Overview of the source code:
.
|-- artifact_eval # steps to reproduce results of Usenix Paper.
|-- ccr # source code of ccr/randomizer
|-- compare # scripts that compare the result between gt and disassembler
|-- extract_gt # scripts that extract ground truth from binary
|-- disassemblers # scripts that we use to extract disassemblers' result
|-- gt # modified gcc/clang toolchain
|-- protobuf_def # protobuf definitions that defines disassembly information and x-ref information
|-- README.md
`-- testsuite # coreutils and findutils that compiled by gcc/clang toolchain
Our toolchains were tested in x64 Ubuntu18.04/20.04 and they could (cross-)compile binaries of following architectures.
- x86/x64
- arm32
- aarch64
- mipsle/mips64le
We shared dataset of x86/arm/mips compiled by gcc-8.1.0 and clang-6.0 and disassembly results of popular disassemblers.
- x86/x64 dataset. Decompressed size is ~56GB.
- mips arm dataset. Decompressed size is ~35GB.
We modified compilers(gcc/clang) to collect the information of basic blocks and reconstruct the information of binary code. And we want to extract the executable file's basic block, jump table, fixup/reference, and function information in the compilation tool and can help to evaluate disassemblers.
For clang, we re-use the implemenation of CCR.
|
=============== =============== =============== | =============
|| || || || || || | || ||
|| preprocess || + || compile || + || assemble || | + || link || => executable
|| || || || || || | || ||
=============== =============== =============== | =============
llvm/clang MC Componment | linker(gold)
For gcc, we modified gcc and gas(GNU assembler). Modifications can be found at gcc modification and gas modification.
| |
=============== =============== | =============== | =============
|| || || || | || || | || ||
|| preprocess || + || compile || | + || assemble || | + || link || => executable
|| || || || | || || | || ||
=============== =============== | =============== | =============
gcc | assembler(gas) | linker(gold)
There exist some differences between llvm toolchains(based on CCR) and gcc toolchains. In llvm, it has MC componment that combines compilation and assembling together internally. While gcc outputs the .s file after compilation, and invokes assembler(gas) to assemble the .s file into an object. So it is easier to extract the basic block and jump table information in compilation and store this information in an object file after assembling in llvm toolchains when compared to gcc toolchains.
As basic block, function, and jump table information can only be collected in the compilation stage, so firstly, we output the related information into .s file, and then we reconstruct these information in assembler(gas).
We provide two ways to build the toolchains of compilers in x86/x64: ubuntu18.04 and docker.
$ git clone git@github.com:junxzm1990/x86-sok.git
$ cd x86-sok/gt
$ bash x86/build.shThe gcc/g++ are installed in gt/build/executable_gcc/bin, clang/clang++ are installed in gt/build/build_clang/bin. We also build glibc by using our toolchain so that the compiled glibc contains the information emitted by the compiler. Glibc is installed in gt/build/glibc_build_32 or gt/build/glibc_build_64.
For convenience, we provide config scripts to set CC, CXX, CFLAGS, CXXFLAGS, LDFLAGS. These configs are gt/gcc64.rc, gt/gcc32.rc, gt/clang64.rc and gt/clang32.rc.
Before compiling, we can set proper configure by:
# for example, to compile the source code by gcc
$ source gcc64.rc
# set the proper optimization level
$ export CFLAGS="-O2 $CFLAGS" && export CXXFLAGS="-O2 $CXXFLAGS"If you prefer to use Docker, we also provide the script to build docker image.
# install docker firstly
$ curl -fsSL https://get.docker.com/ | sudo sh
$ sudo usermod -aG docker [user_id]
# build our toolchain
$ git clone git@github.com:junxzm1990/x86-sok.git
$ cd x86-sok/gt
$ docker build -t x86_gt -f ./x86/Dockerfile .
