xref: /freebsd/contrib/llvm-project/compiler-rt/lib/fuzzer/FuzzerLoop.cpp (revision 5f757f3ff9144b609b3c433dfd370cc6bdc191ad) 
1 //===- FuzzerLoop.cpp - Fuzzer's main loop --------------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 // Fuzzer's main loop.
9 //===----------------------------------------------------------------------===//
10 
11 #include "FuzzerCorpus.h"
12 #include "FuzzerIO.h"
13 #include "FuzzerInternal.h"
14 #include "FuzzerMutate.h"
15 #include "FuzzerPlatform.h"
16 #include "FuzzerRandom.h"
17 #include "FuzzerTracePC.h"
18 #include <algorithm>
19 #include <cstring>
20 #include <memory>
21 #include <mutex>
22 #include <set>
23 
24 #if defined(__has_include)
25 #if __has_include(<sanitizer / lsan_interface.h>)
26 #include <sanitizer/lsan_interface.h>
27 #endif
28 #endif
29 
30 #define NO_SANITIZE_MEMORY
31 #if defined(__has_feature)
32 #if __has_feature(memory_sanitizer)
33 #undef NO_SANITIZE_MEMORY
34 #define NO_SANITIZE_MEMORY __attribute__((no_sanitize_memory))
35 #endif
36 #endif
37 
38 namespace fuzzer {
39 static const size_t kMaxUnitSizeToPrint = 256;
40 
41 thread_local bool Fuzzer::IsMyThread;
42 
43 bool RunningUserCallback = false;
44 
45 // Only one Fuzzer per process.
46 static Fuzzer *F;
47 
48 // Leak detection is expensive, so we first check if there were more mallocs
49 // than frees (using the sanitizer malloc hooks) and only then try to call lsan.
50 struct MallocFreeTracer {
51   void Start(int TraceLevel) {
52     this->TraceLevel = TraceLevel;
53     if (TraceLevel)
54       Printf("MallocFreeTracer: START\n");
55     Mallocs = 0;
56     Frees = 0;
57   }
58   // Returns true if there were more mallocs than frees.
59   bool Stop() {
60     if (TraceLevel)
61       Printf("MallocFreeTracer: STOP %zd %zd (%s)\n", Mallocs.load(),
62              Frees.load(), Mallocs == Frees ? "same" : "DIFFERENT");
63     bool Result = Mallocs > Frees;
64     Mallocs = 0;
65     Frees = 0;
66     TraceLevel = 0;
67     return Result;
68   }
69   std::atomic<size_t> Mallocs;
70   std::atomic<size_t> Frees;
71   int TraceLevel = 0;
72 
73   std::recursive_mutex TraceMutex;
74   bool TraceDisabled = false;
75 };
76 
77 static MallocFreeTracer AllocTracer;
78 
79 // Locks printing and avoids nested hooks triggered from mallocs/frees in
80 // sanitizer.
81 class TraceLock {
82 public:
83   TraceLock() : Lock(AllocTracer.TraceMutex) {
84     AllocTracer.TraceDisabled = !AllocTracer.TraceDisabled;
85   }
86   ~TraceLock() { AllocTracer.TraceDisabled = !AllocTracer.TraceDisabled; }
87 
88   bool IsDisabled() const {
89     // This is already inverted value.
90     return !AllocTracer.TraceDisabled;
91   }
92 
93 private:
94   std::lock_guard<std::recursive_mutex> Lock;
95 };
96 
97 ATTRIBUTE_NO_SANITIZE_MEMORY
98 void MallocHook(const volatile void *ptr, size_t size) {
99   size_t N = AllocTracer.Mallocs++;
100   F->HandleMalloc(size);
101   if (int TraceLevel = AllocTracer.TraceLevel) {
102     TraceLock Lock;
103     if (Lock.IsDisabled())
104       return;
105     Printf("MALLOC[%zd] %p %zd\n", N, ptr, size);
106     if (TraceLevel >= 2 && EF)
107       PrintStackTrace();
108   }
109 }
110 
111 ATTRIBUTE_NO_SANITIZE_MEMORY
112 void FreeHook(const volatile void *ptr) {
113   size_t N = AllocTracer.Frees++;
114   if (int TraceLevel = AllocTracer.TraceLevel) {
115     TraceLock Lock;
116     if (Lock.IsDisabled())
117       return;
118     Printf("FREE[%zd]   %p\n", N, ptr);
119     if (TraceLevel >= 2 && EF)
120       PrintStackTrace();
121   }
122 }
123 
124 // Crash on a single malloc that exceeds the rss limit.
125 void Fuzzer::HandleMalloc(size_t Size) {
126   if (!Options.MallocLimitMb || (Size >> 20) < (size_t)Options.MallocLimitMb)
127     return;
128   Printf("==%d== ERROR: libFuzzer: out-of-memory (malloc(%zd))\n", GetPid(),
129          Size);
130   Printf("   To change the out-of-memory limit use -rss_limit_mb=<N>\n\n");
131   PrintStackTrace();
132   DumpCurrentUnit("oom-");
133   Printf("SUMMARY: libFuzzer: out-of-memory\n");
134   PrintFinalStats();
135   _Exit(Options.OOMExitCode); // Stop right now.
