Profile-guided-Fuzzing

Profile-guided System Optimizations for Accelerated Greybox Fuzzing

Code structure and explanation of terms

Directory structure

The project consists of three main subdirectories:

AFL : Improved version of AFL based on 2.57b gcc
- AFL/llvm_mode: code for "Profile-guided State Recovery".
- AFL/var_mode: scripts for "Profile-guided State Recovery".
- AFL/gcc_mode: gcc mode for AFL.
AFLplusplus: Improved version of AFL++ based on 4.01c
- AFLplusplus/instrumentation/afl-llvm-var-rec.so.cc: code for "Profile-guided State Recovery".
- AFLplusplus/utils/var_mode: scripts for "Profile-guided State Recovery".
abstractFS: code for "Profile-guided OS Abstraction"

Terminology Explanation and Corresponding Codes

FS: fork server, the default build method of target binary
SS: snapshot mode, which was implemented in Linux Kernel in AFL, and LKM in AFL++
PM: persistent mode
PM_REC: persistent mode with profile-guided state recovery
PM_VOS: persistent mode on top of our profile-guided OS abstraction.
PM_REC_VOS: persistent mode with both profile-guided state recovery and OS abstraction.

The following macros in the code are used to enable the modes above.

VAR_REC in AFL/llvm_mode/afl-llvm-pass.so.cc: required by PM_REC and PM_REC_VOS for AFL
AFL_LLVM_VAR_REC in AFLplusplus/instrumentation/afl-llvm-var-rec.so.cc: required by PM_REC and PM_REC_VOS for AFL++
AFL_SNAPSHOT: enable snapshot kernel mode (AFL/llvm_mode/afl-llvm-rt.o.c)
AFL_RT_VAR_REC: enable variable recover mode (AFL/llvm_mode/afl-llvm-rt.o.c)
AFL_RT_PERSIST: enable persistent mode with wrap for exit (AFL/llvm_mode/afl-llvm-rt.o.c)

For profiling of time consumed by fuzzing (2.2 Motivating Study), you need to enable these macros : PROFILING_SYS_USR, PROFILING_FORK and PROFILING, which are located in these files:

AFL/afl-fuzz.c
AFL/llvm_mode/afl-llvm-rt.o.c
AFLplusplus/src/afl-fuzz.c
AFLplusplus/instrumentation/afl-compiler-rt.o.c

How to build AFL/AFL++/VOS (General Steps)

AFL:

make && cd llvm_mode && make

AFLplusplus:

make distrib

abstractFS: Please refer to this separate README

VAR_REC: enable variable recovery mode for LLVM pass in AFL/llvm_mode/afl-llvm-pass.so.cc; and the macro was AFL_LLVM_VAR_REC in AFL++.
PROFILING_SYS_USR, PROFILING_FORK and PROFILING was for profiling of time.
AFL_SNAPSHOT: enable snapshot kernel mode
AFL_RT_VAR_REC: enable variable recover mode
AFL_RT_PERSIST: enable persistent mode with wrap for exit.

Reproduce Experiment

Distribution of Time (2.2 Motivating Study)

Edit AFL/llvm_mode/afl-llvm-rt.o.c and enable macros(starts with PROFILING) from line 47 to line 49 .(Edit line 47 to line 49 in AFLplusplus/instrumentation/afl-compiler-rt.o.c for AFLplusplus)
Buid AFL with export CFLAGS="-DPROFILING_SYS_USR=1 -DPROFILING=1 -DPROFILING_FORK=1"
Rebuild the target program with afl-clang-fast
Fuzz the target program with environment variable AFL_PERFORM_DRY_RUN_ONLY=1, and the input seeds can be an existing corpus.

The following uses objdump as an example:

Option 1: Build from source code:

cd AFL
make clean
CFLAGS="-DPROFILING_SYS_USR=1 -DPROFILING=1 -DPROFILING_FORK=1" make
cd llvm_mode
# enable macros that start with PROFILING
make
sudo make install
sudo mkdir -p /out/

# Download the target src:
wget -c https://d29yy0w4awjqw3.cloudfront.net/fuzz/afl/Dec/binutils-2.38-per.tar.gz
tar -xzf binutils-2.38-per.tar.gz

# PM by default
cd binutils-2.38
CC=afl-clang-fast ./configure --disable-shared
make -j4
sudo cp binutils/objdump /out/objdump

Option 2: Build with Docker:

cd AFL/benchmarks/binutils-2.38
docker build -t benchmark-afl-objdump .
docker run --privileged --shm-size=256m --rm -it benchmark-afl-objdump bash

MODE=profile bash build.sh

Run profiling to collect the time distribution during fuzzing (for Section 2).

