Revision as of 13:25, 16 December 2021

Change Proposal Name

Changes/DIGLIM

Summary

Digest Lists Integrity Module (DIGLIM) provides a repository of file digests from authenticated sources, such as RPM headers, to be used by kernel services for remote attestation and/or appraisal.

Owner

Name: Roberto Sassu
Email: <roberto.sassu@huawei.com>

Current status

Targeted release: [[Releases/<36> | Fedora Linux <36> ]]
Last updated: 2021-12-16
FESCo issue: <will be assigned by the Wrangler>
Tracker bug: <will be assigned by the Wrangler>
Release notes tracker: <will be assigned by the Wrangler>

Detailed Description

Integrity Measurement Architecture (IMA), a kernel service for remote attestation and secure boot at application level, has been integrated in the kernel since a long time. However, two main barriers limited its wide adoption. First, it extends a Platform Control Register (PCR) of the Trusted Platform Module (TPM) in an unpredictable way (due to parallel execution of software), making it impossible to use that PCR for sealing policies of TPM keys. Second, it requires that a file signature is added for each file to be appraised in the package header.

Digest Lists Integrity Module (DIGLIM) takes a different approach. It makes it possible for IMA to extend a PCR in a predictable way, or to verify the authenticity of files by querying an in-kernel repository of authenticated reference values, built from information already available in existing packages (FILEDIGESTS section of the RPM header, signed by the RSAHEADER section).

DIGLIM is not specifically tied to IMA. Since it is based on the hash table implementation of the kernel, it can store data of different types or be used by other kernel subsystems. It might for example store fsverity digests, to achieve the goal of another proposed [change] with less overhead (by adding to the RPM header digests instead of signatures). It might also be used by other kernel services, such as Integrity Policy Enforcement (IPE), a new LSM being proposed for inclusion in the upstream kernel.

A preliminary performance evaluation showed that DIGLIM did not introduce a significant overhead. A repository of executables and shared libraries digests, of a Fedora 33 minimal installation, occupies less than 800k of memory.

Feedback

DIGLIM has been proposed some time ago, and was previously known as IMA Digest Lists.

The original implementation was found to be too invasive, as both the management of the repository of reference values and the new measurement and appraisal mechanisms based on the query of the repository needed to coexist with the existing code. DIGLIM is now implemented as a standalone module, which includes the repository management part, and exposes a simple API so that IMA and other kernel services can use it to implement the query part (much simpler).

At the time IMA Digest Lists was published, the proposal of adding file signatures to the package header was deemed to be more mature and suitable for adoption. From [previous] and [current] discussions, it seems that Linux distribution vendors are a bit reluctant to make such change, especially due to the increased size of the packages. DIGLIM just requires a modification of the kernel, rpm and dracut, and could work on old distribution versions once the modified packages are installed.

Another remote attestation-specific issue is that the approach of measuring only unknown software reduces the amount of information available to remote verifiers for the integrity evaluation of the system being attested. In particular, a measurement list made with the DIGLIM approach does not show which file have been actually accessed and when. This tradeoff was chosen to make the PCR value extended with software measurements predictable and to allow the usage of sealing policies based on that PCR.

Benefit to Fedora

The main benefits of DIGLIM have been elaborated [here].

Briefly summarizing: DIGLIM brings the benefits of kernel services for integrity detection (measurement) and protection (appraisal) to Linux distributions, and relieves the distributions for the burden of the integrity functionality.

More specifically, it will make a system running Fedora attestable without the need of using dedicated remote attestation protocols. In fact, the assertion that a system is running a specific set of software will be implicitly implied by the ability of that system to correctly respond to the other peer in the TLS handshake protocol. This could be achieved with widely available software such as the Apache web server, the tpm2 openssl engine and a browser. Also [Keylime], a Red Hat-based solution for remote attestation, could make use of the proposed scheme.

It will also make Fedora able to detect tampering of its components at a more privileged level, the kernel, without the interference of user space programs. Once tampering has been detected, the actions of the altered component are prevented before that component gets the chance to perform any action. Fedora could be configured to also allow the usage of components provided by the user, if he wishes so (DIGLIM has a tool to build custom digest lists).

