1 //===- SafeStack.cpp - Safe Stack Insertion -------------------------------===// 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 // 9 // This pass splits the stack into the safe stack (kept as-is for LLVM backend) 10 // and the unsafe stack (explicitly allocated and managed through the runtime 11 // support library). 12 // 13 // http://clang.llvm.org/docs/SafeStack.html 14 // 15 //===----------------------------------------------------------------------===// 16 17 #include "SafeStackLayout.h" 18 #include "llvm/ADT/APInt.h" 19 #include "llvm/ADT/ArrayRef.h" 20 #include "llvm/ADT/BitVector.h" 21 #include "llvm/ADT/SmallPtrSet.h" 22 #include "llvm/ADT/SmallVector.h" 23 #include "llvm/ADT/Statistic.h" 24 #include "llvm/Analysis/AssumptionCache.h" 25 #include "llvm/Analysis/BranchProbabilityInfo.h" 26 #include "llvm/Analysis/DomTreeUpdater.h" 27 #include "llvm/Analysis/InlineCost.h" 28 #include "llvm/Analysis/LoopInfo.h" 29 #include "llvm/Analysis/ScalarEvolution.h" 30 #include "llvm/Analysis/ScalarEvolutionExpressions.h" 31 #include "llvm/Analysis/StackLifetime.h" 32 #include "llvm/Analysis/TargetLibraryInfo.h" 33 #include "llvm/CodeGen/TargetLowering.h" 34 #include "llvm/CodeGen/TargetPassConfig.h" 35 #include "llvm/CodeGen/TargetSubtargetInfo.h" 36 #include "llvm/IR/Argument.h" 37 #include "llvm/IR/Attributes.h" 38 #include "llvm/IR/ConstantRange.h" 39 #include "llvm/IR/Constants.h" 40 #include "llvm/IR/DIBuilder.h" 41 #include "llvm/IR/DataLayout.h" 42 #include "llvm/IR/DerivedTypes.h" 43 #include "llvm/IR/Dominators.h" 44 #include "llvm/IR/Function.h" 45 #include "llvm/IR/IRBuilder.h" 46 #include "llvm/IR/InstIterator.h" 47 #include "llvm/IR/Instruction.h" 48 #include "llvm/IR/Instructions.h" 49 #include "llvm/IR/IntrinsicInst.h" 50 #include "llvm/IR/Intrinsics.h" 51 #include "llvm/IR/MDBuilder.h" 52 #include "llvm/IR/Module.h" 53 #include "llvm/IR/Type.h" 54 #include "llvm/IR/Use.h" 55 #include "llvm/IR/User.h" 56 #include "llvm/IR/Value.h" 57 #include "llvm/InitializePasses.h" 58 #include "llvm/Pass.h" 59 #include "llvm/Support/Casting.h" 60 #include "llvm/Support/Debug.h" 61 #include "llvm/Support/ErrorHandling.h" 62 #include "llvm/Support/MathExtras.h" 63 #include "llvm/Support/raw_ostream.h" 64 #include "llvm/Target/TargetMachine.h" 65 #include "llvm/Transforms/Utils/BasicBlockUtils.h" 66 #include "llvm/Transforms/Utils/Cloning.h" 67 #include "llvm/Transforms/Utils/Local.h" 68 #include <algorithm> 69 #include <cassert> 70 #include <cstdint> 71 #include <string> 72 #include <utility> 73 74 using namespace llvm; 75 using namespace llvm::safestack; 76 77 #define DEBUG_TYPE "safe-stack" 78 79 namespace llvm { 80 81 STATISTIC(NumFunctions, "Total number of functions"); 82 STATISTIC(NumUnsafeStackFunctions, "Number of functions with unsafe stack"); 83 STATISTIC(NumUnsafeStackRestorePointsFunctions, 84 "Number of functions that use setjmp or exceptions"); 85 86 STATISTIC(NumAllocas, "Total number of allocas"); 87 STATISTIC(NumUnsafeStaticAllocas, "Number of unsafe static allocas"); 88 STATISTIC(NumUnsafeDynamicAllocas, "Number of unsafe dynamic allocas"); 89 STATISTIC(NumUnsafeByValArguments, "Number of unsafe byval arguments"); 90 STATISTIC(NumUnsafeStackRestorePoints, "Number of setjmps and landingpads"); 91 92 } // namespace llvm 93 94 /// Use __safestack_pointer_address even if the platform has a faster way of 95 /// access safe stack pointer. 96 static cl::opt<bool> 97 SafeStackUsePointerAddress("safestack-use-pointer-address", 98 cl::init(false), cl::Hidden); 99 100 // Disabled by default due to PR32143. 101 static cl::opt<bool> ClColoring("safe-stack-coloring", 102 cl::desc("enable safe stack coloring"), 103 cl::Hidden, cl::init(false)); 104 105 namespace { 106 107 /// Rewrite an SCEV expression for a memory access address to an expression that 108 /// represents offset from the given alloca. 