nyx.md

Snapshot Fuzzing in Nyx

NYX supports both source-based and binary-only fuzzing.

Currently, libafl_nyx only supports afl++'s instruction type. To install it, you can use sudo apt install aflplusplus. Or compile from the source:

git clone https://github.com/AFLplusplus/AFLplusplus
cd AFLplusplus
make all # this will not compile afl's additional extensions

Then you should compile the target with the afl++ compiler wrapper:

export CC=afl-clang-fast
export CXX=afl-clang-fast++
# the following line depends on your target
./configure --enable-shared=no
make

For binary-only fuzzing, Nyx uses intel-PT(Intel® Processor Trace). You can find the list of supported CPUs at https://www.intel.com/content/www/us/en/support/articles/000056730/processors.html.

Preparing the Nyx working directory

This step is used to pack the target into Nyx's kernel. Don't worry, we have a template shell script in our example:

the parameter's meaning is listed below:

git clone https://github.com/nyx-fuzz/packer
python3 "./packer/packer/nyx_packer.py" \
    ./libxml2/xmllint \   # your target binary
    /tmp/nyx_libxml2 \    # the nyx work directory
    afl \                 # instruction type
    instrumentation \
    -args "/tmp/input" \  # the args of the program, means that we will run `xmllint /tmp/input` in each run.
    -file "/tmp/input" \  # the input will be generated in `/tmp/input`. If no `--file`, then input will be passed through stdin
    --fast_reload_mode \
    --purge || exit

Then, you can generate the config file:

python3 ./packer/packer/nyx_config_gen.py /tmp/nyx_libxml2/ Kernel || exit

Standalone fuzzing

In the example fuzzer you first need to run ./setup_libxml2.sh. It will prepare your target and create your nyx work directory in /tmp/libxml2. After that, you can start to write your code.

First, to create Nyxhelper:

let share_dir = Path::new("/tmp/nyx_libxml2/");
let cpu_id = 0; // use first cpu
let parallel_mode = false; // close parallel_mode
let mut helper = NyxHelper::new(share_dir, cpu_id, true, parallel_mode, None).unwrap(); // we don't need to set the last parameter in standalone mode, we just use None, here

Then, fetch trace_bits, create an observer and the NyxExecutor:

let observer = unsafe { StdMapObserver::from_mut_ptr("trace", helper.trace_bits, helper.map_size) };
let mut executor = NyxExecutor::new(&mut helper, tuple_list!(observer)).unwrap();

Finally, use them normally and pass them into fuzzer.fuzz_loop(&mut stages, &mut executor, &mut state, &mut mgr) to start fuzzing.

Parallel fuzzing

In the example fuzzer you first need to run ./setup_libxml2.sh as described before.

Parallel fuzzing relies on Launcher, so spawn logic should be written in the scoop of anonymous function run_client:

let mut run_client = |state: Option<_>, mut restarting_mgr, _core_id: usize| {}

In run_client, you need to create NyxHelper first:

let share_dir = Path::new("/tmp/nyx_libxml2/");
let cpu_id = _core_id as u32;
let parallel_mode = true;
let mut helper = NyxHelper::new(
    share_dir, // nyx work directory
    cpu_id,    // current cpu id
    true,      // open snap_mode
    parallel_mode, // open parallel mode
    Some(parent_cpu_id.id as u32), // the cpu-id of main instance, there is only one main instance, other instances will be treated as secondaries
)
.unwrap();

Then you can fetch the trace_bits and create an observer and NyxExecutor

let observer = unsafe { StdMapObserver::from_mut_ptr("trace", helper.trace_bits, helper.map_size) }
let mut executor = NyxExecutor::new(&mut helper, tuple_list!(observer)).unwrap();

Finally, open a Launcher as usual to start fuzzing:

match Launcher::builder()
    .shmem_provider(shmem_provider)
    .configuration(EventConfig::from_name("default"))
    .monitor(monitor)
    .run_client(&mut run_client)
    .cores(&cores)
    .broker_port(broker_port)
    // .stdout_file(Some("/dev/null"))
    .build()
    .launch()
{
    Ok(()) => (),
    Err(Error::ShuttingDown) => println!("Fuzzing stopped by user. Good bye."),
    Err(err) => panic!("Failed to run launcher: {err:?}"),
}