# check the image
$ docker image ls
REPOSITORY TAG IMAGE ID CREATED SIZE
x86_gt latest 85f6fb2d4257 2 minutes ago 1.4GB
# launch the image
$ docker run --rm -it x86_gt:latest /bin/bash
# configure CC, CXX, CFLAGS, CXXFLAGS, LDFLAGS inside container
root@fc44258775ac:/gt_x86# source ./gcc64.rc
root@fc44258775ac:/gt_x86# export CFLAGS="-O2 $CFLAGS" && export CXXFLAGS="-O2 $CXXFLAGS"Or pull the image from Docker Hub:
$ docker pull bin2415/x86_gt:0.1
# check the image
$ docker image ls
REPOSITORY TAG IMAGE ID CREATED SIZE
bin2415/x86_gt 0.1 85f6fb2d4257 3 minutes ago 20.5GB
# launch the image
$ docker run --rm -it bin2415/x86_gt:0.1 /bin/bash
# configure CC, CXX, CFLAGS, CXXFLAGS, LDFLAGS inside container
root@fc44258775ac:/gt_x86# source ./gcc64.rc
root@fc44258775ac:/gt_x86# export CFLAGS="-O2 $CFLAGS" && export CXXFLAGS="-O2 $CXXFLAGS"We cross-compiled arm32 and aarch64 binaries in x86/x64 architecture. We need to install qemu:
sudo apt-get install qemu binfmt-support qemu-user-static$ docker pull z472421519/arm32_gt
$ docker image ls
REPOSITORY TAG IMAGE ID CREATED SIZE
z472421519/arm32_gt latest beb7bba8d960 7 hours ago 5.11GB
$ docker run --rm -it z472421519/arm32_gt /bin/bash
# configure CC, CXX, CFLAGS, CXXFLAGS, LDFLAGS inside container
root@32380fe55c2a:/gt_arm32# source gcc32_arm.rc
root@32380fe55c2a:/gt_arm32# export CFLAGS="-O2 $CFLAGS" && export CXXFLAGS="-O2 $CXXFLAGS"
# mthumb
root@32380fe55c2a:/gt_arm32# source gcc32_arm_mthumb.rc$ docker pull z472421519/aarch64_gt
$ docker image ls
REPOSITORY TAG IMAGE ID CREATED SIZE
z472421519/aarch64_gt latest aae089d22450 4 hours ago 5.25GB
$ docker run --rm -it z472421519/aarch64_gt /bin/bash
# configure CC, CXX, CFLAGS, CXXFLAGS, LDFLAGS inside container
root@5e9ee548ff5d:/gt_aarch64# source gcc64_arm.rc
root@5e9ee548ff5d:/gt_aarch64# export CFLAGS="-O2 $CFLAGS" && export CXXFLAGS="-O2 $CXXFLAGS"We cross-compiled mips binaries in x86/x64 architecture. We need to install qemu:
$ docker pull z472421519/mips32_gt
$ docker image ls
REPOSITORY TAG IMAGE ID CREATED SIZE
z472421519/mips32_gt latest 9c708cc17998 25 hours ago 4.42GB
$ docker run --rm -it z472421519/mips32_gt /bin/bash
# configure CC, CXX, CFLAGS, CXXFLAGS, LDFLAGS inside container
root@7605562e48b3:/gt_mips32# source gcc32_mips.rc
root@7605562e48b3:/gt_mips32# export CFLAGS="-O2 $CFLAGS" && export CXXFLAGS="-O2 $CXXFLAGS"$ docker pull z472421519/mips64_gt
$ docker image ls
REPOSITORY TAG IMAGE ID CREATED SIZE
z472421519/mips64_gt latest 0eaaf0cfacc3 20 hours ago 5.48GB
$ docker run --rm -it z472421519/mips64_gt /bin/bash
# configure CC, CXX, CFLAGS, CXXFLAGS, LDFLAGS inside container
root@76ca6fcc9f1d:/gt_mips# source gcc64_mips.rc
root@76ca6fcc9f1d:/gt_mips# export CFLAGS="-O2 $CFLAGS" && export CXXFLAGS="-O2 $CXXFLAGS"Here are examples that explain how to use our x86/x64 toolchain to compile binary(arm and mips toolchains are the same with x86/x64).