109 /// 110 /// The implementation simply replaces all mentions of the alloca with zero. 111 class AllocaOffsetRewriter : public SCEVRewriteVisitor<AllocaOffsetRewriter> { 112 const Value *AllocaPtr; 113 114 public: 115 AllocaOffsetRewriter(ScalarEvolution &SE, const Value *AllocaPtr) 116 : SCEVRewriteVisitor(SE), AllocaPtr(AllocaPtr) {} 117 118 const SCEV *visitUnknown(const SCEVUnknown *Expr) { 119 if (Expr->getValue() == AllocaPtr) 120 return SE.getZero(Expr->getType()); 121 return Expr; 122 } 123 }; 124 125 /// The SafeStack pass splits the stack of each function into the safe 126 /// stack, which is only accessed through memory safe dereferences (as 127 /// determined statically), and the unsafe stack, which contains all 128 /// local variables that are accessed in ways that we can't prove to 129 /// be safe. 130 class SafeStack { 131 Function &F; 132 const TargetLoweringBase &TL; 133 const DataLayout &DL; 134 DomTreeUpdater *DTU; 135 ScalarEvolution &SE; 136 137 Type *StackPtrTy; 138 Type *IntPtrTy; 139 Type *Int32Ty; 140 Type *Int8Ty; 141 142 Value *UnsafeStackPtr = nullptr; 143 144 /// Unsafe stack alignment. Each stack frame must ensure that the stack is 145 /// aligned to this value. We need to re-align the unsafe stack if the 146 /// alignment of any object on the stack exceeds this value. 147 /// 148 /// 16 seems like a reasonable upper bound on the alignment of objects that we 149 /// might expect to appear on the stack on most common targets. 150 enum { StackAlignment = 16 }; 151 152 /// Return the value of the stack canary. 153 Value *getStackGuard(IRBuilder<> &IRB, Function &F); 154 155 /// Load stack guard from the frame and check if it has changed. 156 void checkStackGuard(IRBuilder<> &IRB, Function &F, Instruction &RI, 157 AllocaInst *StackGuardSlot, Value *StackGuard); 158 159 /// Find all static allocas, dynamic allocas, return instructions and 160 /// stack restore points (exception unwind blocks and setjmp calls) in the 161 /// given function and append them to the respective vectors. 162 void findInsts(Function &F, SmallVectorImpl<AllocaInst *> &StaticAllocas, 163 SmallVectorImpl<AllocaInst *> &DynamicAllocas, 164 SmallVectorImpl<Argument *> &ByValArguments, 165 SmallVectorImpl<Instruction *> &Returns, 166 SmallVectorImpl<Instruction *> &StackRestorePoints); 167 168 /// Calculate the allocation size of a given alloca. Returns 0 if the 169 /// size can not be statically determined. 170 uint64_t getStaticAllocaAllocationSize(const AllocaInst* AI); 171 172 /// Allocate space for all static allocas in \p StaticAllocas, 173 /// replace allocas with pointers into the unsafe stack. 174 /// 175 /// \returns A pointer to the top of the unsafe stack after all unsafe static 176 /// allocas are allocated. 177 Value *moveStaticAllocasToUnsafeStack(IRBuilder<> &IRB, Function &F, 178 ArrayRef<AllocaInst *> StaticAllocas, 179 ArrayRef<Argument *> ByValArguments, 180 Instruction *BasePointer, 181 AllocaInst *StackGuardSlot); 182 183 /// Generate code to restore the stack after all stack restore points 184 /// in \p StackRestorePoints. 185 /// 186 /// \returns A local variable in which to maintain the dynamic top of the 187 /// unsafe stack if needed. 188 AllocaInst * 189 createStackRestorePoints(IRBuilder<> &IRB, Function &F, 190 ArrayRef<Instruction *> StackRestorePoints, 191 Value *StaticTop, bool NeedDynamicTop); 192 193 /// Replace all allocas in \p DynamicAllocas with code to allocate 194 /// space dynamically on the unsafe stack and store the dynamic unsafe stack 195 /// top to \p DynamicTop if non-null. 196 void moveDynamicAllocasToUnsafeStack(Function &F, Value *UnsafeStackPtr, 197 AllocaInst *DynamicTop, 198 ArrayRef<AllocaInst *> DynamicAllocas); 199 200 bool IsSafeStackAlloca(const Value *AllocaPtr, uint64_t AllocaSize); 201 202 bool IsMemIntrinsicSafe(const MemIntrinsic *MI, const Use &U, 203 const Value *AllocaPtr, uint64_t AllocaSize); 204 bool IsAccessSafe(Value *Addr, uint64_t Size, const Value *AllocaPtr, 205 uint64_t AllocaSize); 206 207 bool ShouldInlinePointerAddress(CallInst &CI); 208 void TryInlinePointerAddress(); 209 210 public: 211 SafeStack(Function &F, const TargetLoweringBase &TL, const DataLayout &DL, 212 DomTreeUpdater *DTU, ScalarEvolution &SE) 213 : F(F), TL(TL), DL(DL), DTU(DTU), SE(SE), 214 StackPtrTy(Type::getInt8PtrTy(F.getContext())), 215 IntPtrTy(DL.getIntPtrType(F.getContext())), 216 Int32Ty(Type::getInt32Ty(F.getContext())), 217 Int8Ty(Type::getInt8Ty(F.getContext())) {} 218 219 // Run the transformation on the associated function. 220 // Returns whether the function was changed. 