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llvm-project/llvm/lib/Fuzzer/FuzzerTraceState.cpp

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//===- FuzzerTraceState.cpp - Trace-based fuzzer mutator ------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
// This file implements a mutation algorithm based on instruction traces and
// on taint analysis feedback from DFSan.
//
// Instruction traces are special hooks inserted by the compiler around
// interesting instructions. Currently supported traces:
// * __sanitizer_cov_trace_cmp -- inserted before every ICMP instruction,
// receives the type, size and arguments of ICMP.
//
// Every time a traced event is intercepted we analyse the data involved
// in the event and suggest a mutation for future executions.
// For example if 4 bytes of data that derive from input bytes {4,5,6,7}
// are compared with a constant 12345,
// we try to insert 12345, 12344, 12346 into bytes
// {4,5,6,7} of the next fuzzed inputs.
//
// The fuzzer can work only with the traces, or with both traces and DFSan.
//
// DataFlowSanitizer (DFSan) is a tool for
// generalised dynamic data flow (taint) analysis:
// http://clang.llvm.org/docs/DataFlowSanitizer.html .
//
// The approach with DFSan-based fuzzing 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 with DFSan:
// * lib/Fuzzer/Fuzzer*.cpp is compiled w/o any instrumentation.
// * The code under test is compiled with DFSan *and* with instruction traces.
// * 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::ApplyTraceBasedMutation() tries to use the data recorded
// by __dfsw_* hooks to guide the fuzzing towards new application states.
//
// Parts of this code will 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 (-fsanitize=dataflow is optional):
(
cd $LLVM/lib/Fuzzer/
clang -fPIC -c -g -O2 -std=c++11 Fuzzer*.cpp
clang++ -O0 -std=c++11 -fsanitize-coverage=edge,trace-cmp \
-fsanitize=dataflow \
test/SimpleCmpTest.cpp Fuzzer*.o
./a.out -use_traces=1
)
*/
#include "FuzzerDFSan.h"
#include "FuzzerInternal.h"
#include <algorithm>
#include <cstring>
#include <unordered_map>
#if !LLVM_FUZZER_SUPPORTS_DFSAN
// Stubs for dfsan for platforms where dfsan does not exist and weak
// functions don't work.
extern "C" {
dfsan_label dfsan_create_label(const char *desc, void *userdata) { return 0; }
void dfsan_set_label(dfsan_label label, void *addr, size_t size) {}
void dfsan_add_label(dfsan_label label, void *addr, size_t size) {}
const struct dfsan_label_info *dfsan_get_label_info(dfsan_label label) {
return nullptr;
}
dfsan_label dfsan_read_label(const void *addr, size_t size) { return 0; }
} // extern "C"
#endif // !LLVM_FUZZER_SUPPORTS_DFSAN
namespace fuzzer {
// 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);
// Other size, ==
if (CmpType == ICMP_EQ) return Arg1 == Arg2;
// assert(0 && "unsupported cmp and type size combination");
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};
}
};
// For now, very simple: put Size bytes of Data at position Pos.
struct TraceBasedMutation {
size_t Pos;
size_t Size;
uint64_t Data;
};
class TraceState {
public:
TraceState(const Fuzzer::FuzzingOptions &Options, const Unit &CurrentUnit)
: Options(Options), CurrentUnit(CurrentUnit) {}
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);
void DFSanSwitchCallback(uint64_t PC, size_t ValSizeInBits, uint64_t Val,
size_t NumCases, uint64_t *Cases, dfsan_label L);
void TraceCmpCallback(uintptr_t PC, size_t CmpSize, size_t CmpType,
uint64_t Arg1, uint64_t Arg2);
void TraceSwitchCallback(uintptr_t PC, size_t ValSizeInBits, uint64_t Val,
size_t NumCases, uint64_t *Cases);
int TryToAddDesiredData(uint64_t PresentData, uint64_t DesiredData,
size_t DataSize);
void StartTraceRecording() {
if (!Options.UseTraces) return;
RecordingTraces = true;
Mutations.clear();
}
size_t StopTraceRecording(FuzzerRandomBase &Rand) {
RecordingTraces = false;
return Mutations.size();
}
void ApplyTraceBasedMutation(size_t Idx, fuzzer::Unit *U);
private:
bool IsTwoByteData(uint64_t Data) {
int64_t Signed = static_cast<int64_t>(Data);
Signed >>= 16;
return Signed == 0 || Signed == -1L;
}
bool RecordingTraces = false;
std::vector<TraceBasedMutation> Mutations;
LabelRange LabelRanges[1 << (sizeof(dfsan_label) * 8)] = {};
const Fuzzer::FuzzingOptions &Options;
const Unit &CurrentUnit;
};
LabelRange TraceState::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 TraceState::ApplyTraceBasedMutation(size_t Idx, fuzzer::Unit *U) {
assert(Idx < Mutations.size());
auto &M = Mutations[Idx];
if (Options.Verbosity >= 3)
Printf("TBM %zd %zd %zd\n", M.Pos, M.Size, M.Data);
if (M.Pos + M.Size > U->size()) return;
memcpy(U->data() + M.Pos, &M.Data, M.Size);
}
void TraceState::DFSanCmpCallback(uintptr_t PC, size_t CmpSize, size_t CmpType,
uint64_t Arg1, uint64_t Arg2, dfsan_label L1,
dfsan_label L2) {
assert(ReallyHaveDFSan());
if (!RecordingTraces) return;
if (L1 == 0 && L2 == 0)
return; // Not actionable.
