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      1 //===- FuzzerLoop.cpp - Fuzzer's main loop --------------------------------===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 // Fuzzer's main loop.
     10 //===----------------------------------------------------------------------===//
     11 
     12 #include "FuzzerInternal.h"
     13 #include <algorithm>
     14 
     15 #if defined(__has_include)
     16 # if __has_include(<sanitizer/coverage_interface.h>)
     17 #  include <sanitizer/coverage_interface.h>
     18 # endif
     19 #endif
     20 
     21 extern "C" {
     22 // Re-declare some of the sanitizer functions as "weak" so that
     23 // libFuzzer can be linked w/o the sanitizers and sanitizer-coverage
     24 // (in which case it will complain at start-up time).
     25 __attribute__((weak)) void __sanitizer_print_stack_trace();
     26 __attribute__((weak)) void __sanitizer_reset_coverage();
     27 __attribute__((weak)) size_t __sanitizer_get_total_unique_caller_callee_pairs();
     28 __attribute__((weak)) size_t __sanitizer_get_total_unique_coverage();
     29 __attribute__((weak))
     30 void __sanitizer_set_death_callback(void (*callback)(void));
     31 __attribute__((weak)) size_t __sanitizer_get_number_of_counters();
     32 __attribute__((weak))
     33 uintptr_t __sanitizer_update_counter_bitset_and_clear_counters(uint8_t *bitset);
     34 }
     35 
     36 namespace fuzzer {
     37 static const size_t kMaxUnitSizeToPrint = 256;
     38 
     39 static void MissingWeakApiFunction(const char *FnName) {
     40   Printf("ERROR: %s is not defined. Exiting.\n"
     41          "Did you use -fsanitize-coverage=... to build your code?\n", FnName);
     42   exit(1);
     43 }
     44 
     45 #define CHECK_WEAK_API_FUNCTION(fn)                                            \
     46   do {                                                                         \
     47     if (!fn)                                                                   \
     48       MissingWeakApiFunction(#fn);                                             \
     49   } while (false)
     50 
     51 // Only one Fuzzer per process.
     52 static Fuzzer *F;
     53 
     54 Fuzzer::Fuzzer(UserSuppliedFuzzer &USF, FuzzingOptions Options)
     55     : USF(USF), Options(Options) {
     56   SetDeathCallback();
     57   InitializeTraceState();
     58   assert(!F);
     59   F = this;
     60 }
     61 
     62 void Fuzzer::SetDeathCallback() {
     63   CHECK_WEAK_API_FUNCTION(__sanitizer_set_death_callback);
     64   __sanitizer_set_death_callback(StaticDeathCallback);
     65 }
     66 
     67 void Fuzzer::PrintUnitInASCII(const Unit &U, const char *PrintAfter) {
     68   PrintASCII(U, PrintAfter);
     69 }
     70 
     71 void Fuzzer::StaticDeathCallback() {
     72   assert(F);
     73   F->DeathCallback();
     74 }
     75 
     76 void Fuzzer::DeathCallback() {
     77   Printf("DEATH:\n");
     78   if (CurrentUnit.size() <= kMaxUnitSizeToPrint) {
     79     Print(CurrentUnit, "\n");
     80     PrintUnitInASCII(CurrentUnit, "\n");
     81   }
     82   WriteUnitToFileWithPrefix(CurrentUnit, "crash-");
     83 }
     84 
     85 void Fuzzer::StaticAlarmCallback() {
     86   assert(F);
     87   F->AlarmCallback();
     88 }
     89 
     90 void Fuzzer::AlarmCallback() {
     91   assert(Options.UnitTimeoutSec > 0);
     92   size_t Seconds =
     93       duration_cast<seconds>(system_clock::now() - UnitStartTime).count();
     94   if (Seconds == 0) return;
     95   if (Options.Verbosity >= 2)
     96     Printf("AlarmCallback %zd\n", Seconds);
     97   if (Seconds >= (size_t)Options.UnitTimeoutSec) {
     98     Printf("ALARM: working on the last Unit for %zd seconds\n", Seconds);
     99     Printf("       and the timeout value is %d (use -timeout=N to change)\n",
    100            Options.UnitTimeoutSec);
    101     if (CurrentUnit.size() <= kMaxUnitSizeToPrint) {
    102       Print(CurrentUnit, "\n");
    103       PrintUnitInASCII(CurrentUnit, "\n");