221 bool run(); 222 }; 223 224 uint64_t SafeStack::getStaticAllocaAllocationSize(const AllocaInst* AI) { 225 uint64_t Size = DL.getTypeAllocSize(AI->getAllocatedType()); 226 if (AI->isArrayAllocation()) { 227 auto C = dyn_cast<ConstantInt>(AI->getArraySize()); 228 if (!C) 229 return 0; 230 Size *= C->getZExtValue(); 231 } 232 return Size; 233 } 234 235 bool SafeStack::IsAccessSafe(Value *Addr, uint64_t AccessSize, 236 const Value *AllocaPtr, uint64_t AllocaSize) { 237 AllocaOffsetRewriter Rewriter(SE, AllocaPtr); 238 const SCEV *Expr = Rewriter.visit(SE.getSCEV(Addr)); 239 240 uint64_t BitWidth = SE.getTypeSizeInBits(Expr->getType()); 241 ConstantRange AccessStartRange = SE.getUnsignedRange(Expr); 242 ConstantRange SizeRange = 243 ConstantRange(APInt(BitWidth, 0), APInt(BitWidth, AccessSize)); 244 ConstantRange AccessRange = AccessStartRange.add(SizeRange); 245 ConstantRange AllocaRange = 246 ConstantRange(APInt(BitWidth, 0), APInt(BitWidth, AllocaSize)); 247 bool Safe = AllocaRange.contains(AccessRange); 248 249 LLVM_DEBUG( 250 dbgs() << "[SafeStack] " 251 << (isa<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ") 252 << *AllocaPtr << "\n" 253 << " Access " << *Addr << "\n" 254 << " SCEV " << *Expr 255 << " U: " << SE.getUnsignedRange(Expr) 256 << ", S: " << SE.getSignedRange(Expr) << "\n" 257 << " Range " << AccessRange << "\n" 258 << " AllocaRange " << AllocaRange << "\n" 259 << " " << (Safe ? "safe" : "unsafe") << "\n"); 260 261 return Safe; 262 } 263 264 bool SafeStack::IsMemIntrinsicSafe(const MemIntrinsic *MI, const Use &U, 265 const Value *AllocaPtr, 266 uint64_t AllocaSize) { 267 if (auto MTI = dyn_cast<MemTransferInst>(MI)) { 268 if (MTI->getRawSource() != U && MTI->getRawDest() != U) 269 return true; 270 } else { 271 if (MI->getRawDest() != U) 272 return true; 273 } 274 275 const auto *Len = dyn_cast<ConstantInt>(MI->getLength()); 276 // Non-constant size => unsafe. FIXME: try SCEV getRange. 277 if (!Len) return false; 278 return IsAccessSafe(U, Len->getZExtValue(), AllocaPtr, AllocaSize); 279 } 280 281 /// Check whether a given allocation must be put on the safe 282 /// stack or not. The function analyzes all uses of AI and checks whether it is 283 /// only accessed in a memory safe way (as decided statically). 284 bool SafeStack::IsSafeStackAlloca(const Value *AllocaPtr, uint64_t AllocaSize) { 285 // Go through all uses of this alloca and check whether all accesses to the 286 // allocated object are statically known to be memory safe and, hence, the 287 // object can be placed on the safe stack. 288 SmallPtrSet<const Value *, 16> Visited; 289 SmallVector<const Value *, 8> WorkList; 290 WorkList.push_back(AllocaPtr); 291 292 // A DFS search through all uses of the alloca in bitcasts/PHI/GEPs/etc. 293 while (!WorkList.empty()) { 294 const Value *V = WorkList.pop_back_val(); 295 for (const Use &UI : V->uses()) { 296 auto I = cast<const Instruction>(UI.getUser()); 297 assert(V == UI.get()); 298 299 switch (I->getOpcode()) { 300 case Instruction::Load: 301 if (!IsAccessSafe(UI, DL.getTypeStoreSize(I->getType()), AllocaPtr, 302 AllocaSize)) 303 return false; 304 break; 305 306 case Instruction::VAArg: 307 // "va-arg" from a pointer is safe. 308 break; 309 case Instruction::Store: 310 if (V == I->getOperand(0)) { 311 // Stored the pointer - conservatively assume it may be unsafe. 312 LLVM_DEBUG(dbgs() 313 << "[SafeStack] Unsafe alloca: " << *AllocaPtr 314 << "\n store of address: " << *I << "\n"); 315 return false; 316 } 317 318 if (!IsAccessSafe(UI, DL.getTypeStoreSize(I->getOperand(0)->getType()), 319 AllocaPtr, AllocaSize)) 320 return false; 321 break; 322 323 case Instruction::Ret: 324 // Information leak. 325 return false; 326 327 case Instruction::Call: 328 case Instruction::Invoke: { 329 const CallBase &CS = *cast<CallBase>(I); 330 331 if (I->isLifetimeStartOrEnd()) 332 continue; 333 334 if (const MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) { 335 if (!IsMemIntrinsicSafe(MI, UI, AllocaPtr, AllocaSize)) { 336 LLVM_DEBUG(dbgs() 337 << "[SafeStack] Unsafe alloca: " << *AllocaPtr 338 << "\n unsafe memintrinsic: " << *I << "\n"); 339 return false; 340 } 341 continue; 342 } 343 344 // LLVM 'nocapture' attribute is only set for arguments whose address 345 // is not stored, passed around, or used in any other non-trivial way. 346 // We assume that passing a pointer to an object as a 'nocapture 347 // readnone' argument is safe. 348 // FIXME: a more precise solution would require an interprocedural 349 // analysis here, which would look at all uses of an argument inside 350 // the function being called. 