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Xen Project 15 Years down the Line


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What do “Crazy in Love” by Beyonce and the “Xen Project” have in common? They are both 15-year-old hits. Flash forward to today. The Xen Project is used by more than 10 million users, powers some of the largest clouds on the planet, and is starting to build momentum in embedded and safety-conscious market segments. The Xen Project played a key role in developing technologies outside of the hypervisor, like hardware virtualization, and open source security disclosure standards that impact entire industries.

The Xen Project’s success and longevity can be attributed to its flexible architecture, but more importantly to enabling community members to contribute ideas and code, even if they are not core to the project's main use-case. We will share how the project has supported new technologies and ideas (sometimes in the form of failures and sometimes wins) and will derive best practices that may help other projects .

Published in: Technology
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Xen Project 15 Years down the Line

  1. 1. Xen Project 15 Years Down the Line: Thinking Outside of the Conceived Tech Comfort Zone
  2. 2. Lars Kurth Community Manger, Xen Project Chairman, Xen Project Advisory Board Director, Open Source, Citrix Contributors Andrew Cooper: Committer, Xen Project ◉ Christopher Clark: Contributor, Xen Project Mihai Donțu: Chief Linux Officer, Bitdefender ◉ George Dunlap: Committer, Xen Project lars_kurth
  3. 3. Happy Birthday!
  4. 4. What is Xen and Xen Project? Versatile Virtualization Platform Designed to be a component in a SW stack Ease of use for end-users was never a design goal Xen Hypervisor = “Engine” Taken by integrators to build a product, service, … Analogy: integrators build a “car” with Xen as “engine” Xen Project Development community with several sub projects that develop technologies related to Xen – Hypervisor – PV Drivers – Unikernel related projects: MirageOS, Unikraft
  5. 5. Rewind to the Beginning
  6. 6. Original Use Cases Server Consolidation Co-located hosting facilities, Distributed web services Cloud Computing Secure Computing Platforms and Application Mobility High availability, Fault tolerance, Checkpointing
  7. 7. Original Design Goals Modular architecture Via disaggregation Flexible architecture Via use of system services High degree of customisability Initial goal: server and possibility of desktop products
  8. 8. OpenXT, SecureView (desktop, laptops, tablets) Defense Applications Unikernels Cyberchaff (HalVM) Defense Applications Xenon Hypervisor family, Magrana Server, … Cloud Computing Amazon Web Services, Tencent, Alibaba Cloud, Oracle Cloud, IBM SoftLayer, Rackspace, … Server Virtualization Linux Distros, Citrix Hypervisor, Huawei UVP, Oracle VM, XCP-ng ARLX/Virtuosity OA, Bromium uXen, Crucible Hypervisor Embedded Defense / Security Applications Embedded/ Automotive Virtuosity, XILINX Xen Zynq, Perseus, GlobalLogic Nautilus, EPAM Fusion General purpose desktop and mobile Virtualization XenClient, NxTop, Neosphere, Samsung, Qubes OS VMI Bitdefender, AIS, Zentific
  9. 9. So, how did we get to such a diverse product eco-system?