    104     }
    105     WriteUnitToFileWithPrefix(CurrentUnit, "timeout-");
    106     Printf("==%d== ERROR: libFuzzer: timeout after %d seconds\n", GetPid(),
    107            Seconds);
    108     if (__sanitizer_print_stack_trace)
    109       __sanitizer_print_stack_trace();
    110     Printf("SUMMARY: libFuzzer: timeout\n");
    111     exit(1);
    112   }
    113 }
    114 
    115 void Fuzzer::PrintStats(const char *Where, const char *End) {
    116   size_t Seconds = secondsSinceProcessStartUp();
    117   size_t ExecPerSec = (Seconds ? TotalNumberOfRuns / Seconds : 0);
    118 
    119   if (Options.OutputCSV) {
    120     static bool csvHeaderPrinted = false;
    121     if (!csvHeaderPrinted) {
    122       csvHeaderPrinted = true;
    123       Printf("runs,block_cov,bits,cc_cov,corpus,execs_per_sec,tbms,reason\n");
    124     }
    125     Printf("%zd,%zd,%zd,%zd,%zd,%zd,%zd,%s\n", TotalNumberOfRuns,
    126            LastRecordedBlockCoverage, TotalBits(),
    127            LastRecordedCallerCalleeCoverage, Corpus.size(), ExecPerSec,
    128            TotalNumberOfExecutedTraceBasedMutations, Where);
    129   }
    130 
    131   if (!Options.Verbosity)
    132     return;
    133   Printf("#%zd\t%s", TotalNumberOfRuns, Where);
    134   if (LastRecordedBlockCoverage)
    135     Printf(" cov: %zd", LastRecordedBlockCoverage);
    136   if (auto TB = TotalBits())
    137     Printf(" bits: %zd", TB);
    138   if (LastRecordedCallerCalleeCoverage)
    139     Printf(" indir: %zd", LastRecordedCallerCalleeCoverage);
    140   Printf(" units: %zd exec/s: %zd", Corpus.size(), ExecPerSec);
    141   if (TotalNumberOfExecutedTraceBasedMutations)
    142     Printf(" tbm: %zd", TotalNumberOfExecutedTraceBasedMutations);
    143   Printf("%s", End);
    144 }
    145 
    146 void Fuzzer::RereadOutputCorpus() {
    147   if (Options.OutputCorpus.empty()) return;
    148   std::vector<Unit> AdditionalCorpus;
    149   ReadDirToVectorOfUnits(Options.OutputCorpus.c_str(), &AdditionalCorpus,
    150                          &EpochOfLastReadOfOutputCorpus);
    151   if (Corpus.empty()) {
    152     Corpus = AdditionalCorpus;
    153     return;
    154   }
    155   if (!Options.Reload) return;
    156   if (Options.Verbosity >= 2)
    157     Printf("Reload: read %zd new units.\n",  AdditionalCorpus.size());
    158   for (auto &X : AdditionalCorpus) {
    159     if (X.size() > (size_t)Options.MaxLen)
    160       X.resize(Options.MaxLen);
    161     if (UnitHashesAddedToCorpus.insert(Hash(X)).second) {
    162       CurrentUnit.clear();
    163       CurrentUnit.insert(CurrentUnit.begin(), X.begin(), X.end());
    164       if (RunOne(CurrentUnit)) {
    165         Corpus.push_back(X);
    166         PrintStats("RELOAD");
    167       }
    168     }
    169   }
    170 }
    171 
    172 void Fuzzer::ShuffleAndMinimize() {
    173   bool PreferSmall = (Options.PreferSmallDuringInitialShuffle == 1 ||
    174                       (Options.PreferSmallDuringInitialShuffle == -1 &&
    175                        USF.GetRand().RandBool()));
    176   if (Options.Verbosity)
    177     Printf("PreferSmall: %d\n", PreferSmall);
    178   PrintStats("READ  ");
    179   std::vector<Unit> NewCorpus;
    180   if (Options.ShuffleAtStartUp) {
    181     std::random_shuffle(Corpus.begin(), Corpus.end(), USF.GetRand());
    182     if (PreferSmall)
    183       std::stable_sort(
    184           Corpus.begin(), Corpus.end(),
    185           [](const Unit &A, const Unit &B) { return A.size() < B.size(); });
    186   }
    187   Unit &U = CurrentUnit;
    188   for (const auto &C : Corpus) {
    189     for (size_t First = 0; First < 1; First++) {
    190       U.clear();
    191       size_t Last = std::min(First + Options.MaxLen, C.size());
    192       U.insert(U.begin(), C.begin() + First, C.begin() + Last);
    193       if (Options.OnlyASCII)
    194         ToASCII(U);
    195       if (RunOne(U)) {
    196         NewCorpus.push_back(U);