351 auto B = CS.arg_begin(), E = CS.arg_end(); 352 for (auto A = B; A != E; ++A) 353 if (A->get() == V) 354 if (!(CS.doesNotCapture(A - B) && (CS.doesNotAccessMemory(A - B) || 355 CS.doesNotAccessMemory()))) { 356 LLVM_DEBUG(dbgs() << "[SafeStack] Unsafe alloca: " << *AllocaPtr 357 << "\n unsafe call: " << *I << "\n"); 358 return false; 359 } 360 continue; 361 } 362 363 default: 364 if (Visited.insert(I).second) 365 WorkList.push_back(cast<const Instruction>(I)); 366 } 367 } 368 } 369 370 // All uses of the alloca are safe, we can place it on the safe stack. 371 return true; 372 } 373 374 Value *SafeStack::getStackGuard(IRBuilder<> &IRB, Function &F) { 375 Value *StackGuardVar = TL.getIRStackGuard(IRB); 376 Module *M = F.getParent(); 377 378 if (!StackGuardVar) { 379 TL.insertSSPDeclarations(*M); 380 return IRB.CreateCall(Intrinsic::getDeclaration(M, Intrinsic::stackguard)); 381 } 382 383 return IRB.CreateLoad(StackPtrTy, StackGuardVar, "StackGuard"); 384 } 385 386 void SafeStack::findInsts(Function &F, 387 SmallVectorImpl<AllocaInst *> &StaticAllocas, 388 SmallVectorImpl<AllocaInst *> &DynamicAllocas, 389 SmallVectorImpl<Argument *> &ByValArguments, 390 SmallVectorImpl<Instruction *> &Returns, 391 SmallVectorImpl<Instruction *> &StackRestorePoints) { 392 for (Instruction &I : instructions(&F)) { 393 if (auto AI = dyn_cast<AllocaInst>(&I)) { 394 ++NumAllocas; 395 396 uint64_t Size = getStaticAllocaAllocationSize(AI); 397 if (IsSafeStackAlloca(AI, Size)) 398 continue; 399 400 if (AI->isStaticAlloca()) { 401 ++NumUnsafeStaticAllocas; 402 StaticAllocas.push_back(AI); 403 } else { 404 ++NumUnsafeDynamicAllocas; 405 DynamicAllocas.push_back(AI); 406 } 407 } else if (auto RI = dyn_cast<ReturnInst>(&I)) { 408 if (CallInst *CI = I.getParent()->getTerminatingMustTailCall()) 409 Returns.push_back(CI); 410 else 411 Returns.push_back(RI); 412 } else if (auto CI = dyn_cast<CallInst>(&I)) { 413 // setjmps require stack restore. 414 if (CI->getCalledFunction() && CI->canReturnTwice()) 415 StackRestorePoints.push_back(CI); 416 } else if (auto LP = dyn_cast<LandingPadInst>(&I)) { 417 // Exception landing pads require stack restore. 418 StackRestorePoints.push_back(LP); 419 } else if (auto II = dyn_cast<IntrinsicInst>(&I)) { 420 if (II->getIntrinsicID() == Intrinsic::gcroot) 421 report_fatal_error( 422 "gcroot intrinsic not compatible with safestack attribute"); 423 } 424 } 425 for (Argument &Arg : F.args()) { 426 if (!Arg.hasByValAttr()) 427 continue; 428 uint64_t Size = DL.getTypeStoreSize(Arg.getParamByValType()); 429 if (IsSafeStackAlloca(&Arg, Size)) 430 continue; 431 432 ++NumUnsafeByValArguments; 433 ByValArguments.push_back(&Arg); 434 } 435 } 436 437 AllocaInst * 438 SafeStack::createStackRestorePoints(IRBuilder<> &IRB, Function &F, 439 ArrayRef<Instruction *> StackRestorePoints, 440 Value *StaticTop, bool NeedDynamicTop) { 441 assert(StaticTop && "The stack top isn't set."); 442 443 if (StackRestorePoints.empty()) 444 return nullptr; 445 446 // We need the current value of the shadow stack pointer to restore 447 // after longjmp or exception catching. 448 449 // FIXME: On some platforms this could be handled by the longjmp/exception 450 // runtime itself. 451 452 AllocaInst *DynamicTop = nullptr; 453 if (NeedDynamicTop) { 454 // If we also have dynamic alloca's, the stack pointer value changes 455 // throughout the function. For now we store it in an alloca. 456 DynamicTop = IRB.CreateAlloca(StackPtrTy, /*ArraySize=*/nullptr, 457 "unsafe_stack_dynamic_ptr"); 458 IRB.CreateStore(StaticTop, DynamicTop); 459 } 460 461 // Restore current stack pointer after longjmp/exception catch. 