  10. 10. Strong Security mindset by main Xen Developers
  11. 11. From the Beginning Disaggregation was part of the original Xen conception Influenced by microkernel thinking VMn Guest OS Applications VM0 (or Dom0) Dom0 Kernel Native Driver System Services XS TSDE Scheduler MMU Timers Interrupts
  12. 12. From the Beginning Disaggregation was part of the original Xen conception Influenced by microkernel thinking VMn Guest OS Applications VM0 (or Dom0) Dom0 Kernel System Services XS TS Scheduler MMU Timers Interrupts Driver Domain Guest OS Native Driver Service Domain Guest OS System Services DE Disaggregate Disaggregate
  13. 13. From the Beginning Disaggregation was part of the original Xen conception Influenced by microkernel thinking The PV protocols were specifically designed for untrusted backends and untrusted native device drivers Particularly the grant tables Security technologies were always in maintainers minds They were up-streamed without resistance Sometimes with a lot of support from maintainers
  14. 14. Today: Used by … OpenXT, SecureView (desktop, laptops, tablets) Defense Applications Unikernels Defense Applications Xenon Hypervisor family, Magrana Server, … Cloud Computing Server Virtualization ARLX/Virtuosity OA, Crucible Hypervisor Embedded Defense / Security Applications Automotive Virtuosity, GlobalLogic Nautilus, EPAM Fusion General purpose desktop and mobile Virtualization Qubes OS VMI
  15. 15. Tension: Core vs. non-Core Usage Many security technologies were not made easy to use Disaggregation is a good example Product schedule pressure, led to – Core team members choosing the quick to implement / more performant approach ➜ New features went into Dom0 first – Maintainers reviewing non-Core contributions: takes effort to understand and guide contributors to the best approach ➜ This did often not happen E.g. Xen has no build capability for disaggregated domains Led to duplication amongst vendors Increased the barrier to adoption for newcomers
  16. 16. Strong Security Mindset Enabled non-Core Security Contributions
  17. 17. From Military Clouds to Desktop/Tablet Use Cases on x86
  18. 18. Xen Summit: 2007, New York, USA
  19. 19. Xen Summit: 2007, New York, USA US DoD employees presented approaches to Apply EAL5 Common Criteria Security Clearance for Xen Xen Security Modules (XSM) EAL5 CC related research led to the Xenon Separation VMM family Today: widely used by DoD departments XSM was subsequently upstreamed Defense Applications Xenon Hypervisor family, Magrana Server, … Server Virtualization Linux Distros, Citrix Hypervisor, Huawei UVP, Oracle VM, XCP-ng
  20. 20. 2012: The Xenon Separation VMM Secure virtualization infrastructure for military clouds (pdf) “ We reduce the size of the code base by dropping support for selected features that are not needed to run commodity operating systems, e.g. Windows 7 or Linux. Because the internal design and construction of the base Xen VMM is highly modular, removing some of the features does not disable any of the remaining features. The total effort required was about 3 engineers over a period of 2 years, and includes the effort of keeping up with the Xen community. ”
  21. 21. x86: Desktop / Tablet Use Cases 2009: Virtual Computer releases NxTop 1.0 NxTop is the first of 3 Xen based client solutions Citrix and Neocleus release their first solutions in 2010 2012: Snowden-approved Qubes OS 1.0 releases Today, Qubes OS 4.0 is the first technology to use PVHv2 in production 2013: Citrix and DoD collaborate to create SecureView In 2015, XenClient is discontinued and released as OpenXT SecureView continues to be developed on top of OpenXT OpenXT, SecureView (desktop, laptops, tablets) Defense Applications General purpose desktop Virtualization XenClient, NxTop, Neosphere, Qubes OS
  22. 22. Reflection Early & continued engagement of Security Researchers Security feature contributions before being productized Xen became an attractive platform for security research Enabler: The Xen community accepted contributions Modular Architecture Enabled specialised and certifiable products for defence use But: Innovations were not attempted to be up-streamed
  23. 23. Reflection Attempts to commercialize Xen on Desktop Enabled a new products leveraging Xen’s security features They also relied on removing upstream Xen code (on x86) BUT: None of these Xen capabilities were used in Server/Cloud Related Story: GPU Passthrough & Virtualization Were developed for Desktop Use Cases on Xen TODAY: GPU Virtualization is widely used in Server/Cloud
  24. 24. Virtual Machine Introspection: from Research to Commercial Server Products
  25. 25. Georgia Tech: 2007, Atlanta, USA
  26. 26. Georgia Tech: 2007, Atlanta, USA 2007: Virtual Machine Introspection for Xen hatched at Georgia Tech – 2003: Initial Research by Tal Garfinkel & Mendel Rosenblum – Bryan Payne created a project called XenAccess Later expanded scope to other hypervisors as LibVMI 2009: XenAccess and mem-events APIs were added Used for security research and specialist security apps Enabler: The project accepted these changes with active help from maintainers
