The node s corresponds to the basic block whose leader is the. Control flow graph factory eclipse plugins, bundles and. Control flow graphs control flow graph cfg graph representation of computation and control flow in the program framework for static analysis of program controlflow nodes are basic blocks straightline, singleentry code, no branching except at end of sequence edges represent possible flow of control from the. I control ow graph cfg is a directed graph in which the nodes. Controlflow analysis sample exercises and solutions. Reconstruct controlflow graph from x86 instruction trace. Reverse engineering stack exchange is a question and answer site for researchers and developers who explore the principles of a system through analysis of its structure, function, and operation. Cyclomatic complexity is a software metric used to measure the complexity of a program. Models operations in the functional modelno conditionals. In such cases, the complexity of determining the control. For a good example of this obfuscation, check apples fairplay code, e. A general model for hiding control flow researchgate. So far i have found a couple eclipse plugins heavily dependent on eclipse apis and standalone tools cannot embed in my code.
Formal verification of control flow graph flattening. Cs412cs4 introduction to compilers tim teitelbaum lecture. Then b 1 is a predecessor of b 2, and b 2 is a successor. In this paper, we formally verify in coq an advanced code obfuscationcalled controlflow graph flattening, that is used in. Our controlflow graph flattening is a program transformation operating over c programs, that is in tegrated into the compcert formally verified compiler. Thes e are used for global optimizations as opposed to optimizations local to basic block. Avrora control flow graph tool ucla compilers group. Control flow graph, dominators and natural loops for the program below. Control flow graph the control flow graph g n, e of a program consists of a set of nodes n and a set of edge e. You can access this graph by right clicking on a function or method and selecting graphical viewscluster control flow. The control flow graphs of the original and the obfuscated code show the change in the structure of the program, i. In this paper we provide a uniform and detailed formal. I determining the execution order of program statements or instructions i control ow graph cfg speci es all possible execution paths i important control ow constructs program constructs important to control ow i basic block. Our control flow graph flattening is a program transformation operating over c programs, that is integrated into the compcert formally verified compiler.
Control flow graph nodes represent computation each node is a basic block basic block is a sequence of instructions with no branches out of middle of basic block no branches into middle of basic block basic blocks should be maximal execution of basic block starts with first instruction. Formal verification of controlflow graph flattening acm digital. Allocation and mapping scheduling asap, alap, listbased scheduling controldata flow graph represents control dependencies. There is a directed edge from block b 1 to block 2 if 2 immediately follows 1 in some execution sequence. Determine the dominators of each node in the cfg 3. We would like to show you a description here but the site wont allow us. This report aims to remove the dispatcher added in the flattenedprogram and rebuild the control flow of its original program. All lir instructions are numbered serially using the block order and every. Formal verification of controlflow graph flattening core. A general model for hiding control flow esat ku leuven. A control flow path is a graphical representation of all paths that might be traversed through a program during its execution. Control flow graphs nodes statements or basic blocks maximal sequence of code with branching only allowed at end edges possible transfer of control example. Retrust workshop jan cappaert an overview of cfg flattening 723 introduction control flow graph cfg nodes. These are used for global optimizations as opposed to optimizations local to basic block.
In this paper, we formally verify in coq an advanced code obfuscation called control flow graph flattening, that is used in stateoftheart program obfuscators. For example, our antibranchanalysis transformation flattens a function prior to replacing direct branches by calls to a branch function since this creates more opportunities for encoding. Conceptually, we can distinguish between two broad classes of obfuscating. Since theresults on the impossibility of perfect and universal obfuscation,many obfuscation techniques have been proposed in the literature,ranging from simple variable encoding to hiding the control flow ofa program. Control flow graphs we will now discuss flow graphs. Control flow analysis sample exercises 2 spring 2010 problem1. Control flow graphs control flow graph cfg graph representation of computation and control flow in the program framework to statically analyze program controlflow in a cfg. Either kind of graph is referred to as a cfg in statementlevel cfg, we often use a node to explicitly represent merging of control control merges when two different cfg nodes point to the same node note. In computer science, a controlflow graph cfg is a representation, using graph notation, of all paths that might be traversed through a program during its execution. The semantics preservation proof of our program obfuscator relies on a simulation proof performed on a realistic language, the clight language of compcert. Controlflow flattening preserves the constanttime policy.
Control flow graphs i control ow analysis aims to determine the execution order of program statements or instructions i basic block. It refers to the order in which the individual statements, instructions, or function calls of an imperative or functional program are executed or evaluated. Aka flow cycle allows patient to determine their own i time by terminating the breath once a certain percentage of the peak inspiratory flow is met may improve preload and eliminate vq mismatching improves patientventilator dsysynchrony may tremendously improve oxygenation and ventilation in spontaneously breathing patients. A new version of the control flow graph has been added that allows much more interactivity. There is an edge from node n 1 to node n 2 if the control may flow from the last statement in n. Formal verification of controlflow graph flattening irisa. What might be a good java library to generate control flow graphs in java.