-
Example 1: a simple c code
root@5e8606df7f20:/gt_x86# cd test root@5e8606df7f20:/gt_x86/test# source ../gcc64.rc root@5e8606df7f20:/gt_x86/test# export CFLAGS="-O0 $CFLAGS" root@5e8606df7f20:/gt_x86/test# $CC $CFLAGS -o test_switch test_switch.c [bbinfo]: DEBUG, the target binary format is: size 64, is big endian 0 Update shuffleInfo Done! Successfully wrote the ShuffleInfo to the .rand section! # check the .rand section in the executable root@5e8606df7f20:/gt_x86/test# readelf -S test_switch | grep -A1 rand [35] .rand PROGBITS 0000000000000000 000034ec 000000000000025b 0000000000000000 0 0 1
-
Example 2: compile coreutils
# download coreutils root@1a16bbde2f79:/gt_x86/test# wget -c https://ftp.gnu.org/gnu/coreutils/coreutils-8.30.tar.xz root@1a16bbde2f79:/gt_x86/test# tar -xvf coreutils-8.30.tar.xz && cd coreutils-8.30 root@1a16bbde2f79:/gt_x86/test/coreutils-8.30# mkdir build_gcc_O2 && cd build_gcc_O2 root@1a16bbde2f79:/gt_x86/test/coreutils-8.30/build_gcc_O2# source /gt_x86/gcc64.rc && export CFLAGS="-O2 $CFLAGS" root@1a16bbde2f79:/gt_x86/test/coreutils-8.30/build_gcc_O2# export FORCE_UNSAFE_CONFIGURE=1 && ../configure --prefix=$PWD root@1a16bbde2f79:/gt_x86/test/coreutils-8.30/build_gcc_O2# make -j && make install # the compiled binaries are installed in /gt_x86/test/coreutils-8.30/build_gcc_O2/bin root@1a16bbde2f79:/gt_x86/test/coreutils-8.30/build_gcc_O2# ls bin '[' cat chroot cut dircolors expand fold install logname mknod nohup pathchk ptx rmdir sha256sum sleep stty tee true unexpand vdir b2sum chcon cksum date dirname expr groups join ls mktemp nproc pinky pwd runcon sha384sum sort sum test truncate uniq wc base32 chgrp comm dd du factor head kill md5sum mv numfmt pr readlink seq sha512sum split sync timeout tsort unlink who base64 chmod cp df echo false hostid link mkdir nice od printenv realpath sha1sum shred stat tac touch tty uptime whoami basename chown csplit dir env fmt id ln mkfifo nl paste printf rm sha224sum shuf stdbuf tail tr uname users yes
We use the example of test_switch to show how to extract ground truth.
# copy the gt info from binary
root@5e8606df7f20:/gt_x86/test# objcopy --dump-section .rand=test_switch.gt.gz test_switch && gzip -d test_switch.gt.gz
# there has test_switch.gt in current directory
root@5e8606df7f20:/gt_x86/test# ls
test_switch test_switch.c test_switch.gt
# extract disassembly result, and the result is saved in /tmp/gtBlock_test_switch.pb
root@5e8606df7f20:/gt_x86/test# python3 ../../extract_gt/extractBB.py -b test_switch -m test_switch.gt -o /tmp/gtBlock_test_switch.pb
...
...
INFO:=======================================================
INFO:[Summary]: padding cnt is 9
INFO:[Summary]: handcoded bytes is 0
INFO:[Summary]: handcoded number is 0
INFO:[Summary]: Jump tables is 1
INFO:[Summary]: Tail indirect call is 2
INFO:[Summary]: overlapping instructions is 0
INFO:[Summary]: Non-returning function is 2
INFO:[Summary]: Multi-entry function is 0
INFO:[Summary]: overlapping functions is 0
INFO:[Summary]: tail call count is is 1
# extract x-ref result, the result is saved in /tmp/gtRef_test_switch.pb
# Only support x86/x64 binary
root@5e8606df7f20:/gt_x86/test# python3 ../../extract_gt/extractXref.py -b test_switch -m test_switch.gt -o /tmp/gtRef_test_switch.pbNote that the definition of disassembly and x-ref result is in protobuf_def/blocks.proto and protobuf_def/refInf.proto.