136 }
137 
138 Fuzzer::Fuzzer(UserCallback CB, InputCorpus &Corpus, MutationDispatcher &MD,
139                const FuzzingOptions &Options)
140     : CB(CB), Corpus(Corpus), MD(MD), Options(Options) {
141   if (EF->__sanitizer_set_death_callback)
142     EF->__sanitizer_set_death_callback(StaticDeathCallback);
143   assert(!F);
144   F = this;
145   TPC.ResetMaps();
146   IsMyThread = true;
147   if (Options.DetectLeaks && EF->__sanitizer_install_malloc_and_free_hooks)
148     EF->__sanitizer_install_malloc_and_free_hooks(MallocHook, FreeHook);
149   TPC.SetUseCounters(Options.UseCounters);
150   TPC.SetUseValueProfileMask(Options.UseValueProfile);
151 
152   if (Options.Verbosity)
153     TPC.PrintModuleInfo();
154   if (!Options.OutputCorpus.empty() && Options.ReloadIntervalSec)
155     EpochOfLastReadOfOutputCorpus = GetEpoch(Options.OutputCorpus);
156   MaxInputLen = MaxMutationLen = Options.MaxLen;
157   TmpMaxMutationLen = 0;  // Will be set once we load the corpus.
158   AllocateCurrentUnitData();
159   CurrentUnitSize = 0;
160   memset(BaseSha1, 0, sizeof(BaseSha1));
161 }
162 
163 void Fuzzer::AllocateCurrentUnitData() {
164   if (CurrentUnitData || MaxInputLen == 0)
165     return;
166   CurrentUnitData = new uint8_t[MaxInputLen];
167 }
168 
169 void Fuzzer::StaticDeathCallback() {
170   assert(F);
171   F->DeathCallback();
172 }
173 
174 void Fuzzer::DumpCurrentUnit(const char *Prefix) {
175   if (!CurrentUnitData)
176     return; // Happens when running individual inputs.
177   ScopedDisableMsanInterceptorChecks S;
178   MD.PrintMutationSequence();
179   Printf("; base unit: %s\n", Sha1ToString(BaseSha1).c_str());
180   size_t UnitSize = CurrentUnitSize;
181   if (UnitSize <= kMaxUnitSizeToPrint) {
182     PrintHexArray(CurrentUnitData, UnitSize, "\n");
183     PrintASCII(CurrentUnitData, UnitSize, "\n");
184   }
185   WriteUnitToFileWithPrefix({CurrentUnitData, CurrentUnitData + UnitSize},
186                             Prefix);
187 }
188 
189 NO_SANITIZE_MEMORY
190 void Fuzzer::DeathCallback() {
191   DumpCurrentUnit("crash-");
192   PrintFinalStats();
193 }
194 
195 void Fuzzer::StaticAlarmCallback() {
196   assert(F);
197   F->AlarmCallback();
198 }
199 
200 void Fuzzer::StaticCrashSignalCallback() {
201   assert(F);
202   F->CrashCallback();
203 }
204 
205 void Fuzzer::StaticExitCallback() {
206   assert(F);
207   F->ExitCallback();
208 }
209 
210 void Fuzzer::StaticInterruptCallback() {
211   assert(F);
212   F->InterruptCallback();
213 }
214 
215 void Fuzzer::StaticGracefulExitCallback() {
216   assert(F);
217   F->GracefulExitRequested = true;
218   Printf("INFO: signal received, trying to exit gracefully\n");
219 }
220 
221 void Fuzzer::StaticFileSizeExceedCallback() {
222   Printf("==%lu== ERROR: libFuzzer: file size exceeded\n", GetPid());
223   exit(1);
224 }
225 
226 void Fuzzer::CrashCallback() {
227   if (EF->__sanitizer_acquire_crash_state &&
228       !EF->__sanitizer_acquire_crash_state())
229     return;
230   Printf("==%lu== ERROR: libFuzzer: deadly signal\n", GetPid());
231   PrintStackTrace();
232   Printf("NOTE: libFuzzer has rudimentary signal handlers.\n"
233          "      Combine libFuzzer with AddressSanitizer or similar for better "
234          "crash reports.\n");
235   Printf("SUMMARY: libFuzzer: deadly signal\n");
236   DumpCurrentUnit("crash-");
237   PrintFinalStats();
238   _Exit(Options.ErrorExitCode); // Stop right now.
239 }
240 
241 void Fuzzer::ExitCallback() {
242   if (!RunningUserCallback)
243     return; // This exit did not come from the user callback
244   if (EF->__sanitizer_acquire_crash_state &&
245       !EF->__sanitizer_acquire_crash_state())
246     return;
247   Printf("==%lu== ERROR: libFuzzer: fuzz target exited\n", GetPid());
248   PrintStackTrace();
249   Printf("SUMMARY: libFuzzer: fuzz target exited\n");
250   DumpCurrentUnit("crash-");
251   PrintFinalStats();
252   _Exit(Options.ErrorExitCode);
253 }
254 
255 void Fuzzer::MaybeExitGracefully() {
256   if (!F->GracefulExitRequested) return;
257   Printf("==%lu== INFO: libFuzzer: exiting as requested\n", GetPid());
258   RmDirRecursive(TempPath("FuzzWithFork", ".dir"));
259   F->PrintFinalStats();
260   _Exit(0);
261 }
262 
263 int Fuzzer::InterruptExitCode() {
264   assert(F);
265   return F->Options.InterruptExitCode;
266 }
267 
268 void Fuzzer::InterruptCallback() {
269   Printf("==%lu== libFuzzer: run interrupted; exiting\n", GetPid());
270   PrintFinalStats();
271   ScopedDisableMsanInterceptorChecks S; // RmDirRecursive may call opendir().
272   RmDirRecursive(TempPath("FuzzWithFork", ".dir"));
273   // Stop right now, don't perform any at-exit actions.
