1 //===-- SanitizerCoverage.cpp - coverage instrumentation for sanitizers ---===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // Coverage instrumentation that works with AddressSanitizer
11 // and potentially with other Sanitizers.
12 //
13 // We create a Guard variable with the same linkage
14 // as the function and inject this code into the entry block (CoverageLevel=1)
15 // or all blocks (CoverageLevel>=2):
16 // if (Guard < 0) {
17 //    __sanitizer_cov(&Guard);
18 // }
19 // The accesses to Guard are atomic. The rest of the logic is
20 // in __sanitizer_cov (it's fine to call it more than once).
21 //
22 // With CoverageLevel>=3 we also split critical edges this effectively
23 // instrumenting all edges.
24 //
25 // CoverageLevel>=4 add indirect call profiling implented as a function call.
26 //
27 // This coverage implementation provides very limited data:
28 // it only tells if a given function (block) was ever executed. No counters.
29 // But for many use cases this is what we need and the added slowdown small.
30 //
31 //===----------------------------------------------------------------------===//
32 
33 #include "llvm/Transforms/Instrumentation.h"
34 #include "llvm/ADT/ArrayRef.h"
35 #include "llvm/ADT/SmallVector.h"
36 #include "llvm/IR/CallSite.h"
37 #include "llvm/IR/DataLayout.h"
38 #include "llvm/IR/Function.h"
39 #include "llvm/IR/IRBuilder.h"
40 #include "llvm/IR/InlineAsm.h"
41 #include "llvm/IR/LLVMContext.h"
42 #include "llvm/IR/MDBuilder.h"
43 #include "llvm/IR/Module.h"
44 #include "llvm/IR/Type.h"
45 #include "llvm/Support/CommandLine.h"
46 #include "llvm/Support/Debug.h"
47 #include "llvm/Support/raw_ostream.h"
48 #include "llvm/Transforms/Scalar.h"
49 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
50 #include "llvm/Transforms/Utils/ModuleUtils.h"
51 
52 using namespace llvm;
53 
54 #define DEBUG_TYPE "sancov"
55 
56 static const char *const kSanCovModuleInitName = "__sanitizer_cov_module_init";
57 static const char *const kSanCovName = "__sanitizer_cov";
58 static const char *const kSanCovWithCheckName = "__sanitizer_cov_with_check";
59 static const char *const kSanCovIndirCallName = "__sanitizer_cov_indir_call16";
60 static const char *const kSanCovTraceEnter = "__sanitizer_cov_trace_func_enter";
61 static const char *const kSanCovTraceBB = "__sanitizer_cov_trace_basic_block";
62 static const char *const kSanCovTraceCmp = "__sanitizer_cov_trace_cmp";
63 static const char *const kSanCovModuleCtorName = "sancov.module_ctor";
64 static const uint64_t    kSanCtorAndDtorPriority = 2;
65 
66 static cl::opt<int> ClCoverageLevel("sanitizer-coverage-level",
67        cl::desc("Sanitizer Coverage. 0: none, 1: entry block, 2: all blocks, "
68                 "3: all blocks and critical edges, "
69                 "4: above plus indirect calls"),
70        cl::Hidden, cl::init(0));
71 
72 static cl::opt<unsigned> ClCoverageBlockThreshold(
73     "sanitizer-coverage-block-threshold",
74     cl::desc("Use a callback with a guard check inside it if there are"
75              " more than this number of blocks."),
76     cl::Hidden, cl::init(500));
77 
78 static cl::opt<bool>
79     ClExperimentalTracing("sanitizer-coverage-experimental-tracing",
80                           cl::desc("Experimental basic-block tracing: insert "
81                                    "callbacks at every basic block"),
82                           cl::Hidden, cl::init(false));
83 
84 static cl::opt<bool>
85     ClExperimentalCMPTracing("sanitizer-coverage-experimental-trace-compares",
86                              cl::desc("Experimental tracing of CMP and similar "
87                                       "instructions"),
88                              cl::Hidden, cl::init(false));
89 
90 // Experimental 8-bit counters used as an additional search heuristic during
91 // coverage-guided fuzzing.
92 // The counters are not thread-friendly:
93 //   - contention on these counters may cause significant slowdown;
94 //   - the counter updates are racy and the results may be inaccurate.
95 // They are also inaccurate due to 8-bit integer overflow.
