compiler-rt/lib/fuzzer/dataflow/DataFlow.cpp

   1 /*===- DataFlow.cpp - a standalone DataFlow tracer                  -------===//
   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 // An experimental data-flow tracer for fuzz targets.
   9 // It is based on DFSan and SanitizerCoverage.
  10 // https://clang.llvm.org/docs/DataFlowSanitizer.html
  11 // https://clang.llvm.org/docs/SanitizerCoverage.html#tracing-data-flow
  12 //
  13 // It executes the fuzz target on the given input while monitoring the
  14 // data flow for every instrumented comparison instruction.
  15 //
  16 // The output shows which functions depend on which bytes of the input,
  17 // and also provides basic-block coverage for every input.
  18 //
  19 // Build:
  20 //   1. Compile this file (DataFlow.cpp) with -fsanitize=dataflow -mllvm
  21 //       -dfsan-fast-16-labels and -O2.
  22 //   2. Compile DataFlowCallbacks.cpp with -O2 -fPIC.
  23 //   3. Build the fuzz target with -g -fsanitize=dataflow
  24 //       -mllvm -dfsan-fast-16-labels
  25 //       -fsanitize-coverage=trace-pc-guard,pc-table,bb,trace-cmp
  26 //   4. Link those together with -fsanitize=dataflow
  27 //
  28 //  -fsanitize-coverage=trace-cmp inserts callbacks around every comparison
  29 //  instruction, DFSan modifies the calls to pass the data flow labels.
  30 //  The callbacks update the data flow label for the current function.
  31 //  See e.g. __dfsw___sanitizer_cov_trace_cmp1 below.
  32 //
  33 //  -fsanitize-coverage=trace-pc-guard,pc-table,bb instruments function
  34 //  entries so that the comparison callback knows that current function.
  35 //  -fsanitize-coverage=...,bb also allows to collect basic block coverage.
  36 //
  37 //
  38 // Run:
  39 //   # Collect data flow and coverage for INPUT_FILE
  40 //   # write to OUTPUT_FILE (default: stdout)
  41 //   export DFSAN_OPTIONS=warn_unimplemented=0
  42 //   ./a.out INPUT_FILE [OUTPUT_FILE]
  43 //
  44 //   # Print all instrumented functions. llvm-symbolizer must be present in PATH
  45 //   ./a.out
  46 //
  47 // Example output:
  48 // ===============
  49 //  F0 11111111111111
  50 //  F1 10000000000000
  51 //  C0 1 2 3 4 5
  52 //  C1 8
  53 //  ===============
  54 // "FN xxxxxxxxxx": tells what bytes of the input does the function N depend on.
  55 // "CN X Y Z T": tells that a function N has basic blocks X, Y, and Z covered
  56 //    in addition to the function's entry block, out of T total instrumented
  57 //    blocks.
  58 //
  59 //===----------------------------------------------------------------------===*/
  60
  61 #include <assert.h>
  62 #include <stdio.h>
  63 #include <stdlib.h>
  64 #include <stdint.h>
  65 #include <string.h>
  66
  67 #include <execinfo.h>  // backtrace_symbols_fd
  68
  69 #include "DataFlow.h"
  70
  71 extern "C" {
  72 extern int LLVMFuzzerTestOneInput(const unsigned char *Data, size_t Size);
  73 __attribute__((weak)) extern int LLVMFuzzerInitialize(int *argc, char ***argv);
  74 } // extern "C"
  75
  76 CallbackData __dft;
  77 static size_t InputLen;
  78 static size_t NumIterations;
  79 static dfsan_label **FuncLabelsPerIter;  // NumIterations x NumFuncs;
  80
  81 static inline bool BlockIsEntry(size_t BlockIdx) {
  82   return __dft.PCsBeg[BlockIdx * 2 + 1] & PCFLAG_FUNC_ENTRY;
  83 }
  84
  85 const int kNumLabels = 16;
  86
  87 // Prints all instrumented functions.
  88 static int PrintFunctions() {
  89   // We don't have the symbolizer integrated with dfsan yet.
  90   // So use backtrace_symbols_fd and pipe it through llvm-symbolizer.
  91   // TODO(kcc): this is pretty ugly and may break in lots of ways.
  92   //      We'll need to make a proper in-process symbolizer work with DFSan.