We provide script to extract ground truth in batch. It searchs all the binaries in a directory.
ubuntu@ubuntu:/x86-sok/extract_gt: bash run_extract_linux.sh -d <directory> -s ./extractBB.py -p gtBlock
# only support x86/x64 binary
ubuntu@ubuntu:/x86-sok/extract_gt: bash run_extract_linux.sh -d <directory> -s ./extractXref.py -p gtRefWe prepare an example in extract_gt/pemap/testto explain how to extract ground truth.
# extract fixup info, this step must be completed in windows, as we need to use dumpbin tool
windows@windows:/extract_gt/pemap# python3 dumpfixup.py -p ./test/7zDec.pdb -b ./test/7zDec.exe -o ./test/gtRef_7zDec.pb
# extract disassembly info. Note that we need the fixup info
windows@windows:/extract_gt/pemap# make
windows@windows:/extract_gt/pemap# ./PEMap -iwRFE -P ./test/7zDec.pdb -r ./test/gtRef_7zDec.pb -e ./test/7zDec.exe -o ./test/gtBlock_7zDec.pbInstall dependencies:
apt-get update && \
apt-get install -y \
build-essential \
cmake \
git \
sqlite3 \
wget \
bison \
zlib1g-dev \
python3 \
python3-pip
pip3 install protobuf \
capstone \
pyelftools \
sqlalchemyWe can use scripts in compare folder to compare results between ground truth and comapred tools.
For example, if we want to compare instructions, we can use compareInsts.py:
ubuntu@ubuntu:/x86_sok/compare# python3 compareInsts.py -b <binary path> -g <ground truth> -c <compared>Note that before comparring the non-return, we need to extend the non-return lists based on ground truth:
# extend the non-rets
ubuntu@ubuntu:/x86_sok/compare# python3 findNonRets.py -b <binary path> -g <ground truth> -o <ground truth with extended non-rets>
# compare
ubuntu@ubuntu:/x86_sok/compare# python3 compareNonRet.py -b <binary path> -g <ground turht with extended non-rets> -c <compared>OracleGT supports two open-source compilers(gcc, llvm/clang) to collect the ground truth of binary disassembly(i.e., instruction recovery, function entry detection, and jump table reconstruction) when compiling. Here we dissect every part insider compiler, assembler, and linker to illustrate how to port new compilers.
In LLVM, MachineFunction represents the function and MachineMasicBlock holds a sequence of MachineInstrs which represent instructions of specific
architecture. MCFragment represents continuous bytecodes inside the generated Object. In order to mark the boundary of Function and Basic Block(Instruction) inside Object, we borrow the design of CCR which traces the boundary from MachineBasicBlock level to MCFragment.
=============== ================ ================ ========== ============== ==========
|| || || || || || || || || || || ||
|| Machine || => || Machine || => || MachineInstr || => || MCInst || => || MCFragment || => || Object ||
|| Function || || BasicBlock || || || || || || || || ||
|| || || || || || || || || || || ||
=============== ================ ================ ========== ============== ==========
MC Componment
Specifically, we leverage MachineBasicBlock as the basic unit of codes. In MCAsmInfo, we bookkeep information of MachineBasicBlocks to trace the information of every basic block when assembling.
class MCAsmInfo {
...
//Essential bookkeeping information for reordering in the future (installation time)
// (a) MachineBasicBlocks (map)
// * MFID_MBBID: <size, offset, # of fixups within MBB, alignments, type, sectionName, contains inline assemble>
// - The type field represents when the block is the end of MF or Object where MBB = 0, MF = 1, Obj = 2, and if now block is special mode all type add 1 << 6 such as TBB(thumb basic block) = 64 and TF(thumb function) = 65
// - The sectionOrdinal field is for C++ only; it tells current BBL belongs to which section!
// MBBSize, MBBoffset, numFixups, alignSize, MBBtype, sectionName, assembleType
mutable std::map<std::string, std::tuple<unsigned, unsigned, unsigned, unsigned, unsigned, std::string, unsigned>> MachineBasicBlocks;
// * MFID: fallThrough-ability
mutable std::map<std::string, bool> canMBBFallThrough;
// * MachineFunctionID: size
...