  27. 27. Commercial interest in VMI 2013 to 2015: Intel launched its Haswell & Broadwell CPUs Specifically VMFUNC, EPTP and #VE capabilities New HW capabilities of Haswell & Broadwell generated commercial interest in VMI by multiple vendors 2014 to 2015: The XenAccess and mem-events APIs were re-architected into the VMI subsystem In parallel: related companion technologies such as alt2pm are being developed
  28. 28. Productization 2015 to 2016: Citrix and Bitdefender collaborated to bring VMI to market through XenServer 7.0 and Bidefender HVI Today: Similar products are available from AIS and Zentific Today: ongoing contributions by security vendors to alt2pm indicate future productization
  29. 29. Reflection Few security features made it into Server/Cloud For example: VMI & Live Patching WHY? HW capabilities were not enough It was too early or the market wasn’t ready Example: Dynamic Root of Trust related technologies Complex and Use Case dependent Example: Xen Security Modules - requires Specialist expertise; configuration is Use Case dependent
  30. 30. From Desktop / Mobile Use Cases to Embedded / Automotive
  31. 31. 2008, Seoul, Korea
  32. 32. Samsung releases Secure Xen on Arm port This Xen port used paravirtualization and was kept as a Xen fork hosted by the Xen Project as requested by Samsung 2008 to 2014: Samsung regularly shows Xen demos Dual mobile operating systems running on Samsung devices and later Nexus 10 Demos and presentations covered – Innovations in real-time capabilities based on Xen – GPU sharing technologies based on Xen 2008, Seoul, Korea
  33. 33. This showed what is possible Inspiring others to investigate and research along similar lines
  34. 34. 2012, Cambridge, UK
  35. 35. 2012, Cambridge, UK Xen on Arm reboot Patches for upstream Xen on Arm support are posted Armv7 and v8 are fully supported upstream by March 2014 The primary motivation for this work was to target Arm based servers Developers learned from the earlier Arm port: – Clean and simple architecture – Perfect match between Xen and Arm ISA – Much smaller code size compared to Xen on x86
  36. 36. Upstream support and simplicity of Arm port enabled embedded Use Cases on Arm
  37. 37. The missing Evolutionary Link From x86 to Arm 2010: Dornerworks contributes the ARINC653 Scheduler Launches ARLX (initially for x86) taking a similar approach to Xenon 2014: Dornerworks pioneers safety certification for Xen OpenXT, SecureView (desktop, laptops, tablets) Defense Applications General purpose desktop Virtualization XenClient, NxTop, Neosphere, Qubes OS ARLX/Virtuosity OA, Crucible Hypervisor Embedded Defense / Security Applications
  38. 38. A new Evolutionary Wave 2014: Xen moves into embedded and automotive The Xen Project launched an automotive initiative Xen based distros and products are being developed 2015: First automotive Xen based platform GlobalLogic introduces the Nautilus platform at CES 2015 2015: First embedded Arm-only Xen Distro Xen Zynq Distribution for XILINX The last few years: R&D Similar order of magnitude to earlier waves
  39. 39. Sedimentation: from Software to Hardware
  40. 40. Sedimentation: Functionality implemented in Software being fully or partly implemented in Hardware Example: PV Interrupt and Timers ➜ using IO APIC and Posted Interrupts Silicon vendors have always worked closely with Xen Xen’s had a significant impact on virtualization related technology in Hardware I wanted to tell this story, but: It’s very difficult to explain And much of the work was performed under NDAs
  41. 41. What have we learned? What can you learn from Xen?
  42. 42. Culture enables Innovation Accept changes for non-Core Use Cases In our case this was not planned: we inherited the culture But: do not sacrifice due diligence and future-proofing Help people trying to adopt Xen for non-Core Use Cases We were bad at this until about 3 years ago Work with new ideas, forks and distributions Developer Events: allow air-time for new ideas Forks are not always bad: Samsung fork hosted by us OpenXT (distro): close collaboration is key
  43. 43. Process enables Innovation Feature/Configuration Classification Experimental ➜ Tech Preview ➜ Supported Marked non-Core functionality as Experimental or Preview Maintainership Contributors need to step up for larger non-Core Features Proves longer term commitment by the contributor Deprecation of Features Intent to deprecate is announced on list: identify objections Remove non-core Features, if stale or not used
  44. 44. Tension need to be Managed Vendors have different Priorities These can lead to conflicts Non-Core vs. Core arguments can be ugly Active community management is required New Processes can lead to Tensions Security Vulnerability Management led to problems Who deals with a Vulnerability in non-Core code? We didn’t understand this ➜ created tension and rejection of non-Core features until we modified the process
  45. 45. Process enables Innovation Security Support The security team does not handle non-Core Vulnerabilities – Supported Feature without Security Support – Delegated Security Support (e.g. ARINC653 scheduler) KCONFIG based Configuration Management Larger non-core features are build or run-time disabled Subprojects as incubators for New Ideas Can be used to foster innovation on the periphery Examples: MirageOS, Automotive Project, Unikraft
  46. 46. Picture by Lars Kurth
  47. 47. References