The lecture by Norman Feske for Summer Systems School'12. Genode Components SSS'12 - Education event, organized by ksys labs[1] in 2012, for students interested in system software development and information security. Genode[2] - The Genode operating-system framework provides a uniform API for applications on top of 8 existing microkernels/hypervisors: Linux, L4ka::Pistachio, L4/Fiasco, OKL4, NOVA, Fiasco.OC, Codezero, and a custom kernel for the MicroBlaze architecture. 1. http://ksyslabs.org/ 2. http://genode.org

1. Genode OS Framework - Components
Norman Feske
<norman.feske@genode-labs.com>

2. Outline
1. Classification of components
2. Kernelization example
3. Unified configuration concept
4. Session routing
5. Components overview
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3. Outline
1. Classification of components
2. Kernelization example
3. Unified configuration concept
4. Session routing
5. Components overview
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4. Classification
Kernel enables base platform
Device driver translates device interface to API
Protocol stack translates API to API
Application is leaf node in process tree
Runtime environment has one or more children
Resource multiplexer has multiple clients
combinations are possible
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5. Kernel
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6. Device driver
Translates device interface to session interface
Uses core’s IO MEM, IO PORT, IRQ services
Single client
Contains no policy
Enforces policy (device-access arbitration)
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7. Device driver (2)
Critical because of DMA
MMU protects physical memory from driver code
Driver code accesses device via MMIO
Device has access to whole physical memory (DMA)
→ Device driver can access whole physical memory
IOMMUs can help ...but are no golden bullet
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8. Device driver (3)
Even with no IOMMU, isolating drivers has benefits
Taming classes of non-DMA-related bugs
Memory leaks
Synchronization problems, dead-locks
Flawed driver logic, wrong state machines
Device initialization
Minimizing attack surface from the outside
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9. Protocol stack
Translates API to another (or the same) API
Does not enforce policy
Single client
May be co-located with device driver
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10. Protocol stack (2)
Libraries
Library Translation
Qt4 Qt4 API → various Genode sessions
lwIP socket API → NIC session
Components translating sessions
Component Translation
TCP terminal Terminal session → NIC session
iso9660 ROM session → Block session
ffat fs File-system session → Block session
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11. Protocol stack (3)
Components that filter sessions
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12. Protocol stack (4)
Operate on session interfaces, not physical resources
→ May be instantiated any number of times
→ Critical for availablility
→ Not neccessarily critical for integrity and confidentiality
→ Information leakage constrained to used interfaces
complex code should go in here
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13. Application
Leaf node in process tree
Uses services
Implements application logic
Provides no service
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14. Runtime environment
Hosts other processes as children
Defines and imposes policy!
Examples
Init
Virtual machine monitor
Debugger
Python interpreter
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15. Resource multiplexer
Multiplexes session interface
Multiple clients → Potential multi-level component
Free from policy
Enforce policy dictated by parent
Prone to cross-client information leakage
Prone to resource-exhaustion-based DoS
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16. Resource multiplexer (2)
→ Often as critical as the kernel
→ Must be as low complex as possible
→ Must work on client-provided resources
→ Must employ heap partitioning
only a few resource multiplexers needed
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17. Outline
1. Classification of components
2. Kernelization example
3. Unified configuration concept
4. Session routing
5. Components overview
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18. Kernelizing the GUI server
Persistent security problems of GUIs
Impersonation
(Trojan horses, phishing, man in the middle)
Spyware
(input loggers, arcane observers)
Robustness/availability risks
(resource-exhaustion-based denial of service
GUI belongs to TCB → low complexity is important!
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19. Starting point: DOpE as secure GUI
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20. DOpE as secure GUI - Drawbacks
Prone to resource exhaustion by malicious clients
Provides custom look and feel*
Stands in the way when using legacy software
May be enhanced by theme support
Complexity of 12,000 LOC
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21. Straight-forward attempt: Shrinking DOpE
Revisiting the implementation
Keeping only essential functionality
→ 7,000 LOC
We loose:
Majority of widgets (grid, scale, scrollbar, etc.)
Flexible command interface
Coolness, fancyness, convenience
Real-time support
7,000 LOC are too much for such a crippled GUI!
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22. Bottom-up approach
What do we really need in the GUI server?
