Slashdot Treat

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2. Terra: A Virtual Machine-Based Platform for Trusted Computing Tal Garfinkel, Ben Pfaff, Jim Chow, Mendel Rosenblum, Dan Boneh (Stanford) SOSP’03 Presented by: Michael LeMay

3. Introduction • VM-based architecture for supporting various security models on a single physical machine • Context: Old paper, not fully implementable at the time and many of the techniques are outdated, but principles have still been very influential

4. Outline • Background • Security Requirements • Terra Design • Limitations of Terra • Enhanced Technologies • Conclusion

5. Standard Operating Systems • Large codebases • Difficult to verify correctness and bug-freeness • Offer poor isolation between applications • Compromise in one can affect entire system • Security reduced to level of most vulnerable application • Applications with varying security requirements are unable to share a machine • Don’t provide trusted paths

6. Closed-Box Platforms • Advantages: • Greater security provided by custom hardware and software, perhaps including tamper-resistance • Embedded cryptographic keys can be used to authenticate platform to remote entity • Disadvantages: • Expensive • Unable to utilize standard software for commodity systems

7. Example Closed Boxes • Automated Teller Machines • Many cellphones • Game consoles • All three of the above have been cracked! • Advanced meters • These can be easily attacked • Are there any other closed-box platforms you can think of?

8. What is a closed-box, really? • Something that doesn’t support standard development interfaces by default • Linux: GDB, /dev/kmem, cp, etc. • Open-box • Cellphone: Windows Mobile File Explorer • PS3: ? • Closed boxes

9. Terra Objectives • Combine best aspects of open- and closed-box platforms: • Strong support for privacy and integrity • Support for standard hardware and software • Provide semantics of dedicated, tamper-evident hardware platform to each application • Doesn’t actually use trusted hardware in implementation! Think about implications…

10. Realization • Trusted Virtual Machine Monitor (TVMM) • Assurances: • Isolates VMs • Will not falsely attest VM state • Will not disclose or allow tampering with contents of closed-box VM • These assurances are root-secure • Limitations: • Unable to guarantee availability • Relies on Management VM to provide additional functionality

11. Terra Architecture

12. Trusted Platform Module

13. TPM Interconnection

14. TPM 1.0 Components TCG 1.0 Architecture Overview

15. Credential Types • TPM contains 5 types of credentials: • Important: • Endorsement or EK credential: uniquely identifies TPM, privacy concern • Identity or AIK credential: Issued by privacy CA to preserve privacy of EK credential • Not-so-important: • Conformance credential: Certifies that TPM meets specifications • Platform credential: Identifies TPM manufacturer and capabilities • Validation credential: Associated with peripheral or software to guarantee integrity

16. Threat Model • Threat model dictated by hardware capabilities: • Tamper-evident, not tamper-resistant TPM • Sets bit internally when compromised, but doesn’t zero information • Hardware-protected CPU and memory against adversaries lacking electrical analysis equipment and expertise • Joe pointed out that this assumption was violated on the Xbox • Unprotected disk • Can be removed and inserted into new machine

17. Remote Attestation • Three phases: • Measurement: machine to be attested must measure its properties locally • Attestation: transfer measurements from machine being attested to remote machine • Verification: remote machine examines measurements transferred during attestation and decides whether they are valid and acceptable

18. Linux Integrity Measurement

19. Linux Attestation

20. Linux Verification

21. Terra Attestation Process • Lower layers certify higher layers: • TPM → Firmware → Boot Loader → TVMM → VM → Application • For each layer above TPM: • Upper layer generates public/private keypair • Upper layer requests that lower layer certify its public key and perhaps other data • Lower layer signs certificate with hash over attestable parts of requests as the common name (main identifier) and the hashed data as auxiliary information

22. TVMM Attestation (cont.) • VM disk contents included in attestation • Simple hash tree used to optimize performance • Permits VM to run for indefinite time using false disk hash • Encrypted, integrity-protected, and non-encrypted disks all supported • Keys used to protect disks placed in sealed storage, to prevent attackers from removing disks and performing an offline compromise

23. Attestation Verification • Verify certificate in each layer by ensuring that it is signed by lower layer • TPM certificate is signed by TPM manufacturer, which is also responsible for issuing CRLs • No TPM manufacturer currently does this • Check software hashes and attested data contained within certificates, ensure they are all trusted.

24. Attestation Binding • Verification must be bound to attested process in some way • Exchange certificate chains during SSL handshake • If software is good, it will not persist session key • Prevents system from rebooting and continuing execution in unattested state • This problem was pointed out by John

25. Attestation Limitations • In Terra, PCRs are not necessarily utilized, so no boot history is maintained • Verifying entity must have comprehensive and up-to-date list of trusted software configurations • A simple patch or software upgrade generates entirely new hash • Difficult to obtain meaningful security assurances from simple software hashes

26. Policy-Reduced Integrity Measurement Architecture JaegerSS 2006

27. Attestation Limitations (cont.) • Compromising a TPM key undermines entire process • TPM vendors do not maintain CAs or CRLs • Platform privacy compromised by attestation • Endorsement Key uniquely identifies platform • Privacy CAs issue alternative keys (AIKs), but have an unsustainable business model • Terra proposes group signatures

