Efficient Concolic Execution Via Branch Condition Synthesis
SYNFUZZ: Efficient Concolic Execution via Branch Condition Synthesis Wookhyun Han∗, Md Lutfor Rahmany, Yuxuan Chenz, Chengyu Songy, Byoungyoung Leex, Insik Shin∗ ∗KAIST, yUC Riverside, zPurdue, xSeoul National University Abstract—Concolic execution is a powerful program analysis the path exploration as if the target branch has been taken. To technique for exploring execution paths in a systematic manner. generate a concrete input that can follow the same path, the Compare to random-mutation-based fuzzing, concolic execution engine can ask the SMT solver to provide a feasible assignment is especially good at exploring paths that are guarded by complex and tight branch predicates (e.g., (a*b) == 0xdeadbeef). The to all the symbolic input bytes that satisfy the collected path drawback, however, is that concolic execution engines are much constraints. Thanks to the recent advances in SMT solvers, slower than native execution. One major source of the slowness is compare to random mutation based fuzzing, concolic execution that concolic execution engines have to the interpret instructions is known to be much more efficient at exploring paths that to maintain the symbolic expression of program variables. In this are guarded by complex and tight branch predicates (e.g., work, we propose SYNFUZZ, a novel approach to perform scal- (a*b) == 0xdeadbeef able concolic execution. SYNFUZZ achieves this goal by replacing ). interpretation with dynamic taint analysis and program synthesis. However, a critical limitation of concolic execution is its In particular, to flip a conditional branch, SYNFUZZ first uses scalability [6, 9, 61]. More specifically, a concolic execution operation-aware taint analysis to record a partial expression (i.e., engine usually takes a very long time to explore “deep” a sketch) of its branch predicate.
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