    197         if (Options.Verbosity >= 2)
    198           Printf("NEW0: %zd L %zd\n", LastRecordedBlockCoverage, U.size());
    199       }
    200     }
    201   }
    202   Corpus = NewCorpus;
    203   for (auto &X : Corpus)
    204     UnitHashesAddedToCorpus.insert(Hash(X));
    205   PrintStats("INITED");
    206 }
    207 
    208 bool Fuzzer::RunOne(const Unit &U) {
    209   UnitStartTime = system_clock::now();
    210   TotalNumberOfRuns++;
    211 
    212   PrepareCoverageBeforeRun();
    213   ExecuteCallback(U);
    214   bool Res = CheckCoverageAfterRun();
    215 
    216   auto UnitStopTime = system_clock::now();
    217   auto TimeOfUnit =
    218       duration_cast<seconds>(UnitStopTime - UnitStartTime).count();
    219   if (!(TotalNumberOfRuns & (TotalNumberOfRuns - 1)) &&
    220       secondsSinceProcessStartUp() >= 2)
    221     PrintStats("pulse ");
    222   if (TimeOfUnit > TimeOfLongestUnitInSeconds &&
    223       TimeOfUnit >= Options.ReportSlowUnits) {
    224     TimeOfLongestUnitInSeconds = TimeOfUnit;
    225     Printf("Slowest unit: %zd s:\n", TimeOfLongestUnitInSeconds);
    226     WriteUnitToFileWithPrefix(U, "slow-unit-");
    227   }
    228   return Res;
    229 }
    230 
    231 void Fuzzer::RunOneAndUpdateCorpus(Unit &U) {
    232   if (TotalNumberOfRuns >= Options.MaxNumberOfRuns)
    233     return;
    234   if (Options.OnlyASCII)
    235     ToASCII(U);
    236   if (RunOne(U))
    237     ReportNewCoverage(U);
    238 }
    239 
    240 void Fuzzer::ExecuteCallback(const Unit &U) {
    241   const uint8_t *Data = U.data();
    242   uint8_t EmptyData;
    243   if (!Data)
    244     Data = &EmptyData;
    245   int Res = USF.TargetFunction(Data, U.size());
    246   (void)Res;
    247   assert(Res == 0);
    248 }
    249 
    250 size_t Fuzzer::RecordBlockCoverage() {
    251   CHECK_WEAK_API_FUNCTION(__sanitizer_get_total_unique_coverage);
    252   return LastRecordedBlockCoverage = __sanitizer_get_total_unique_coverage();
    253 }
    254 
    255 size_t Fuzzer::RecordCallerCalleeCoverage() {
    256   if (!Options.UseIndirCalls)
    257     return 0;
    258   if (!__sanitizer_get_total_unique_caller_callee_pairs)
    259     return 0;
    260   return LastRecordedCallerCalleeCoverage =
    261              __sanitizer_get_total_unique_caller_callee_pairs();
    262 }
    263 
    264 void Fuzzer::PrepareCoverageBeforeRun() {
    265   if (Options.UseCounters) {
    266     size_t NumCounters = __sanitizer_get_number_of_counters();
    267     CounterBitmap.resize(NumCounters);
    268     __sanitizer_update_counter_bitset_and_clear_counters(0);
    269   }
    270   RecordBlockCoverage();
    271   RecordCallerCalleeCoverage();
    272 }
    273 
    274 bool Fuzzer::CheckCoverageAfterRun() {
    275   size_t OldCoverage = LastRecordedBlockCoverage;
    276   size_t NewCoverage = RecordBlockCoverage();
    277   size_t OldCallerCalleeCoverage = LastRecordedCallerCalleeCoverage;
    278   size_t NewCallerCalleeCoverage = RecordCallerCalleeCoverage();
    279   size_t NumNewBits = 0;
    280   if (Options.UseCounters)
    281     NumNewBits = __sanitizer_update_counter_bitset_and_clear_counters(
    282         CounterBitmap.data());
    283   return NewCoverage > OldCoverage ||
    284          NewCallerCalleeCoverage > OldCallerCalleeCoverage || NumNewBits;
    285 }
    286 
    287 void Fuzzer::WriteToOutputCorpus(const Unit &U) {
    288   if (Options.OutputCorpus.empty()) return;
    289   std::string Path = DirPlusFile(Options.OutputCorpus, Hash(U));
    290   WriteToFile(U, Path);
    291   if (Options.Verbosity >= 2)
    292     Printf("Written to %s\n", Path.c_str());
    293   assert(!Options.OnlyASCII || IsASCII(U));
    294 }
    295 
    296 void Fuzzer::WriteUnitToFileWithPrefix(const Unit &U, const char *Prefix) {
    297   if (!Options.SaveArtifacts)
    298     return;
    299   std::string Path = Options.ArtifactPrefix + Prefix + Hash(U);
    300   if (!Options.ExactArtifactPath.empty())