28. Attestation Limitations (cont.) • Attestation can increase vendor lock-in and platform discrimination by permitting verifying entities to check the exact, complete software stack of the system. • Attestation can only guarantee past and present system properties, it can say very little about the future. • Owner can always turn machine off • Operator can often load new software that violates trust (can be prevented)

29. Attestation Limitations (cont.) • John pointed out that TPM revocation is an issue. Fortunately, TPMs are unlikely to be compromised while the system is running. • Must decide how much state to attest. Should updating the high scores in Trusted Quake break the attestation? • Use separate images for configuration data

30. Attestation Limitations (cont.) • Can’t directly detect MITM exploits • Attestation simply tells you what software is running on system, not the identity of the system • Could corrupt DNS or routing tables and run legitimate server, client wouldn’t be able to detect. • Is this a bad thing? • No, leads to privacy problems.

31. Attestation Limitations (cont.) • Useful for clients attempting to verify security of servers? • No, clients couldn’t possibly be provided with source code for major websites, so attestation would be meaningless. • Is isolation important from the standpoint of attestation? • Somewhat orthogonal, but often an important property being attested.

32. Management VM • Analogous to Xen Dom0 • Performs administrative functions: • Create virtual device (NIC, block dev, etc.) • Creates new VM • Attach/detach virtual device to/from VM • Powers VM up or down • Suspends and resumes VM • Hosts drivers

33. Driver Security • Terra designers do not wish to include drivers in TCB, since they are often buggy • They suggest nooks, but the VM-based driver isolation technique we discussed would also be applicable • Just one of the problems with the suggested Terra architecture

34. Security-Enhanced Xen • Would provide significant benefits to Terra • Mandatory Access Control (MAC) for VM objects and commands • Would permit controlled data sharing between Terra VMs, using shared memory buffers • Currently implemented by IBM as sHype • Xen Security Modules (XSM) provides extended hooks, backwards compatibility with sHype, and support for SELinux-style Type Enforcement policies

35. Security-Enhanced Xen (cont.) • Better TPM support: • Trusted/secure boot • TPM virtualization • Dom0 decomposition • Break management interface into pieces, allow different domains to use various parts • Run drivers in separate domains • Secure I/O • IO-MMU support http://www.xensource.com/files/xs0106_intel_xen_security.pdf, http://www.xensource.com/files/XenSecurity_SHand.pdf

36. TPM Virtualization http://www.xensource.com/files/XenSecurity_Intel_CRozas.pdf

37. Intel LaGrande

38. Intel Trusted Execution Technology (TET) http://www.intel.com/technology/security/downloads/arch-overview.pdf

39. TET System Architecture

40. TET System Implementation • Enter VMM mode using GETSEC[SENTER] instruction, measures VMM before transferring control • CPU provides internal RAM that can execute code after hashing code and verifying against embedded digital signature. Enter Authenticated Code (AC) mode using GETSEC[ENTERACCS] instruction. • Will only run software signed by Intel • Is this a good thing? What if Intel decides they don’t like ATI, so you have to choose between an ATI graphics card and an Intel processor? http://download.intel.com/technology/security/downloads/31516803.pdf

41. ARM TrustZone http://www.arm.com/products/esd/trustzone_home.html

42. Microsoft NGSCB • Microsoft, AMD, HP, IBM, Infineon, Intel, Sun, … all members of TCG • Uses TPM to partitionsystem into two parts:Nexus and L.H.S. • NCAs: Nexus Comput-ing Agents • Only two compartments

43. NGSCB Architecture – WinHEC 2004 • Little device diversity • Only a few drivers • KLOC • Great device diversity • Thousands of drivers • MLOC • Compartments are Windows-based • Significantly reduced footprint • Strongly Isolated, hardened and armored • Secure device ownership • Nexus or service compartments • Windows • Owns most HW • Only real-time OS • Security benefits via scenarios Biddle, 2004

44. Additional Questions • What are some closed-box platforms that could not be easily adapted to run within Terra? • What are some closed-box platforms that could benefit from Terra? • What changes to Terra or its infrastructure are necessary to shrink the first list and/or expand the second?

45. Additional Questions (cont.) • Are Terra-provided closed-box platforms more secure than standard closed-box platforms? • Use tamper-evident hardware for key storage • Would your answer change if the TPM were integrated into the CPU so it can’t be snooped?

46. Conclusion • Very influential general architecture • Proposed before much needed functionality was available, but could be easily updated to use new functionality • More general than NGSCB, but should benefit from NGSCB-inspired hardware

47. Appendices

48. Attested Meter • Distributed Energy Resource management • Demand Reducation/Load Management • Automated Meter Reading/Real Time Pricing

49. Problem • For real-time pricing to work, power company has to know exactly how much power was used by each customer at each point in time • Could be privacy problem • User should be able to access consumer portal software on meter from local network • We’re taking a closed-box platform, a meter, and adding an isolated open-box application • Same thing suggested by Ravinder for Xbox

50. Attested Meter Architecture