There is an tarball of corpus as a sample .

AFL_NO_AFFINITY=1 AFL_PERFORM_DRY_RUN_ONLY=1 afl-fuzz -i /out/objdump_corpus -o /dev/shm/output_objdump -f /dev/shm/afl_bin_input /out/objdump -d @@

# results FYI
Profiling information: 
7545 ms total work, 151133 ns/work,             
33129 ms total running, 663538 ns/run, 
1487 ms total write testcase, 29794 ns/write             
3005 ms total forking, 60192 ns/fork, 
28235 ms total purely run, 565523 ns/purely run             
44263 ns/system running, 503925 ns/user running             
7545 ms total pre-fuzzing, 151133 ns/pre-fuzzing,             
total execution is 49928

A full example of result for profiling time distribution page fault and syscall of objdump: Link

Reproduce the "5. Evaluation" part

Build&Run Target with "profile-guided state recovery"

Collectiong Global Objects:

Rebuild target program with afl-clang-fast variable AFL_VAR_TRACE=1
Run target with existing corpus to collect variable info (e.g. for testcase in /out/output_objdump/queue/id\:0* ; do ./objdump -d $testcase ; done)
The /tmp/.fs_globals.txt file will be verbose information for variable. (cat /tmp/.fs_globals.txt | sort -u > /out/global_objdump.txt)

Let's take objdump as an example:

cd binutils-2.38
CC=afl-clang-fast ./configure --disable-shared
make clean
AFL_VAR_TRACE=1 make -j4

# collect the variable information
# NOTE: the corpus_objdump the AFL queue with saved test cases in it
for testcase in ./corpus_objdump/queue/id\:0* ; do ./objdump -s $testcase ; done 

cat /tmp/.fs_globals.txt | sort -u > /out/global_objdump.txt`

Rebuid Target Binary with state recovery(PM_REC)

Note: Setting AFL_VAR_REC=1 environment variable is required for AFL++.

Rebuild target program with variable AFL_VAR_SNAPSHOT=1
Generate the assembly code from variable information: python AFL/var_mode/gen_asm.py /path/to/target_binary /out/global_objdump.txt /tmp/var.s
Comple .s to .o: cd AFL/var_mode && gcc -c /tmp/var.s
Rebuild target program with environment variable AFL_VAR_SNAPSHOT=1 AFL_VAR_REC=objdump (target binary name)

Let's take objdump as an example:

# generate the PM_REC object
cd binutils-2.38
CC=afl-clang-fast ./configure --disable-shared
make clean
AFL_VAR_SNAPSHOT=1 make -j4

# /out/global_objdump.txt is the txt file with global info we collected above
python AFL/var_mode/gen_asm.py ./binutils/objdump /out/global_objdump.txt /tmp/var.s
# Just compile the var.s, and we will get var.o
cd AFL/var_mode  && gcc -c /tmp/var.s

# rebuild the AFL llvm runtime object
cd AFL/llvm_mode
# enable "AFL_RT_VAR_REC" macro at AFL/llvm_mode/afl-llvm-rt.o.c to enable the state recover mode
make clean
make  # It's OK to get the testing warning prompt, pls ignore it.
cd .. && sudo make install

# rebuilt the target binary
cd /Path/to/binutils-2.38
LDFLAGS="-Wl,-wrap,_exit -Wl,-wrap,exit -Wl,-wrap,_Exit" AFL_VAR_REC=nothing ./configure --disable-shared
make clean
AFL_VAR_REC=objdump AFL_VAR_SNAPSHOT=1  make -j4
# sudo cp -f binutils/objdump /out/objdump

Then, we will get a PM_REC version of objdump, and it can be verified with the 100% fuzzing stability in persistent mode.

afl-fuzz  -i /out/seeds -o /dev/shm/output_objdump -f /dev/shm/afl_input -m none -- /out/objdump -d @@

Run Target with "profile-guided OS abstraction(VOS)"

Follow the README for abstractFS, and set FS_AFL_SHM_ID to enable PM_VOS or PM_REC_VOS

e.g.

FS_AFL_SHM_ID=6789 afl-fuzz  -i /out/seeds -o /dev/shm/output_objdump -f /dev/shm/afl_input -m none -- /out/objdump -d @@

emptyiscolor / Profile-guided-Fuzzing

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