diff options
Diffstat (limited to 'instrumentation/afl-llvm-pass.so.cc')
| -rw-r--r-- | instrumentation/afl-llvm-pass.so.cc | 200 |
1 files changed, 173 insertions, 27 deletions
diff --git a/instrumentation/afl-llvm-pass.so.cc b/instrumentation/afl-llvm-pass.so.cc index 0f773aba..fe9e2e40 100644 --- a/instrumentation/afl-llvm-pass.so.cc +++ b/instrumentation/afl-llvm-pass.so.cc @@ -85,7 +85,8 @@ class AFLCoverage : public ModulePass { uint32_t ctx_k = 0; uint32_t map_size = MAP_SIZE; uint32_t function_minimum_size = 1; - char * ctx_str = NULL, *caller_str = NULL, *skip_nozero = NULL; + const char * ctx_str = NULL, *caller_str = NULL, *skip_nozero = NULL; + const char * use_threadsafe_counters = nullptr; }; @@ -182,6 +183,26 @@ bool AFLCoverage::runOnModule(Module &M) { char *neverZero_counters_str = getenv("AFL_LLVM_NOT_ZERO"); #endif skip_nozero = getenv("AFL_LLVM_SKIP_NEVERZERO"); + use_threadsafe_counters = getenv("AFL_LLVM_THREADSAFE_INST"); + + if ((isatty(2) && !getenv("AFL_QUIET")) || !!getenv("AFL_DEBUG")) { + + if (use_threadsafe_counters) { + if (!getenv("AFL_LLVM_NOT_ZERO")) { + skip_nozero = "1"; + SAYF(cCYA "afl-llvm-pass" VERSION cRST " using thread safe counters\n"); + } + else { + SAYF(cCYA "afl-llvm-pass" VERSION cRST + " using thread safe not-zero-counters\n"); + } + } + else + { + SAYF(cCYA "afl-llvm-pass" VERSION cRST " using non-thread safe instrumentation\n"); + } + + } unsigned PrevLocSize = 0; unsigned PrevCallerSize = 0; @@ -388,7 +409,6 @@ bool AFLCoverage::runOnModule(Module &M) { #endif // other constants we need - ConstantInt *Zero = ConstantInt::get(Int8Ty, 0); ConstantInt *One = ConstantInt::get(Int8Ty, 1); Value * PrevCtx = NULL; // CTX sensitive coverage @@ -410,6 +430,7 @@ bool AFLCoverage::runOnModule(Module &M) { if (F.size() < function_minimum_size) continue; + std::list<Value *> todo; for (auto &BB : F) { BasicBlock::iterator IP = BB.getFirstInsertionPt(); @@ -628,37 +649,63 @@ bool AFLCoverage::runOnModule(Module &M) { /* Update bitmap */ - LoadInst *Counter = IRB.CreateLoad(MapPtrIdx); - Counter->setMetadata(M.getMDKindID("nosanitize"), MDNode::get(C, None)); - Value *Incr = IRB.CreateAdd(Counter, One); + if (use_threadsafe_counters) {/* Atomic */ -#if LLVM_VERSION_MAJOR < 9 - if (neverZero_counters_str != - NULL) { // with llvm 9 we make this the default as the bug in llvm is - // then fixed -#else - if (!skip_nozero) { - -#endif - /* hexcoder: Realize a counter that skips zero during overflow. - * Once this counter reaches its maximum value, it next increments to 1 - * - * Instead of - * Counter + 1 -> Counter - * we inject now this - * Counter + 1 -> {Counter, OverflowFlag} - * Counter + OverflowFlag -> Counter - */ + #if LLVM_VERSION_MAJOR < 9 + if (neverZero_counters_str != + NULL) { // with llvm 9 we make this the default as the bug in llvm is then fixed + #else + if (!skip_nozero) { - auto cf = IRB.CreateICmpEQ(Incr, Zero); - auto carry = IRB.CreateZExt(cf, Int8Ty); - Incr = IRB.CreateAdd(Incr, carry); + #endif + // register MapPtrIdx in a todo list + todo.push_back(MapPtrIdx); + } + else + { + IRB.CreateAtomicRMW(llvm::AtomicRMWInst::BinOp::Add, MapPtrIdx, One, + llvm::AtomicOrdering::Monotonic); + } } + else + { + + LoadInst *Counter = IRB.CreateLoad(MapPtrIdx); + Counter->setMetadata(M.getMDKindID("nosanitize"), MDNode::get(C, None)); + + Value *Incr = IRB.CreateAdd(Counter, One); + + #if LLVM_VERSION_MAJOR < 9 + if (neverZero_counters_str != + NULL) { // with llvm 9 we make this the default as the bug in llvm is + // then fixed + #else + if (!skip_nozero) { + + #endif + /* hexcoder: Realize a counter that skips zero during overflow. + * Once this counter reaches its maximum value, it next increments to 1 + * + * Instead of + * Counter + 1 -> Counter + * we inject now this + * Counter + 1 -> {Counter, OverflowFlag} + * Counter + OverflowFlag -> Counter + */ + + ConstantInt *Zero = ConstantInt::get(Int8Ty, 0); + auto cf = IRB.CreateICmpEQ(Incr, Zero); + auto carry = IRB.CreateZExt(cf, Int8Ty); + Incr = IRB.CreateAdd(Incr, carry); + + } + + IRB.CreateStore(Incr, MapPtrIdx) + ->setMetadata(M.getMDKindID("nosanitize"), MDNode::get(C, None)); - IRB.CreateStore(Incr, MapPtrIdx) - ->setMetadata(M.getMDKindID("nosanitize"), MDNode::get(C, None)); + } /* non atomic case */ /* Update prev_loc history vector (by placing cur_loc at the head of the vector and shuffle the other elements back by one) */ @@ -715,6 +762,105 @@ bool AFLCoverage::runOnModule(Module &M) { } + if (use_threadsafe_counters) { /*Atomic NeverZero */ + // handle the list of registered blocks to instrument + for (auto val : todo) { + /* hexcoder: Realize a thread-safe counter that skips zero during overflow. Once this counter reaches its maximum value, it next increments to 1 + * + * Instead of + * Counter + 1 -> Counter + * we inject now this + * Counter + 1 -> {Counter, OverflowFlag} + * Counter + OverflowFlag -> Counter + */ + + /* equivalent c code looks like this + * Thanks to + https://preshing.com/20150402/you-can-do-any-kind-of-atomic-read-modify-write-operation/ + + int old = atomic_load_explicit(&Counter, memory_order_relaxed); + int new; + do { + if (old == 255) { + new = 1; + } else { + new = old + 1; + } + } while (!atomic_compare_exchange_weak_explicit(&Counter, &old, new, + memory_order_relaxed, memory_order_relaxed)); + + */ + + Value * MapPtrIdx = val; + Instruction * MapPtrIdxInst = cast<Instruction>(val); + BasicBlock::iterator it0(&(*MapPtrIdxInst)); + ++it0; + IRBuilder<> IRB(&(*it0)); + + // load the old counter value atomically + LoadInst *Counter = IRB.CreateLoad(MapPtrIdx); + Counter->setAlignment(llvm::Align()); + Counter->setAtomic(llvm::AtomicOrdering::Monotonic); + Counter->setMetadata(M.getMDKindID("nosanitize"), MDNode::get(C, None)); + + BasicBlock *BB = IRB.GetInsertBlock(); + // insert a basic block with the corpus of a do while loop + // the calculation may need to repeat, if atomic compare_exchange is not successful + + BasicBlock::iterator it(*Counter); + it++; // split after load counter + BasicBlock *end_bb = BB->splitBasicBlock(it); + end_bb->setName("injected"); + + // insert the block before the second half of the split + BasicBlock *do_while_bb = + BasicBlock::Create(C, "injected", end_bb->getParent(), end_bb); + + // set terminator of BB from target end_bb to target do_while_bb + auto term = BB->getTerminator(); + BranchInst::Create(do_while_bb, BB); + term->eraseFromParent(); + + // continue to fill instructions into the do_while loop + IRB.SetInsertPoint(do_while_bb, do_while_bb->getFirstInsertionPt()); + + PHINode *PN = IRB.CreatePHI(Int8Ty, 2); + + // compare with maximum value 0xff + auto *Cmp = IRB.CreateICmpEQ(Counter, ConstantInt::get(Int8Ty, -1)); + + // increment the counter + Value *Incr = IRB.CreateAdd(Counter, One); + + // select the counter value or 1 + auto *Select = IRB.CreateSelect(Cmp, One, Incr); + + // try to save back the new counter value + auto *CmpXchg = IRB.CreateAtomicCmpXchg( + MapPtrIdx, PN, Select, llvm::AtomicOrdering::Monotonic, + llvm::AtomicOrdering::Monotonic); + CmpXchg->setAlignment(llvm::Align()); + CmpXchg->setWeak(true); + CmpXchg->setMetadata(M.getMDKindID("nosanitize"), MDNode::get(C, None)); + + // get the result of trying to update the Counter + Value *Success = + IRB.CreateExtractValue(CmpXchg, ArrayRef<unsigned>({1})); + // get the (possibly updated) value of Counter + Value *OldVal = + IRB.CreateExtractValue(CmpXchg, ArrayRef<unsigned>({0})); + + // initially we use Counter + PN->addIncoming(Counter, BB); + // on retry, we use the updated value + PN->addIncoming(OldVal, do_while_bb); + + // if the cmpXchg was not successful, retry + IRB.CreateCondBr(Success, end_bb, do_while_bb); + } + + } + } /* |