}MachineBasicBlocks is a map, the key is the unique identifier of every basic block and the value is a pair of information:
- the size of basic block
- offset of basic block inside section of
Object - the number of fixups
- the type of basic block: is the current basic block is the boundary of function or if the basic block has special mode(such as thumb mode)
- section name
- the type of assembly codes
Next, we are going to introduce how to collect those information at the backend of LLVM.
To record the size of the basic block and the offset inside the fragment, we trace the process of assembling MCInst into bytes. Specifically, MCELFStreamer is the basic class that assemble
MCInst into MCFragment.
void MCELFStreamer::EmitInstToData(const MCInst &Inst,
const MCSubtargetInfo &STI) {
// current offset inside DF fragment
unsigned FragOffset = DF->getContents().size();
// emit current instruction into DF Fragment
DF->getContents().append(Code.begin(), Code.end());
...
// Obtain the parent of this instruction (MFID_MBBID)
std::string ID = Inst.getParent(); // get the unique identifier of its parent basic block
unsigned EmittedBytes = Code.size();
unsigned numFixups = Fixups.size();
const MCAsmInfo *MAI = Assembler.getContext().getAsmInfo();
// check if current basic block is in special mode. such as thumb mode.
bool SpecialMode = STI.getSpecialMode();
// upate the size of current instruction and the number of fixups
bool initFlag = MAI->updateByteCounter(ID, EmittedBytes, numFixups, /*isAlign=*/ false, /*isInline=*/ false, /*isSpecialMode*/SpecialMode);
if (initFlag) // if current instruction is the start of basic block, update the offset inside fragment
MAI->updateOffset(ID,FragOffset);
}The size of some instructions(relexable instructions, such as jmp .label) could not determined in EmitInstToData, we trace the size of relexable instructions in MCAssembler::relaxInstruction:
bool MCAssembler::relaxInstruction(MCAsmLayout &Layout,
MCRelaxableFragment &F) {
std::string ID = F.getInst().getParent();
unsigned relaxedBytes = F.getRelaxedBytes();
unsigned fixupCtr = F.getFixup();
unsigned curBytes = F.getInst().getByteCtr();
if (relaxedBytes < curBytes) {
// RelaxableFragment always contains relaxedBytes and fixupCtr variable
// for the adjustment in case of re-evaluation (simple hack but tricky)
// not here
MAI->updateByteCounter(ID, curBytes - relaxedBytes, 1 - fixupCtr,
/*isAlign=*/ false, /*isInline=*/ false , /*isSpecialMode*/SpecialMode);
F.setRelaxedBytes(curBytes);
F.setFixup(1);
// If this fixup points to Jump Table Symbol, update it.
F.getFixups()[0].setFixupParentID(ID);
}
}To update the offset of the basic block inside the final object, we hook the process of organizing fragments into an object by operating MCAsmLayout:
void updateReorderInfoValues(const MCAsmLayout &Layout) {
const MCAsmInfo *MAI = Layout.getAssembler().getContext().getAsmInfo();
const MCObjectFileInfo *MOFI = Layout.getAssembler().getContext().getObjectFileInfo();
for (MCSection &Sec : Layout.getAssembler()) {
MCSectionELF &ELFSec = static_cast<MCSectionELF &>(Sec);
std::string tmpSN, sectionName = ELFSec.getSectionName();
if (sectionName.find(".text") == 0) {
// Per each fragment in a .text section
unsigned nowFragOffset = 0;
for (MCFragment &MCF : Sec) {
nowFragOffset = MCF.getOffset();
for (std::string ID : MCF.getAllMBBs()) {
std::get<1>(MAI->MachineBasicBlocks[ID]) += nowFragOffset; // update the offset of current basic block
...
