//===- FuzzerDFSan.cpp - DFSan-based fuzzer mutator -----------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
// DataFlowSanitizer (DFSan) is a tool for
// generalised dynamic data flow (taint) analysis:
// http://clang.llvm.org/docs/DataFlowSanitizer.html .
//
// This file implements a mutation algorithm based on taint
// analysis feedback from DFSan.
//
// The approach has some similarity to "Taint-based Directed Whitebox Fuzzing"
// by Vijay Ganesh & Tim Leek & Martin Rinard:
// http://dspace.mit.edu/openaccess-disseminate/1721.1/59320,
// but it uses a full blown LLVM IR taint analysis and separate instrumentation
// to analyze all of the "attack points" at once.
//
// Workflow:
// * lib/Fuzzer/Fuzzer*.cpp is compiled w/o any instrumentation.
// * The code under test is compiled with DFSan *and* with special extra hooks
// that are inserted before dfsan. Currently supported hooks:
// - __sanitizer_cov_trace_cmp: inserted before every ICMP instruction,
// receives the type, size and arguments of ICMP.
// * Every call to HOOK(a,b) is replaced by DFSan with
// __dfsw_HOOK(a, b, label(a), label(b)) so that __dfsw_HOOK
// gets all the taint labels for the arguments.
// * At the Fuzzer startup we assign a unique DFSan label
// to every byte of the input string (Fuzzer::CurrentUnit) so that for any
// chunk of data we know which input bytes it has derived from.
// * The __dfsw_* functions (implemented in this file) record the
// parameters (i.e. the application data and the corresponding taint labels)
// in a global state.
// * Fuzzer::MutateWithDFSan() tries to use the data recorded by __dfsw_*
// hooks to guide the fuzzing towards new application states.
// For example if 4 bytes of data that derive from input bytes {4,5,6,7}
// are compared with a constant 12345 and the comparison always yields
// the same result, we try to insert 12345, 12344, 12346 into bytes
// {4,5,6,7} of the next fuzzed inputs.
//
// This code does not function when DFSan is not linked in.
// Instead of using ifdefs and thus requiring a separate build of lib/Fuzzer
// we redeclare the dfsan_* interface functions as weak and check if they
// are nullptr before calling.
// If this approach proves to be useful we may add attribute(weak) to the
// dfsan declarations in dfsan_interface.h
//
// This module is in the "proof of concept" stage.
// It is capable of solving only the simplest puzzles
// like test/dfsan/DFSanSimpleCmpTest.cpp.
//===----------------------------------------------------------------------===//
/* Example of manual usage:
(
cd $LLVM/lib/Fuzzer/
clang -fPIC -c -g -O2 -std=c++11 Fuzzer*.cpp
clang++ -O0 -std=c++11 -fsanitize-coverage=3 \
-mllvm -sanitizer-coverage-experimental-trace-compares=1 \
-fsanitize=dataflow -fsanitize-blacklist=./dfsan_fuzzer_abi.list \
test/dfsan/DFSanSimpleCmpTest.cpp Fuzzer*.o
./a.out
)
*/
#include "FuzzerInternal.h"
#include <sanitizer/dfsan_interface.h>
#include <cstring>
#include <iostream>
#include <unordered_map>
extern "C" {
__attribute__((weak))
dfsan_label dfsan_create_label(const char *desc, void *userdata);
__attribute__((weak))
void dfsan_set_label(dfsan_label label, void *addr, size_t size);
__attribute__((weak))
void dfsan_add_label(dfsan_label label, void *addr, size_t size);
__attribute__((weak))
const struct dfsan_label_info *dfsan_get_label_info(dfsan_label label);
} // extern "C"
namespace {
// These values are copied from include/llvm/IR/InstrTypes.h.
// We do not include the LLVM headers here to remain independent.