if (L1 != 0 && L2 != 0)
return; // Probably still actionable.
bool Res = ComputeCmp(CmpSize, CmpType, Arg1, Arg2);
uint64_t Data = L1 ? Arg2 : Arg1;
LabelRange LR = L1 ? GetLabelRange(L1) : GetLabelRange(L2);
for (size_t Pos = LR.Beg; Pos + CmpSize <= LR.End; Pos++) {
Mutations.push_back({Pos, CmpSize, Data});
Mutations.push_back({Pos, CmpSize, Data + 1});
Mutations.push_back({Pos, CmpSize, Data - 1});
}
if (CmpSize > LR.End - LR.Beg)
Mutations.push_back({LR.Beg, (unsigned)(LR.End - LR.Beg), Data});
if (Options.Verbosity >= 3)
Printf("DFSanCmpCallback: PC %lx S %zd T %zd A1 %llx A2 %llx R %d L1 %d L2 "
"%d MU %zd\n",
PC, CmpSize, CmpType, Arg1, Arg2, Res, L1, L2, Mutations.size());
}
void TraceState::DFSanSwitchCallback(uint64_t PC, size_t ValSizeInBits,
uint64_t Val, size_t NumCases,
uint64_t *Cases, dfsan_label L) {
assert(ReallyHaveDFSan());
if (!RecordingTraces) return;
if (!L) return; // Not actionable.
LabelRange LR = GetLabelRange(L);
size_t ValSize = ValSizeInBits / 8;
bool TryShort = IsTwoByteData(Val);
for (size_t i = 0; i < NumCases; i++)
TryShort &= IsTwoByteData(Cases[i]);
for (size_t Pos = LR.Beg; Pos + ValSize <= LR.End; Pos++)
for (size_t i = 0; i < NumCases; i++)
Mutations.push_back({Pos, ValSize, Cases[i]});
if (TryShort)
for (size_t Pos = LR.Beg; Pos + 2 <= LR.End; Pos++)
for (size_t i = 0; i < NumCases; i++)
Mutations.push_back({Pos, 2, Cases[i]});
if (Options.Verbosity >= 3)
Printf("DFSanSwitchCallback: PC %lx Val %zd SZ %zd # %zd L %d: {%d, %d} "
"TryShort %d\n",
PC, Val, ValSize, NumCases, L, LR.Beg, LR.End, TryShort);
}
int TraceState::TryToAddDesiredData(uint64_t PresentData, uint64_t DesiredData,
size_t DataSize) {
int Res = 0;
const uint8_t *Beg = CurrentUnit.data();
const uint8_t *End = Beg + CurrentUnit.size();
for (const uint8_t *Cur = Beg; Cur < End; Cur++) {
Cur = (uint8_t *)memmem(Cur, End - Cur, &PresentData, DataSize);
if (!Cur)
break;
size_t Pos = Cur - Beg;
assert(Pos < CurrentUnit.size());
if (Mutations.size() > 100000U) return Res; // Just in case.
