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Relocatable Addressing Model for KLEE

The relocatable addressing model enables dynamic merging and splitting of object representations. More details can be found in this paper. This tool is an implementation of that model on top of KLEE.

Build

Requirements

Install the following packages:

sudo apt-get install cmake bison flex libboost-all-dev python perl zlib1g-dev build-essential curl libcap-dev git cmake libncurses5-dev python-minimal python-pip unzip libtcmalloc-minimal4 libgoogle-perftools-dev libsqlite3-dev doxygen
pip3 install tabulate wllvm

LLVM 7.0

wget https://releases.llvm.org/7.0.0/llvm-7.0.0.src.tar.xz
wget https://releases.llvm.org/7.0.0/cfe-7.0.0.src.tar.xz
wget https://releases.llvm.org/7.0.0/compiler-rt-7.0.0.src.tar.xz
tar xJf llvm-7.0.0.src.tar.xz
tar xJf cfe-7.0.0.src.tar.xz
tar xJf compiler-rt-7.0.0.src.tar.xz
mv cfe-7.0.0.src llvm-7.0.0.src/tools/clang
mv compiler-rt-7.0.0.src compiler-rt
mkdir llvm-7.0.0.obj
cd llvm-7.0.0.obj
cmake CMAKE_BUILD_TYPE:STRING=Release -DLLVM_ENABLE_THREADS:BOOL=ON -DLLVM_ENABLE_PROJECTS:STRING=compiler-rt ../llvm-7.0.0.src
make -j4

Update the following environment variables:

export PATH=<llvm_build_dir>/bin:$PATH
export LLVM_COMPILER=clang

minisat

git clone https://github.com/stp/minisat.git
cd minisat
mkdir build
cd build
cmake -DCMAKE_INSTALL_PREFIX=/usr/local/ ../
sudo make install

STP

git clone https://github.com/stp/stp.git
cd stp
git checkout tags/2.3.3
mkdir build
cd build
cmake ..
make
sudo make install

klee-uclibc

git clone https://github.com/klee/klee-uclibc.git
cd klee-uclibc
git checkout 038b7dc050c07a7b4d941b48a0f548eea3089214 # we used that version in our experiments
./configure --make-llvm-lib
make

Our Tool

To build our tool, which is an extension of KLEE, do the following:

mkdir <klee_ram_build_dir>
cd <klee_ram_build_dir>
CXXFLAGS="-fno-rtti" cmake \
    -DENABLE_SOLVER_STP=ON \
    -DENABLE_POSIX_RUNTIME=ON \
    -DENABLE_KLEE_UCLIBC=ON \
    -DKLEE_UCLIBC_PATH=<klee_uclibc_dir> \
    -DLLVM_CONFIG_BINARY=<llvm_build_dir>/bin/llvm-config \
    -DLLVMCC=<llvm_build_dir>/bin/clang \
    -DLLVMCXX=<llvm_build_dir>/bin/clang++ \
    -DENABLE_UNIT_TESTS=OFF \
    -DKLEE_RUNTIME_BUILD_TYPE=Release+Asserts \
    -DENABLE_SYSTEM_TESTS=ON \
    -DENABLE_TCMALLOC=ON \
    <klee_ram_dir>
make -j4

Usage

Command Line Options

We extended KLEE with several command line options. The main options are:

  • use-sym-addr: use the addressing model described in the paper
  • merge-objects: enable dynamic merging of objects
  • split-objects: enable dynamic splitting of objects

Merging related options:

  • reuse-segments: reuse previously allocated segments (supported with deterministic allocator)
  • use-context-resolve: use context-based resolution
  • use-kcontext=k: use k-context abstraction for context-based resolution (default: k = 0)

Splitting related options:

  • split-threshold=N: split objects larger than N bytes
  • partition-size=N: set the size of the split objects

Example

Suppose that we have the following program:

#include <stdio.h>
#include <stdlib.h>
#include <klee/klee.h>

#define N (2)

int main(int argc, char *argv[]) {
    char **array = calloc(N, sizeof(char *));
    for (unsigned int i = 0; i < N; i++) {
        array[i] = calloc(256, 1);
    }

    unsigned int i = klee_range(0, N, "i");
    unsigned int j = klee_range(0, 100, "j");
    if (array[i][j] == 7) {
        printf("...\n");
    }

    return 0;
}

Compile the program:

clang -c -g -emit-llvm -I <klee_include_dir> <source_file> -o <bitcode_file>

Baseline KLEE

When we analyze this program with baseline KLEE:

klee -libc=uclibc <bitcode_file>

we get 2 explored paths, since the symbolic pointer array[i][j] is resolved to two objects.

Merging

To analyze the program with the dynamic merging approach, use the following command:

klee -libc=uclibc -use-sym-addr -merge-objects <bitcode_file>

Now, you will see that only one path is explored, since the two objects pointed by the symbolic pointer are dynamically merged into one segment.

Splitting

To analyze the program with the dynamic splitting approach, use the following command:

klee -libc=uclibc -use-sym-addr -split-objects -split-threshold=100 -partition-size=64 <bitcode_file>

Here, when a big object (w.r.t. the specified threshold) is accessed with a symbolic offset, it is split to smaller objects of at most 64 bytes. As in baseline KLEE, the symbolic pointer array[i][j] is resolved here to two objects, which leads to a fork. Then, each of the forked states accesses a big object (of size 256) with a symbolic offset, so the accessed object is dynamically split into 4 objects. After the split, the symbolic pointer array[i][j] is resolved to the first two smaller objects (since j < 100), and we have an additional fork. In total we have 4 explored paths, which is more than we have with baseline KLEE, but the created SMT arrays are smaller. That can be seen if looking at the query log:

klee -use-query-log=all:kquery -libc=uclibc -use-sym-addr -split-objects -split-threshold=100 -partition-size=64 <bitcode_file>
vi <klee_out_dir>/all-queries.kquery

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