    301     Path = Options.ExactArtifactPath;  // Overrides ArtifactPrefix.
    302   WriteToFile(U, Path);
    303   Printf("artifact_prefix='%s'; Test unit written to %s\n",
    304          Options.ArtifactPrefix.c_str(), Path.c_str());
    305   if (U.size() <= kMaxUnitSizeToPrint)
    306     Printf("Base64: %s\n", Base64(U).c_str());
    307 }
    308 
    309 void Fuzzer::SaveCorpus() {
    310   if (Options.OutputCorpus.empty()) return;
    311   for (const auto &U : Corpus)
    312     WriteToFile(U, DirPlusFile(Options.OutputCorpus, Hash(U)));
    313   if (Options.Verbosity)
    314     Printf("Written corpus of %zd files to %s\n", Corpus.size(),
    315            Options.OutputCorpus.c_str());
    316 }
    317 
    318 void Fuzzer::PrintStatusForNewUnit(const Unit &U) {
    319   if (!Options.PrintNEW)
    320     return;
    321   PrintStats("NEW   ", "");
    322   if (Options.Verbosity) {
    323     Printf(" L: %zd ", U.size());
    324     USF.PrintMutationSequence();
    325     Printf("\n");
    326   }
    327 }
    328 
    329 void Fuzzer::ReportNewCoverage(const Unit &U) {
    330   Corpus.push_back(U);
    331   UnitHashesAddedToCorpus.insert(Hash(U));
    332   PrintStatusForNewUnit(U);
    333   WriteToOutputCorpus(U);
    334   if (Options.ExitOnFirst)
    335     exit(0);
    336 }
    337 
    338 void Fuzzer::Merge(const std::vector<std::string> &Corpora) {
    339   if (Corpora.size() <= 1) {
    340     Printf("Merge requires two or more corpus dirs\n");
    341     return;
    342   }
    343   auto InitialCorpusDir = Corpora[0];
    344   ReadDir(InitialCorpusDir, nullptr);
    345   Printf("Merge: running the initial corpus '%s' of %d units\n",
    346          InitialCorpusDir.c_str(), Corpus.size());
    347   for (auto &U : Corpus)
    348     RunOne(U);
    349 
    350   std::vector<std::string> ExtraCorpora(Corpora.begin() + 1, Corpora.end());
    351 
    352   size_t NumTried = 0;
    353   size_t NumMerged = 0;
    354   for (auto &C : ExtraCorpora) {
    355     Corpus.clear();
    356     ReadDir(C, nullptr);
    357     Printf("Merge: merging the extra corpus '%s' of %zd units\n", C.c_str(),
    358            Corpus.size());
    359     for (auto &U : Corpus) {
    360       NumTried++;
    361       if (RunOne(U)) {
    362         WriteToOutputCorpus(U);
    363         NumMerged++;
    364       }
    365     }
    366   }
    367   Printf("Merge: written %zd out of %zd units\n", NumMerged, NumTried);
    368 }
    369 
    370 void Fuzzer::MutateAndTestOne() {
    371   auto &U = CurrentUnit;
    372   USF.StartMutationSequence();
    373 
    374   U = ChooseUnitToMutate();
    375 
    376   for (int i = 0; i < Options.MutateDepth; i++) {
    377     StartTraceRecording();
    378     size_t Size = U.size();
    379     U.resize(Options.MaxLen);
    380     size_t NewSize = USF.Mutate(U.data(), Size, U.size());
    381     assert(NewSize > 0 && "Mutator returned empty unit");
    382     assert(NewSize <= (size_t)Options.MaxLen &&
    383            "Mutator return overisized unit");
    384     U.resize(NewSize);
    385     RunOneAndUpdateCorpus(U);
    386     size_t NumTraceBasedMutations = StopTraceRecording();
    387     size_t TBMWidth =
    388         std::min((size_t)Options.TBMWidth, NumTraceBasedMutations);
    389     size_t TBMDepth =
    390         std::min((size_t)Options.TBMDepth, NumTraceBasedMutations);
    391     Unit BackUp = U;
    392     for (size_t w = 0; w < TBMWidth; w++) {
    393       U = BackUp;
    394       for (size_t d = 0; d < TBMDepth; d++) {
    395         TotalNumberOfExecutedTraceBasedMutations++;
    396         ApplyTraceBasedMutation(USF.GetRand()(NumTraceBasedMutations), &U);
    397         RunOneAndUpdateCorpus(U);
    398       }
    399     }
    400   }
    401 }
    402 
    403 // Returns an index of random unit from the corpus to mutate.