462 for (Instruction *I : StackRestorePoints) { 463 ++NumUnsafeStackRestorePoints; 464 465 IRB.SetInsertPoint(I->getNextNode()); 466 Value *CurrentTop = 467 DynamicTop ? IRB.CreateLoad(StackPtrTy, DynamicTop) : StaticTop; 468 IRB.CreateStore(CurrentTop, UnsafeStackPtr); 469 } 470 471 return DynamicTop; 472 } 473 474 void SafeStack::checkStackGuard(IRBuilder<> &IRB, Function &F, Instruction &RI, 475 AllocaInst *StackGuardSlot, Value *StackGuard) { 476 Value *V = IRB.CreateLoad(StackPtrTy, StackGuardSlot); 477 Value *Cmp = IRB.CreateICmpNE(StackGuard, V); 478 479 auto SuccessProb = BranchProbabilityInfo::getBranchProbStackProtector(true); 480 auto FailureProb = BranchProbabilityInfo::getBranchProbStackProtector(false); 481 MDNode *Weights = MDBuilder(F.getContext()) 482 .createBranchWeights(SuccessProb.getNumerator(), 483 FailureProb.getNumerator()); 484 Instruction *CheckTerm = 485 SplitBlockAndInsertIfThen(Cmp, &RI, /* Unreachable */ true, Weights, DTU); 486 IRBuilder<> IRBFail(CheckTerm); 487 // FIXME: respect -fsanitize-trap / -ftrap-function here? 488 FunctionCallee StackChkFail = 489 F.getParent()->getOrInsertFunction("__stack_chk_fail", IRB.getVoidTy()); 490 IRBFail.CreateCall(StackChkFail, {}); 491 } 492 493 /// We explicitly compute and set the unsafe stack layout for all unsafe 494 /// static alloca instructions. We save the unsafe "base pointer" in the 495 /// prologue into a local variable and restore it in the epilogue. 496 Value *SafeStack::moveStaticAllocasToUnsafeStack( 497 IRBuilder<> &IRB, Function &F, ArrayRef<AllocaInst *> StaticAllocas, 498 ArrayRef<Argument *> ByValArguments, Instruction *BasePointer, 499 AllocaInst *StackGuardSlot) { 500 if (StaticAllocas.empty() && ByValArguments.empty()) 501 return BasePointer; 502 503 DIBuilder DIB(*F.getParent()); 504 505 StackLifetime SSC(F, StaticAllocas, StackLifetime::LivenessType::May); 506 static const StackLifetime::LiveRange NoColoringRange(1, true); 507 if (ClColoring) 508 SSC.run(); 509 510 for (auto *I : SSC.getMarkers()) { 511 auto *Op = dyn_cast<Instruction>(I->getOperand(1)); 512 const_cast<IntrinsicInst *>(I)->eraseFromParent(); 513 // Remove the operand bitcast, too, if it has no more uses left. 514 if (Op && Op->use_empty()) 515 Op->eraseFromParent(); 516 } 517 518 // Unsafe stack always grows down. 519 StackLayout SSL(StackAlignment); 520 if (StackGuardSlot) { 521 Type *Ty = StackGuardSlot->getAllocatedType(); 522 unsigned Align = 523 std::max(DL.getPrefTypeAlignment(Ty), StackGuardSlot->getAlignment()); 524 SSL.addObject(StackGuardSlot, getStaticAllocaAllocationSize(StackGuardSlot), 525 Align, SSC.getFullLiveRange()); 526 } 527 528 for (Argument *Arg : ByValArguments) { 529 Type *Ty = Arg->getParamByValType(); 530 uint64_t Size = DL.getTypeStoreSize(Ty); 531 if (Size == 0) 532 Size = 1; // Don't create zero-sized stack objects. 533 534 // Ensure the object is properly aligned. 535 unsigned Align = std::max((unsigned)DL.getPrefTypeAlignment(Ty), 536 Arg->getParamAlignment()); 537 SSL.addObject(Arg, Size, Align, SSC.getFullLiveRange()); 538 } 539 540 for (AllocaInst *AI : StaticAllocas) { 541 Type *Ty = AI->getAllocatedType(); 542 uint64_t Size = getStaticAllocaAllocationSize(AI); 543 if (Size == 0) 544 Size = 1; // Don't create zero-sized stack objects. 545 546 // Ensure the object is properly aligned. 547 unsigned Align = 548 std::max((unsigned)DL.getPrefTypeAlignment(Ty), AI->getAlignment()); 549 550 SSL.addObject(AI, Size, Align, 551 ClColoring ? SSC.getLiveRange(AI) : NoColoringRange); 552 } 553 554 SSL.computeLayout(); 555 unsigned FrameAlignment = SSL.getFrameAlignment(); 556 557 // FIXME: tell SSL that we start at a less-then-MaxAlignment aligned location 558 // (AlignmentSkew). 559 if (FrameAlignment > StackAlignment) { 560 // Re-align the base pointer according to the max requested alignment. 561 assert(isPowerOf2_32(FrameAlignment)); 562 IRB.SetInsertPoint(BasePointer->getNextNode()); 563 BasePointer = cast<Instruction>(IRB.CreateIntToPtr( 564 IRB.CreateAnd(IRB.CreatePtrToInt(BasePointer, IntPtrTy), 565 ConstantInt::get(IntPtrTy, ~uint64_t(FrameAlignment - 1))), 566 StackPtrTy)); 567 } 568 569 IRB.SetInsertPoint(BasePointer->getNextNode()); 570 571 if (StackGuardSlot) { 572 unsigned Offset = SSL.getObjectOffset(StackGuardSlot); 573 Value *Off = IRB.CreateGEP(Int8Ty, BasePointer, // BasePointer is i8* 574 ConstantInt::get(Int32Ty, -Offset)); 575 Value *NewAI = 576 IRB.CreateBitCast(Off, StackGuardSlot->getType(), "StackGuardSlot"); 577 578 // Replace alloc with the new location. 579 StackGuardSlot->replaceAllUsesWith(NewAI); 580 StackGuardSlot->eraseFromParent(); 581 } 582 583 for (Argument *Arg : ByValArguments) { 584 unsigned Offset = SSL.getObjectOffset(Arg); 585 MaybeAlign Align(SSL.getObjectAlignment(Arg)); 586 Type *Ty = Arg->getParamByValType(); 587 588 uint64_t Size = DL.getTypeStoreSize(Ty); 589 if (Size == 0) 590 Size = 1; // Don't create zero-sized stack objects. 