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From:   Roberto Sassu <roberto.sassu@huawei.com>
To:     Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
CC:     "zohar@linux.ibm.com" <zohar@linux.ibm.com>,
        "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
        "linux-integrity@vger.kernel.org" <linux-integrity@vger.kernel.org>,
        "linux-security-module@vger.kernel.org" 
        <linux-security-module@vger.kernel.org>,
        "linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
        "linux-kselftest@vger.kernel.org" <linux-kselftest@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [RFC][PATCH v2 01/12] diglim: Overview
Thread-Topic: [RFC][PATCH v2 01/12] diglim: Overview
Thread-Index: AQHXgjyiIl/bO9ShVkChZdaV+Ejoq6tYHDYAgAAmNRA=
Date:   Wed, 28 Jul 2021 11:40:34 +0000
Message-ID: <08123f69c0fa431889f6bbd1b8a499ce@huawei.com>
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        <20210726163700.2092768-2-roberto.sassu@huawei.com>
 <20210728131000.16788919@coco.lan>
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> From: Mauro Carvalho Chehab [mailto:mchehab+huawei@kernel.org]
> Sent: Wednesday, July 28, 2021 1:10 PM
> Em Mon, 26 Jul 2021 18:36:49 +0200
> Roberto Sassu <roberto.sassu@huawei.com> escreveu:
> 
> > 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
> > index 000000000000..a54fe2453715
> > --- /dev/null
> > +++ b/Documentation/security/diglim/architecture.rst
> > @@ -0,0 +1,45 @@
> > +.. 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
> 
> "before"? This is at the beginning of this document ;-)
> 
> You should probably add a reference to introduction.rst here, like:
> 
> 	As mentioned at Documentation/security/diglim/introduction.rst, ...

Hi Mauro

ok.

> > +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.
> 
> This probably applies to Documentation/security as a hole, but the
> best is to split the documents on two separate parts:
> 	- the kAPI and internals;
> 	- the admin-guide part.
> 
> The audience for the admin-guide is distribution pagagers and
> syssadmins.

Ok. I will create an admin-guide.
 
> > diff --git a/Documentation/security/diglim/index.rst
> b/Documentation/security/diglim/index.rst
> > new file mode 100644
> > index 000000000000..0fc5ab019bc0
> > --- /dev/null
> > +++ b/Documentation/security/diglim/index.rst
> > @@ -0,0 +1,11 @@
> > +.. 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
> > --- /dev/null
> > +++ b/Documentation/security/diglim/introduction.rst
> > @@ -0,0 +1,631 @@
> > +.. 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
> 
> I would replace:
> 
> 	"is a new component added to" -> "is a component of"
> 
> As this is the kind of text that tends to be outdated with time...
> Imagine someone reading this paragraph maybe 10 years in the future ;-)

Ok.

> > +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),
> 
> 	-ETOMANY_already
> 
> as "already" available... can be "already" ... "already" include...
> 
> I would simplify the above text removing such redundancy.

Ok.

> > +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.
> 
> I found this paragraph a little bit confusing to understand. Could you
> please improve the description?
> 
> I mean:
> 
> 	what improved by one quarter?
> 	what improved by "less than half of the time"?

Ok. I didn't want to make the text too heavy. The tests are described
in the Preliminary Performance Evaluation section.

> > +
> > +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).
> 
> I don't think it makes sense to compare it with a transactional database.
> 
> I would say, instead, something like:
> 
> 	The inserts on DIGLIM are atomic: if an error occurs during the
> addition
> 	of a digest list, it rolls back the entire insert operation.

Ok, better.

> > +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_commu
> nication_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
> 
> The above won't generate any cross-references with Sphinx.
> 
> For it correct syntax, see:
> 	https://www.sphinx-
> doc.org/en/master/usage/restructuredtext/basics.html#citations

Ok, will fix it.

> > +
> > +
> > +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.
> 
> Sounds a weird description for me. (ISC)2 defines integrity on its
> glossary[1] as:
> 
> 	"Guarding against improper information modification or destruction
> and
> 	 includes ensuring information non-repudiation and authenticity."
> 
> [1] https://www.isc2.org/Certifications/CISSP/CISSP-Student-Glossary

Ok, I meant integrity in the context of trusted computing.

https://trustedcomputinggroup.org/wp-content/uploads/IWG_ArchitecturePartII_v1.0.pdf

In general the term "integrity" is used to denote the pristine state of a
component (page 13).

> > +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
> > +------------
> 
> I would rename this chapter to "Benefits".

Ok.

> > +
> > +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:
> > +
> > +::
> 
> You could just use:
> 
> 	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:
> > +
> > +::
> 
> Same here.

Ok.

Thanks

Roberto

HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063
Managing Director: Li Peng, Li Jian, Shi Yanli

> > +
> > + 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
> 
> 
> 
> Thanks,
> Mauro