Here is a presentation about Maemo 6 Platfrom Security, which was given during FOSDEM 2010 event.

1. Maemo 6
Platform Security
Overview
Elena Reshetova
1

2. Outline
• What is Platform Security?
• Maemo 6 Device modes & Boot process
• Access Control
• Our criteria
• Basic principles & concepts
• Aegis Security Policy & SW distribution
• Installation and Run-time views
• Shared libraries case
• Integrity Protection
• Aegis Validator
• Aegis Protected Storage
• IPC Security
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3. What is Platform Security?
• Set of a mechanisms and
techniques, which are used to
protect the entire SW platform
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4. Device modes
• Open source strategy • Bigger developer offering
• The same functionality as earlier • Optional copy protection (DRM)
• Compile and flash your own kernel • More use cases for a device usage
• Made a low-level platform • Games, Commercial applications
development • More business models
• Ovi Store
• Comes with Music
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5. Hardware enablers & Boot process
• Trusted Execution
Environment (TrEE) (for
instance ARM Trust Zone)
with two main keys:
• Root public key Restrict security
• Root device specific key functionality
* includes:
• DRM keys are disabled
• Content from the previous
mode can’t be decrypted
Integrity isn’t OK
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6. Access Control
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7. Access control in Linux
• Classical Unix AC
• Based on multiuser model
• Discretionary AC
• POSIX capabilities aren’t really in use (root has all, others none)
• Our criteria:
• Process level mandatory access control needed
• Minimal changes to the current model (enforcement phase)
• Good level of flexibility and granularity, easy to understand concept (KISS)
• Existing security extensions, no good match to criteria
• FreeBSD AC, MLS, Biba, SELinux, RBAC, AppArmor, TOMOYO Linux, …
• Our approach:
• Apply, and minimally extend Classical Unix AC to meet set criteria
• Re-use multiuser-model for application-level access control
• Architecture outlined in the next slides.
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8. Access Control – Principles & Concepts
• Principle of least privileges
• Every application should be able to access only limited set of needed resources
• Protected resources
• Things like Cellular functionality, Location information and so on
• No final list yet – work in progress
• Resource token
• Abstract name describing a protected resource
• Cellular, Location, and etc.
• Application must declare resources, it needs
• Aegis Manifest File
• No security APIs by default  Development is almost unchanged
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9. Aegis Manifest File
• An optional xml file inside Debian package
• Declares needed and provided credentials
• Resource tokens
• UIDs, GUIs
• POSIX capabilities
• Should be generated automatically by SDK based on the source code
• A D-Bus policy can be generated from Aegis Manifest during installation phase
• May contain a package signature
• Used for authorized security policy updates
• Application Identifier
AppID = {SWSourceID, PackageName, AppName}
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10. Software Distribution
• SW comes inside Debian packages
• Each package has SW source (known or unknown)
• SW repository (based on the repository signing)
• Any virtual entity (based on the package signing) as single developer, web page and etc.
• Each known SW source has a asymmetric key pair
• Public key is known to a device
• Private key is used to sign the packages
• Each SW source is assigned a trust level
• Update of SW package is possible only from the same SW source or from a SW source with
higher trust level
• SW source trust is based on the
Quality Assurance level of the SW source
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11. Aegis Security Policy
• Contains mapping between SW sources and allowed credentials
• Accessible only to Installer
• Allows to create different security levels on the devices
• The allowed credential set for each SW source is based on the risk level
• Can be updated via authorized policy updates
• Special domains:
• Unknown
• Developer
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12. Components Interaction – Installation time
Aegis Application
1. Application arrives to the Manifest
Aegis Installer together 1.
with Aegis Manifest
2. Aegis installer checks the Aegis
Aegis Security policy for the D-Bus D-Bus Daemon Security
policy Installer
information policy D-Bus
extensions
3. Aegis installer modifies User mode
the Credentials’ possession
3.
list according to the
“Intersection rule” Kernel mode
[4.] Aegis installer possibly
modifies D-Bus policy Credentials’
Possession
list
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13. Intersection rule
Example
SW source
Aegis Manifest
credentials set:
credentials set:
What credentials
intersection application can
What application
get, if it is certified
wants to access?
by this SW source?
Result credentials set:
What credentials application
has during run-time?
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14. Components Interaction – Run-time
1. Process Credentials Assigner gets the Aegis Application
allowed credentials set from the Manifest
Credentials’ possession list
2. Process Credentials Assigner
modifies process’ credentials
(process task structure) according to Aegis
D-Bus Daemon Security
the received credentials D-Bus
policy Installer
policy D-Bus
3a. File AC extensions
• No changes User mode
3b. D-Bus
• Additional process credentials are
taken into consideration by the d- Kernel mode
Process
bus daemon File’s AC lists
credentials
3c. Application by itself Credentials’
Possession
• Application calls libcreds library to list
“Linux Kernel
get process credentials, and makes a Reference monitor”
decision based on its own policy Process
Credentials
assigner
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15. Loading the shared libraries
No!
Yes
Cellular,
UserData
Application OK Call
Library A
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16. Integrity Protection
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17. Integrity protection – Aegis Validator
• Ensures integrity of the
executable components
(binaries, libraries, ...)
Yes
• Run-time
• Against Offline attacks
• Kernel module Storage of
• Calculates a cryptographic Aegis reference
hash of the file (currently Validator hashes
No!
SHA-1)
• Reference hashes Get the
policy
• Stored in the Aegis
Protected Storage
• Come inside of the package
or can be computed during
installation time
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18. Privacy Protection - Aegis Protected Storage
• Ensures integrity of data and
configuration files after
installation Place the files
Integrity
Check
Application into status
Protected
• Additional features: integrity
Storage
• Data encryption inside the
storage
• Private, shared and global or Data file
externally signed storages Aegis
Protected
• Interface to TrEE, which is used Configuration Storage APIs
to sign/verify, encrypt/decrypt file
the data
• Access to a protected storage is
defined by an application
identifier or application group
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19. Secure IPC
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20. Secure IPC inside device
• Maemo Crypt API
• Ensures integrity and
confidentially of the
transmitted data
• Signing
• Encryption
• No key management from
applications
• Different levels
• Based on application ID
• Based on the resource token
Check the signature
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21. Conclusions & QA
• Most of the Security FW will be open sourced
• Public project “Maemo 6 Platform Security”
• http://maemo.gitorious.org/
• Your questions, feedback and reports are welcomed!
• http://wiki.maemo.org/MaemoSecurity
• http://talk.maemo.org/forumdisplay.php?f=45
• https://bugs.maemo.org/
• More details will still follow…
Thank you!
elena.reshetova@nokia.com
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