Code Verification for Practical Machine Architectures

Download

The software for the x86isa project developed over the course of this program is available for download (licensed under BSD 3-Clause) as a part of the ACL2 community books.

Here is the github page: ACL2 System and Books as Maintained by the Community.

The x86isa books are located at: acl2/books/projects/x86isa and documentation is available here.

People



Keshav Kini

(PhD Student)

J Moore

(Professor)

Ben Selfridge

(PhD Student)

Nathan Wetzler

(PhD Candidate)

Previous Members of the CRASH Team:



Natahlie Beavers

(Undergraduate Student)

Soumava Ghosh

(Masters Student)

Robert Krug

(Research Engineering/

Scientist Associate IV)

Corbyn Salisbury

(Undergraduate Student) Théo Zimmermann

(CS Graduate Student)

Problem Description

Research Goals

Develop an executable, formal specification for a significant subset of the x86 instruction set architecture (ISA). Our focus is on the 64-bit mode of Intel's IA-32e mode. Our current version of the model has a simulation speed of ~3.3 million instructions/second in its programmer-level mode (where we operate at the level of linear memory) and and ~920,000 instructions/second with a two-level page table configuration in its system-level mode (where we operate at the level of physical memory). We support almost 120 general-purpose instructions (221 opcodes) and 80 SSE/SSE2 instructions. Construct a mechanized proof assistant for x86 binary code. The development of a formal specification, discussed above, is a critical step towards reaching this goal. The efficient executability of that specification is also critical, in order to validate the model by co-simulation against actual x86 execution. We will use the ACL2 theorem prover to carry out code proofs, both using BDD/SAT-based symbolic simulation and by developing methods based on general-purpose theorem proving techniques, especially rewriting and induction. Improve the ACL2 theorem proving environment. This is a long-term goal that our research group continues to pursue. ACL2 is our core formal verification technology, so improvements to ACL2 support the research goals discussed above, such as the ``abstract stobjs'' feature. Develop tools to gain confidence in satisfiability (SAT) solvers. Researchers develop high performance applications called SAT solvers to efficiently solve satisfiability problems, and any problem that can be encoded into a Boolean formula can be investigated with SAT solvers. It is easy to check a solution to a satisfiability problem if one can be found. However, if a solver outputs that a formula is unsatisfiable, we must trust that the solver exhausted all possible assignments. Existing verification tools cannot verify all techniques used in state-of-the-art solvers. Create automated, sophisticated satisfiability encodings with respect to software verification. The encoding of problems, such as software verification, into Boolean formulas has a huge impact on the performance of SAT solvers. We will develop techniques that, given a certain high-level description, will make a high quality translation of the problem into a Boolean formula.

Technical Approach

Our previous work suggests that we can build ACL2 proof infrastructure on top of that model, though the complexity of the x86 architecture presents new challenges. In support of this work, we will continue to improve the ACL2 proof environment. We will also employ symbolic simulation, which is an effective approach to software verification, and develop capabilities to apply, in a sound way, BDDs and SAT techniques, which together are the most used techniques for symbolic simulation.

Dissemination of Research Results

models/y86/

SOFTWARE

The ACL2 theorem proving system has been publicly available for about two decades, and is currently available from the ACL2 home page. It is in regular use at several companies, including AMD, Centaur Technology (VIA Technology), IBM, and Rockwell Collins. It has and continues to be used by U.S. government personnel, some of whom have expressed interest in our x86 model in particular.

Visit the ACL2 home page to obtain the latest version of ACL2 and to view that system's documentation.

PUBLICATIONS

This link to our project's publications page lists 30 publications from this project.









