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Implementing TALT

Explore the innovative techniques discussed at ALADDIN REU Symposium 2003 focusing on grid computing, typed assembly language, safety establishment, and trusted theorem proving methods. Learn about TALT, Typed Assembly Language, safety verification, and certificate generation methodologies.

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Implementing TALT

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  1. Implementing TALT William Lovas with Karl Crary ALADDIN REU Symposium 2003

  2. Grid Computing • Low-cost supercomputing using idle cycles of Internet-connected PCs • Cray X1 supercomputer: $8.4 million • Pentium 4, 2.2 GHz: $699 (with rebate!) • Getting everyone else’s PCs to do your work for you: priceless ALADDIN REU Symposium 2003

  3. Grid Computing PCs on The Internet Developer ALADDIN REU Symposium 2003

  4. Grid Computing • SETI@Home project at Berkeley • scanning radio signals for signs of intelligence • Folding@Home project at Stanford • studying diseases related to protein folding • distributed.net • cracking encryption algorithms since 1997 ALADDIN REU Symposium 2003

  5. Grid Computing • Very powerful: distributed.net, 22 hours to brute force 1 DES key out of 256 (= over 72 quadrillion!) • distributed.net equivalent to 160,000 Pentium II 266 MHz PCs ALADDIN REU Symposium 2003

  6. Grid Computing • Few examples, because grid computing depends on users’ trust in the code they run • ConCert Project: to develop a framework for trustless grid computing ALADDIN REU Symposium 2003

  7. Roadmap • Motivation: check! • Methodology of TALT: the “how” and “why” • A taste of TALT: to whet your appetite • My work on TALT: what I accomplished, what I learned ALADDIN REU Symposium 2003

  8. Establishing Safety • How can we verify that code is safe? • High-level languages use type systems… • Why can’t low-level languages, too? ALADDIN REU Symposium 2003

  9. Typed Assembly Language • Formalizes a subset of x86 instruction set • Adds a type system that demonstrates safety • Idea: employ powerful tools from type theory to tame the assembly language beast! • subtyping, polymorphism ALADDIN REU Symposium 2003

  10. TALT -- TAL Two • Refines and extends the ideas from TAL • Establishes a framework for future type systems • One type system won’t meet everyone’s needs “Two type systems good => Four type systems better!” -- Benjamin C. Pierce ALADDIN REU Symposium 2003

  11. Trusted Twelf proof checker … and meta-theorem prover Safety policy (SP) safe machine states, safe transitions Runtime Untrusted Code Type system (TS) Safety proof (TS(p) => SP(p)) Machine-checkable, via Twelf How TALT works ALADDIN REU Symposium 2003

  12. How TALT works code type system Twelf type system safety proof safety policy code runtime ALADDIN REU Symposium 2003

  13. A taste of TALT • Many interesting ideas, let’s talk about 3: • Register file subtyping • Universal polymorphism • Sized kinds white lies ahead! ALADDIN REU Symposium 2003

  14. A taste of TALT Register file subtyping ALADDIN REU Symposium 2003

  15. A taste of TALT • Register file type looks like • { r0: t0, r1: t1, … rn: tn } • Suppose a code-block expects: • { eax: int, ebx: int } • Okay if register file actually has type: • { eax: int, ebx: int, ecx: int } • Because of register file subtyping! ALADDIN REU Symposium 2003

  16. A taste of TALT Universal polymorphism ALADDIN REU Symposium 2003

  17. A taste of TALT • Suppose a function f leaves the stack unchanged • Stack pointer stored in register esp • How does a calling function know? • f has a type polymorphic in esp! • Just like SML: - fun id x = x; val id = fn : 'a -> 'a ALADDIN REU Symposium 2003

  18. A taste of TALT Sized kinds ALADDIN REU Symposium 2003

  19. A taste of TALT • Kinds: the “types of types” • In TALT, the kind of a type specifies the size of that type’s values • A 4-byte word has type B4, which has kind T4 • Pair of words has type B4*B4, which has kind T8 • Typing rules know the sizes of operands • Essential for complex addressing modes ALADDIN REU Symposium 2003

  20. My work on TALT • Implementation of infrastructure • Runtime • Certificate generator • “Assembler” • Creation of new code as well as simplification/extension of existing code ALADDIN REU Symposium 2003

  21. Runtime implementation • Runtime provides primitive operations, like malloc, exit, return • Works directly with machine code, so written in C, with some x86 assembly • Great care taken to adhere to specification: runtime is trusted! ALADDIN REU Symposium 2003

  22. Certificate Generation • TALT binary looks like this: magic number machine code code certificate ALADDIN REU Symposium 2003

  23. Certificate Generation • Certificate generator generates: magic number machine code code certificate ALADDIN REU Symposium 2003

  24. Certificate Generation • When I arrived… • Certificate was a typing derivation in the TALT type system • Partially implemented and buggy derivation generator • Discovery: typing derivation too big to use as a practical certificate ALADDIN REU Symposium 2003

  25. Certificate Generation • And now… • Certificate is an XTALT program, in a notation that Twelf understands • Certificate generator is 97% complete (and hopefully not buggy!) • Code is much simpler • Type system is a little simpler, too ALADDIN REU Symposium 2003

  26. “Assembler” • Next step: translate XTALT programs into straight x86 assembly • Assembly can be run through a standard assembler to produce machine code ALADDIN REU Symposium 2003

  27. “Assembler” • Now we also have: magic number machine code code certificate ALADDIN REU Symposium 2003

  28. “Assembler” • Then, only have to put the pieces together to produce TALT binaries! ALADDIN REU Symposium 2003

  29. Summary • Implemented TALT runtime in C, assembly • Implemented certificate generator in SML • Simplified typing rules • Simplified code • Hope to implement “assembler” by next week • Very close to a working system! ALADDIN REU Symposium 2003

  30. Summary • Didn’t “discover” anything new, but … • Learned a lot about type theory, and … • Hacked on some interesting code! Questions? ALADDIN REU Symposium 2003

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