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Diffstat (limited to 'nyx_mode/README.md')
| -rw-r--r-- | nyx_mode/README.md | 49 |
1 files changed, 35 insertions, 14 deletions
diff --git a/nyx_mode/README.md b/nyx_mode/README.md index eee7d363..7a2a8e6c 100644 --- a/nyx_mode/README.md +++ b/nyx_mode/README.md @@ -84,9 +84,17 @@ Then the final step: we generate the Nyx package configuration: python3 nyx_mode/packer/packer/nyx_config_gen.py PACKAGE-DIRECTORY Kernel ``` - ## Fuzzing with Nyx mode +Note that you need to load the kvm kernel modules for Nyx: +``` +sudo modprobe -r kvm-intel +sudo modprobe -r kvm +sudo modprobe kvm enable_vmware_backdoor=y +sudo modprobe kvm-intel +cat /sys/module/kvm/parameters/enable_vmware_backdoor | grep -q Y && echi OK || echo KVM module problem +``` + All the hard parts are done, fuzzing with Nyx mode is easy - just supply the `PACKAGE-DIRECTORY` as fuzzing target and specify the `-X` option to afl-fuzz: @@ -94,16 +102,8 @@ All the hard parts are done, fuzzing with Nyx mode is easy - just supply the afl-fuzz -i in -o out -X -- ./PACKAGE-DIRECTORY ``` -Most likely your first run will fail because the Linux modules have to be -specially set up, but afl-fuzz will tell you this on startup and how to rectify -the situation: - -``` -sudo modprobe -r kvm-intel # or kvm-amd for AMD processors -sudo modprobe -r kvm -sudo modprobe kvm enable_vmware_backdoor=y -sudo modprobe kvm-intel # or kvm-amd for AMD processors -``` +If you get a forkserver error upon starting then you did not load the Linux +kvm kernel modules, see above. If you want to fuzz in parallel (and you should!), then this has to be done in a special way: @@ -150,12 +150,12 @@ afl-cmin -i in_dir -o out_dir -X -- ./PACKAGE-DIRECTORY On each program startup of one the AFL++ tools in Nyx mode, a Nyx VM is spawned, and a bootstrapping procedure is performed inside the VM to prepare the target environment. As a consequence, due to the bootstrapping procedure, the launch performance is much slower compared to other modes. However, this can be optimized by reusing an existing fuzzing snapshot to avoid the slow re-execution of the bootstrap procedure. -A fuzzing snapshot is automatically created and stored in the output directory at `out_dir/workdir/snapshot/` by the first parent process of `afl-fuzz` if parallel mode is used. To enable this feature, set the path to an existing snapshot directory in the `NYX_REUSE_SNAPSHOT` environment variable and use the tools as usual: +A fuzzing snapshot is automatically created and stored in the output directory at `out_dir/workdir/snapshot/` by the first parent process of `afl-fuzz` if parallel mode is used. To enable this feature, set the path to an existing snapshot directory in the `AFL_NYX_REUSE_SNAPSHOT` environment variable and use the tools as usual: ```shell afl-fuzz -i ./in_dir -o ./out_dir -Y -M 0 ./PACKAGE-DIRECTORY -NYX_REUSE_SNAPSHOT=./out_dir/workdir/snapshot/ afl-analyze -i in_file -X -- ./PACKAGE-DIRECTORY +AFL_NYX_REUSE_SNAPSHOT=./out_dir/workdir/snapshot/ afl-analyze -i in_file -X -- ./PACKAGE-DIRECTORY ``` @@ -311,7 +311,28 @@ command: ``` If you want to disable fast snapshots (except for crashes), you can simply set -the `NYX_DISABLE_SNAPSHOT_MODE` environment variable. +the `AFL_NYX_DISABLE_SNAPSHOT_MODE` environment variable. + +### Nyx crash reports + +If the Nyx agent detects a crash in the target application, it can pass +additional information on that crash to AFL++ (assuming that the agent +implements this feature). For each saved crashing input AFL++ will also create +an additional file in the `crashes` directory with a `.log` file extension. +Crash reports generated by the default agent shipped with the Nyx packer will +contain information such as the faulting address and signal number. +Additionally, if the target is compiled with AddressSanitizer, the crash report +will also contain the entire ASan report. + +From a technical perspective, the crash report is passed from QEMU-Nyx to AFL++ +via a shared memory region called Nyx Auxiliary Buffer which is by default 4096 +bytes in size. In this shared memory region a specific amount is reserved for +the header (1408 bytes) and the remaining bytes can be used to transfer crash +reports (also the `hprintf` feature utilizes the very same shared memory for +transferring data). By default a crash report will be truncated to 2688 bytes. +However, if you want to increase the size of the shared memory region, you can +set the `AFL_NYX_AUX_SIZE` environment variable to a higher value (keep in +mind that this value must be a multiple of 4096). ### Run AFL++Nyx with a custom agent |