Notice

This repo is incomplete and depreciated

For full code, please refer to: https://github.com/yiluwusbu/DEVFUZZ

AFL Proxy

This is AFL proxy(AP). This repo contains a lighweight proxy program(ap) launched by AFL. A library aplib used by client to communicate with AP.

|--------\    spawn AP process                   IPC with client using
|  AFL    | <------------------> [./ap fuzz.data]<------------------>   QEMU[KVM]
``````^```    create fuzz data         |          /dev/shm/afl-proxy       |
       \                               |                                   |
        \                              |                                   |
         \   code coverage bitmap      | enable perf-pt(PIDX) <------ap_attach_pt(PIDX)
          `--------------------------> |                                vmx_on()

At a high level, AP creates a shared memory(/dev/shm/afl-proxy) and accepts requests from the real client, QEMU e.g. Client get fuzz data location through SHM. The code coverage information is provided by client by explicitly calling ap_log_pc(uint64_t) at each basicblock or it could be provided by PT. If using PT, client need to call ap_attach_pt(PIDX) to enable PT-monitor in ap. Also, if PT is used, clients don't have to call ** ap_log_pc** at each basic block thus saving time. The client program should be linked with aplib.

AP supports two different modes to collect code coverage. One is through explicit call to ap_log_pc(uint64_t pc), another is through PT.

AP relies on Linux perf subsystem to collect PT trace.

Second Stage Analysis

The device model build can be break down into two stage:

1. s2e symbolic execution - produce first device model that can pass probing

2. dynamic analysis to produce PCI bus master support model -- improve first model with DMA support

To run 2nd step, the guest kernel must be patched with 0001-sfp-Add-hypercall-to-let-host-know-dma-buffer-locati.patch

Installation

• download AFL from https://github.com/google/AFL.git and compile
• compile afl-proxy and aplib

$(afl-proxy): make

• download QEMU from https://github.com/lzto/qemu and compile sfpv2-fuzz branch
• prepare rootfs image TODO
• prepare target kernel TODO

S2E Repos:

https://github.com/lzto/guest-images https://github.com/lzto/s2e https://github.com/lzto/s2e-linux-kernel

Run AFL proxy

First, run AP using the following command

cd run
./run.sh

After AP is launched, start QEMU in another terminal

Coding Style

use LLVM coding style and run make indent

Limitations

• only single core/thread is supported when using PT

APLib Environment Variables

• AP_DISABLED=0,1: disable ap proxy - some device probing logic still works but won't connect to ap for fuzzing
• AP_DUMP_RW=0,1,2,3: dump device memory trace, nodump-0/r-1/w-2/rw-3
• AP_DUMP_FILE=filename: where to dump trace, default is stdout
• EXPORT_DEVMEM=0,1: export device memory(PCI bar e.g.) through shared memory (/dev/shm/)
• NO_REDIRECT_READ=0,1: do not redirect read to AP - 0 redirect - 1 direct
• SFP_SHMID=number: add suffix to shm file so that multiple instances can be launched
• USE_DMA=0,1: try to support DMA
• USE_IRQ=0,non-zero-value-X: generate interrupt every X milliseconds, 0 to disable, this can be overriden by upper layer device model
• WAITGDB=0,1: stop and waiting for gdb to attach at launch, useful for debugging aplib

PT and ALF coverage update

pt_attach() is called when KVM thread is created and ap_exit() is called when one fuzzing test is done. AFL will update coverage information when ap_exit() is called.

Misc

• s2e-tools: tools to convert s2e result to device model, prepare s2e project, check status and upload artifact to model archive server

Builtin Device Models

Device models are under afl-proxy/aplib/, you are more than welcome to send pull request, contribute and improve existing device models.