Scope

Proposal owners:
- Maintain the following patch sets for the Linux kernel, and possibly have them accepted in the upstream kernel:
- Port the digest_list rpm plugin from openEuler to Fedora:
  - [digest_list rpm plugin]
- Create dracut configuration file/module for copying RPM headers to the initial ram disk (optimization: copy only RPM headers related to files in the initial ram disk)
- Introduce script to enable IMA measurement/appraisal execution policies in the boot loader configuration:
  - [script]

Other developers:
- Review the changes proposed above

Release engineering: #Releng issue number
- Discuss with Release engineering team about the possibility of enabling IMA measurement and/or appraisal policies since first boot (a checkbox in Anaconda would cause the boot loader configuration to be updated to enable such policies)
- The feature might be enabled later by the user without any change required for the image generation

Policies and guidelines: N/A

Trademark approval: N/A

Alignment with Objectives: Yes

Upgrade/compatibility impact

The user should ensure that software from the old distribution is packaged and the package header is signed, or the user should create and sign a custom digest list for the software he wishes to use after the upgrade.

How To Test

A Fedora kernel package with DIGLIM is available in [copr].

The installation instructions have been published to the linux-integrity kernel mailing list [here].

User Experience

Both integrity detection and protection will be transparent for the user. For protection, the user will notice a change only if his actions (or of a malicious software on his behalf) are not in accordance with the integrity policy being enforced (e.g. the user executes an unsigned binary).

Dependencies

kernel
rpm
dracut

The feature owners will be responsible to submit all the changes necessary and will not depend on other developers' work.

Contingency Plan

Contingency mechanism: remove provided patches from the packages
Contingency deadline: rebuilding the packages without the new patches can be done at any time
Blocks release? No

Documentation

The most comprehensive documentation can be found [here].

Release Notes

Release notes will be derived from the documentation.

