
+
+For RPMs, file digests can be found in the ``RPMTAG_FILEDIGESTS`` section
+of ``RPMTAG_IMMUTABLE``, whose signature is in ``RPMTAG_RSAHEADER``. For
+DEBs, file digests (unsafe to use due to a weak digest algorithm) can be
+found in the ``md5sum`` file, which can be indirectly verified from
+``Release.gpg``.
+
+The following figure highlights the differences between the current and the
+proposed approach.
+
+::
+
+ IMA appraisal (current solution, with file signatures):
+
+                                                         appraise
+                                                      +-----------+
+                                                      V           |
+ +-------------------------+-----+         +-------+-----+        |
+ | RPM header              |     | ima rpm | file1 | sig |        |
+ | ...                     |     | plugin  +-------+-----+     +-----+
+ | file1 sig [to be added] | sig |-------->      ...           | IMA |
+ | ...                     |     |         +-------+-----+     +-----+
+ | fileN sig [to be added] |     |         | fileN | sig |
+ +-------------------------+-----+         +-------+-----+
+
+In this case, file signatures must be added to the RPM header, so that the
+``ima`` rpm plugin can extract them together with the file content. The RPM
+header signature is not used.
+
+::
+
+ IMA appraisal (with DIGLIM):
+
+                                    kernel hash table
+                                    with RPM header content
+                                    +---+    +--------------+
+                                    |   |--->| file1 digest |
+                                    +---+    +--------------+
+                                     ...
+                                    +---+         appraise (file1)
+                                    |   |  <--------------+
+ +----------------+-----+           +---+                 |
+ | RPM header     |     |             ^                   |
+ | ...            |     | digest_list |                   |
+ | file1 digest   | sig | rpm plugin  |    +-------+   +-----+
+ | ...            |     |-------------+--->| file1 |   | IMA |
+ | fileN digest   |     |                  +-------+   +-----+
+ +----------------+-----+                                 |
+                     ^                                    |
+                     +------------------------------------+
+                             appraise (RPM header)
+
+In this case, the RPM header is used as it is, and its signature is used
+for IMA appraisal. Then, the ``digest_list`` rpm plugin executes the user
+space parser to parse the RPM header and add the extracted digests to an
+hash table in the kernel. IMA appraisal of the files in the RPM package
+consists in searching their digest in the hash table.
+
+Other than reusing available information as digest list, another advantage
+is the lower computational overhead compared to the solution with file
+signatures (only one signature verification for many files and digest
+lookup, instead of per file signature verification, see `Preliminary
+Performance Evaluation`_ for more details).
+
+
+Lifecycle
+---------
+
+The lifecycle of DIGLIM is represented in the following figure:
+
+::
+
+ Vendor premises (release process with modifications):
+
+ +------------+   +-----------------------+   +------------------------+
+ | 1. build a |   | 2. generate and sign  |   | 3. publish the package |
+ |    package |-->|    a digest list from |-->|    and digest list in  |
+ |            |   |    packaged files     |   |    a repository        |
+ +------------+   +-----------------------+   +------------------------+
+                                                                 |
+                                                                 |
+ User premises:                                                  |
+                                                                 V
+ +---------------------+   +------------------------+   +-----------------+
+ | 6. use digest lists |   | 5. download the digest |   | 4. download and |
+ |    for measurement  |<--|    list and upload to  |<--|    install the  |
+ |    and/or appraisal |   |    the kernel          |   |    package      |
+ +---------------------+   +------------------------+   +-----------------+
+
+The figure above represents all the steps when a digest list is
+generated separately. However, as mentioned in `Contribution`_, in most
+cases existing packages can be already used as a source for digest lists,
+limiting the effort for software vendors.
+
+If, for example, RPMs are used as a source for digest lists, the figure
+above becomes:
+
+::
+
+ Vendor premises (release process without modifications):
+
+ +------------+   +------------------------+
+ | 1. build a |   | 2. publish the package |
+ |    package |-->|    in a repository     |---------------------+
+ |            |   |                        |                     |
+ +------------+   +------------------------+                     |
+                                                                 |
+                                                                 |
+ User premises:                                                  |
+                                                                 V
+ +---------------------+   +------------------------+   +-----------------+
+ | 5. use digest lists |   | 4. extract digest list |   | 3. download and |
+ |    for measurement  |<--|    from the package    |<--|    install the  |
+ |    and/or appraisal |   |    and upload to the   |   |    package      |
+ |                     |   |    kernel              |   |                 |
+ +---------------------+   +------------------------+   +-----------------+
+
+Step 4 can be performed with the ``digest_list`` rpm plugin and the user
+space parser, without changes to rpm itself.
+
+
+Security Assumptions
+--------------------
+
+As mentioned in the `Introduction`_, DIGLIM will be primarily used in
+conjunction with IMA to enforce a mandatory policy on all user space
+processes, including those owned by root. Even root, in a system with a
+locked-down kernel, cannot affect the enforcement of the mandatory policy
+or, if changes are permitted, it cannot do so without being detected.
