Proposal 50: Learn the IMA keyrings and keys from the log

Signed-off-by: Stefan Berger <[email protected]>

Author: stefanberger

50-learn-ima-keys.md

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+# enhancement-50: Learn the keys IMA is using for signature verification
+
+<!--
+This is the title of your enhancement.  Keep it short, simple, and descriptive.  A good
+title can help communicate what the enhancement is and should be considered as part of
+any review.
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+<!--
+A table of contents is helpful for quickly jumping to sections of a enhancement and for
+highlighting any additional information provided beyond the standard enhancement
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+<!-- toc -->
+- [Release Signoff Checklist](#release-signoff-checklist)
+- [Summary](#summary)
+- [Motivation](#motivation)
+  - [Goals](#goals)
+  - [Non-Goals](#non-goals)
+- [Proposal](#proposal)
+  - [User Stories (optional)](#user-stories-optional)
+    - [Story 1](#story-1)
+    - [Story 2](#story-2)
+  - [Notes/Constraints/Caveats (optional)](#notesconstraintscaveats-optional)
+  - [Risks and Mitigations](#risks-and-mitigations)
+- [Design Details](#design-details)
+  - [Test Plan](#test-plan)
+  - [Upgrade / Downgrade Strategy](#upgrade--downgrade-strategy)
+- [Drawbacks](#drawbacks)
+- [Alternatives](#alternatives)
+- [Infrastructure Needed (optional)](#infrastructure-needed-optional)
+<!-- /toc -->
+
+## Release Signoff Checklist
+
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+**Note:** This checklist is iterative and should be reviewed and updated every time this enhancement is being considered for a milestone.
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+
+## Summary
+
+<!--
+This section is incredibly important for producing high quality user-focused
+documentation such as release notes or a development roadmap.  It should be
+possible to collect this information before implementation begins in order to
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+A good summary is probably at least a paragraph in length.
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+
+IMA's policy implements support for policy rules that cause keys loaded onto kernel
+keyrings to be logged in the IMA measurement log in 'ima-buf' entries. This now
+provides the opportunity to also learn the keys that IMA is using for signature verification
+from these 'ima-buf' entries, where the DER-encoded public key is reported as part
+of the measurement log entry. The learned keys can then be used to verify the
+subsequent signatures found in the log.
+
+
+## Motivation
+
+Recent extensions to Keylime's allowlist (policy) enable Keylime to verify 'ima-buf'
+entries similar to verifying file entries and their allowed hashes. If IMA is now
+reporting keys loaded onto keyrings then the allowlist must have the corresponding
+entries for the keyrings, otherwise the system will fail log verification.
+Having these entries in the allowlist implies that the system administrator agrees
+to the list of keys being loaded and therefore Keylime can also learn which keys are
+used by a given system for signature verification and also use those keys from the
+measurement log to verify the signatures itself rather than the administrator having
+to provide the keys.
+
+<!--
+This section is for explicitly listing the motivation, goals and non-goals of
+this enhancement.  Describe why the change is important and the benefits to users.
+-->
+
+### Goals
+
+<!--
+List the specific goals of the enhancement.  What is it trying to achieve?  How will we
+know that this has succeeded?
+-->
+
+The goal of this enhancement is to make the management of IMA signature verification
+keys easier. Since a system administrator has to provide allowed keys' hashes in
+the allowlist already he should not have to provide the IMA signature verification
+keys for Keylime to be able to verify file signatures.
+
+### Non-Goals
+
+<!--
+What is out of scope for this enhancement?  Listing non-goals helps to focus discussion
+and make progress.
+-->
+
+## Proposal
+
+<!--
+This is where we get down to the specifics of what the proposal actually is.
+This should have enough detail that reviewers can understand exactly what
+you're proposing, but should not include things like API designs or
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+-->
+
+Based on data from the 'ima-buf' log entries where IMA reports keys loaded
+onto a system's keyrings, Keylime will learn which keyrings are in use
+on a system and can then model those keyrings and the keys associated with
+them. It can then use those keys for signature verification.
+
+The modeled keys and keyrings will be persisted in the database to support
+incremental attestation.
+
+### User Stories (optional)
+
+<!--
+Detail the things that people will be able to do if this enhancement is implemented.
+Include as much detail as possible so that people can understand the "how" of
+the system.  The goal here is to make this feel real for users without getting
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+
+#### Story 1
+
+A system administrator using an IMA policy rule like the following does not
+need to manage a system's IMA signature verification keys anymore since Keylime
+will learn about the existence of the .ima keyring and the keys loaded onto it.
+
+   measure func=KEY_CHECK keyrings=.ima
+
+### Notes/Constraints/Caveats (optional)
+
+<!--
+What are the caveats to the proposal?
+What are some important details that didn't come across above.
+Go in to as much detail as necessary here.
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+
+### Risks and Mitigations
+
+<!--
+What are the risks of this proposal and how do we mitigate.  Think broadly.
+For example, consider both security and how this will impact the larger
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+
+## Design Details
+
+<!--
+This section should contain enough information that the specifics of your
+change are understandable.  This may include API specs (though not always
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+-->
+
+The Keyime database will need to be extended with a column for storing
+the keyrings and keys learned from the IMA log.
+Every time a system is attestated to starting with log entry 0 the previously
+learned keyring and keys are discarded since the IMA log is expected to
+again report the keyrings and keys.
+
+### Test Plan
+
+<!--
+**Note:** *Not required until targeted at a release.*
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+All code is expected to have adequate tests (eventually with coverage
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+
+### Upgrade / Downgrade Strategy
+
+<!--
+If applicable, how will the component be upgraded and downgraded? Make sure
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+Consider the following in developing an upgrade/downgrade strategy for this enhancement
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+The keylime database will be upgradable and downgradable with an
+SQL Alchemy script.
+
+### Dependencie requirements
+
+<!--
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+No new dependencies will be introduced.
+
+## Drawbacks
+
+<!--
+Why should this enhancement _not_ be implemented?
+-->
+
+None known.
+
+## Alternatives
+
+<!--
+What other approaches did you consider and why did you rule them out?  These do
+not need to be as detailed as the proposal, but should include enough
+information to express the idea and why it was not acceptable.
+-->
+
+If a system administrator does not provide this type of an IMA policy rule then
+he/she will have to provide the IMA signature verification keys as before.
+
+## Infrastructure Needed (optional)
+
+<!--
+Use this section if you need things infrastructure related specific to your enhancement.  Examples include a
+new subproject, repos requested, github webhook, changes to CI (travis).
+-->