// If these values ever change, an assertion in ComputeCmp will fail.
enum Predicate {
ICMP_EQ = 32, ///< equal
ICMP_NE = 33, ///< not equal
ICMP_UGT = 34, ///< unsigned greater than
ICMP_UGE = 35, ///< unsigned greater or equal
ICMP_ULT = 36, ///< unsigned less than
ICMP_ULE = 37, ///< unsigned less or equal
ICMP_SGT = 38, ///< signed greater than
ICMP_SGE = 39, ///< signed greater or equal
ICMP_SLT = 40, ///< signed less than
ICMP_SLE = 41, ///< signed less or equal
};
template <class U, class S>
bool ComputeCmp(size_t CmpType, U Arg1, U Arg2) {
switch(CmpType) {
case ICMP_EQ : return Arg1 == Arg2;
case ICMP_NE : return Arg1 != Arg2;
case ICMP_UGT: return Arg1 > Arg2;
case ICMP_UGE: return Arg1 >= Arg2;
case ICMP_ULT: return Arg1 < Arg2;
case ICMP_ULE: return Arg1 <= Arg2;
case ICMP_SGT: return (S)Arg1 > (S)Arg2;
case ICMP_SGE: return (S)Arg1 >= (S)Arg2;
case ICMP_SLT: return (S)Arg1 < (S)Arg2;
case ICMP_SLE: return (S)Arg1 <= (S)Arg2;
default: assert(0 && "unsupported CmpType");
}
return false;
}
static bool ComputeCmp(size_t CmpSize, size_t CmpType, uint64_t Arg1,
uint64_t Arg2) {
if (CmpSize == 8) return ComputeCmp<uint64_t, int64_t>(CmpType, Arg1, Arg2);
if (CmpSize == 4) return ComputeCmp<uint32_t, int32_t>(CmpType, Arg1, Arg2);
if (CmpSize == 2) return ComputeCmp<uint16_t, int16_t>(CmpType, Arg1, Arg2);
if (CmpSize == 1) return ComputeCmp<uint8_t, int8_t>(CmpType, Arg1, Arg2);
assert(0 && "unsupported type size");
return true;
}
// As a simplification we use the range of input bytes instead of a set of input
// bytes.
struct LabelRange {
uint16_t Beg, End; // Range is [Beg, End), thus Beg==End is an empty range.
LabelRange(uint16_t Beg = 0, uint16_t End = 0) : Beg(Beg), End(End) {}
static LabelRange Join(LabelRange LR1, LabelRange LR2) {
if (LR1.Beg == LR1.End) return LR2;
if (LR2.Beg == LR2.End) return LR1;
return {std::min(LR1.Beg, LR2.Beg), std::max(LR1.End, LR2.End)};
}
LabelRange &Join(LabelRange LR) {
return *this = Join(*this, LR);
}
static LabelRange Singleton(const dfsan_label_info *LI) {
uint16_t Idx = (uint16_t)(uintptr_t)LI->userdata;
assert(Idx > 0);
return {(uint16_t)(Idx - 1), Idx};
}
};
std::ostream &operator<<(std::ostream &os, const LabelRange &LR) {
return os << "[" << LR.Beg << "," << LR.End << ")";
}
class DFSanState {
public:
DFSanState(const fuzzer::Fuzzer::FuzzingOptions &Options)
: Options(Options) {}
struct CmpSiteInfo {
size_t ResCounters[2] = {0, 0};
size_t CmpSize = 0;
LabelRange LR;
std::unordered_map<uint64_t, size_t> CountedConstants;
};
LabelRange GetLabelRange(dfsan_label L);
void DFSanCmpCallback(uintptr_t PC, size_t CmpSize, size_t CmpType,
uint64_t Arg1, uint64_t Arg2, dfsan_label L1,
dfsan_label L2);
bool Mutate(fuzzer::Unit *U);
private:
std::unordered_map<uintptr_t, CmpSiteInfo> PcToCmpSiteInfoMap;
LabelRange LabelRanges[1 << (sizeof(dfsan_label) * 8)] = {};
const fuzzer::Fuzzer::FuzzingOptions &Options;
};
LabelRange DFSanState::GetLabelRange(dfsan_label L) {
LabelRange &LR = LabelRanges[L];
if (LR.Beg < LR.End || L == 0)
return LR;
const dfsan_label_info *LI = dfsan_get_label_info(L);
if (LI->l1 || LI->l2)
return LR = LabelRange::Join(GetLabelRange(LI->l1), GetLabelRange(LI->l2));
return LR = LabelRange::Singleton(LI);
}
void DFSanState::DFSanCmpCallback(uintptr_t PC, size_t CmpSize, size_t CmpType,
uint64_t Arg1, uint64_t Arg2, dfsan_label L1,
dfsan_label L2) {
if (L1 == 0 && L2 == 0)
return; // Not actionable.