}
}
std::get<5>(MAI->MachineBasicBlocks[ID]) = sectionName; // update section name
}
...To trace the information of jump tables, we record the information into relocation in EmitInstToData:
void MCELFStreamer::EmitInstToData(const MCInst &Inst,
const MCSubtargetInfo &STI) {
std::string ID = Inst.getParent(); //Declared in MCInst.h,(MFID_MBBID)
...
for fixup in fixups
{
//This part needs special treatment according to different architectures
//1.Different jump table prefixes
//2.Different fixup types require special handling
if(".LJTI" in fixup.sym or "$JTI" in fixup.sym)
{
fixups[i].setIsJumpTableRef(true); //Set the fixup to be associated with a jump table
fixups[i].setSymbolRefFixupName(fixup.sym);
}
}
for fixup in addedfixups // handle special instruction such as tbb
{
fixups[i].setIsJumpTableRef(true);
fixups[i].setSymbolRefFixupName(fixup.sym);
}
}To store the ground truth information, the tool creates a new section .gt in the binary
void ELFObjectWriter::writeSectionData(const MCAssembler &Asm, MCSection &Sec,
const MCAsmLayout &Layout) {
...
if (section name is ".gt") {
Asm.WriteRandInfo(Layout); // write addtion info into .rand section
}
...
}
void WriteRandInfo(Layout)
{
...
if(section name is ".text") // force on .text section
{
for fragment in fragments
{
totalOffset = fragment.offset
for BB in BBs
{
BB.updateOffset(totalOffset)//update the offset with BBsize and fragment offset
totalOffset += BB.size
function.size += BB.size
if BB is function end
BB.updateType(func_type) //if BB is func end, update the BB type
}
}
}
...
}
Void Layout(layout)
{
for section in sections
for fragment in fragments
{
for fixup in fixups
if(jumptable) // if fixup is related to a jumptable,update the info to fixuplist declared in MCAsmInfo.h
updateFixuplist();
for fixup in addedfixups // handle special fake fixup, to record the jumptable
if(jumptable)
updateFixuplist();
}
}In order to pass information from GCC compiler to GNU Assembler, The tool defines some directives[1] to mark basic block information, function information, inline information, and jump table information
| Label | Information |
|---|---|
| bbInfo_BB | mark the basic block begin location |
| bbInfo_BE | mark the basic block end location |
| bbInfo_FUNB | mark the function start location |
| bbInfo_FUNE | mark the function end location |
| bbInfo_JMPTBL | mark the jump table information |
| bbInfo_INLINEB | mark the asm inline start information |
| bbInfo_INLINEE | mark the asm inline end information |
The assembly code generated by instrumented GCC is shown as follows:
.LFB5:
.cfi_startproc
.bbInfo_FUNB
.bbInfo_BB 0
pushq %rbp
.cfi_def_cfa_offset 16
.cfi_offset 6, -16
movq %rsp, %rbp
.cfi_def_cfa_register 6
leaq .LC0(%rip), %rdi
call puts@PLT
movl $-1, %edi
.bbInfo_BE 0
call exit@PLT
.cfi_endproc
.LFE5:
.bbInfo_FUNE
....
.L10:
.bbInfo_JMPTBL 35 4
.long .L39-.L10
.long .L8-.L10
.long .L38-.L10
.long .L8-.L10
.long .L8-.L10
.long .L37-.L10
.long .L36-.L10
.long .L8-.L10
....In order to output these labels, the tool created bbinfo2asm.c and instrumented final.c and cfg.c.
In bbinfo2asm, the tool defines the following functions:
// output the basic block begin label
extern void bbinfo2_asm_block_begin(uint32_t);
// output the basic block end label
extern void bbinfo2_asm_block_end(uint32_t);
// output the jump table information, including table size and entry size
extern void bbinfo2_asm_jumptable(uint32_t table_size, uint32_t entry_size);
// output the function begin label
extern void bbinfo2_asm_func_begin();
// output the function end label
extern void bbinfo2_asm_func_end();
// output the asm inline start label
extern void bbinfo2_asm_inline_start();
extern void bbinfo2_asm_inline_end();//final.c
final_start_function_1()
{
...
bbinfo2_asm_func_begin();//Output the bbInfo_FUNC Label
...