+
+Given that the target of the enforcement are user space processes, DIGLIM
+cannot be placed in the target, as a Mandatory Access Control (MAC) design
+is required to have the components responsible to enforce the mandatory
+policy separated from the target.
+
+While locking-down a system and limiting actions with a mandatory policy is
+generally perceived by users as an obstacle, it has noteworthy benefits for
+the users themselves.
+
+First, it would timely block attempts by malicious software to steal or
+misuse user assets. Although users could query the package managers to
+detect them, detection would happen after the fact, or it wouldn't happen
+at all if the malicious software tampered with package managers. With a
+mandatory policy enforced by the kernel, users would still be able to
+decide which software they want to be executed except that, unlike package
+managers, the kernel is not affected by user space processes or root.
+
+Second, it might make systems more easily verifiable from outside, due to
+the limited actions the system allows. When users connect to a server, not
+only they would be able to verify the server identity, which is already
+possible with communication protocols like TLS, but also if the software
+running on that server can be trusted to handle their sensitive data.
+
+
+Adoption
+--------
+
+A former version of DIGLIM is used in the following OSes:
+
+- openEuler 20.09
+  https://github.com/openeuler-mirror/kernel/tree/openEuler-20.09
+
+- openEuler 21.03
+  https://github.com/openeuler-mirror/kernel/tree/openEuler-21.03
+
+Originally, DIGLIM was part of IMA (known as IMA Digest Lists). In this
+version, it has been redesigned as a standalone module with an API that
+makes its functionality accessible by IMA and, eventually, other
+subsystems.
+
+User Space Support
+------------------
+
+Digest lists can be generated and managed with ``digest-list-tools``:
+
+https://github.com/openeuler-mirror/digest-list-tools
+
+It includes two main applications:
+
+- ``gen_digest_lists``: generates digest lists from files in the
+  filesystem or from the RPM database (more digest list sources can be
+  supported);
+- ``manage_digest_lists``: converts and uploads digest lists to the
+  kernel.
+
+Integration with rpm is done with the ``digest_list`` plugin:
+
+https://gitee.com/src-openeuler/rpm/blob/master/Add-digest-list-plugin.patch
+
+This plugin writes the RPM header and its signature to a file, so that the
+file is ready to be appraised by IMA, and calls the user space parser to
+convert and upload the digest list to the kernel.
+
+
+Simple Usage Example (Tested with Fedora 33)
+--------------------------------------------
+
+1. Digest list generation (RPM headers and their signature are copied to
+   the specified directory):
+
+.. code-block:: bash
+
+ # mkdir /etc/digest_lists
+ # gen_digest_lists -t file -f rpm+db -d /etc/digest_lists -o add
+
+2. Digest list upload with the user space parser:
+
+.. code-block:: bash
+
+ # manage_digest_lists -p add-digest -d /etc/digest_lists
+
+3. First digest list query:
+
+.. code-block:: bash
+
+ # echo sha256-$(sha256sum /bin/cat) > /sys/kernel/security/integrity/diglim/digest_query
+ # cat /sys/kernel/security/integrity/diglim/digest_query
+   sha256-[...]-0-file_list-rpm-coreutils-8.32-18.fc33.x86_64 (actions: 0): version: 1, algo: sha256, type: 2, modifiers: 1, count: 106, datalen: 3392
+
+4. Second digest list query:
+
+.. code-block:: bash
+
+ # echo sha256-$(sha256sum /bin/zip) > /sys/kernel/security/integrity/diglim/digest_query
+ # cat /sys/kernel/security/integrity/diglim/digest_query
+   sha256-[...]-0-file_list-rpm-zip-3.0-27.fc33.x86_64 (actions: 0): version: 1, algo: sha256, type: 2, modifiers: 1, count: 4, datalen: 128
+
+
+Preliminary Performance Evaluation
+----------------------------------
+
+This section provides an initial estimation of the overhead introduced by
+DIGLIM. The estimation has been performed on a Fedora 33 virtual machine
+with 1447 packages installed. The virtual machine has 16 vCPU (host CPU:
+AMD Ryzen Threadripper PRO 3955WX 16-Cores) and 2G of RAM (host memory:
+64G). The virtual machine also has a vTPM with libtpms and swtpm as
+backend.
+
+After writing the RPM headers to files, the size of the directory
+containing them is 36M.
+
+After converting the RPM headers to the compact digest list, the size of
+the data being uploaded to the kernel is 3.6M.
+
+The time to load the entire RPM database is 0.628s.
