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AGL framework overview
======================
Foreword
--------
This document describes what we intend to do. It may happen that our
current implementation and the content of this document differ.
In case of differences, it is assumed that this document is right
and the implementation is wrong.
Introduction
------------
During the first works in having the security model of Tizen
integrated in AGL (Automotive Grade Linux) distribution, it became
quickly obvious that the count of components specific to Tizen
to integrate was huge.
Here is a minimal list of what was needed:
- platform/appfw/app-installers
- platform/core/security/cert-svc
- platform/core/appfw/ail
- platform/core/appfw/aul-1
- platform/core/appfw/libslp-db-util
- platform/core/appfw/pkgmgr-info
- platform/core/appfw/slp-pkgmgr
But this list isn't complete because many dependencies are hidden.
Those hidden dependencies are including some common libraries but also many
tizen specific sub-components (iniparser, bundle, dlog, libtzplatform-config,
db-util, vconf-buxton, ...).
This is an issue because AGL is not expected to be Tizen. Taking it would
either need to patch it for removing unwanted components or to take all
of them.
However, a careful study of the core components of the security framework
of Tizen showed that their dependencies to Tizen are light (and since some
of our work, there is no more dependency to tizen).
Those components are **cynara**, **security-manager**, **D-Bus aware of cynara**.
Luckily, these core security components of Tizen are provided
by [meta-intel-iot-security][meta-intel], a set of yocto layers.
These layers were created by Intel to isolate Tizen specific security
components from the initial port of Tizen to Yocto.
The 3 layers are providing components for:
* Implementing Smack LSM
* Implementing Integrity Measurement Architecture
* Implementing Tizen Security Framework
The figure below shows the history of these layers.
![Security_model_history][Security_model_history]
We took the decision to use these security layers that provide the
basis of the Tizen security, the security framework.
For the components of the application framework, built top of
the security framework, instead of pulling the huge set of packages
from Tizen, we decided to refit it by developing a tiny set of
components that would implement the same behaviour but without all
the dependencies and with minor architectural improvements for AGL.
These components are **afm-system-daemon** and **afm-user-daemon**.
They provides infrastructure for installing, uninstalling,
launching, terminating, pausing and resuming applications in
a multi user secure environment.
A third component exists in the framework, the binder **afb-daemon**.
The binder provides the easiest way to provide secured API for
any tier. Currently, the use of the binder is not absolutely mandatory.
This documentation explains the framework created by IoT.bzh
by rewriting the Tizen Application Framework. Be aware of the
previous foreword.
<!-- pagebreak -->
Overview
--------
The figure below shows the major components of the framework
and their interactions going through the following scenario:
APPLICATION installs an other application and then launch it.
![AppFW-APP_install_sequences][AppFW-APP_install_sequences]{style width:70%}
Let follow the sequence of calls:
1. APPLICATION calls its **binder** to install the OTHER application.
2. The binding **afm-main-binding** of the **binder** calls, through
**D-Bus** system, the system daemon to install the OTHER application.
3. The system **D-Bus** checks wether APPLICATION has the permission
or not to install applications by calling **CYNARA**.
4. The system **D-Bus** transmits the request to **afm-system-daemon**.
**afm-system-daemon** checks the application to install, its
signatures and rights and install it.
5. **afm-system-daemon** calls **SECURITY-MANAGER** for fulfilling
security context of the installed application.
6. **SECURITY-MANAGER** calls **CYNARA** to install initial permissions
for the application.
7. APPLICATION call its binder to start the nearly installed OTHER application.
8. The binding **afm-main-binding** of the **binder** calls, through
**D-Bus** session, the user daemon to launch the OTHER application.
9. The session **D-Bus** checks wether APPLICATION has the permission
or not to start an application by calling **CYNARA**.
10. The session **D-Bus** transmits the request to **afm-user-daemon**.
11. **afm-user-daemon** checks wether APPLICATION has the permission
or not to start the OTHER application **CYNARA**.
12. **afm-user-daemon** uses **SECURITY-MANAGER** features to set
the security context for the OTHER application.
13. **afm-user-daemon** launches the OTHER application.
This scenario does not cover all the features of the frameworks.