}
final_end_function()
{
...
bbinfo2_asm_func_end();//Output the bbInfo_FUNE Label
,,,
}
dump_basic_block_mark(inst)
{
flag = 0;
for edge in edges
if(edge_fall_through(edge))
flag = 1;
if inst is the first instruction of BB
bbinfo2_asm_block_begin(flag);//Output the bbInfo_BB Label
if inst is the last instruction of BB
bbinfo2_asm_block_end(flag);//Output the bbInfo_BE Label
}
final_1()
{
...
for inst in insts
dump_basic_block_mark(inst);
...
}
app_enable()
{
...
if (! app_on)
{
...
bbinfo2_asm_inline_start();//Output the bbInfo_INLINEB Label
...
}
...
}
app_app_disable()
{
...
if (app_on)
{
...
bbinfo2_asm_inline_end();//Output the bbInfo_INLINEE Label
...
}
...
}
//And to get basic block information, comment out flag_debug_asm.//cfg.c
// if the edge is fall through, return true
edge_fall_through(edge e){
if(e.flag is fallthrough)
return true;
return false;
}Recommendation: Assembler is not related to compiler optimizations, we could leave the
GASas it is until it is not fit in new GCC compilers.
The process of assembling could be deemed as a state machine: when processing directive, it defines the current state and trigger the specific action to handle the following sequence bytes. So we could add specific directives to pass information from compiler to assembler and represent the specific state inside the assembler.
Specifically, in order to migrate to new gas, we could do following modifications:
const pseudo_typeS bbInfo_pseudo_table[] = {
{"bbinfo_jmptbl", jmptable_bbInfo_handler, 0}, // handle jump table
{"bbinfo_funb", funcb_bbInfo_handler, 0}, // handler start of a function
{"bbinfo_fune", funce_bbInfo_handler, 0}, // handle end of a function
{"bbinfo_bb", bb_bbInfo_handler, 0}, // handle start of a basic block(bb)
{"bbinfo_be", be_bbInfo_handler, 0}, // handler end of a bb
{"bbinfo_inlineb", inlineb_bbInfo_handler, 0}, // handle start of inline pseudo-bb
{"bbinfo_inlinee", inlinee_bbInfo_handler, 0}, // handle end of inline pseudo-bb
{NULL, NULL, 0}
};The modified GCC emits corresponding directives to pass the boundary of function, basic block, and the information of jump tables. On the assembler side, we could reconstruct this information when handling specific directives. In order to represent the information, we could use the following structures:
// basic block related information
struct basic_block{
uint32_t ID; // basic block id, every basic block has unique id in an object
uint8_t type; // basic block type: basic block or function boundary.
// 0 represent basic block with normal mode ie. arm
// 1 represents function start with normal mode ie. arm
// 2 represents object end with normal mode ie. arm
// 4 represent basic block with special mode ie. thumb
// 5 represents function start with special mode ie. thumb
// 6 represents object end with special mode ie. thumb
uint32_t offset; // offset from the section
int size; // basic block size, include alignment size
uint32_t alignment; // basic block alignment size
uint32_t num_fixs; // number fixups
unsigned char fall_through; // whether the basic block is fall through
asection *sec; // which section the basic block belongs to
struct basic_block *next; // link next basic blosk
uint8_t is_begin; // if current instruction is the first instruction of this basic block
uint8_t is_inline; // if current basic block contains inline assemble code or current basic block
fragS *parent_frag; // this basic block belongs to which frag.
};The tool uses basic_block to represent the basic unit that contains continuous instructions. When met bbinfo_bb, the tool initializes a new basic_block:
- Update the
fall_throughfield according to the value obtained bybbinfo_bbdirective. Fragmentis the basic unit inside the assembler, it represents continuous fixed regions. The tool associatesbasic_blockwith fragment when initializing and updating the offset inside the current fragment.- Update
secfield which represents which section it belongs to.
The tool hooks the process of emitting instructions into fragment, and record every instruction in the current basic_block. In gas/config directory, it defines architecture-related functions to emit instructions into the fragment. For example, for AArch64, gas/config/tc-aarch64.c::output_inst(struct aarch64_inst *new_inst) function do that work.