274   _Exit(Options.InterruptExitCode);
275 }
276 
277 NO_SANITIZE_MEMORY
278 void Fuzzer::AlarmCallback() {
279   assert(Options.UnitTimeoutSec > 0);
280   // In Windows and Fuchsia, Alarm callback is executed by a different thread.
281   // NetBSD's current behavior needs this change too.
282 #if !LIBFUZZER_WINDOWS && !LIBFUZZER_NETBSD && !LIBFUZZER_FUCHSIA
283   if (!InFuzzingThread())
284     return;
285 #endif
286   if (!RunningUserCallback)
287     return; // We have not started running units yet.
288   size_t Seconds =
289       duration_cast<seconds>(system_clock::now() - UnitStartTime).count();
290   if (Seconds == 0)
291     return;
292   if (Options.Verbosity >= 2)
293     Printf("AlarmCallback %zd\n", Seconds);
294   if (Seconds >= (size_t)Options.UnitTimeoutSec) {
295     if (EF->__sanitizer_acquire_crash_state &&
296         !EF->__sanitizer_acquire_crash_state())
297       return;
298     Printf("ALARM: working on the last Unit for %zd seconds\n", Seconds);
299     Printf("       and the timeout value is %d (use -timeout=N to change)\n",
300            Options.UnitTimeoutSec);
301     DumpCurrentUnit("timeout-");
302     Printf("==%lu== ERROR: libFuzzer: timeout after %zu seconds\n", GetPid(),
303            Seconds);
304     PrintStackTrace();
305     Printf("SUMMARY: libFuzzer: timeout\n");
306     PrintFinalStats();
307     _Exit(Options.TimeoutExitCode); // Stop right now.
308   }
309 }
310 
311 void Fuzzer::RssLimitCallback() {
312   if (EF->__sanitizer_acquire_crash_state &&
313       !EF->__sanitizer_acquire_crash_state())
314     return;
315   Printf("==%lu== ERROR: libFuzzer: out-of-memory (used: %zdMb; limit: %dMb)\n",
316          GetPid(), GetPeakRSSMb(), Options.RssLimitMb);
317   Printf("   To change the out-of-memory limit use -rss_limit_mb=<N>\n\n");
318   PrintMemoryProfile();
319   DumpCurrentUnit("oom-");
320   Printf("SUMMARY: libFuzzer: out-of-memory\n");
321   PrintFinalStats();
322   _Exit(Options.OOMExitCode); // Stop right now.
323 }
324 
325 void Fuzzer::PrintStats(const char *Where, const char *End, size_t Units,
326                         size_t Features) {
327   size_t ExecPerSec = execPerSec();
328   if (!Options.Verbosity)
329     return;
330   Printf("#%zd\t%s", TotalNumberOfRuns, Where);
331   if (size_t N = TPC.GetTotalPCCoverage())
332     Printf(" cov: %zd", N);
333   if (size_t N = Features ? Features : Corpus.NumFeatures())
334     Printf(" ft: %zd", N);
335   if (!Corpus.empty()) {
336     Printf(" corp: %zd", Corpus.NumActiveUnits());
337     if (size_t N = Corpus.SizeInBytes()) {
338       if (N < (1 << 14))
339         Printf("/%zdb", N);
340       else if (N < (1 << 24))
341         Printf("/%zdKb", N >> 10);
342       else
343         Printf("/%zdMb", N >> 20);
344     }
345     if (size_t FF = Corpus.NumInputsThatTouchFocusFunction())
346       Printf(" focus: %zd", FF);
347   }
348   if (TmpMaxMutationLen)
349     Printf(" lim: %zd", TmpMaxMutationLen);
350   if (Units)
351     Printf(" units: %zd", Units);
352 
353   Printf(" exec/s: %zd", ExecPerSec);
354   Printf(" rss: %zdMb", GetPeakRSSMb());
355   Printf("%s", End);
356 }
357 
358 void Fuzzer::PrintFinalStats() {
359   if (Options.PrintFullCoverage)
360     TPC.PrintCoverage(/*PrintAllCounters=*/true);
361   if (Options.PrintCoverage)
362     TPC.PrintCoverage(/*PrintAllCounters=*/false);
363   if (Options.PrintCorpusStats)
364     Corpus.PrintStats();
365   if (!Options.PrintFinalStats)
366     return;
367   size_t ExecPerSec = execPerSec();
368   Printf("stat::number_of_executed_units: %zd\n", TotalNumberOfRuns);
369   Printf("stat::average_exec_per_sec:     %zd\n", ExecPerSec);
370   Printf("stat::new_units_added:          %zd\n", NumberOfNewUnitsAdded);
371   Printf("stat::slowest_unit_time_sec:    %ld\n", TimeOfLongestUnitInSeconds);
372   Printf("stat::peak_rss_mb:              %zd\n", GetPeakRSSMb());
373 }
374 
375 void Fuzzer::SetMaxInputLen(size_t MaxInputLen) {
376   assert(this->MaxInputLen == 0); // Can only reset MaxInputLen from 0 to non-0.