591 592 Value *Off = IRB.CreateGEP(Int8Ty, BasePointer, // BasePointer is i8* 593 ConstantInt::get(Int32Ty, -Offset)); 594 Value *NewArg = IRB.CreateBitCast(Off, Arg->getType(), 595 Arg->getName() + ".unsafe-byval"); 596 597 // Replace alloc with the new location. 598 replaceDbgDeclare(Arg, BasePointer, DIB, DIExpression::ApplyOffset, 599 -Offset); 600 Arg->replaceAllUsesWith(NewArg); 601 IRB.SetInsertPoint(cast<Instruction>(NewArg)->getNextNode()); 602 IRB.CreateMemCpy(Off, Align, Arg, Arg->getParamAlign(), Size); 603 } 604 605 // Allocate space for every unsafe static AllocaInst on the unsafe stack. 606 for (AllocaInst *AI : StaticAllocas) { 607 IRB.SetInsertPoint(AI); 608 unsigned Offset = SSL.getObjectOffset(AI); 609 610 replaceDbgDeclare(AI, BasePointer, DIB, DIExpression::ApplyOffset, -Offset); 611 replaceDbgValueForAlloca(AI, BasePointer, DIB, -Offset); 612 613 // Replace uses of the alloca with the new location. 614 // Insert address calculation close to each use to work around PR27844. 615 std::string Name = std::string(AI->getName()) + ".unsafe"; 616 while (!AI->use_empty()) { 617 Use &U = *AI->use_begin(); 618 Instruction *User = cast<Instruction>(U.getUser()); 619 620 Instruction *InsertBefore; 621 if (auto *PHI = dyn_cast<PHINode>(User)) 622 InsertBefore = PHI->getIncomingBlock(U)->getTerminator(); 623 else 624 InsertBefore = User; 625 626 IRBuilder<> IRBUser(InsertBefore); 627 Value *Off = IRBUser.CreateGEP(Int8Ty, BasePointer, // BasePointer is i8* 628 ConstantInt::get(Int32Ty, -Offset)); 629 Value *Replacement = IRBUser.CreateBitCast(Off, AI->getType(), Name); 630 631 if (auto *PHI = dyn_cast<PHINode>(User)) 632 // PHI nodes may have multiple incoming edges from the same BB (why??), 633 // all must be updated at once with the same incoming value. 634 PHI->setIncomingValueForBlock(PHI->getIncomingBlock(U), Replacement); 635 else 636 U.set(Replacement); 637 } 638 639 AI->eraseFromParent(); 640 } 641 642 // Re-align BasePointer so that our callees would see it aligned as 643 // expected. 644 // FIXME: no need to update BasePointer in leaf functions. 645 unsigned FrameSize = alignTo(SSL.getFrameSize(), StackAlignment); 646 647 // Update shadow stack pointer in the function epilogue. 648 IRB.SetInsertPoint(BasePointer->getNextNode()); 649 650 Value *StaticTop = 651 IRB.CreateGEP(Int8Ty, BasePointer, ConstantInt::get(Int32Ty, -FrameSize), 652 "unsafe_stack_static_top"); 653 IRB.CreateStore(StaticTop, UnsafeStackPtr); 654 return StaticTop; 655 } 656 657 void SafeStack::moveDynamicAllocasToUnsafeStack( 658 Function &F, Value *UnsafeStackPtr, AllocaInst *DynamicTop, 659 ArrayRef<AllocaInst *> DynamicAllocas) { 660 DIBuilder DIB(*F.getParent()); 661 662 for (AllocaInst *AI : DynamicAllocas) { 663 IRBuilder<> IRB(AI); 664 665 // Compute the new SP value (after AI). 666 Value *ArraySize = AI->getArraySize(); 667 if (ArraySize->getType() != IntPtrTy) 668 ArraySize = IRB.CreateIntCast(ArraySize, IntPtrTy, false); 669 670 Type *Ty = AI->getAllocatedType(); 671 uint64_t TySize = DL.getTypeAllocSize(Ty); 672 Value *Size = IRB.CreateMul(ArraySize, ConstantInt::get(IntPtrTy, TySize)); 673 674 Value *SP = IRB.CreatePtrToInt(IRB.CreateLoad(StackPtrTy, UnsafeStackPtr), 675 IntPtrTy); 676 SP = IRB.CreateSub(SP, Size); 677 678 // Align the SP value to satisfy the AllocaInst, type and stack alignments. 679 unsigned Align = std::max( 680 std::max((unsigned)DL.getPrefTypeAlignment(Ty), AI->getAlignment()), 681 (unsigned)StackAlignment); 682 683 assert(isPowerOf2_32(Align)); 684 Value *NewTop = IRB.CreateIntToPtr( 685 IRB.CreateAnd(SP, ConstantInt::get(IntPtrTy, ~uint64_t(Align - 1))), 686 StackPtrTy); 687 688 // Save the stack pointer. 689 IRB.CreateStore(NewTop, UnsafeStackPtr); 690 if (DynamicTop) 691 IRB.CreateStore(NewTop, DynamicTop); 692 693 Value *NewAI = IRB.CreatePointerCast(NewTop, AI->getType()); 694 if (AI->hasName() && isa<Instruction>(NewAI)) 695 NewAI->takeName(AI); 696 697 replaceDbgDeclare(AI, NewAI, DIB, DIExpression::ApplyOffset, 0); 698 AI->replaceAllUsesWith(NewAI); 699 AI->eraseFromParent(); 700 } 701 702 if (!DynamicAllocas.empty()) { 703 // Now go through the instructions again, replacing stacksave/stackrestore. 