Shortly because details will be revealed in the next chapters,
the components are:
* ***SECURITY-MANAGER***: in charge of setting Smack contexts and rules,
of setting groups, and, of creating initial content of *CYNARA* rules
for applications.
* ***CYNARA***: in charge of handling API access permissions by users and by
applications.
* ***D-Bus***: in charge of checking security of messaging. The usual D-Bus
security rules are enhanced by *CYNARA* checking rules.
* ***afm-system-daemon***: in charge of installing and uninstalling applications.
* ***afm-user-daemon***: in charge of listing applications, querying application details,
starting, terminating, pausing, resuming applications and their instances
for a given user context.
* ***afb-binder***: in charge of serving resources and features through an
HTTP interface.
* ***afm-main-binding***: This binding allows applications to use the API
of the AGL framework.
Links between the "Security framework" and the "Application framework"
----------------------------------------------------------------------
The security framework refers to the security model used to ensure
security and to the tools that are provided for implementing that model.
The security model refers to how DAC (Discretionary Access Control),
MAC (Mandatory Access Control) and Capabilities are used by the system
to ensure security and privacy. It also includes features of reporting
using audit features and by managing logs and alerts.
The application framework manages the applications:
installing, uninstalling, starting, pausing, listing ...
The application framework uses the security model/framework
to ensure the security and the privacy of the applications that
it manages.
The application framework must be compliant with the underlying
security model/framework. But it should hide it to the applications.
The security framework
----------------------
The implemented security model is the security model of Tizen 3.
This model is described [here][tizen-secu-3].
The security framework then comes from Tizen 3 but through
the [meta-intel].
It includes: **Security-Manager**, **Cynara**
and **D-Bus** compliant to Cynara.
Two patches are applied to the security-manager. The goal of these patches
is to remove specific dependencies with Tizen packages that are not needed
by AGL.
None of these patches adds or removes any behaviour.
**In theory, the security framework/model is an implementation details
that should not impact the layers above the application framework**.
The security framework of Tizen provides "nice lad" a valuable component to
scan log files and analyse auditing. This component is still in development.
The application framework
-------------------------
The application framework on top of the security framework
provides the components to install and uninstall applications
and to run it in a secured environment.
The goal is to manage applications and to hide the details of
the security framework to the applications.
For the reasons explained in introduction, we did not used the
application framework of Tizen as is but used an adaptation of it.
The basis is kept identical: the applications are distributed
in a digitally signed container that must match the specifications
of widgets (web applications). This is described by the technical
recommendations [widgets] and [widgets-digsig] of the W3 consortium.
This model allows the distribution of HTML, QML and binary applications.
The management of signatures of the widget packages.
This basis is not meant as being rigid and it can be extended in the
future to include for example incremental delivery.
[meta-intel]: https://github.com/01org/meta-intel-iot-security "A collection of layers providing security technologies"
[widgets]: http://www.w3.org/TR/widgets "Packaged Web Apps"
[widgets-digsig]: http://www.w3.org/TR/widgets-digsig "XML Digital Signatures for Widgets"
[libxml2]: http://xmlsoft.org/html/index.html "libxml2"
[openssl]: https://www.openssl.org "OpenSSL"
[xmlsec]: https://www.aleksey.com/xmlsec "XMLSec"
[json-c]: https://github.com/json-c/json-c "JSON-c"
[d-bus]: http://www.freedesktop.org/wiki/Software/dbus "D-Bus"
[libzip]: http://www.nih.at/libzip "libzip"
[cmake]: https://cmake.org "CMake"
[security-manager]: https://wiki.tizen.org/wiki/Security/Tizen_3.X_Security_Manager "Security-Manager"
[app-manifest]: http://www.w3.org/TR/appmanifest "Web App Manifest"
[tizen-security]: https://wiki.tizen.org/wiki/Security "Tizen security home page"
[tizen-secu-3]: https://wiki.tizen.org/wiki/Security/Tizen_3.X_Overview "Tizen 3 security overview"
[AppFW-APP_install_sequences]: pictures/AppFW-APP_install_sequences.svg
[Security_model_history]: pictures/Security_model_history.svg
|
