llvm/lib/CodeGen/SafeStack.cpp

   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/SmallPtrSet.h"
  21 #include "llvm/ADT/SmallVector.h"
  22 #include "llvm/ADT/Statistic.h"
  23 #include "llvm/Analysis/AssumptionCache.h"
  24 #include "llvm/Analysis/BranchProbabilityInfo.h"
  25 #include "llvm/Analysis/DomTreeUpdater.h"
  26 #include "llvm/Analysis/InlineCost.h"
  27 #include "llvm/Analysis/LoopInfo.h"
  28 #include "llvm/Analysis/ScalarEvolution.h"
  29 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
  30 #include "llvm/Analysis/StackLifetime.h"
  31 #include "llvm/Analysis/TargetLibraryInfo.h"
  32 #include "llvm/CodeGen/TargetLowering.h"
  33 #include "llvm/CodeGen/TargetPassConfig.h"
  34 #include "llvm/CodeGen/TargetSubtargetInfo.h"
  35 #include "llvm/IR/Argument.h"
  36 #include "llvm/IR/Attributes.h"
  37 #include "llvm/IR/ConstantRange.h"
  38 #include "llvm/IR/Constants.h"
  39 #include "llvm/IR/DIBuilder.h"
  40 #include "llvm/IR/DataLayout.h"
  41 #include "llvm/IR/DerivedTypes.h"
  42 #include "llvm/IR/Dominators.h"
  43 #include "llvm/IR/Function.h"
  44 #include "llvm/IR/IRBuilder.h"
  45 #include "llvm/IR/InstIterator.h"
  46 #include "llvm/IR/Instruction.h"
  47 #include "llvm/IR/Instructions.h"
  48 #include "llvm/IR/IntrinsicInst.h"
  49 #include "llvm/IR/Intrinsics.h"
  50 #include "llvm/IR/MDBuilder.h"
  51 #include "llvm/IR/Metadata.h"
  52 #include "llvm/IR/Module.h"
  53 #include "llvm/IR/Type.h"
  54 #include "llvm/IR/Use.h"
  55 #include "llvm/IR/Value.h"
  56 #include "llvm/InitializePasses.h"
  57 #include "llvm/Pass.h"
  58 #include "llvm/Support/Casting.h"
  59 #include "llvm/Support/Debug.h"
  60 #include "llvm/Support/ErrorHandling.h"
  61 #include "llvm/Support/MathExtras.h"
  62 #include "llvm/Support/raw_ostream.h"
  63 #include "llvm/Target/TargetMachine.h"
  64 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
  65 #include "llvm/Transforms/Utils/Cloning.h"
  66 #include "llvm/Transforms/Utils/Local.h"
  67 #include <algorithm>
  68 #include <cassert>
  69 #include <cstdint>
  70 #include <optional>
  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 static cl::opt<bool> ClColoring("safe-stack-coloring",
 101                                 cl::desc("enable safe stack coloring"),
 102                                 cl::Hidden, cl::init(true));
 103
 104 namespace {
 105
 106 /// The SafeStack pass splits the stack of each function into the safe
 107 /// stack, which is only accessed through memory safe dereferences (as
 108 /// determined statically), and the unsafe stack, which contains all
 109 /// local variables that are accessed in ways that we can't prove to
 110 /// be safe.
 111 class SafeStack {
 112   Function &F;
 113   const TargetLoweringBase &TL;
 114   const DataLayout &DL;
 115   DomTreeUpdater *DTU;
 116   ScalarEvolution &SE;
 117
 118   Type *StackPtrTy;
 119   Type *IntPtrTy;
 120   Type *Int32Ty;
 121   Type *Int8Ty;
 122
 123   Value *UnsafeStackPtr = nullptr;
 124
 125   /// Unsafe stack alignment. Each stack frame must ensure that the stack is
 126   /// aligned to this value. We need to re-align the unsafe stack if the
 127   /// alignment of any object on the stack exceeds this value.
 128   ///
 129   /// 16 seems like a reasonable upper bound on the alignment of objects that we
 130   /// might expect to appear on the stack on most common targets.
 131   static constexpr Align StackAlignment = Align::Constant<16>();
 132
 133   /// Return the value of the stack canary.
 134   Value *getStackGuard(IRBuilder<> &IRB, Function &F);
 135
 136   /// Load stack guard from the frame and check if it has changed.
 137   void checkStackGuard(IRBuilder<> &IRB, Function &F, Instruction &RI,
 138                        AllocaInst *StackGuardSlot, Value *StackGuard);
 139
 140   /// Find all static allocas, dynamic allocas, return instructions and
 141   /// stack restore points (exception unwind blocks and setjmp calls) in the
 142   /// given function and append them to the respective vectors.