377   assert(MaxInputLen);
378   this->MaxInputLen = MaxInputLen;
379   this->MaxMutationLen = MaxInputLen;
380   AllocateCurrentUnitData();
381   Printf("INFO: -max_len is not provided; "
382          "libFuzzer will not generate inputs larger than %zd bytes\n",
383          MaxInputLen);
384 }
385 
386 void Fuzzer::SetMaxMutationLen(size_t MaxMutationLen) {
387   assert(MaxMutationLen && MaxMutationLen <= MaxInputLen);
388   this->MaxMutationLen = MaxMutationLen;
389 }
390 
391 void Fuzzer::CheckExitOnSrcPosOrItem() {
392   if (!Options.ExitOnSrcPos.empty()) {
393     static auto *PCsSet = new std::set<uintptr_t>;
394     auto HandlePC = [&](const TracePC::PCTableEntry *TE) {
395       if (!PCsSet->insert(TE->PC).second)
396         return;
397       std::string Descr = DescribePC("%F %L", TE->PC + 1);
398       if (Descr.find(Options.ExitOnSrcPos) != std::string::npos) {
399         Printf("INFO: found line matching '%s', exiting.\n",
400                Options.ExitOnSrcPos.c_str());
401         _Exit(0);
402       }
403     };
404     TPC.ForEachObservedPC(HandlePC);
405   }
406   if (!Options.ExitOnItem.empty()) {
407     if (Corpus.HasUnit(Options.ExitOnItem)) {
408       Printf("INFO: found item with checksum '%s', exiting.\n",
409              Options.ExitOnItem.c_str());
410       _Exit(0);
411     }
412   }
413 }
414 
415 void Fuzzer::RereadOutputCorpus(size_t MaxSize) {
416   if (Options.OutputCorpus.empty() || !Options.ReloadIntervalSec)
417     return;
418   std::vector<Unit> AdditionalCorpus;
419   std::vector<std::string> AdditionalCorpusPaths;
420   ReadDirToVectorOfUnits(
421       Options.OutputCorpus.c_str(), &AdditionalCorpus,
422       &EpochOfLastReadOfOutputCorpus, MaxSize,
423       /*ExitOnError*/ false,
424       (Options.Verbosity >= 2 ? &AdditionalCorpusPaths : nullptr));
425   if (Options.Verbosity >= 2)
426     Printf("Reload: read %zd new units.\n", AdditionalCorpus.size());
427   bool Reloaded = false;
428   for (size_t i = 0; i != AdditionalCorpus.size(); ++i) {
429     auto &U = AdditionalCorpus[i];
430     if (U.size() > MaxSize)
431       U.resize(MaxSize);
432     if (!Corpus.HasUnit(U)) {
433       if (RunOne(U.data(), U.size())) {
434         CheckExitOnSrcPosOrItem();
435         Reloaded = true;
436         if (Options.Verbosity >= 2)
437           Printf("Reloaded %s\n", AdditionalCorpusPaths[i].c_str());
438       }
439     }
440   }
441   if (Reloaded)
442     PrintStats("RELOAD");
443 }
444 
445 void Fuzzer::PrintPulseAndReportSlowInput(const uint8_t *Data, size_t Size) {
446   auto TimeOfUnit =
447       duration_cast<seconds>(UnitStopTime - UnitStartTime).count();
448   if (!(TotalNumberOfRuns & (TotalNumberOfRuns - 1)) &&
449       secondsSinceProcessStartUp() >= 2)
450     PrintStats("pulse ");
451   auto Threshhold =
452       static_cast<long>(static_cast<double>(TimeOfLongestUnitInSeconds) * 1.1);
453   if (TimeOfUnit > Threshhold && TimeOfUnit >= Options.ReportSlowUnits) {
454     TimeOfLongestUnitInSeconds = TimeOfUnit;
455     Printf("Slowest unit: %ld s:\n", TimeOfLongestUnitInSeconds);
456     WriteUnitToFileWithPrefix({Data, Data + Size}, "slow-unit-");
457   }
458 }
459 
460 static void WriteFeatureSetToFile(const std::string &FeaturesDir,
461                                   const std::string &FileName,
462                                   const std::vector<uint32_t> &FeatureSet) {
463   if (FeaturesDir.empty() || FeatureSet.empty()) return;
464   WriteToFile(reinterpret_cast<const uint8_t *>(FeatureSet.data()),
465               FeatureSet.size() * sizeof(FeatureSet[0]),
466               DirPlusFile(FeaturesDir, FileName));
467 }
468 
469 static void RenameFeatureSetFile(const std::string &FeaturesDir,
470                                  const std::string &OldFile,
471                                  const std::string &NewFile) {
472   if (FeaturesDir.empty()) return;
473   RenameFile(DirPlusFile(FeaturesDir, OldFile),
474              DirPlusFile(FeaturesDir, NewFile));
475 }
476 
477 static void WriteEdgeToMutationGraphFile(const std::string &MutationGraphFile,
478                                          const InputInfo *II,
479                                          const InputInfo *BaseII,
480                                          const std::string &MS) {
481   if (MutationGraphFile.empty())
482     return;
483 
484   std::string Sha1 = Sha1ToString(II->Sha1);
485 
486   std::string OutputString;
487 
488   // Add a new vertex.
489   OutputString.append("\"");
490   OutputString.append(Sha1);
491   OutputString.append("\"\n");
492 
493   // Add a new edge if there is base input.