704 for (inst_iterator It = inst_begin(&F), Ie = inst_end(&F); It != Ie;) { 705 Instruction *I = &*(It++); 706 auto II = dyn_cast<IntrinsicInst>(I); 707 if (!II) 708 continue; 709 710 if (II->getIntrinsicID() == Intrinsic::stacksave) { 711 IRBuilder<> IRB(II); 712 Instruction *LI = IRB.CreateLoad(StackPtrTy, UnsafeStackPtr); 713 LI->takeName(II); 714 II->replaceAllUsesWith(LI); 715 II->eraseFromParent(); 716 } else if (II->getIntrinsicID() == Intrinsic::stackrestore) { 717 IRBuilder<> IRB(II); 718 Instruction *SI = IRB.CreateStore(II->getArgOperand(0), UnsafeStackPtr); 719 SI->takeName(II); 720 assert(II->use_empty()); 721 II->eraseFromParent(); 722 } 723 } 724 } 725 } 726 727 bool SafeStack::ShouldInlinePointerAddress(CallInst &CI) { 728 Function *Callee = CI.getCalledFunction(); 729 if (CI.hasFnAttr(Attribute::AlwaysInline) && 730 isInlineViable(*Callee).isSuccess()) 731 return true; 732 if (Callee->isInterposable() || Callee->hasFnAttribute(Attribute::NoInline) || 733 CI.isNoInline()) 734 return false; 735 return true; 736 } 737 738 void SafeStack::TryInlinePointerAddress() { 739 auto *CI = dyn_cast<CallInst>(UnsafeStackPtr); 740 if (!CI) 741 return; 742 743 if(F.hasOptNone()) 744 return; 745 746 Function *Callee = CI->getCalledFunction(); 747 if (!Callee || Callee->isDeclaration()) 748 return; 749 750 if (!ShouldInlinePointerAddress(*CI)) 751 return; 752 753 InlineFunctionInfo IFI; 754 InlineFunction(*CI, IFI); 755 } 756 757 bool SafeStack::run() { 758 assert(F.hasFnAttribute(Attribute::SafeStack) && 759 "Can't run SafeStack on a function without the attribute"); 760 assert(!F.isDeclaration() && "Can't run SafeStack on a function declaration"); 761 762 ++NumFunctions; 763 764 SmallVector<AllocaInst *, 16> StaticAllocas; 765 SmallVector<AllocaInst *, 4> DynamicAllocas; 766 SmallVector<Argument *, 4> ByValArguments; 767 SmallVector<Instruction *, 4> Returns; 768 769 // Collect all points where stack gets unwound and needs to be restored 770 // This is only necessary because the runtime (setjmp and unwind code) is 771 // not aware of the unsafe stack and won't unwind/restore it properly. 772 // To work around this problem without changing the runtime, we insert 773 // instrumentation to restore the unsafe stack pointer when necessary. 774 SmallVector<Instruction *, 4> StackRestorePoints; 775 776 // Find all static and dynamic alloca instructions that must be moved to the 777 // unsafe stack, all return instructions and stack restore points. 778 findInsts(F, StaticAllocas, DynamicAllocas, ByValArguments, Returns, 779 StackRestorePoints); 780 781 if (StaticAllocas.empty() && DynamicAllocas.empty() && 782 ByValArguments.empty() && StackRestorePoints.empty()) 783 return false; // Nothing to do in this function. 784 785 if (!StaticAllocas.empty() || !DynamicAllocas.empty() || 786 !ByValArguments.empty()) 787 ++NumUnsafeStackFunctions; // This function has the unsafe stack. 788 789 if (!StackRestorePoints.empty()) 790 ++NumUnsafeStackRestorePointsFunctions; 791 792 IRBuilder<> IRB(&F.front(), F.begin()->getFirstInsertionPt()); 793 // Calls must always have a debug location, or else inlining breaks. So 794 // we explicitly set a artificial debug location here. 795 if (DISubprogram *SP = F.getSubprogram()) 796 IRB.SetCurrentDebugLocation( 797 DILocation::get(SP->getContext(), SP->getScopeLine(), 0, SP)); 798 if (SafeStackUsePointerAddress) { 799 FunctionCallee Fn = F.getParent()->getOrInsertFunction( 800 "__safestack_pointer_address", StackPtrTy->getPointerTo(0)); 801 UnsafeStackPtr = IRB.CreateCall(Fn); 802 } else { 803 UnsafeStackPtr = TL.getSafeStackPointerLocation(IRB); 804 } 805 806 // Load the current stack pointer (we'll also use it as a base pointer). 807 // FIXME: use a dedicated register for it ? 808 Instruction *BasePointer = 809 IRB.CreateLoad(StackPtrTy, UnsafeStackPtr, false, "unsafe_stack_ptr"); 810 assert(BasePointer->getType() == StackPtrTy); 811 812 AllocaInst *StackGuardSlot = nullptr; 813 // FIXME: implement weaker forms of stack protector. 814 if (F.hasFnAttribute(Attribute::StackProtect) || 815 F.hasFnAttribute(Attribute::StackProtectStrong) || 816 F.hasFnAttribute(Attribute::StackProtectReq)) { 817 Value *StackGuard = getStackGuard(IRB, F); 818 StackGuardSlot = IRB.CreateAlloca(StackPtrTy, nullptr); 819 IRB.CreateStore(StackGuard, StackGuardSlot); 820 821 for (Instruction *RI : Returns) { 822 IRBuilder<> IRBRet(RI); 823 checkStackGuard(IRBRet, F, *RI, StackGuardSlot, StackGuard); 824 } 825 } 826 827 // The top of the unsafe stack after all unsafe static allocas are 828 // allocated. 