+
+After loading the digest lists to the kernel, the slab usage due to
+indexing is (obtained with slab_nomerge in the kernel command line):
+
+::
+
+ OBJS   ACTIVE  USE OBJ SIZE  SLABS OBJ/SLAB CACHE SIZE NAME
+ 118144 118144 100%    0,03K    923      128      3692K digest_list_item_ref_cache
+ 102400 102400 100%    0,03K    800      128      3200K digest_item_cache
+   2646   2646 100%    0,09K     63       42       252K digest_list_item_cache
+
+The stats, obtained from the ``digests_count`` interface, introduced later,
+are:
+
+::
+
+ Parser digests: 0
+ File digests: 99100
+ Metadata digests: 0
+ Digest list digests: 1423
+
+On this installation, this would be the worst case in which all files are
+measured and/or appraised, which is currently not recommended without
+enforcing an integrity policy protecting mutable files. Infoflow LSM is a
+component to accomplish this task:
+
+https://patchwork.kernel.org/project/linux-integrity/cover/20190818235745.1417-1-roberto.sassu@huawei.com/
+
+The first manageable goal of IMA with DIGLIM is to use an execution policy,
+with measurement and/or appraisal of files executed or mapped in memory as
+executable (in addition to kernel modules and firmware). In this
+case, the digest list contains the digest only for those files. The numbers
+above change as follows.
+
+After converting the RPM headers to the compact digest list, the size of
+the data being uploaded to the kernel is 208K.
+
+The time to load the digest of binaries and shared libraries is 0.062s.
+
+After loading the digest lists to the kernel, the slab usage due to
+indexing is:
+
+::
+
+ OBJS ACTIVE  USE OBJ SIZE  SLABS OBJ/SLAB CACHE SIZE NAME
+ 7168   7168 100%    0,03K     56      128       224K digest_list_item_ref_cache
+ 7168   7168 100%    0,03K     56      128       224K digest_item_cache
+ 1134   1134 100%    0,09K     27       42       108K digest_list_item_cache
+
+
+The stats, obtained from the ``digests_count`` interface, are:
+
+::
+
+ Parser digests: 0
+ File digests: 5986
+ Metadata digests: 0
+ Digest list digests: 1104
+
+
+Comparison with IMA
+~~~~~~~~~~~~~~~~~~~
+
+This section compares the performance between the current solution for IMA
+measurement and appraisal, and IMA with DIGLIM.
+
+
+Workload A (without DIGLIM):
+
+#. cat file[0-5985] > /dev/null
+
+
+Workload B (with DIGLIM):
+
+#. echo $PWD/0-file_list-compact-file[0-1103] > <securityfs>/integrity/diglim/digest_list_add
+#. cat file[0-5985] > /dev/null
+
+
+Workload A execution time without IMA policy:
+
+::
+
+ real	0m0,155s
+ user	0m0,008s
+ sys	0m0,066s
+
+
+Measurement
+...........
+
+IMA policy:
+
+::
+
+ measure fowner=2000 func=FILE_CHECK mask=MAY_READ use_diglim=allow pcr=11 ima_template=ima-sig
+
+``use_diglim`` is a policy keyword not yet supported by IMA.
+
+
+Workload A execution time with IMA and 5986 files with signature measured:
+
+::
+
+ real	0m8,273s
+ user	0m0,008s
+ sys	0m2,537s
+
+
+Workload B execution time with IMA, 1104 digest lists with signature
+measured and uploaded to the kernel, and 5986 files with signature accessed
+but not measured (due to the file digest being found in the hash table):
+
+::
+
+ real	0m1,837s
+ user	0m0,036s
+ sys	0m0,583s
+
+
+Appraisal
+.........
+
+IMA policy:
+
+::
+
+ appraise fowner=2000 func=FILE_CHECK mask=MAY_READ use_diglim=allow
+
+``use_diglim`` is a policy keyword not yet supported by IMA.
+
+
+Workload A execution time with IMA and 5986 files with file signature
+appraised:
+
+::
+
+ real	0m2,197s
+ user	0m0,011s
+ sys	0m2,022s
+
+
+Workload B execution time with IMA, 1104 digest lists with signature
+appraised and uploaded to the kernel, and with 5986 files with signature
+not verified (due to the file digest being found in the hash table):
+
+::
+
+ real	0m0,982s
+ user	0m0,020s
+ sys	0m0,865s
diff --git a/Documentation/security/index.rst b/Documentation/security/index.rst
index 16335de04e8c..6c3aea41c55b 100644
--- a/Documentation/security/index.rst
+++ b/Documentation/security/index.rst
@@ -17,3 +17,4 @@ Security Documentation
    tpm/index
    digsig
    landlock
+   diglim/index
diff --git a/MAINTAINERS b/MAINTAINERS
index 6c8be735cc91..c914dadd7e65 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -5452,6 +5452,15 @@ L:	linux-gpio@vger.kernel.org
 S:	Maintained
 F:	drivers/gpio/gpio-gpio-mm.c
 
+DIGLIM
+M:	Roberto Sassu <roberto.sassu@huawei.com>
+L:	linux-integrity@vger.kernel.org
+S:	Supported
+T:	git://git.kernel.org/pub/scm/linux/kernel/git/zohar/linux-integrity.git
+F:	Documentation/security/diglim/architecture.rst
+F:	Documentation/security/diglim/index.rst
+F:	Documentation/security/diglim/introduction.rst
+
 DIOLAN U2C-12 I2C DRIVER
 M:	Guenter Roeck <linux@roeck-us.net>
 L:	linux-i2c@vger.kernel.org
-- 
2.25.1