@@ Line 1: / Line 1: @@
-{{admon/important | Comments and Explanations | The page source contains comments providing guidance to fill out each section. They are invisible when viewing this page. To read it, choose the "view source" link.<br/> '''Copy the source to a ''new page'' before making changes!  DO NOT EDIT THIS TEMPLATE FOR YOUR CHANGE PROPOSAL.'''}}
-{{admon/tip | Guidance | For details on how to fill out this form, see the [https://docs.fedoraproject.org/en-US/program_management/changes_guide/ documentation].}}
-<!-- The actual name of your proposed change page should look something like: Changes/Your_Change_Proposal_Name.  This keeps all change proposals in the same namespace -->
 = Change Proposal Name =
-Changes/DIGLIM_RA_APPRAISAL
+Changes/DIGLIM
 == Summary ==
-Digest Lists Integrity Module (DIGLIM) provides a repository of file digests from authenticated sources, such as RPM headers, to be used by kernel services for remote attestation and/or secure boot.
+Digest Lists Integrity Module (DIGLIM) provides a repository of file digests from authenticated sources, such as RPM headers, to be used by kernel services for remote attestation and/or appraisal.
-<!-- A sentence or two summarizing what this change is and what it will do. This information is used for the overall changeset summary page for each release. Note that motivation for the change should be in the Benefit to Fedora section below, and this part should answer the question "What?" rather than "Why?". -->
 == Owner ==
-<!--
-For change proposals to qualify as self-contained, owners of all affected packages need to be included here. Alternatively, a SIG can be listed as an owner if it owns all affected packages.
-This should link to your home wiki page so we know who you are.
--->
 * Name: [[User:robertosassu| Roberto Sassu]]
-<!-- Include you email address that you can be reached should people want to contact you about helping with your change, status is requested, or technical issues need to be resolved. If the change proposal is owned by a SIG, please also add a primary contact person. -->
+* Email: <roberto.sassu@huawei.com>
-* Email: <your email address so we can contact you, invite you to meetings, etc. Please provide your Bugzilla email address if it is different from your email in FAS>
-<!--- UNCOMMENT only for Changes with assigned Shepherd (by FESCo)
-* FESCo shepherd: [[User:FASAccountName| Shehperd name]] <email address>
--->
 == Current status ==
@@ Line 32: / Line 15: @@
 <!-- The Wrangler announces the Change to the devel-announce list and changes the category to Category:ChangeAnnounced (no action required) -->
 <!-- After review, the Wrangler will move your page to Category:ChangeReadyForFesco... if it still needs more work it will move back to Category:ChangePageIncomplete-->
+[[Category:SystemWideChange]]
-<!-- Select proper category, default is Self Contained Change -->
+* Targeted release: [[Releases/<36> | Fedora Linux <36> ]]
-[[Category:SelfContainedChange]]
+* Last updated: {{REVISIONYEAR}}-{{REVISIONMONTH}}-{{REVISIONDAY2}}
-<!-- [[Category:SystemWideChange]] -->
-* Targeted release: [[Releases/<number> | Fedora Linux <number> ]]
-* Last updated: <!-- this is an automatic macro — you don't need to change this line -->  {{REVISIONYEAR}}-{{REVISIONMONTH}}-{{REVISIONDAY2}}
-<!-- After the change proposal is accepted by FESCo, tracking bug is created in Bugzilla and linked to this page
-Bugzilla state meanings:
-ASSIGNED -> accepted by FESCo with ongoing development
-MODIFIED -> change is substantially done and testable
-ON_QA -> change is fully code complete
--->
 * FESCo issue: <will be assigned by the Wrangler>
 * Tracker bug: <will be assigned by the Wrangler>
@@ Line 50: / Line 24: @@
 == Detailed Description ==
-<!-- Expand on the summary, if appropriate.  A couple sentences suffices to explain the goal, but the more details you can provide the better. -->
+Integrity Measurement Architecture (IMA), a kernel service for remote attestation and secure boot at application level, has been integrated in the kernel since a long time. However, two main barriers limited its wide adoption. First, it extends a Platform Control Register (PCR) of the Trusted Platform Module (TPM) in an unpredictable way (due to parallel execution of software), making it impossible to use that PCR for sealing policies of TPM keys. Second, it requires that a file signature is added for each file to be appraised in the package header.
+Digest Lists Integrity Module (DIGLIM) takes a different approach. It makes it possible for IMA to extend a PCR in a predictable way, or to verify the authenticity of files by querying an in-kernel repository of authenticated reference values, built from information already available in existing packages (FILEDIGESTS section of the RPM header, signed by the RSAHEADER section).
+DIGLIM is not specifically tied to IMA. Since it is based on the hash table implementation of the kernel, it can store data of different types or be used by other kernel subsystems. It might for example store fsverity digests, to achieve the goal of another proposed [[//fedoraproject.org/wiki/Changes/FsVerityRPM change]] with less overhead (by adding to the RPM header digests instead of signatures). It might also be used by other kernel services, such as Integrity Policy Enforcement (IPE), a new LSM being proposed for inclusion in the upstream kernel.