96 static cl::opt<bool> ClUse8bitCounters("sanitizer-coverage-8bit-counters",
97                                        cl::desc("Experimental 8-bit counters"),
98                                        cl::Hidden, cl::init(false));
99 
100 namespace {
101 
102 class SanitizerCoverageModule : public ModulePass {
103  public:
SanitizerCoverageModule(int CoverageLevel=0)104    SanitizerCoverageModule(int CoverageLevel = 0)
105        : ModulePass(ID),
106          CoverageLevel(std::max(CoverageLevel, (int)ClCoverageLevel)) {}
107   bool runOnModule(Module &M) override;
108   bool runOnFunction(Function &F);
109   static char ID;  // Pass identification, replacement for typeid
getPassName() const110   const char *getPassName() const override {
111     return "SanitizerCoverageModule";
112   }
113 
114  private:
115   void InjectCoverageForIndirectCalls(Function &F,
116                                       ArrayRef<Instruction *> IndirCalls);
117   void InjectTraceForCmp(Function &F, ArrayRef<Instruction *> CmpTraceTargets);
118   bool InjectCoverage(Function &F, ArrayRef<BasicBlock *> AllBlocks);
119   void SetNoSanitizeMetada(Instruction *I);
120   void InjectCoverageAtBlock(Function &F, BasicBlock &BB, bool UseCalls);
NumberOfInstrumentedBlocks()121   unsigned NumberOfInstrumentedBlocks() {
122     return SanCovFunction->getNumUses() + SanCovWithCheckFunction->getNumUses();
123   }
124   Function *SanCovFunction;
125   Function *SanCovWithCheckFunction;
126   Function *SanCovIndirCallFunction;
127   Function *SanCovModuleInit;
128   Function *SanCovTraceEnter, *SanCovTraceBB;
129   Function *SanCovTraceCmpFunction;
130   InlineAsm *EmptyAsm;
131   Type *IntptrTy, *Int64Ty;
132   LLVMContext *C;
133   const DataLayout *DL;
134 
135   GlobalVariable *GuardArray;
136   GlobalVariable *EightBitCounterArray;
137 
138   int CoverageLevel;
139 };
140 
141 }  // namespace
142 
runOnModule(Module & M)143 bool SanitizerCoverageModule::runOnModule(Module &M) {
144   if (!CoverageLevel) return false;
145   C = &(M.getContext());
146   DL = &M.getDataLayout();
147   IntptrTy = Type::getIntNTy(*C, DL->getPointerSizeInBits());
148   Type *VoidTy = Type::getVoidTy(*C);
149   IRBuilder<> IRB(*C);
150   Type *Int8PtrTy = PointerType::getUnqual(IRB.getInt8Ty());
151   Type *Int32PtrTy = PointerType::getUnqual(IRB.getInt32Ty());
152   Int64Ty = IRB.getInt64Ty();
153 
154   Function *CtorFunc =
155       Function::Create(FunctionType::get(VoidTy, false),
156                        GlobalValue::InternalLinkage, kSanCovModuleCtorName, &M);
157   ReturnInst::Create(*C, BasicBlock::Create(*C, "", CtorFunc));
158   appendToGlobalCtors(M, CtorFunc, kSanCtorAndDtorPriority);
159 
160   SanCovFunction = checkSanitizerInterfaceFunction(
161       M.getOrInsertFunction(kSanCovName, VoidTy, Int32PtrTy, nullptr));
162   SanCovWithCheckFunction = checkSanitizerInterfaceFunction(
163       M.getOrInsertFunction(kSanCovWithCheckName, VoidTy, Int32PtrTy, nullptr));
164   SanCovIndirCallFunction =
165       checkSanitizerInterfaceFunction(M.getOrInsertFunction(
166           kSanCovIndirCallName, VoidTy, IntptrTy, IntptrTy, nullptr));
167   SanCovTraceCmpFunction =
168       checkSanitizerInterfaceFunction(M.getOrInsertFunction(
169           kSanCovTraceCmp, VoidTy, Int64Ty, Int64Ty, Int64Ty, nullptr));
170 
171   SanCovModuleInit = checkSanitizerInterfaceFunction(M.getOrInsertFunction(
172       kSanCovModuleInitName, Type::getVoidTy(*C), Int32PtrTy, IntptrTy,
173       Int8PtrTy, Int8PtrTy, nullptr));
174   SanCovModuleInit->setLinkage(Function::ExternalLinkage);
175   // We insert an empty inline asm after cov callbacks to avoid callback merge.
