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Mimesis

Mimesis is a formal model extraction tool that automatically generates a model describing all packet forwarding behavior given a software network function as input. It utilizes S2E, KLEE, and LLVM for symbolic execution on the binary of the input network function to analyze its packet forwarding behavior, and translates the resulting SMT formulas to BDD-based structures. The extracted model covers all (potentially stateful) packet forwarding behavior and is compactly encoded in our custom format. The model output can be queried independently or used in other formal analysis, including network verification.

Environment setup

We provide a convenience script depends/setup.sh to automate the setup process for the dependencies required to build and run Mimesis. Currently the script only supports Arch Linux and Ubuntu 22.04. Please read depends/setup.sh for the details if one wants to install them manually.

After cloning the repository, enter the directory and run the following command. This will set up S2E and build the QEMU VM image required for the symbolic analysis. The results will be at the s2e/ directory.

$ ./depends/setup.sh

Important

After running the setup script, it is crucial to logout and re-login again for the new group configuration to take effect. Otherwise, there may be permission errors from Docker. Alternatively, you can also reboot the OS entirely.

Build Mimesis and S2E

To build Mimesis, including the core libraries, example target programs, SystemTap modules, and the custom S2E plugin, please run:

$ ./scripts/build.sh --mimesis --stap --s2e

Note

If any Mimesis code, SystemTap scripts, or the S2E code in src/s2e/ are modified, you can rebuild all of them by running the command again.

Run unit tests (optional)

After building Mimesis, you can run the unit tests to make sure the essential functions like libps are working properly.

$ ./scripts/test.sh

Usage

Here we demonstrate step by step how to use Mimesis to extract a formal model from an example network function program, user-hello-world, which is a simple echo server that sends any received packet to its ingress interface without modification.

Create a new analysis project

The first step is to create a new analysis project via S2E with the following command. The created project will be located at s2e/projects/mimesis/.

$ ./scripts/s2e.sh -n ./build/targets/user-hello-world

Important

Creating a new analysis project will remove the previously created projects (maybe of a different target program). You can manually save the previous project directories if so desired.

Note

By default the model is created with 4 interfaces. It is possible to explicitly specify the number of interfaces for the extracted model with command-line options, such as ./scripts/s2e.sh -i 8 -n <target program>. See ./scripts/s2e.sh -h for more options.

Run the symbolic execution

Once the project is created, you can start the analysis by running the following command. The -c option force-removes any files of previous runs, and the -r option starts the symbolic execution.

$ ./scripts/s2e.sh -c -r

(TODO: Explain how to interpret the result.)

Remove the analysis projects (Optional)

When the symbolic execution is completed, you can remove the created projects by running the following command.

$ ./scripts/s2e.sh --rm

Future work

The current prototype is built upon S2E and KLEE. However, the core idea of Mimesis is not tied to a specific implementation. It is possible to implement Mimesis on other symbolic analysis tools such as Angr. This may be helpful to expand the scope of supported programs to DPDK-based network functions, which are not currently supported due to the limitation of S2E's QEMU.