+A preliminary performance evaluation showed that DIGLIM did not introduce a significant overhead. A repository of executables and shared libraries digests, of a Fedora 33 minimal installation, occupies less than 800k of memory.
 == Feedback ==
+DIGLIM has been proposed some time ago, and was previously known as IMA Digest Lists.
+The original implementation was found to be too invasive, as both the management of the repository of reference values and the new measurement and appraisal mechanisms based on the query of the repository needed to coexist with the existing code. DIGLIM is now implemented as a standalone module, which includes the repository management part, and exposes a simple API so that IMA and other kernel services can use it to implement the query part (much simpler).
+At the time IMA Digest Lists was published, the proposal of adding file signatures to the package header was deemed to be more mature and suitable for adoption. From [[//pagure.io/fesco/issue/2547 previous]] and [[//lists.fedoraproject.org/archives/list/devel@lists.fedoraproject.org/thread/JE2HGLJMLEKUJW3YBP6MQJWP43CSTC57/ current]] discussions, it seems that Linux distribution vendors are a bit reluctant to make such change, especially due to the increased size of the packages. DIGLIM just requires a modification of the kernel, rpm and dracut, and could work on old distribution versions once the modified packages are installed.
+Another remote attestation-specific issue is that the approach of measuring only unknown software reduces the amount of information available to remote verifiers for the integrity evaluation of the system being attested. In particular, a measurement list made with the DIGLIM approach does not show which file have been actually accessed and when. This tradeoff was chosen to make the PCR value extended with software measurements predictable and to allow the usage of sealing policies based on that PCR.
 <!-- Summarize the feedback from the community and address why you chose not to accept proposed alternatives. This section is optional for all change proposals but is strongly suggested. Incorporating feedback here as it is raised gives FESCo a clearer view of your proposal and leaves a good record for the future. If you get no feedback, that is useful to note in this section as well. For innovative or possibly controversial ideas, consider collecting feedback before you file the change proposal. -->
 == Benefit to Fedora ==
-<!-- What is the benefit to the distribution?  Will the software we generate be improved? How will the process of creating Fedora releases be improved?
+The main benefits of DIGLIM have been elaborated [[//lore.kernel.org/linux-integrity/20210914163401.864635-1-roberto.sassu@huawei.com/ here]].
-      Be sure to include the following areas if relevant:
-      If this is a major capability update, what has changed?
-           For example: This change introduces Python 5 that runs without the Global Interpreter Lock and is fully multithreaded.
-      If this is a new functionality, what capabilities does it bring?
-           For example: This change allows package upgrades to be performed automatically and rolled-back at will.
-      Does this improve some specific package or set of packages?
-           For example: This change modifies a package to use a different language stack that reduces install size by removing dependencies.
-      Does this improve specific Spins or Editions?
-           For example: This change modifies the default install of Fedora Workstation to be more in line with the base install of Fedora Server.
-      Does this make the distribution more efficient?
-           For example: This change replaces thousands of individual %post scriptlets in packages with one script that runs at the end.
-      Is this an improvement to maintainer processes?
-           For example: Gating Fedora packages on automatic QA tests will make rawhide more stable and allow changes to be implemented more smoothly.
-      Is this an improvement targeted as specific contributors?
-           For example: Ensuring that a minimal set of tools required for contribution to Fedora are installed by default eases the onboarding of new contributors.
-     When a Change has multiple benefits, it's better to list them all.
+Briefly summarizing: DIGLIM brings the benefits of kernel services for integrity detection (measurement) and protection (appraisal) to Linux distributions, and relieves the distributions for the burden of the integrity functionality.
-     Consider these Change pages from previous editions as inspiration:
+More specifically, it will make a system running Fedora attestable without the need of using dedicated remote attestation protocols. In fact, the assertion that a system is running a specific set of software will be implicitly implied by the ability of that system to correctly respond to the other peer in the TLS handshake protocol. This could be achieved with widely available software such as the Apache web server, the tpm2 openssl engine and a browser. Also [[//keylime.dev/ Keylime]], a Red Hat-based solution for remote attestation, could make use of the proposed scheme.
-     https://fedoraproject.org/wiki/Changes/Annobin (low-level and technical, invisible to users)
-     https://fedoraproject.org/wiki/Changes/ParallelInstallableDebuginfo (low-level, but visible to advanced users)