494   if (BaseII) {
495     std::string BaseSha1 = Sha1ToString(BaseII->Sha1);
496     OutputString.append("\"");
497     OutputString.append(BaseSha1);
498     OutputString.append("\" -> \"");
499     OutputString.append(Sha1);
500     OutputString.append("\" [label=\"");
501     OutputString.append(MS);
502     OutputString.append("\"];\n");
503   }
504 
505   AppendToFile(OutputString, MutationGraphFile);
506 }
507 
508 bool Fuzzer::RunOne(const uint8_t *Data, size_t Size, bool MayDeleteFile,
509                     InputInfo *II, bool ForceAddToCorpus,
510                     bool *FoundUniqFeatures) {
511   if (!Size)
512     return false;
513   // Largest input length should be INT_MAX.
514   assert(Size < std::numeric_limits<uint32_t>::max());
515 
516   if(!ExecuteCallback(Data, Size)) return false;
517   auto TimeOfUnit = duration_cast<microseconds>(UnitStopTime - UnitStartTime);
518 
519   UniqFeatureSetTmp.clear();
520   size_t FoundUniqFeaturesOfII = 0;
521   size_t NumUpdatesBefore = Corpus.NumFeatureUpdates();
522   TPC.CollectFeatures([&](uint32_t Feature) {
523     if (Corpus.AddFeature(Feature, static_cast<uint32_t>(Size), Options.Shrink))
524       UniqFeatureSetTmp.push_back(Feature);
525     if (Options.Entropic)
526       Corpus.UpdateFeatureFrequency(II, Feature);
527     if (Options.ReduceInputs && II && !II->NeverReduce)
528       if (std::binary_search(II->UniqFeatureSet.begin(),
529                              II->UniqFeatureSet.end(), Feature))
530         FoundUniqFeaturesOfII++;
531   });
532   if (FoundUniqFeatures)
533     *FoundUniqFeatures = FoundUniqFeaturesOfII;
534   PrintPulseAndReportSlowInput(Data, Size);
535   size_t NumNewFeatures = Corpus.NumFeatureUpdates() - NumUpdatesBefore;
536   if (NumNewFeatures || ForceAddToCorpus) {
537     TPC.UpdateObservedPCs();
538     auto NewII =
539         Corpus.AddToCorpus({Data, Data + Size}, NumNewFeatures, MayDeleteFile,
540                            TPC.ObservedFocusFunction(), ForceAddToCorpus,
541                            TimeOfUnit, UniqFeatureSetTmp, DFT, II);
542     WriteFeatureSetToFile(Options.FeaturesDir, Sha1ToString(NewII->Sha1),
543                           NewII->UniqFeatureSet);
544     WriteEdgeToMutationGraphFile(Options.MutationGraphFile, NewII, II,
545                                  MD.MutationSequence());
546     return true;
547   }
548   if (II && FoundUniqFeaturesOfII &&
549       II->DataFlowTraceForFocusFunction.empty() &&
550       FoundUniqFeaturesOfII == II->UniqFeatureSet.size() &&
551       II->U.size() > Size) {
552     auto OldFeaturesFile = Sha1ToString(II->Sha1);
553     Corpus.Replace(II, {Data, Data + Size}, TimeOfUnit);
554     RenameFeatureSetFile(Options.FeaturesDir, OldFeaturesFile,
555                          Sha1ToString(II->Sha1));
556     return true;
557   }
558   return false;
559 }
560 
561 void Fuzzer::TPCUpdateObservedPCs() { TPC.UpdateObservedPCs(); }
562 
563 size_t Fuzzer::GetCurrentUnitInFuzzingThead(const uint8_t **Data) const {
564   assert(InFuzzingThread());
565   *Data = CurrentUnitData;
566   return CurrentUnitSize;
567 }
568 
569 void Fuzzer::CrashOnOverwrittenData() {
570   Printf("==%d== ERROR: libFuzzer: fuzz target overwrites its const input\n",
571          GetPid());
572   PrintStackTrace();
573   Printf("SUMMARY: libFuzzer: overwrites-const-input\n");
574   DumpCurrentUnit("crash-");
575   PrintFinalStats();
576   _Exit(Options.ErrorExitCode); // Stop right now.
577 }
578 
579 // Compare two arrays, but not all bytes if the arrays are large.
580 static bool LooseMemeq(const uint8_t *A, const uint8_t *B, size_t Size) {
581   const size_t Limit = 64;
582   if (Size <= 64)
583     return !memcmp(A, B, Size);
584   // Compare first and last Limit/2 bytes.
585   return !memcmp(A, B, Limit / 2) &&
586          !memcmp(A + Size - Limit / 2, B + Size - Limit / 2, Limit / 2);
587 }
588 
589 // This method is not inlined because it would cause a test to fail where it
590 // is part of the stack unwinding. See D97975 for details.
591 ATTRIBUTE_NOINLINE bool Fuzzer::ExecuteCallback(const uint8_t *Data,
592                                                 size_t Size) {
593   TPC.RecordInitialStack();
594   TotalNumberOfRuns++;
595   assert(InFuzzingThread());
596   // We copy the contents of Unit into a separate heap buffer
597   // so that we reliably find buffer overflows in it.
