--- /dev/null
+//===- 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"
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