+It will also make Fedora able to detect tampering of its components at a more privileged level, the kernel, without the interference of user space programs. Once tampering has been detected, the actions of the altered component are prevented before that component gets the chance to perform any action. Fedora could be configured to also allow the usage of components provided by the user, if he wishes so (DIGLIM has a tool to build custom digest lists).
-     https://fedoraproject.org/wiki/Changes/VirtualBox_Guest_Integration (primarily a UX change)
-     https://fedoraproject.org/wiki/Changes/NoMoreAlpha (an improvement to distro processes)
-     https://fedoraproject.org/wiki/Changes/perl5.26 (major upgrade to a popular software stack, visible to users of that stack)
--->
 == Scope ==
 * Proposal owners:
-<!-- What work do the feature owners have to accomplish to complete the feature in time for release?  Is it a large change affecting many parts of the distribution or is it a very isolated change? What are those changes?-->
+** Maintain the following patch sets for the Linux kernel, and possibly have them accepted in the upstream kernel:
+*** [[//lore.kernel.org/linux-integrity/20210409114313.4073-1-roberto.sassu@huawei.com/ IMA execution policies]]
+*** [[//lore.kernel.org/linux-integrity/20210914163401.864635-1-roberto.sassu@huawei.com/ DIGLIM basic features]]
+*** [[//lore.kernel.org/linux-integrity/20210915163145.1046505-1-roberto.sassu@huawei.com/ DIGLIM advanced features]]
+*** [[//lore.kernel.org/linux-integrity/20210930115533.878169-1-roberto.sassu@huawei.com/ DIGLIM integration with IMA]]
+** Port the digest_list rpm plugin from openEuler to Fedora:
+*** [[//gitee.com/src-openeuler/rpm/blob/master/Add-digest-list-plugin.patch digest_list rpm plugin]]
+** Create dracut configuration file/module for copying RPM headers to the initial ram disk (optimization: copy only RPM headers related to files in the initial ram disk)
+** Introduce script to enable IMA measurement/appraisal execution policies in the boot loader configuration:
+*** [[//gitee.com/openeuler/digest-list-tools/blob/master/scripts/setup_grub2 script]]
-* Other developers: <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
+* Other developers:
-<!-- What work do other developers have to accomplish to complete the feature in time for release?  Is it a large change affecting many parts of the distribution or is it a very isolated change? What are those changes?-->
+** Review the changes proposed above
-* Release engineering: [https://pagure.io/releng/issues #Releng issue number] <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
+* Release engineering: [https://pagure.io/releng/issues #Releng issue number]
-<!-- Does this feature require coordination with release engineering (e.g. changes to installer image generation or update package delivery)?  Is a mass rebuild required?  include a link to the releng issue.
+** Discuss with Release engineering team about the possibility of enabling IMA measurement and/or appraisal policies since first boot (a checkbox in Anaconda would cause the boot loader configuration to be updated to enable such policies)
-The issue is required to be filed prior to feature submission, to ensure that someone is on board to do any process development work and testing and that all changes make it into the pipeline; a bullet point in a change is not sufficient communication -->
+** The feature might be enabled later by the user without any change required for the image generation
-* Policies and guidelines: N/A (not needed for this Change) <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
+* Policies and guidelines: N/A
-<!-- Do the packaging guidelines or other documents need to be updated for this feature?  If so, does it need to happen before or after the implementation is done?  If a FPC ticket exists, add a link here. Please submit a pull request with the proposed changes before submitting your Change proposal. -->
-* Trademark approval: N/A (not needed for this Change)
+* Trademark approval: N/A
-<!-- If your Change may require trademark approval (for example, if it is a new Spin), file a ticket ( https://pagure.io/Fedora-Council/tickets/issues ) requesting trademark approval from the Fedora Council. This approval will be done via the Council's consensus-based process. -->
-* Alignment with Objectives:
+* Alignment with Objectives: Yes
-<!-- Does your proposal align with the current Fedora Objectives: https://docs.fedoraproject.org/en-US/project/objectives/ ? It's okay if it doesn't, but it's something to consider -->
 == Upgrade/compatibility impact ==
-<!-- What happens to systems that have had a previous versions of Fedora installed and are updated to the version containing this change? Will anything require manual configuration or data migration? Will any existing functionality be no longer supported? -->
+The user should ensure that software from the old distribution is packaged and the package header is signed, or the user should create and sign a custom digest list for the software he wishes to use after the upgrade.
-<!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
 == How To Test ==
-<!-- This does not need to be a full-fledged document. Describe the dimensions of tests that this change implementation is expected to pass when it is done.  If it needs to be tested with different hardware or software configurations, indicate them.  The more specific you can be, the better the community testing can be.
+A Fedora kernel package with DIGLIM is available in [[//copr.fedorainfracloud.org/coprs/robertosassu/DIGLIM/ copr]].