    404 // Hypothesis: units added to the corpus last are more likely to be interesting.
    405 // This function gives more wieght to the more recent units.
    406 size_t Fuzzer::ChooseUnitIdxToMutate() {
    407     size_t N = Corpus.size();
    408     size_t Total = (N + 1) * N / 2;
    409     size_t R = USF.GetRand()(Total);
    410     size_t IdxBeg = 0, IdxEnd = N;
    411     // Binary search.
    412     while (IdxEnd - IdxBeg >= 2) {
    413       size_t Idx = IdxBeg + (IdxEnd - IdxBeg) / 2;
    414       if (R > (Idx + 1) * Idx / 2)
    415         IdxBeg = Idx;
    416       else
    417         IdxEnd = Idx;
    418     }
    419     assert(IdxBeg < N);
    420     return IdxBeg;
    421 }
    422 
    423 // Experimental search heuristic: drilling.
    424 // - Read, shuffle, execute and minimize the corpus.
    425 // - Choose one random unit.
    426 // - Reset the coverage.
    427 // - Start fuzzing as if the chosen unit was the only element of the corpus.
    428 // - When done, reset the coverage again.
    429 // - Merge the newly created corpus into the original one.
    430 void Fuzzer::Drill() {
    431   // The corpus is already read, shuffled, and minimized.
    432   assert(!Corpus.empty());
    433   Options.PrintNEW = false;  // Don't print NEW status lines when drilling.
    434 
    435   Unit U = ChooseUnitToMutate();
    436 
    437   CHECK_WEAK_API_FUNCTION(__sanitizer_reset_coverage);
    438   __sanitizer_reset_coverage();
    439 
    440   std::vector<Unit> SavedCorpus;
    441   SavedCorpus.swap(Corpus);
    442   Corpus.push_back(U);
    443   assert(Corpus.size() == 1);
    444   RunOne(U);
    445   PrintStats("DRILL ");
    446   std::string SavedOutputCorpusPath; // Don't write new units while drilling.
    447   SavedOutputCorpusPath.swap(Options.OutputCorpus);
    448   Loop();
    449 
    450   __sanitizer_reset_coverage();
    451 
    452   PrintStats("REINIT");
    453   SavedOutputCorpusPath.swap(Options.OutputCorpus);
    454   for (auto &U : SavedCorpus)
    455     RunOne(U);
    456   PrintStats("MERGE ");
    457   Options.PrintNEW = true;
    458   size_t NumMerged = 0;
    459   for (auto &U : Corpus) {
    460     if (RunOne(U)) {
    461       PrintStatusForNewUnit(U);
    462       NumMerged++;
    463       WriteToOutputCorpus(U);
    464     }
    465   }
    466   PrintStats("MERGED");
    467   if (NumMerged && Options.Verbosity)
    468     Printf("Drilling discovered %zd new units\n", NumMerged);
    469 }
    470 
    471 void Fuzzer::Loop() {
    472   system_clock::time_point LastCorpusReload = system_clock::now();
    473   if (Options.DoCrossOver)
    474     USF.SetCorpus(&Corpus);
    475   while (true) {
    476     SyncCorpus();
    477     auto Now = system_clock::now();
    478     if (duration_cast<seconds>(Now - LastCorpusReload).count()) {
    479       RereadOutputCorpus();
    480       LastCorpusReload = Now;
    481     }
    482     if (TotalNumberOfRuns >= Options.MaxNumberOfRuns)
    483       break;
    484     if (Options.MaxTotalTimeSec > 0 &&
    485         secondsSinceProcessStartUp() >
    486         static_cast<size_t>(Options.MaxTotalTimeSec))
    487       break;
    488     // Perform several mutations and runs.
    489     MutateAndTestOne();
    490   }
    491 
    492   PrintStats("DONE  ", "\n");
    493 }
    494 
    495 void Fuzzer::SyncCorpus() {
    496   if (Options.SyncCommand.empty() || Options.OutputCorpus.empty()) return;
    497   auto Now = system_clock::now();
    498   if (duration_cast<seconds>(Now - LastExternalSync).count() <
    499       Options.SyncTimeout)
    500     return;
    501   LastExternalSync = Now;
    502   ExecuteCommand(Options.SyncCommand + " " + Options.OutputCorpus);
    503 }
    504 
    505 }  // namespace fuzzer
    506