598   uint8_t *DataCopy = new uint8_t[Size];
599   memcpy(DataCopy, Data, Size);
600   if (EF->__msan_unpoison)
601     EF->__msan_unpoison(DataCopy, Size);
602   if (EF->__msan_unpoison_param)
603     EF->__msan_unpoison_param(2);
604   if (CurrentUnitData && CurrentUnitData != Data)
605     memcpy(CurrentUnitData, Data, Size);
606   CurrentUnitSize = Size;
607   int CBRes = 0;
608   {
609     ScopedEnableMsanInterceptorChecks S;
610     AllocTracer.Start(Options.TraceMalloc);
611     UnitStartTime = system_clock::now();
612     TPC.ResetMaps();
613     RunningUserCallback = true;
614     CBRes = CB(DataCopy, Size);
615     RunningUserCallback = false;
616     UnitStopTime = system_clock::now();
617     assert(CBRes == 0 || CBRes == -1);
618     HasMoreMallocsThanFrees = AllocTracer.Stop();
619   }
620   if (!LooseMemeq(DataCopy, Data, Size))
621     CrashOnOverwrittenData();
622   CurrentUnitSize = 0;
623   delete[] DataCopy;
624   return CBRes == 0;
625 }
626 
627 std::string Fuzzer::WriteToOutputCorpus(const Unit &U) {
628   if (Options.OnlyASCII)
629     assert(IsASCII(U));
630   if (Options.OutputCorpus.empty())
631     return "";
632   std::string Path = DirPlusFile(Options.OutputCorpus, Hash(U));
633   WriteToFile(U, Path);
634   if (Options.Verbosity >= 2)
635     Printf("Written %zd bytes to %s\n", U.size(), Path.c_str());
636   return Path;
637 }
638 
639 void Fuzzer::WriteUnitToFileWithPrefix(const Unit &U, const char *Prefix) {
640   if (!Options.SaveArtifacts)
641     return;
642   std::string Path = Options.ArtifactPrefix + Prefix + Hash(U);
643   if (!Options.ExactArtifactPath.empty())
644     Path = Options.ExactArtifactPath; // Overrides ArtifactPrefix.
645   WriteToFile(U, Path);
646   Printf("artifact_prefix='%s'; Test unit written to %s\n",
647          Options.ArtifactPrefix.c_str(), Path.c_str());
648   if (U.size() <= kMaxUnitSizeToPrint)
649     Printf("Base64: %s\n", Base64(U).c_str());
650 }
651 
652 void Fuzzer::PrintStatusForNewUnit(const Unit &U, const char *Text) {
653   if (!Options.PrintNEW)
654     return;
655   PrintStats(Text, "");
656   if (Options.Verbosity) {
657     Printf(" L: %zd/%zd ", U.size(), Corpus.MaxInputSize());
658     MD.PrintMutationSequence(Options.Verbosity >= 2);
659     Printf("\n");
660   }
661 }
662 
663 void Fuzzer::ReportNewCoverage(InputInfo *II, const Unit &U) {
664   II->NumSuccessfullMutations++;
665   MD.RecordSuccessfulMutationSequence();
666   PrintStatusForNewUnit(U, II->Reduced ? "REDUCE" : "NEW   ");
667   WriteToOutputCorpus(U);
668   NumberOfNewUnitsAdded++;
669   CheckExitOnSrcPosOrItem(); // Check only after the unit is saved to corpus.
670   LastCorpusUpdateRun = TotalNumberOfRuns;
671 }
672 
673 // Tries detecting a memory leak on the particular input that we have just
674 // executed before calling this function.
675 void Fuzzer::TryDetectingAMemoryLeak(const uint8_t *Data, size_t Size,
676                                      bool DuringInitialCorpusExecution) {
677   if (!HasMoreMallocsThanFrees)
678     return; // mallocs==frees, a leak is unlikely.
679   if (!Options.DetectLeaks)
680     return;
681   if (!DuringInitialCorpusExecution &&
682       TotalNumberOfRuns >= Options.MaxNumberOfRuns)
683     return;
684   if (!&(EF->__lsan_enable) || !&(EF->__lsan_disable) ||
685       !(EF->__lsan_do_recoverable_leak_check))
686     return; // No lsan.
687   // Run the target once again, but with lsan disabled so that if there is
688   // a real leak we do not report it twice.
689   EF->__lsan_disable();
690   ExecuteCallback(Data, Size);
691   EF->__lsan_enable();
692   if (!HasMoreMallocsThanFrees)
693     return; // a leak is unlikely.
694   if (NumberOfLeakDetectionAttempts++ > 1000) {
695     Options.DetectLeaks = false;
696     Printf("INFO: libFuzzer disabled leak detection after every mutation.\n"
697            "      Most likely the target function accumulates allocated\n"
698            "      memory in a global state w/o actually leaking it.\n"
699            "      You may try running this binary with -trace_malloc=[12]"
700            "      to get a trace of mallocs and frees.\n"
701            "      If LeakSanitizer is enabled in this process it will still\n"
702            "      run on the process shutdown.\n");
703     return;
704   }
705   // Now perform the actual lsan pass. This is expensive and we must ensure
706   // we don't call it too often.
707   if (EF->__lsan_do_recoverable_leak_check()) { // Leak is found, report it.
708     if (DuringInitialCorpusExecution)
709       Printf("\nINFO: a leak has been found in the initial corpus.\n\n");
710     Printf("INFO: to ignore leaks on libFuzzer side use -detect_leaks=0.\n\n");
711     CurrentUnitSize = Size;
712     DumpCurrentUnit("leak-");
713     PrintFinalStats();
714     _Exit(Options.ErrorExitCode); // not exit() to disable lsan further on.
