[libFuzzer] Periodically purge allocator's quarantine to prolong fuzzing sessions.

Summary:
Fuzzing targets that allocate/deallocate a lot of memory tend to consume
a lot of RSS when ASan quarantine is enabled. Purging quarantine between
iterations and returning memory to OS keeps RSS down and should not
reduce the quarantine effectiveness provided the fuzz target does not
preserve state between iterations (in this case this feature can be turned off).

Based on D39153.

Reviewers: vitalybuka

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D39155

llvm-svn: 316382

compiler-rt/lib/fuzzer/FuzzerDriver.cpp

@@ -578,6 +578,7 @@ int FuzzerDriver(int *argc, char ***argv, UserCallback Callback) {
   Options.ReloadIntervalSec = Flags.reload;
   Options.OnlyASCII = Flags.only_ascii;
   Options.DetectLeaks = Flags.detect_leaks;
+  Options.PurgeAllocatorIntervalSec = Flags.purge_allocator_interval;
   Options.TraceMalloc = Flags.trace_malloc;
   Options.RssLimitMb = Flags.rss_limit_mb;
   if (Flags.runs >= 0)

compiler-rt/lib/fuzzer/FuzzerExtFunctions.def

@@ -33,6 +33,7 @@ EXT_FUNC(__sanitizer_install_malloc_and_free_hooks, int,
          (void (*malloc_hook)(const volatile void *, size_t),
           void (*free_hook)(const volatile void *)),
          false);
+EXT_FUNC(__sanitizer_purge_allocator, void, (), false);
 EXT_FUNC(__sanitizer_print_memory_profile, int, (size_t, size_t), false);
 EXT_FUNC(__sanitizer_print_stack_trace, void, (), true);
 EXT_FUNC(__sanitizer_symbolize_pc, void,

compiler-rt/lib/fuzzer/FuzzerFlags.def

@@ -114,6 +114,10 @@ FUZZER_FLAG_INT(close_fd_mask, 0, "If 1, close stdout at startup; "
     "Be careful, this will also close e.g. asan's stderr/stdout.")
 FUZZER_FLAG_INT(detect_leaks, 1, "If 1, and if LeakSanitizer is enabled "
     "try to detect memory leaks during fuzzing (i.e. not only at shut down).")
+FUZZER_FLAG_INT(purge_allocator_interval, 1, "Purge allocator caches and "
+    "quarantines every <N> seconds. When rss_limit_mb is specified (>0), "
+    "purging starts when RSS exceeds 50% of rss_limit_mb. Pass "
+    "purge_allocator_interval=-1 to disable this functionality.")
 FUZZER_FLAG_INT(trace_malloc, 0, "If >= 1 will print all mallocs/frees. "
     "If >= 2 will also print stack traces.")
 FUZZER_FLAG_INT(rss_limit_mb, 2048, "If non-zero, the fuzzer will exit upon"

compiler-rt/lib/fuzzer/FuzzerInternal.h

@@ -96,6 +96,7 @@ private:
   void CrashOnOverwrittenData();
   void InterruptCallback();
   void MutateAndTestOne();
+  void PurgeAllocator();
   void ReportNewCoverage(InputInfo *II, const Unit &U);
   void PrintPulseAndReportSlowInput(const uint8_t *Data, size_t Size);
   void WriteToOutputCorpus(const Unit &U);
@@ -124,6 +125,8 @@ private:
   bool HasMoreMallocsThanFrees = false;
   size_t NumberOfLeakDetectionAttempts = 0;
 
+  system_clock::time_point LastAllocatorPurgeAttemptTime = system_clock::now();
+
   UserCallback CB;
   InputCorpus &Corpus;
   MutationDispatcher &MD;

compiler-rt/lib/fuzzer/FuzzerLoop.cpp

@@ -587,7 +587,7 @@ void Fuzzer::MutateAndTestOne() {
     size_t NewSize = 0;
     NewSize = MD.Mutate(CurrentUnitData, Size, CurrentMaxMutationLen);
     assert(NewSize > 0 && "Mutator returned empty unit");
-    assert(NewSize <= CurrentMaxMutationLen && "Mutator return overisized unit");
+    assert(NewSize <= CurrentMaxMutationLen && "Mutator return oversized unit");
     Size = NewSize;
     II.NumExecutedMutations++;
     if (RunOne(CurrentUnitData, Size, /*MayDeleteFile=*/true, &II))
@@ -598,6 +598,25 @@ void Fuzzer::MutateAndTestOne() {
   }
 }
 
+void Fuzzer::PurgeAllocator() {
+  if (Options.PurgeAllocatorIntervalSec < 0 ||
+      !EF->__sanitizer_purge_allocator) {
+    return;
+  }
+  if (duration_cast<seconds>(system_clock::now() -
+                             LastAllocatorPurgeAttemptTime).count() <
+      Options.PurgeAllocatorIntervalSec) {
+    return;
+  }
+
+  if (Options.RssLimitMb <= 0 ||
+      GetPeakRSSMb() > static_cast<size_t>(Options.RssLimitMb) / 2) {
+    EF->__sanitizer_purge_allocator();
+  }
+
+  LastAllocatorPurgeAttemptTime = system_clock::now();
+}
+
 void Fuzzer::ReadAndExecuteSeedCorpora(const Vector<std::string> &CorpusDirs) {
   const size_t kMaxSaneLen = 1 << 20;
   const size_t kMinDefaultLen = 4096;
@@ -699,6 +718,8 @@ void Fuzzer::Loop(const Vector<std::string> &CorpusDirs) {
 
     // Perform several mutations and runs.
     MutateAndTestOne();
+
+    PurgeAllocator();
   }
 
   PrintStats("DONE  ", "\n");

compiler-rt/lib/fuzzer/FuzzerOptions.h

@@ -54,6 +54,7 @@ struct FuzzingOptions {
   bool DumpCoverage = false;
   bool UseClangCoverage = false;
   bool DetectLeaks = true;
+  int PurgeAllocatorIntervalSec = 1;
   int UseFeatureFrequency = false;
   int  TraceMalloc = 0;
   bool HandleAbrt = false;