829 Value *StaticTop = moveStaticAllocasToUnsafeStack( 830 IRB, F, StaticAllocas, ByValArguments, BasePointer, StackGuardSlot); 831 832 // Safe stack object that stores the current unsafe stack top. It is updated 833 // as unsafe dynamic (non-constant-sized) allocas are allocated and freed. 834 // This is only needed if we need to restore stack pointer after longjmp 835 // or exceptions, and we have dynamic allocations. 836 // FIXME: a better alternative might be to store the unsafe stack pointer 837 // before setjmp / invoke instructions. 838 AllocaInst *DynamicTop = createStackRestorePoints( 839 IRB, F, StackRestorePoints, StaticTop, !DynamicAllocas.empty()); 840 841 // Handle dynamic allocas. 842 moveDynamicAllocasToUnsafeStack(F, UnsafeStackPtr, DynamicTop, 843 DynamicAllocas); 844 845 // Restore the unsafe stack pointer before each return. 846 for (Instruction *RI : Returns) { 847 IRB.SetInsertPoint(RI); 848 IRB.CreateStore(BasePointer, UnsafeStackPtr); 849 } 850 851 TryInlinePointerAddress(); 852 853 LLVM_DEBUG(dbgs() << "[SafeStack] safestack applied\n"); 854 return true; 855 } 856 857 class SafeStackLegacyPass : public FunctionPass { 858 const TargetMachine *TM = nullptr; 859 860 public: 861 static char ID; // Pass identification, replacement for typeid.. 862 863 SafeStackLegacyPass() : FunctionPass(ID) { 864 initializeSafeStackLegacyPassPass(*PassRegistry::getPassRegistry()); 865 } 866 867 void getAnalysisUsage(AnalysisUsage &AU) const override { 868 AU.addRequired<TargetPassConfig>(); 869 AU.addRequired<TargetLibraryInfoWrapperPass>(); 870 AU.addRequired<AssumptionCacheTracker>(); 871 AU.addPreserved<DominatorTreeWrapperPass>(); 872 } 873 874 bool runOnFunction(Function &F) override { 875 LLVM_DEBUG(dbgs() << "[SafeStack] Function: " << F.getName() << "\n"); 876 877 if (!F.hasFnAttribute(Attribute::SafeStack)) { 878 LLVM_DEBUG(dbgs() << "[SafeStack] safestack is not requested" 879 " for this function\n"); 880 return false; 881 } 882 883 if (F.isDeclaration()) { 884 LLVM_DEBUG(dbgs() << "[SafeStack] function definition" 885 " is not available\n"); 886 return false; 887 } 888 889 TM = &getAnalysis<TargetPassConfig>().getTM<TargetMachine>(); 890 auto *TL = TM->getSubtargetImpl(F)->getTargetLowering(); 891 if (!TL) 892 report_fatal_error("TargetLowering instance is required"); 893 894 auto *DL = &F.getParent()->getDataLayout(); 895 auto &TLI = getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F); 896 auto &ACT = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F); 897 898 // Compute DT and LI only for functions that have the attribute. 899 // This is only useful because the legacy pass manager doesn't let us 900 // compute analyzes lazily. 901 902 DominatorTree *DT; 903 bool ShouldPreserveDominatorTree; 904 Optional<DominatorTree> LazilyComputedDomTree; 905 906 // Do we already have a DominatorTree avaliable from the previous pass? 907 // Note that we should *NOT* require it, to avoid the case where we end up 908 // not needing it, but the legacy PM would have computed it for us anyways. 909 if (auto *DTWP = getAnalysisIfAvailable<DominatorTreeWrapperPass>()) { 910 DT = &DTWP->getDomTree(); 911 ShouldPreserveDominatorTree = true; 912 } else { 913 // Otherwise, we need to compute it. 914 LazilyComputedDomTree.emplace(F); 915 DT = LazilyComputedDomTree.getPointer(); 916 ShouldPreserveDominatorTree = false; 917 } 918 919 // Likewise, lazily compute loop info. 920 LoopInfo LI(*DT); 921 922 DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Lazy); 923 924 ScalarEvolution SE(F, TLI, ACT, *DT, LI); 925 926 return SafeStack(F, *TL, *DL, ShouldPreserveDominatorTree ? &DTU : nullptr, 927 SE) 928 .run(); 929 } 930 }; 931 932 } // end anonymous namespace 933 934 char SafeStackLegacyPass::ID = 0; 935 936 INITIALIZE_PASS_BEGIN(SafeStackLegacyPass, DEBUG_TYPE, 937 "Safe Stack instrumentation pass", false, false) 938 INITIALIZE_PASS_DEPENDENCY(TargetPassConfig) 939 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) 940 INITIALIZE_PASS_END(SafeStackLegacyPass, DEBUG_TYPE, 941 "Safe Stack instrumentation pass", false, false) 942 943 FunctionPass *llvm::createSafeStackPass() { return new SafeStackLegacyPass(); } 944