-Remember that you are writing this how to for interested testers to use to check out your change implementation - documenting what you do for testing is OK, but it's much better to document what *I* can do to test your change.
-A good "how to test" should answer these four questions:
-. What special hardware / data / etc. is needed (if any)?
-. How do I prepare my system to test this change? What packages
-need to be installed, config files edited, etc.?
-. What specific actions do I perform to check that the change is
-working like it's supposed to?
-. What are the expected results of those actions?
--->
-<!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
+The installation instructions have been published to the linux-integrity kernel mailing list [[//lore.kernel.org/linux-integrity/48cd737c504d45208377daa27d625531@huawei.com/ here]].
 == User Experience ==
-<!-- If this change proposal is noticeable by users, how will their experiences change as a result?
+Both integrity detection and protection will be transparent for the user. For protection, the user will notice a change only if his actions (or of a malicious software on his behalf) are not in accordance with the integrity policy being enforced (e.g. the user executes an unsigned binary).
- This section partially overlaps with the Benefit to Fedora section above. This section should be primarily about the User Experience, written in a way that does not assume deep technical knowledge. More detailed technical description should be left for the Benefit to Fedora section.
+== Dependencies ==
- Describe what Users will see or notice, for example:
+* kernel
-  - Packages are compressed more efficiently, making downloads and upgrades faster by 10%.
+* rpm
-  - Kerberos tickets can be renewed automatically. Users will now have to authenticate less and become more productive. Credential management improvements mean a user can start their work day with a single sign on and not have to pause for reauthentication during their entire day.
+* dracut
- - Libreoffice is one of the most commonly installed applications on Fedora and it is now available by default to help users "hit the ground running".
- - Green has been scientifically proven to be the most relaxing color. The move to a default background color of green with green text will result in Fedora users being the most relaxed users of any operating system.
--->
-== Dependencies ==
-<!-- What other packages (RPMs) depend on this package?  Are there changes outside the developers' control on which completion of this change depends?  In other words, completion of another change owned by someone else and might cause you to not be able to finish on time or that you would need to coordinate?  Other upstream projects like the kernel (if this is not a kernel change)? -->
-<!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
+The feature owners will be responsible to submit all the changes necessary and will not depend on other developers' work.
@@ Line 149: / Line 101: @@
 <!-- If you cannot complete your feature by the final development freeze, what is the backup plan?  This might be as simple as "Revert the shipped configuration".  Or it might not (e.g. rebuilding a number of dependent packages).  If you feature is not completed in time we want to assure others that other parts of Fedora will not be in jeopardy.  -->
-* Contingency mechanism: (What to do?  Who will do it?) N/A (not a System Wide Change)  <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
+* Contingency mechanism: remove provided patches from the packages
-<!-- When is the last time the contingency mechanism can be put in place?  This will typically be the beta freeze. -->
+* Contingency deadline: rebuilding the packages without the new patches can be done at any time
-* Contingency deadline: N/A (not a System Wide Change)  <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
+* Blocks release? No
-<!-- Does finishing this feature block the release, or can we ship with the feature in incomplete state? -->
-* Blocks release? N/A (not a System Wide Change), Yes/No <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
 == Documentation ==
-<!-- Is there upstream documentation on this change, or notes you have written yourself?  Link to that material here so other interested developers can get involved. -->
-<!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
+The most comprehensive documentation can be found [[//lore.kernel.org/linux-integrity/20210914163401.864635-1-roberto.sassu@huawei.com/ here]].
-N/A (not a System Wide Change)
 == Release Notes ==
-<!-- The Fedora Release Notes inform end-users about what is new in the release.  Examples of past release notes are here: http://docs.fedoraproject.org/release-notes/ -->
-<!-- The release notes also help users know how to deal with platform changes such as ABIs/APIs, configuration or data file formats, or upgrade concerns.  If there are any such changes involved in this change, indicate them here.  A link to upstream documentation will often satisfy this need.  This information forms the basis of the release notes edited by the documentation team and shipped with the release.
-Release Notes are not required for initial draft of the Change Proposal but has to be completed by the Change Freeze.
+Release notes will be derived from the documentation.
--->

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