176   EmptyAsm = InlineAsm::get(FunctionType::get(IRB.getVoidTy(), false),
177                             StringRef(""), StringRef(""),
178                             /*hasSideEffects=*/true);
179 
180   if (ClExperimentalTracing) {
181     SanCovTraceEnter = checkSanitizerInterfaceFunction(
182         M.getOrInsertFunction(kSanCovTraceEnter, VoidTy, Int32PtrTy, nullptr));
183     SanCovTraceBB = checkSanitizerInterfaceFunction(
184         M.getOrInsertFunction(kSanCovTraceBB, VoidTy, Int32PtrTy, nullptr));
185   }
186 
187   // At this point we create a dummy array of guards because we don't
188   // know how many elements we will need.
189   Type *Int32Ty = IRB.getInt32Ty();
190   Type *Int8Ty = IRB.getInt8Ty();
191 
192   GuardArray =
193       new GlobalVariable(M, Int32Ty, false, GlobalValue::ExternalLinkage,
194                          nullptr, "__sancov_gen_cov_tmp");
195   if (ClUse8bitCounters)
196     EightBitCounterArray =
197         new GlobalVariable(M, Int8Ty, false, GlobalVariable::ExternalLinkage,
198                            nullptr, "__sancov_gen_cov_tmp");
199 
200   for (auto &F : M)
201     runOnFunction(F);
202 
203   auto N = NumberOfInstrumentedBlocks();
204 
205   // Now we know how many elements we need. Create an array of guards
206   // with one extra element at the beginning for the size.
207   Type *Int32ArrayNTy = ArrayType::get(Int32Ty, N + 1);
208   GlobalVariable *RealGuardArray = new GlobalVariable(
209       M, Int32ArrayNTy, false, GlobalValue::PrivateLinkage,
210       Constant::getNullValue(Int32ArrayNTy), "__sancov_gen_cov");
211 
212 
213   // Replace the dummy array with the real one.
214   GuardArray->replaceAllUsesWith(
215       IRB.CreatePointerCast(RealGuardArray, Int32PtrTy));
216   GuardArray->eraseFromParent();
217 
218   GlobalVariable *RealEightBitCounterArray;
219   if (ClUse8bitCounters) {
220     // Make sure the array is 16-aligned.
221     static const int kCounterAlignment = 16;
222     Type *Int8ArrayNTy =
223         ArrayType::get(Int8Ty, RoundUpToAlignment(N, kCounterAlignment));
224     RealEightBitCounterArray = new GlobalVariable(
225         M, Int8ArrayNTy, false, GlobalValue::PrivateLinkage,
226         Constant::getNullValue(Int8ArrayNTy), "__sancov_gen_cov_counter");
227     RealEightBitCounterArray->setAlignment(kCounterAlignment);
228     EightBitCounterArray->replaceAllUsesWith(
229         IRB.CreatePointerCast(RealEightBitCounterArray, Int8PtrTy));
230     EightBitCounterArray->eraseFromParent();
231   }
232 
233   // Create variable for module (compilation unit) name
234   Constant *ModNameStrConst =
235       ConstantDataArray::getString(M.getContext(), M.getName(), true);
236   GlobalVariable *ModuleName =
237       new GlobalVariable(M, ModNameStrConst->getType(), true,
238                          GlobalValue::PrivateLinkage, ModNameStrConst);
239 
240   // Call __sanitizer_cov_module_init
241   IRB.SetInsertPoint(CtorFunc->getEntryBlock().getTerminator());
242   IRB.CreateCall4(
243       SanCovModuleInit, IRB.CreatePointerCast(RealGuardArray, Int32PtrTy),
244       ConstantInt::get(IntptrTy, N),
245       ClUse8bitCounters
246           ? IRB.CreatePointerCast(RealEightBitCounterArray, Int8PtrTy)
247           : Constant::getNullValue(Int8PtrTy),
248       IRB.CreatePointerCast(ModuleName, Int8PtrTy));
249   return true;
250 }
251 
runOnFunction(Function & F)252 bool SanitizerCoverageModule::runOnFunction(Function &F) {
253   if (F.empty()) return false;
254   if (F.getName().find(".module_ctor") != std::string::npos)
255     return false;  // Should not instrument sanitizer init functions.