Mutations.push_back({Pos, DataSize, DesiredData});
Mutations.push_back({Pos, DataSize, DesiredData + 1});
Mutations.push_back({Pos, DataSize, DesiredData - 1});
Res++;
}
return Res;
}
void TraceState::TraceCmpCallback(uintptr_t PC, size_t CmpSize, size_t CmpType,
uint64_t Arg1, uint64_t Arg2) {
if (!RecordingTraces) return;
int Added = 0;
if (Options.Verbosity >= 3)
Printf("TraceCmp %zd/%zd: %p %zd %zd\n", CmpSize, CmpType, PC, Arg1, Arg2);
Added += TryToAddDesiredData(Arg1, Arg2, CmpSize);
Added += TryToAddDesiredData(Arg2, Arg1, CmpSize);
if (!Added && CmpSize == 4 && IsTwoByteData(Arg1) && IsTwoByteData(Arg2)) {
Added += TryToAddDesiredData(Arg1, Arg2, 2);
Added += TryToAddDesiredData(Arg2, Arg1, 2);
}
}
void TraceState::TraceSwitchCallback(uintptr_t PC, size_t ValSizeInBits,
uint64_t Val, size_t NumCases,
uint64_t *Cases) {
if (!RecordingTraces) return;
size_t ValSize = ValSizeInBits / 8;
bool TryShort = IsTwoByteData(Val);
for (size_t i = 0; i < NumCases; i++)
TryShort &= IsTwoByteData(Cases[i]);
if (Options.Verbosity >= 3)
Printf("TraceSwitch: %p %zd # %zd; TryShort %d\n", PC, Val, NumCases,
TryShort);
for (size_t i = 0; i < NumCases; i++) {
TryToAddDesiredData(Val, Cases[i], ValSize);
if (TryShort)
TryToAddDesiredData(Val, Cases[i], 2);
}
}
static TraceState *TS;
void Fuzzer::StartTraceRecording() {
if (!TS) return;
if (ReallyHaveDFSan())
for (size_t i = 0; i < static_cast<size_t>(Options.MaxLen); i++)
dfsan_set_label(i + 1, &CurrentUnit[i], 1);
TS->StartTraceRecording();
}
size_t Fuzzer::StopTraceRecording() {
if (!TS) return 0;
return TS->StopTraceRecording(USF.GetRand());
}
void Fuzzer::ApplyTraceBasedMutation(size_t Idx, Unit *U) {
assert(TS);
TS->ApplyTraceBasedMutation(Idx, U);
}
void Fuzzer::InitializeTraceState() {
if (!Options.UseTraces) return;
TS = new TraceState(Options, CurrentUnit);
CurrentUnit.resize(Options.MaxLen);
// The rest really requires DFSan.
if (!ReallyHaveDFSan()) return;
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.
if (L != i + 1) {
Printf("DFSan labels are not starting from 1, exiting\n");
exit(1);
}
}
}
static size_t InternalStrnlen(const char *S, size_t MaxLen) {
size_t Len = 0;
for (; Len < MaxLen && S[Len]; Len++) {}
return Len;
}
} // namespace fuzzer
using fuzzer::TS;
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) {
if (!TS) return;
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;
TS->DFSanCmpCallback(PC, CmpSize, Type, Arg1, Arg2, L1, L2);
}
void __dfsw___sanitizer_cov_trace_switch(uint64_t Val, uint64_t *Cases,
dfsan_label L1, dfsan_label L2) {
if (!TS) return;
uintptr_t PC = reinterpret_cast<uintptr_t>(__builtin_return_address(0));
TS->DFSanSwitchCallback(PC, Cases[1], Val, Cases[0], Cases+2, L1);
}
void dfsan_weak_hook_memcmp(void *caller_pc, const void *s1, const void *s2,
size_t n, dfsan_label s1_label,
dfsan_label s2_label, dfsan_label n_label) {
if (!TS) return;
uintptr_t PC = reinterpret_cast<uintptr_t>(caller_pc);
uint64_t S1 = 0, S2 = 0;
// Simplification: handle only first 8 bytes.
memcpy(&S1, s1, std::min(n, sizeof(S1)));
memcpy(&S2, s2, std::min(n, sizeof(S2)));
dfsan_label L1 = dfsan_read_label(s1, n);
dfsan_label L2 = dfsan_read_label(s2, n);
TS->DFSanCmpCallback(PC, n, fuzzer::ICMP_EQ, S1, S2, L1, L2);
}
void dfsan_weak_hook_strncmp(void *caller_pc, const char *s1, const char *s2,
size_t n, dfsan_label s1_label,
dfsan_label s2_label, dfsan_label n_label) {
if (!TS) return;
uintptr_t PC = reinterpret_cast<uintptr_t>(caller_pc);
uint64_t S1 = 0, S2 = 0;
n = std::min(n, fuzzer::InternalStrnlen(s1, n));
n = std::min(n, fuzzer::InternalStrnlen(s2, n));
// Simplification: handle only first 8 bytes.