715   }
716 }
717 
718 void Fuzzer::MutateAndTestOne() {
719   MD.StartMutationSequence();
720 
721   auto &II = Corpus.ChooseUnitToMutate(MD.GetRand());
722   if (Options.DoCrossOver) {
723     auto &CrossOverII = Corpus.ChooseUnitToCrossOverWith(
724         MD.GetRand(), Options.CrossOverUniformDist);
725     MD.SetCrossOverWith(&CrossOverII.U);
726   }
727   const auto &U = II.U;
728   memcpy(BaseSha1, II.Sha1, sizeof(BaseSha1));
729   assert(CurrentUnitData);
730   size_t Size = U.size();
731   assert(Size <= MaxInputLen && "Oversized Unit");
732   memcpy(CurrentUnitData, U.data(), Size);
733 
734   assert(MaxMutationLen > 0);
735 
736   size_t CurrentMaxMutationLen =
737       Min(MaxMutationLen, Max(U.size(), TmpMaxMutationLen));
738   assert(CurrentMaxMutationLen > 0);
739 
740   for (int i = 0; i < Options.MutateDepth; i++) {
741     if (TotalNumberOfRuns >= Options.MaxNumberOfRuns)
742       break;
743     MaybeExitGracefully();
744     size_t NewSize = 0;
745     if (II.HasFocusFunction && !II.DataFlowTraceForFocusFunction.empty() &&
746         Size <= CurrentMaxMutationLen)
747       NewSize = MD.MutateWithMask(CurrentUnitData, Size, Size,
748                                   II.DataFlowTraceForFocusFunction);
749 
750     // If MutateWithMask either failed or wasn't called, call default Mutate.
751     if (!NewSize)
752       NewSize = MD.Mutate(CurrentUnitData, Size, CurrentMaxMutationLen);
753     assert(NewSize > 0 && "Mutator returned empty unit");
754     assert(NewSize <= CurrentMaxMutationLen && "Mutator return oversized unit");
755     Size = NewSize;
756     II.NumExecutedMutations++;
757     Corpus.IncrementNumExecutedMutations();
758 
759     bool FoundUniqFeatures = false;
760     bool NewCov = RunOne(CurrentUnitData, Size, /*MayDeleteFile=*/true, &II,
761                          /*ForceAddToCorpus*/ false, &FoundUniqFeatures);
762     TryDetectingAMemoryLeak(CurrentUnitData, Size,
763                             /*DuringInitialCorpusExecution*/ false);
764     if (NewCov) {
765       ReportNewCoverage(&II, {CurrentUnitData, CurrentUnitData + Size});
766       break;  // We will mutate this input more in the next rounds.
767     }
768     if (Options.ReduceDepth && !FoundUniqFeatures)
769       break;
770   }
771 
772   II.NeedsEnergyUpdate = true;
773 }
774 
775 void Fuzzer::PurgeAllocator() {
776   if (Options.PurgeAllocatorIntervalSec < 0 || !EF->__sanitizer_purge_allocator)
777     return;
778   if (duration_cast<seconds>(system_clock::now() -
779                              LastAllocatorPurgeAttemptTime)
780           .count() < Options.PurgeAllocatorIntervalSec)
781     return;
782 
783   if (Options.RssLimitMb <= 0 ||
784       GetPeakRSSMb() > static_cast<size_t>(Options.RssLimitMb) / 2)
785     EF->__sanitizer_purge_allocator();
786 
787   LastAllocatorPurgeAttemptTime = system_clock::now();
788 }
789 
790 void Fuzzer::ReadAndExecuteSeedCorpora(std::vector<SizedFile> &CorporaFiles) {
791   const size_t kMaxSaneLen = 1 << 20;
792   const size_t kMinDefaultLen = 4096;
793   size_t MaxSize = 0;
794   size_t MinSize = -1;
795   size_t TotalSize = 0;
796   for (auto &File : CorporaFiles) {
797     MaxSize = Max(File.Size, MaxSize);
798     MinSize = Min(File.Size, MinSize);
799     TotalSize += File.Size;
800   }
801   if (Options.MaxLen == 0)
802     SetMaxInputLen(std::clamp(MaxSize, kMinDefaultLen, kMaxSaneLen));
803   assert(MaxInputLen > 0);
804 
805   // Test the callback with empty input and never try it again.
806   uint8_t dummy = 0;
807   ExecuteCallback(&dummy, 0);
808 
809   if (CorporaFiles.empty()) {
810     Printf("INFO: A corpus is not provided, starting from an empty corpus\n");
811     Unit U({'\n'}); // Valid ASCII input.
812     RunOne(U.data(), U.size());
813   } else {
814     Printf("INFO: seed corpus: files: %zd min: %zdb max: %zdb total: %zdb"
815            " rss: %zdMb\n",
816            CorporaFiles.size(), MinSize, MaxSize, TotalSize, GetPeakRSSMb());
817     if (Options.ShuffleAtStartUp)
818       std::shuffle(CorporaFiles.begin(), CorporaFiles.end(), MD.GetRand());
819 
820     if (Options.PreferSmall) {
821       std::stable_sort(CorporaFiles.begin(), CorporaFiles.end());
822       assert(CorporaFiles.front().Size <= CorporaFiles.back().Size);
823     }
824 
825     // Load and execute inputs one by one.