The used ssa construction algorithm is based on simple and efficient construction of static single assignment form by braun et al. Control flow graph factory is an eclipse plugin which generates control flow graphs from java bytecode, edit them and export to graphxml, dot or several image formats. I need to manipulate control flow graphs for java code in a project. Likewise, because foo will eventually returns to baz and to wherever else it mightve been called from, there will be an edge from the end of foos graph back to the statement after the call to foo in baz. Compilers use control flow graph cfg representations of lowlevel. This metric measures independent paths through the programs source code. While the realcontrol flow of the program is merely disclosed during the execution of the program. A graph approach to quantitative analysis of controlflow. There is a unique entry node and a unique exit node. In this paper, we formally verify in coq an advanced code obfuscationcalled control flow graph flattening, that is used in. Control flow graph tool a control flow graph is a representation of a program where contiguous regions of code without branches, known as basic blocks, are represented as nodes in a graph and edges between nodes indicate the possible flow of the program.
The global controlflow graph optimizing an eventdriven realtime system across kernel boundaries christian dietrich, martin ho. The control flow graph is flattened to a list and the node names are painted on the xaxis. What is a controlflow flattening obfuscation technique. In order to simplify its analysis, it is beneficial to convert the control flow graph into a. Getting coflo to parse your source code coflo must be able to fully parse the source files you give it, which means that any necessary commandline defines and include paths must be specified. Controlflow graph, dominators and natural loops for the program below.
Controlflow analysis sample exercises 2 spring 2010 problem1. Some algorithms are represented best in flow charts to help any user to better understand each step involved in the program or algorithm. A controlflowsensitive analysis and optimization framework for. The basic blocks within one procedure are organized as a control ow graph, or cfg. A control flow graph cfg is a representation, using graph notation, of all paths that might be traversed through a program during its execution. Prosser used boolean connectivity matrices for flow analysis before the cfg is essential to many compiler optimizations and staticanalysis tools. The new graph lets you collapse and expand subsections of the graph by double clicking in the bounding box of that area. We explain what control flow graph flattening is and illustrate why it is successful as protection against static control flow analysis. Heres a typical graph of a function which had this. Allocation and mapping scheduling asap, alap, listbased scheduling controldata flow graph. Sample flowcharts are diagrams or visual representations of the steps taken that make up a process.
Image showing how controlflow flattening obfuscation alters code that contains loop structures. In computer science, a control flow graph cfg is a representation, using graph notation, of all paths that might be traversed through a program during its execution. Compared with other control flow graph obfuscation methods such as control flow flattening 26 and. This is a classic controlflow transformation that removes structured flow. Csc 453 basic blocks and flow graphs university of arizona. After you have succesfully installed the plugin you should get in the outline view the flow chart generator menu item. Control flow graphs and code coverage robertgold faculty of electrical engineering and computer science ingolstadt university of applied sciences, esplanade 10, d85049 ingolstadt, germany email. The targeted obfuscation scheme is the control flow flattening, which is an obfuscation method focusing on hiding the control flow of a program. Prosser used boolean connectivity matrices for flow analysis before. A graph approach to quantitative analysis of controlflow obfuscating transformations article in ieee transactions on information forensics and security 42. Structural operational semantics for control flow graph. Such a graph assists testers in the analysis of a program to understand its behavior in terms of the flow of control.
Inria formal verification of controlflow graph flattening. To achieve the targets, this report presents a deobfuscation model based on thecontrol flow graph of an obfuscated program. The control flow flattening is a control flow obfuscation technique that flattens the control flow graph so that all the basic block will have same predecessor and successor. Automatic generation of several types of control flow graphs from java bytecode. Friedrichalexander university erlangennuremberg 19. Discussion some times we will also consider the statementlevel cfg, where each node is a statement rather than a basic block either kind of graph is referred to as a cfg in statementlevel cfg, we often use a node to explicitly represent merging of control control merges when two different cfg nodes point to the same node note. Also, the merge transformation can optionally flatten functions before. Pure php implementation of a control flow graph cfg with instructions in static single assignment ssa form. May 19, 2014 a cfg captures the flow of control within a program. Other styles of control flow graph output, such as png renderings of the graph, as well as analyses coflo can perform, are described below. Basic blocks and flow graphs control flow graphs we divide the intermediate code of each procedure into basic blocks. This scheme introduces a special block named dispatcher. Pdf protecting a software from unauthorized access is an ever demanding task. Does not require that nodes be fired in a particular order.
Retrust workshop jan cappaert an overview of cfg flattening 323 overview introduction and related research cfg flattening experiments and ideas conclusions and future work. Thus, in this paper, we focus on the protection of source code by means of obfuscation and discuss the adaptation of a control ow. Protecting a software from unauthorized access is an ever demanding task. The node s corresponds to the basic block whose leader is the first statement. The deflattening model makes use of both static analysis and dynamic analysis. In this paper, we formally verify in coq an advanced code obfuscation called controlflow graph flattening, that is used in stateoftheart program obfuscators. Flattening is useful as a precursor to other transformations. Furthermore, we propose a scheme, complementary to control. Formal verification of controlflow graph flattening. Control flow graph cfg a control flow graphcfg, or simply a flow graph, is a directed graph in which. The features of the control flow graph factory are. Viz an entry block through which control enters into the flow graph and the exit block through which all control flow leaves.
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