// in gas/config/tc-aarch64.c
static void
output_inst (struct aarch64_inst *new_inst)
{
...
frag_now->last_bb = mbbs_list_tail;
if (mbbs_list_tail) {
mbbs_list_tail->size += INSN_SIZE; // update current instuction to current basic block
}
...
}The tool leverages fixup to record the information of jump table. Specifically, when met bbinfo_jmptbl directive, it could obtain the information of jump table(The size of jump table and the size of every jump table entry) and associates the information with last fixup.
// handle bbinfo_jmptbl directive
void jmptable_bbInfo_handler(int ignored ATTRIBUTE_UNUSED){
offsetT table_size, entry_size;
table_size = get_absolute_expression();
SKIP_WHITESPACE();
entry_size = get_absolute_expression();
if (last_symbol == NULL){
as_warn("Sorry, the last symbol is null\n");
return;
}
// update the jump table related information of the symbol
S_SET_JMPTBL_SIZE(last_symbol, table_size);
//as_warn("JMPTBL table size is %d\n", table_size);
S_SET_JMPTBL_ENTRY_SZ(last_symbol, entry_size);
}Recommendation: Linker is not related to compiler optimizations, we could leave the
gold asit is until it is not fit in new compilers.
Linker integrates object files(.o) into one executable file and updates informations of final executable file(such as relocations). The tool hooks the process of Gold to updates the offset of every basic block. Specifically, when link finalizes the integration of object files, we update the offsets.
// in gold/layout.cc
off_t
Layout::finalize(const Input_objects* input_objects, Symbol_table* symtab,
Target* target, const Task* task)
{
...
// Run the relaxation loop to lay out sections.
do
{
off = this->relaxation_loop_body(pass, target, symtab, &load_seg,
phdr_seg, segment_headers, file_header,
&shndx);
pass++;
}
while (target->may_relax()
&& target->relax(pass, input_objects, symtab, this, task));
// the part added
bool is_big_endian = parameters->target().is_big_endian();
int binary_format_size = parameters->target().get_size();
if (is_big_endian && binary_format_size == 64){
this->update_shuffleInfo_layout<64, true>();
} else if (!is_big_endian && binary_format_size == 64){
this->update_shuffleInfo_layout<64, false>();
} else if (is_big_endian && binary_format_size == 32){
this->update_shuffleInfo_layout<32, true>();
} else if (!is_big_endian && binary_format_size == 32){
this->update_shuffleInfo_layout<32, false>();
}
...
}In update_shuffleInfo_layout(), the tool iterates every basic block and update its offsets inside executable file.
Finally, the tool hooks the process of generating sections and adds section .gt to store the ground truth of binary disassembly.
// in gold/main.cc
std::string rand(".gt=");
std::string opt_2 = rand+shuffle_bin_gz;
// binpang, support the `-r` option
if (parameters->options().relocatable()){
opt_2 = rand+shuffle_bin;
}
char * const add_section[] = {"objcopy", "--add-section", (char *)opt_2.c_str(), (char *)target.c_str(), (char*)NULL};
if(fork()){
int status;
wait(&status);
}else{
//child exec the objcopy to integrate shufflebin into target
execvp("objcopy", add_section);
_exit(0);
}
- [1] Assembler Directives: https://eng.libretexts.org/Bookshelves/Electrical_Engineering/Electronics/Implementing_a_One_Address_CPU_in_Logisim_(Kann)/02%3A_Assembly_Language/2.03%3A_Assembler_Directives#:~:text=Assembler%20directives%20are%20directions%20to,not%20translated%20into%20machine%20code.
- [2] Intro to the LLVM MC Project: http://blog.llvm.org/2010/04/intro-to-llvm-mc-project.html
- Reproduction of Usenix paper: readme
MIT License.
If your research find one or several components of this work useful, please cite the following paper:
@INPROCEEDINGS {sok-x86,
author = {Chengbin Pang and Ruotong Yu and Yaohui Chen and Eric Koskinen and Georgios Portokalidis and Bing Mao and Jun Xu},
booktitle = {42nd IEEE Symposium on Security and Privacy (SP)},
title = {SoK: All You Ever Wanted to Know About x86/x64 Binary Disassembly But Were Afraid to Ask},
year = {2021},
}