826     for (auto &SF : CorporaFiles) {
827       auto U = FileToVector(SF.File, MaxInputLen, /*ExitOnError=*/false);
828       assert(U.size() <= MaxInputLen);
829       RunOne(U.data(), U.size(), /*MayDeleteFile*/ false, /*II*/ nullptr,
830              /*ForceAddToCorpus*/ Options.KeepSeed,
831              /*FoundUniqFeatures*/ nullptr);
832       CheckExitOnSrcPosOrItem();
833       TryDetectingAMemoryLeak(U.data(), U.size(),
834                               /*DuringInitialCorpusExecution*/ true);
835     }
836   }
837 
838   PrintStats("INITED");
839   if (!Options.FocusFunction.empty()) {
840     Printf("INFO: %zd/%zd inputs touch the focus function\n",
841            Corpus.NumInputsThatTouchFocusFunction(), Corpus.size());
842     if (!Options.DataFlowTrace.empty())
843       Printf("INFO: %zd/%zd inputs have the Data Flow Trace\n",
844              Corpus.NumInputsWithDataFlowTrace(),
845              Corpus.NumInputsThatTouchFocusFunction());
846   }
847 
848   if (Corpus.empty() && Options.MaxNumberOfRuns) {
849     Printf("WARNING: no interesting inputs were found so far. "
850            "Is the code instrumented for coverage?\n"
851            "This may also happen if the target rejected all inputs we tried so "
852            "far\n");
853     // The remaining logic requires that the corpus is not empty,
854     // so we add one fake input to the in-memory corpus.
855     Corpus.AddToCorpus({'\n'}, /*NumFeatures=*/1, /*MayDeleteFile=*/true,
856                        /*HasFocusFunction=*/false, /*NeverReduce=*/false,
857                        /*TimeOfUnit=*/duration_cast<microseconds>(0s), {0}, DFT,
858                        /*BaseII*/ nullptr);
859   }
860 }
861 
862 void Fuzzer::Loop(std::vector<SizedFile> &CorporaFiles) {
863   auto FocusFunctionOrAuto = Options.FocusFunction;
864   DFT.Init(Options.DataFlowTrace, &FocusFunctionOrAuto, CorporaFiles,
865            MD.GetRand());
866   TPC.SetFocusFunction(FocusFunctionOrAuto);
867   ReadAndExecuteSeedCorpora(CorporaFiles);
868   DFT.Clear();  // No need for DFT any more.
869   TPC.SetPrintNewPCs(Options.PrintNewCovPcs);
870   TPC.SetPrintNewFuncs(Options.PrintNewCovFuncs);
871   system_clock::time_point LastCorpusReload = system_clock::now();
872 
873   TmpMaxMutationLen =
874       Min(MaxMutationLen, Max(size_t(4), Corpus.MaxInputSize()));
875 
876   while (true) {
877     auto Now = system_clock::now();
878     if (!Options.StopFile.empty() &&
879         !FileToVector(Options.StopFile, 1, false).empty())
880       break;
881     if (duration_cast<seconds>(Now - LastCorpusReload).count() >=
882         Options.ReloadIntervalSec) {
883       RereadOutputCorpus(MaxInputLen);
884       LastCorpusReload = system_clock::now();
885     }
886     if (TotalNumberOfRuns >= Options.MaxNumberOfRuns)
887       break;
888     if (TimedOut())
889       break;
890 
891     // Update TmpMaxMutationLen
892     if (Options.LenControl) {
893       if (TmpMaxMutationLen < MaxMutationLen &&
894           TotalNumberOfRuns - LastCorpusUpdateRun >
895               Options.LenControl * Log(TmpMaxMutationLen)) {
896         TmpMaxMutationLen =
897             Min(MaxMutationLen, TmpMaxMutationLen + Log(TmpMaxMutationLen));
898         LastCorpusUpdateRun = TotalNumberOfRuns;
899       }
900     } else {
901       TmpMaxMutationLen = MaxMutationLen;
902     }
903 
904     // Perform several mutations and runs.
905     MutateAndTestOne();
906 
907     PurgeAllocator();
908   }
909 
910   PrintStats("DONE  ", "\n");
911   MD.PrintRecommendedDictionary();
912 }
913 
914 void Fuzzer::MinimizeCrashLoop(const Unit &U) {
915   if (U.size() <= 1)
916     return;
917   while (!TimedOut() && TotalNumberOfRuns < Options.MaxNumberOfRuns) {
918     MD.StartMutationSequence();
919     memcpy(CurrentUnitData, U.data(), U.size());
920     for (int i = 0; i < Options.MutateDepth; i++) {
921       size_t NewSize = MD.Mutate(CurrentUnitData, U.size(), MaxMutationLen);
922       assert(NewSize > 0 && NewSize <= MaxMutationLen);
923       ExecuteCallback(CurrentUnitData, NewSize);
924       PrintPulseAndReportSlowInput(CurrentUnitData, NewSize);
925       TryDetectingAMemoryLeak(CurrentUnitData, NewSize,
926                               /*DuringInitialCorpusExecution*/ false);
927     }
928   }
929 }
930 
931 } // namespace fuzzer
932 
933 extern "C" {
934 
935 ATTRIBUTE_INTERFACE size_t
936 LLVMFuzzerMutate(uint8_t *Data, size_t Size, size_t MaxSize) {
937   assert(fuzzer::F);
938   return fuzzer::F->GetMD().DefaultMutate(Data, Size, MaxSize);
939 }
940 
941 } // extern "C"
942