memcpy(&S1, s1, std::min(n, sizeof(S1)));
memcpy(&S2, s2, std::min(n, sizeof(S2)));
dfsan_label L1 = dfsan_read_label(s1, n);
dfsan_label L2 = dfsan_read_label(s2, n);
TS->DFSanCmpCallback(PC, n, fuzzer::ICMP_EQ, S1, S2, L1, L2);
}
void dfsan_weak_hook_strcmp(void *caller_pc, const char *s1, const char *s2,
dfsan_label s1_label, dfsan_label s2_label) {
if (!TS) return;
uintptr_t PC = reinterpret_cast<uintptr_t>(caller_pc);
uint64_t S1 = 0, S2 = 0;
size_t Len1 = strlen(s1);
size_t Len2 = strlen(s2);
size_t N = std::min(Len1, Len2);
if (N <= 1) return; // Not interesting.
// Simplification: handle only first 8 bytes.
memcpy(&S1, s1, std::min(N, sizeof(S1)));
memcpy(&S2, s2, std::min(N, sizeof(S2)));
dfsan_label L1 = dfsan_read_label(s1, Len1);
dfsan_label L2 = dfsan_read_label(s2, Len2);
TS->DFSanCmpCallback(PC, N, fuzzer::ICMP_EQ, S1, S2, L1, L2);
}
void __sanitizer_weak_hook_memcmp(void *caller_pc, const void *s1,
const void *s2, size_t n) {
if (!TS) return;
uintptr_t PC = reinterpret_cast<uintptr_t>(caller_pc);
uint64_t S1 = 0, S2 = 0;
// Simplification: handle only first 8 bytes.
memcpy(&S1, s1, std::min(n, sizeof(S1)));
memcpy(&S2, s2, std::min(n, sizeof(S2)));
TS->TraceCmpCallback(PC, n, fuzzer::ICMP_EQ, S1, S2);
}
void __sanitizer_weak_hook_strncmp(void *caller_pc, const char *s1,
const char *s2, size_t n) {
if (!TS) return;
uintptr_t PC = reinterpret_cast<uintptr_t>(caller_pc);
uint64_t S1 = 0, S2 = 0;
size_t Len1 = fuzzer::InternalStrnlen(s1, n);
size_t Len2 = fuzzer::InternalStrnlen(s2, n);
n = std::min(n, Len1);
n = std::min(n, Len2);
if (n <= 1) return; // Not interesting.
// Simplification: handle only first 8 bytes.
memcpy(&S1, s1, std::min(n, sizeof(S1)));
memcpy(&S2, s2, std::min(n, sizeof(S2)));
TS->TraceCmpCallback(PC, n, fuzzer::ICMP_EQ, S1, S2);
}
void __sanitizer_weak_hook_strcmp(void *caller_pc, const char *s1,
const char *s2) {
if (!TS) return;
uintptr_t PC = reinterpret_cast<uintptr_t>(caller_pc);
uint64_t S1 = 0, S2 = 0;
size_t Len1 = strlen(s1);
size_t Len2 = strlen(s2);
size_t N = std::min(Len1, Len2);
if (N <= 1) return; // Not interesting.
// Simplification: handle only first 8 bytes.
memcpy(&S1, s1, std::min(N, sizeof(S1)));
memcpy(&S2, s2, std::min(N, sizeof(S2)));
TS->TraceCmpCallback(PC, N, fuzzer::ICMP_EQ, S1, S2);
}
__attribute__((visibility("default")))
void __sanitizer_cov_trace_cmp(uint64_t SizeAndType, uint64_t Arg1,
uint64_t Arg2) {
if (!TS) return;
uintptr_t PC = reinterpret_cast<uintptr_t>(__builtin_return_address(0));
uint64_t CmpSize = (SizeAndType >> 32) / 8;
uint64_t Type = (SizeAndType << 32) >> 32;
TS->TraceCmpCallback(PC, CmpSize, Type, Arg1, Arg2);
}
__attribute__((visibility("default")))
void __sanitizer_cov_trace_switch(uint64_t Val, uint64_t *Cases) {
if (!TS) return;
uintptr_t PC = reinterpret_cast<uintptr_t>(__builtin_return_address(0));
TS->TraceSwitchCallback(PC, Cases[1], Val, Cases[0], Cases + 2);
}
} // extern "C"
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