Widgets? → No
Font support? → No
Window decoration? → No
Textual command interface? → No
Look and feel, gradients, translucency? → No
Hardware abstractions (e. g., color-space conversion)? → No
Windows displaying pixel buffers? → YES
Distribution of input events? → YES
Secure labeling? → YES
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23. Buffers and views
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24. User interaction
Input-event handling
Only one receiver of each input event
Focused view defines input routing
Routing controlled by the user only
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25. Client-side window handling
Report motion events to focused view while a button is pressed
→ Client-side window policies (move, resize, stacking)
→ Key for achieving low server-side complexity
Emergency break
→ Special key regains control over misbehaving applications
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26. Trusted path
It is not sufficient to label windows!
A Trojan Horse could present an image of a secure window
Not the secure window must be marked, but all others!
Revoke some degree of freedom from the clients
Dedicated screen area, reserved for the trusted GUI
Revoking the ability to use the whole color space
→ X-Ray mode, activated by special key (x-ray key)
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27. Trusted path (2)
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28. Nitpicker results
Source-code complexity
GUI server Lines of code
X.org > 80,000
Trusted X 30,000
DOpE 12,000
EWS 4,500
Nitpicker < 2,000
Low performance overhead, no additional copy
Low-complexity clients are possible (Scout: 4,000 LOC)
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29. Nitpicker results (2)
Support for legacy software
Protection against spyware
Helps to uncover Trojan horses
Low source-code complexity
→ Poster child of a resource multiplexer
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30. Outline
1. Classification of components
2. Kernelization example
3. Unified configuration concept
4. Session routing
5. Components overview
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31. Traditional approaches to system configuration
Boot-loader configuration
vbeset command in GRUB menu.lst
Command line arguments specified to boot modules
Kernel command line
Custom configuration files
Needs file providers, file name space
Varying syntax → parsing problems
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32. Unified configuration concept
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33. Unified configuration concept (II)
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34. Unified configuration concept (III)
→ Uniform syntax
→ Extensible through custom tags at each level
→ XML parser adds less than 300 LOC to TCB
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35. Outline
1. Classification of components
2. Kernelization example
3. Unified configuration concept
4. Session routing
5. Components overview
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36. Session routing example
<config>
<parent-provides>
<service name="CAP"/>
<service name="LOG"/>
</parent-provides>
<start name="timer">
<resource name="RAM" quantum="1M"/>
<provides> <service name="Timer"/> </provides>
<route>
<service name="CAP"> <parent/> </service>
</route>
</start>
<start name="test-timer">
<resource name="RAM" quantum="1M"/>
<route>
<service name="Timer"> <child name="timer"/> </service>
<service name="LOG"> <parent/> </service>
</route>
</start>
</config>
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37. Using wildcards
<route>
<service name="ROM"> <parent/> </service>
<service name="RAM"> <parent/> </service>
<service name="RM"> <parent/> </service>
<service name="PD"> <parent/> </service>
<service name="CPU"> <parent/> </service>
</route>
generalized:
<route>
<any-service> <parent/> </any-service>
</route>
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38. Combining wildcards with explicit routes
<route>
<service name="LOG"> <child name="nitlog"/> </service>
<any-service> <parent/> </any-service>
</route>
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39. Useful routing template
<route>
<any-service> <parent/> </any-service>
<any-service> <any-child/> </any-service>
</route>
abbreviated:
<route>
<any-service> <parent/> <any-child/> </any-service>
</route>
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40. Poly-instantiating the same binary
<start name="nit_fb">
...
<start name="nit_fb"> <!-- XXX ambiguous name! -->
...
ambiguity resolved:
<start name="nit_fb_1">
<binary name="nit_fb"/> <!-- binary name != process name -->
...
<start name="nit_fb_2"> <!-- unique name -->
<binary name="nit_fb"/>
...
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41. Routing through hierarchies
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42. Routing through hierarchies (2)
<config>
<parent-provides> ... </parent-provides>
<start name="timer"> <resource name="RAM" quantum="1M"/>
<provides> <service name="Timer"/> </provides>
<route> <service name="CAP"> <parent/> </service> </route>
</start>
<start name="init"> <resource name="RAM" quantum="1M"/>
<config>
<parent-provides>
<service name="Timer"/> <service name="LOG"/>
</parent-provides>
<start name="test-timer"> <resource name="RAM" quantum="1M"/>
<route> <service name="Timer"> <parent/> </service>
<service name="LOG"> <parent/> </service> </route>
</start>
</config>
<route> <service name="Timer"> <child name="timer"/> </service>
<any-service> <parent/> </any-service> </route>
</start>
</config>
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43. Real-time priorities
Kernels provide static priorities
How to make the feature available?