if (L1 != 0 && L2 != 0)
return; // Probably still actionable.
bool Res = ComputeCmp(CmpSize, CmpType, Arg1, Arg2);
CmpSiteInfo &CSI = PcToCmpSiteInfoMap[PC];
CSI.CmpSize = CmpSize;
CSI.LR.Join(GetLabelRange(L1)).Join(GetLabelRange(L2));
if (!L1) CSI.CountedConstants[Arg1]++;
if (!L2) CSI.CountedConstants[Arg2]++;
size_t Counter = CSI.ResCounters[Res]++;
if (Options.Verbosity >= 2 &&
(Counter & (Counter - 1)) == 0 &&
CSI.ResCounters[!Res] == 0)
std::cerr << "DFSAN:"
<< " PC " << std::hex << PC << std::dec
<< " S " << CmpSize
<< " T " << CmpType
<< " A1 " << Arg1 << " A2 " << Arg2 << " R " << Res
<< " L" << L1 << GetLabelRange(L1)
<< " L" << L2 << GetLabelRange(L2)
<< " LR " << CSI.LR
<< "\n";
}
bool DFSanState::Mutate(fuzzer::Unit *U) {
for (auto &PCToCmp : PcToCmpSiteInfoMap) {
auto &CSI = PCToCmp.second;
if (CSI.ResCounters[0] * CSI.ResCounters[1] != 0) continue;
if (CSI.ResCounters[0] + CSI.ResCounters[1] < 1000) continue;
if (CSI.CountedConstants.size() != 1) continue;
uintptr_t C = CSI.CountedConstants.begin()->first;
if (U->size() >= CSI.CmpSize) {
size_t RangeSize = CSI.LR.End - CSI.LR.Beg;
size_t Idx = CSI.LR.Beg + rand() % RangeSize;
if (Idx + CSI.CmpSize > U->size()) continue;
C += rand() % 5 - 2;
memcpy(U->data() + Idx, &C, CSI.CmpSize);
return true;
}
}
return false;
}
static DFSanState *DFSan;
} // namespace
namespace fuzzer {
bool Fuzzer::MutateWithDFSan(Unit *U) {
if (!&dfsan_create_label || !DFSan) return false;
return DFSan->Mutate(U);
}
void Fuzzer::InitializeDFSan() {
if (!&dfsan_create_label || !Options.UseDFSan) return;
DFSan = new DFSanState(Options);
CurrentUnit.resize(Options.MaxLen);
for (size_t i = 0; i < static_cast<size_t>(Options.MaxLen); i++) {
dfsan_label L = dfsan_create_label("input", (void*)(i + 1));
// We assume that no one else has called dfsan_create_label before.
assert(L == i + 1);
dfsan_set_label(L, &CurrentUnit[i], 1);
}
}
} // namespace fuzzer
extern "C" {
void __dfsw___sanitizer_cov_trace_cmp(uint64_t SizeAndType, uint64_t Arg1,
uint64_t Arg2, dfsan_label L0,
dfsan_label L1, dfsan_label L2) {
assert(L0 == 0);
uintptr_t PC = reinterpret_cast<uintptr_t>(__builtin_return_address(0));
uint64_t CmpSize = (SizeAndType >> 32) / 8;
uint64_t Type = (SizeAndType << 32) >> 32;
DFSan->DFSanCmpCallback(PC, CmpSize, Type, Arg1, Arg2, L1, L2);
}
} // extern "C"