256   if (CoverageLevel >= 3)
257     SplitAllCriticalEdges(F);
258   SmallVector<Instruction*, 8> IndirCalls;
259   SmallVector<BasicBlock*, 16> AllBlocks;
260   SmallVector<Instruction*, 8> CmpTraceTargets;
261   for (auto &BB : F) {
262     AllBlocks.push_back(&BB);
263     for (auto &Inst : BB) {
264       if (CoverageLevel >= 4) {
265         CallSite CS(&Inst);
266         if (CS && !CS.getCalledFunction())
267           IndirCalls.push_back(&Inst);
268       }
269       if (ClExperimentalCMPTracing)
270         if (isa<ICmpInst>(&Inst))
271           CmpTraceTargets.push_back(&Inst);
272     }
273   }
274   InjectCoverage(F, AllBlocks);
275   InjectCoverageForIndirectCalls(F, IndirCalls);
276   InjectTraceForCmp(F, CmpTraceTargets);
277   return true;
278 }
279 
InjectCoverage(Function & F,ArrayRef<BasicBlock * > AllBlocks)280 bool SanitizerCoverageModule::InjectCoverage(Function &F,
281                                              ArrayRef<BasicBlock *> AllBlocks) {
282   if (!CoverageLevel) return false;
283 
284   if (CoverageLevel == 1) {
285     InjectCoverageAtBlock(F, F.getEntryBlock(), false);
286   } else {
287     for (auto BB : AllBlocks)
288       InjectCoverageAtBlock(F, *BB,
289                             ClCoverageBlockThreshold < AllBlocks.size());
290   }
291   return true;
292 }
293 
294 // On every indirect call we call a run-time function
295 // __sanitizer_cov_indir_call* with two parameters:
296 //   - callee address,
297 //   - global cache array that contains kCacheSize pointers (zero-initialized).
298 //     The cache is used to speed up recording the caller-callee pairs.
299 // The address of the caller is passed implicitly via caller PC.
300 // kCacheSize is encoded in the name of the run-time function.
InjectCoverageForIndirectCalls(Function & F,ArrayRef<Instruction * > IndirCalls)301 void SanitizerCoverageModule::InjectCoverageForIndirectCalls(
302     Function &F, ArrayRef<Instruction *> IndirCalls) {
303   if (IndirCalls.empty()) return;
304   const int kCacheSize = 16;
305   const int kCacheAlignment = 64;  // Align for better performance.
306   Type *Ty = ArrayType::get(IntptrTy, kCacheSize);
307   for (auto I : IndirCalls) {
308     IRBuilder<> IRB(I);
309     CallSite CS(I);
310     Value *Callee = CS.getCalledValue();
311     if (isa<InlineAsm>(Callee)) continue;
312     GlobalVariable *CalleeCache = new GlobalVariable(
313         *F.getParent(), Ty, false, GlobalValue::PrivateLinkage,
314         Constant::getNullValue(Ty), "__sancov_gen_callee_cache");
315     CalleeCache->setAlignment(kCacheAlignment);
316     IRB.CreateCall2(SanCovIndirCallFunction,
317                     IRB.CreatePointerCast(Callee, IntptrTy),
318                     IRB.CreatePointerCast(CalleeCache, IntptrTy));
319   }
320 }
321 
InjectTraceForCmp(Function & F,ArrayRef<Instruction * > CmpTraceTargets)322 void SanitizerCoverageModule::InjectTraceForCmp(
323     Function &F, ArrayRef<Instruction *> CmpTraceTargets) {
324   if (!ClExperimentalCMPTracing) return;
325   for (auto I : CmpTraceTargets) {
326     if (ICmpInst *ICMP = dyn_cast<ICmpInst>(I)) {
327       IRBuilder<> IRB(ICMP);
328       Value *A0 = ICMP->getOperand(0);
329       Value *A1 = ICMP->getOperand(1);
330       if (!A0->getType()->isIntegerTy()) continue;
331       uint64_t TypeSize = DL->getTypeStoreSizeInBits(A0->getType());
332       // __sanitizer_cov_indir_call((type_size << 32) | predicate, A0, A1);
333       IRB.CreateCall3(
334           SanCovTraceCmpFunction,
335           ConstantInt::get(Int64Ty, (TypeSize << 32) | ICMP->getPredicate()),
336           IRB.CreateIntCast(A0, Int64Ty, true),
337           IRB.CreateIntCast(A1, Int64Ty, true));
338     }
339   }
340 }
341 
SetNoSanitizeMetada(Instruction * I)342 void SanitizerCoverageModule::SetNoSanitizeMetada(Instruction *I) {
343   I->setMetadata(
344       I->getParent()->getParent()->getParent()->getMDKindID("nosanitize"),
345       MDNode::get(*C, None));
346 }
347 
InjectCoverageAtBlock(Function & F,BasicBlock & BB,bool UseCalls)348 void SanitizerCoverageModule::InjectCoverageAtBlock(Function &F, BasicBlock &BB,
349                                                     bool UseCalls) {
350   BasicBlock::iterator IP = BB.getFirstInsertionPt(), BE = BB.end();
351   // Skip static allocas at the top of the entry block so they don't become
352   // dynamic when we split the block.  If we used our optimized stack layout,
353   // then there will only be one alloca and it will come first.