Priorities have side effects on otherwise unrelated subsystems
Priority inversion
Priority inversion + time-slice donation = hard-to-find bug
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44. Real-time priorities (2)
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45. Real-time priorities (3)
<config prio_levels="2">
...
<start name="init.1" priority="0">
...
<config prio_levels="4">
...
<!-- priority -1 results in platform priority 112 -->
<start name="init.11" priority="-1"> ... </start>
<!-- priority -2 results in platform priority 96 -->
<start name="init.12" priority="-2">
<config>
<start name="init.121"> ... </start>
</config>
</start>
</config>
</start>
<!-- priority -1 results in platform priority 64 -->
<start name="init.2" priority="-1"> ... </start>
</config>
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46. Configuration concept in practice
Development
Wildcards are handy
Concise configurations, easy to maintain
Deployment
Use explicit routes only
→ Default deny
→ Whitelist only permitted session types
→ Mandatory access control
Absence of wildcards is easy to validate
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47. Outline
1. Classification of components
2. Kernelization example
3. Unified configuration concept
4. Session routing
5. Components overview
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48. Interfaces
LOG Unidirectional debug output
Terminal Bi-directional input and output
synchronous bulk
Timer Facility to block the client
Input Obtain user input
synchronous bulk
Framebuffer Display pixel buffer
synchronous bulk
PCI Represents PCI bus, find and obtain PCI devices
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49. Interfaces (2)
ROM Obtain read-only data modules
shared memory
Block Block-device access
packet stream
File system File-system access
packet stream
NIC Bi-directional transfer of network packets
2 x packet stream
Audio out Audio output
packet stream
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50. Device drivers
Session type Location
Timer os/src/drivers/timer
Block os/src/drivers/atapi
os/src/drivers/ahci
os/src/drivers/sd card
dde linux/src/drivers/usb drv
Input os/src/drivers/input/ps2
dde linux/src/drivers/usb drv
Framebuffer os/src/drivers/framebuffer/vesa
os/src/drivers/framebuffer/sdl
os/src/drivers/framebuffer/pl11x
os/src/drivers/framebuffer/omap4
Audio out linux drivers/src/drivers/audio out
Terminal os/src/drivers/uart
NIC dde ipxe/src/drivers/nic
dde linux/src/drivers/usb drv
PCI os/src/drivers/pci
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51. Resource multiplexers and protocol stacks
Session type Location
LOG os/src/server/terminal log
demo/src/server/nitlog
Framebuffer, demo/src/server/liquid framebuffer
Input os/src/server/nit fb
Nitpicker os/src/server/nitpicker
Terminal os/src/server/terminal crosslink
gems/src/server/terminal
gems/src/server/tcp terminal
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52. Resource multiplexers and protocol stacks (2)
Session type Location
Audio out os/src/server/mixer
NIC os/src/server/nic bridge
ROM os/src/server/rom prefetcher
os/src/server/tar rom
os/src/server/iso9660
Block os/src/server/rom loopdev
os/src/server/part blk
gems/src/server/http block
File system os/src/server/ram fs
libports/src/server/ffat fs
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53. Protocol-stack libraries
API Location
POSIX libports/lib/mk/libc.mk
libports/lib/mk/libc log.mk
libports/lib/mk/libc fs.mk
libports/lib/mk/libc rom.mk
libports/lib/mk/libc lwip.mk
libports/lib/mk/libc ffat.mk
libports/lib/mk/libc lock pipe.mk
libports/lib/mk/libc terminal.mk
Qt4 qt4/lib/mk/qt *
OpenGL libports/lib/mk/gallium.mk
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54. Runtime environments
Runtime Location
Init os/src/init
Loader os/src/server/loader
L4Linux ports-foc/src/l4linux
L4Android ports-foc/src/l4android
OKLinux ports-okl4/src/oklinux
Vancouver ports/src/vancouver
Noux ports/src/noux
GDB Monitor ports/src/app/gdb monitor
Python libports/lib/mk/x86 32/python.mk
Lua libports/lib/mk/moon.mk
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55. Thank you
What we covered today Coming up next...
Components Compositions
1. Classification of components 1. Virtualization techniques
2. Kernelization of the GUI 2. Enslaving services
server 3. Dynamic workloads
3. Unified configuration
concept
4. Session routing
5. Components overview
More information and resources:
http://genode.org
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