  93   FILE *Pipe = popen("sed 's/(+/ /g; s/).*//g' "
  94                      "| llvm-symbolizer "
  95                      "| grep 'dfs\\$' "
  96                      "| sed 's/dfs\\$//g' "
  97                      "| c++filt",
  98                      "w");
  99   for (size_t I = 0; I < __dft.NumGuards; I++) {
 100     uintptr_t PC = __dft.PCsBeg[I * 2];
 101     if (!BlockIsEntry(I)) continue;
 102     void *const Buf[1] = {(void*)PC};
 103     backtrace_symbols_fd(Buf, 1, fileno(Pipe));
 104   }
 105   pclose(Pipe);
 106   return 0;
 107 }
 108
 109 static void PrintBinary(FILE *Out, dfsan_label L, size_t Len) {
 110   char buf[kNumLabels + 1];
 111   assert(Len <= kNumLabels);
 112   for (int i = 0; i < kNumLabels; i++)
 113     buf[i] = (L & (1 << i)) ? '1' : '0';
 114   buf[Len] = 0;
 115   fprintf(Out, "%s", buf);
 116 }
 117
 118 static void PrintDataFlow(FILE *Out) {
 119   for (size_t Func = 0; Func < __dft.NumFuncs; Func++) {
 120     bool HasAny = false;
 121     for (size_t Iter = 0; Iter < NumIterations; Iter++)
 122       if (FuncLabelsPerIter[Iter][Func])
 123         HasAny = true;
 124     if (!HasAny)
 125       continue;
 126     fprintf(Out, "F%zd ", Func);
 127     size_t LenOfLastIteration = kNumLabels;
 128     if (auto Tail = InputLen % kNumLabels)
 129         LenOfLastIteration = Tail;
 130     for (size_t Iter = 0; Iter < NumIterations; Iter++)
 131       PrintBinary(Out, FuncLabelsPerIter[Iter][Func],
 132                   Iter == NumIterations - 1 ? LenOfLastIteration : kNumLabels);
 133     fprintf(Out, "\n");
 134   }
 135 }
 136
 137 static void PrintCoverage(FILE *Out) {
 138   ssize_t CurrentFuncGuard = -1;
 139   ssize_t CurrentFuncNum = -1;
 140   ssize_t NumBlocksInCurrentFunc = -1;
 141   for (size_t FuncBeg = 0; FuncBeg < __dft.NumGuards;) {
 142     CurrentFuncNum++;
 143     assert(BlockIsEntry(FuncBeg));
 144     size_t FuncEnd = FuncBeg + 1;
 145     for (; FuncEnd < __dft.NumGuards && !BlockIsEntry(FuncEnd); FuncEnd++)
 146       ;
 147     if (__dft.BBExecuted[FuncBeg]) {
 148       fprintf(Out, "C%zd", CurrentFuncNum);
 149       for (size_t I = FuncBeg + 1; I < FuncEnd; I++)
 150         if (__dft.BBExecuted[I])
 151           fprintf(Out, " %zd", I - FuncBeg);
 152       fprintf(Out, " %zd\n", FuncEnd - FuncBeg);
 153     }
 154     FuncBeg = FuncEnd;
 155   }
 156 }
 157
 158 int main(int argc, char **argv) {
 159   if (LLVMFuzzerInitialize)
 160     LLVMFuzzerInitialize(&argc, &argv);
 161   if (argc == 1)
 162     return PrintFunctions();
 163   assert(argc == 2 || argc == 3);
 164
 165   const char *Input = argv[1];
 166   fprintf(stderr, "INFO: reading '%s'\n", Input);
 167   FILE *In = fopen(Input, "r");
 168   assert(In);
 169   fseek(In, 0, SEEK_END);
 170   InputLen = ftell(In);
 171   fseek(In, 0, SEEK_SET);
 172   unsigned char *Buf = (unsigned char*)malloc(InputLen);
 173   size_t NumBytesRead = fread(Buf, 1, InputLen, In);
 174   assert(NumBytesRead == InputLen);
 175   fclose(In);
 176
 177   NumIterations = (NumBytesRead + kNumLabels - 1) / kNumLabels;
 178   FuncLabelsPerIter =
 179       (dfsan_label **)calloc(NumIterations, sizeof(dfsan_label *));
 180   for (size_t Iter = 0; Iter < NumIterations; Iter++)
 181     FuncLabelsPerIter[Iter] =
 182         (dfsan_label *)calloc(__dft.NumFuncs, sizeof(dfsan_label));
 183
 184   for (size_t Iter = 0; Iter < NumIterations; Iter++) {
 185     fprintf(stderr, "INFO: running '%s' %zd/%zd\n", Input, Iter, NumIterations);
 186     dfsan_flush();
 187     dfsan_set_label(0, Buf, InputLen);
 188     __dft.FuncLabels = FuncLabelsPerIter[Iter];
 189
 190     size_t BaseIdx = Iter * kNumLabels;
 191     size_t LastIdx = BaseIdx + kNumLabels < NumBytesRead ? BaseIdx + kNumLabels
 192                                                          : NumBytesRead;
 193     assert(BaseIdx < LastIdx);
 194     for (size_t Idx = BaseIdx; Idx < LastIdx; Idx++)
 195       dfsan_set_label(1 << (Idx - BaseIdx), Buf + Idx, 1);
 196     LLVMFuzzerTestOneInput(Buf, InputLen);
 197   }
 198   free(Buf);
 199
 200   bool OutIsStdout = argc == 2;
 201   fprintf(stderr, "INFO: writing dataflow to %s\n",
 202           OutIsStdout ? "<stdout>" : argv[2]);
 203   FILE *Out = OutIsStdout ? stdout : fopen(argv[2], "w");
 204   PrintDataFlow(Out);
 205   PrintCoverage(Out);
 206   if (!OutIsStdout) fclose(Out);
 207 }