354   for (; IP != BE; ++IP) {
355     AllocaInst *AI = dyn_cast<AllocaInst>(IP);
356     if (!AI || !AI->isStaticAlloca())
357       break;
358   }
359 
360   bool IsEntryBB = &BB == &F.getEntryBlock();
361   DebugLoc EntryLoc = IsEntryBB && IP->getDebugLoc()
362                           ? IP->getDebugLoc().getFnDebugLoc()
363                           : IP->getDebugLoc();
364   IRBuilder<> IRB(IP);
365   IRB.SetCurrentDebugLocation(EntryLoc);
366   SmallVector<Value *, 1> Indices;
367   Value *GuardP = IRB.CreateAdd(
368       IRB.CreatePointerCast(GuardArray, IntptrTy),
369       ConstantInt::get(IntptrTy, (1 + NumberOfInstrumentedBlocks()) * 4));
370   Type *Int32PtrTy = PointerType::getUnqual(IRB.getInt32Ty());
371   GuardP = IRB.CreateIntToPtr(GuardP, Int32PtrTy);
372   if (UseCalls) {
373     IRB.CreateCall(SanCovWithCheckFunction, GuardP);
374   } else {
375     LoadInst *Load = IRB.CreateLoad(GuardP);
376     Load->setAtomic(Monotonic);
377     Load->setAlignment(4);
378     SetNoSanitizeMetada(Load);
379     Value *Cmp = IRB.CreateICmpSGE(Constant::getNullValue(Load->getType()), Load);
380     Instruction *Ins = SplitBlockAndInsertIfThen(
381         Cmp, IP, false, MDBuilder(*C).createBranchWeights(1, 100000));
382     IRB.SetInsertPoint(Ins);
383     IRB.SetCurrentDebugLocation(EntryLoc);
384     // __sanitizer_cov gets the PC of the instruction using GET_CALLER_PC.
385     IRB.CreateCall(SanCovFunction, GuardP);
386     IRB.CreateCall(EmptyAsm);  // Avoids callback merge.
387   }
388 
389   if(ClUse8bitCounters) {
390     IRB.SetInsertPoint(IP);
391     Value *P = IRB.CreateAdd(
392         IRB.CreatePointerCast(EightBitCounterArray, IntptrTy),
393         ConstantInt::get(IntptrTy, NumberOfInstrumentedBlocks() - 1));
394     P = IRB.CreateIntToPtr(P, IRB.getInt8PtrTy());
395     LoadInst *LI = IRB.CreateLoad(P);
396     Value *Inc = IRB.CreateAdd(LI, ConstantInt::get(IRB.getInt8Ty(), 1));
397     StoreInst *SI = IRB.CreateStore(Inc, P);
398     SetNoSanitizeMetada(LI);
399     SetNoSanitizeMetada(SI);
400   }
401 
402   if (ClExperimentalTracing) {
403     // Experimental support for tracing.
404     // Insert a callback with the same guard variable as used for coverage.
405     IRB.SetInsertPoint(IP);
406     IRB.CreateCall(IsEntryBB ? SanCovTraceEnter : SanCovTraceBB, GuardP);
407   }
408 }
409 
410 char SanitizerCoverageModule::ID = 0;
411 INITIALIZE_PASS(SanitizerCoverageModule, "sancov",
412     "SanitizerCoverage: TODO."
413     "ModulePass", false, false)
createSanitizerCoverageModulePass(int CoverageLevel)414 ModulePass *llvm::createSanitizerCoverageModulePass(int CoverageLevel) {
415   return new SanitizerCoverageModule(CoverageLevel);
416 }
417