 143   void findInsts(Function &F, SmallVectorImpl<AllocaInst *> &StaticAllocas,
 144                  SmallVectorImpl<AllocaInst *> &DynamicAllocas,
 145                  SmallVectorImpl<Argument *> &ByValArguments,
 146                  SmallVectorImpl<Instruction *> &Returns,
 147                  SmallVectorImpl<Instruction *> &StackRestorePoints);
 148
 149   /// Calculate the allocation size of a given alloca. Returns 0 if the
 150   /// size can not be statically determined.
 151   uint64_t getStaticAllocaAllocationSize(const AllocaInst* AI);
 152
 153   /// Allocate space for all static allocas in \p StaticAllocas,
 154   /// replace allocas with pointers into the unsafe stack.
 155   ///
 156   /// \returns A pointer to the top of the unsafe stack after all unsafe static
 157   /// allocas are allocated.
 158   Value *moveStaticAllocasToUnsafeStack(IRBuilder<> &IRB, Function &F,
 159                                         ArrayRef<AllocaInst *> StaticAllocas,
 160                                         ArrayRef<Argument *> ByValArguments,
 161                                         Instruction *BasePointer,
 162                                         AllocaInst *StackGuardSlot);
 163
 164   /// Generate code to restore the stack after all stack restore points
 165   /// in \p StackRestorePoints.
 166   ///
 167   /// \returns A local variable in which to maintain the dynamic top of the
 168   /// unsafe stack if needed.
 169   AllocaInst *
 170   createStackRestorePoints(IRBuilder<> &IRB, Function &F,
 171                            ArrayRef<Instruction *> StackRestorePoints,
 172                            Value *StaticTop, bool NeedDynamicTop);
 173
 174   /// Replace all allocas in \p DynamicAllocas with code to allocate
 175   /// space dynamically on the unsafe stack and store the dynamic unsafe stack
 176   /// top to \p DynamicTop if non-null.
 177   void moveDynamicAllocasToUnsafeStack(Function &F, Value *UnsafeStackPtr,
 178                                        AllocaInst *DynamicTop,
 179                                        ArrayRef<AllocaInst *> DynamicAllocas);
 180
 181   bool IsSafeStackAlloca(const Value *AllocaPtr, uint64_t AllocaSize);
 182
 183   bool IsMemIntrinsicSafe(const MemIntrinsic *MI, const Use &U,
 184                           const Value *AllocaPtr, uint64_t AllocaSize);
 185   bool IsAccessSafe(Value *Addr, uint64_t Size, const Value *AllocaPtr,
 186                     uint64_t AllocaSize);
 187
 188   bool ShouldInlinePointerAddress(CallInst &CI);
 189   void TryInlinePointerAddress();
 190
 191 public:
 192   SafeStack(Function &F, const TargetLoweringBase &TL, const DataLayout &DL,
 193             DomTreeUpdater *DTU, ScalarEvolution &SE)
 194       : F(F), TL(TL), DL(DL), DTU(DTU), SE(SE),
 195         StackPtrTy(Type::getInt8PtrTy(F.getContext())),
 196         IntPtrTy(DL.getIntPtrType(F.getContext())),
 197         Int32Ty(Type::getInt32Ty(F.getContext())),
 198         Int8Ty(Type::getInt8Ty(F.getContext())) {}
 199
 200   // Run the transformation on the associated function.
 201   // Returns whether the function was changed.
 202   bool run();
 203 };
 204
 205 constexpr Align SafeStack::StackAlignment;
 206
 207 uint64_t SafeStack::getStaticAllocaAllocationSize(const AllocaInst* AI) {
 208   uint64_t Size = DL.getTypeAllocSize(AI->getAllocatedType());
 209   if (AI->isArrayAllocation()) {
 210     auto C = dyn_cast<ConstantInt>(AI->getArraySize());
 211     if (!C)
 212       return 0;
 213     Size *= C->getZExtValue();
 214   }
 215   return Size;
 216 }
 217
 218 bool SafeStack::IsAccessSafe(Value *Addr, uint64_t AccessSize,
 219                              const Value *AllocaPtr, uint64_t AllocaSize) {
 220   const SCEV *AddrExpr = SE.getSCEV(Addr);
 221   const auto *Base = dyn_cast<SCEVUnknown>(SE.getPointerBase(AddrExpr));
 222   if (!Base || Base->getValue() != AllocaPtr) {
 223     LLVM_DEBUG(
 224         dbgs() << "[SafeStack] "
 225                << (isa<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")
 226                << *AllocaPtr << "\n"
 227                << "SCEV " << *AddrExpr << " not directly based on alloca\n");
 228     return false;
 229   }
 230
 231   const SCEV *Expr = SE.removePointerBase(AddrExpr);
 232   uint64_t BitWidth = SE.getTypeSizeInBits(Expr->getType());
 233   ConstantRange AccessStartRange = SE.getUnsignedRange(Expr);
 234   ConstantRange SizeRange =
 235       ConstantRange(APInt(BitWidth, 0), APInt(BitWidth, AccessSize));
 236   ConstantRange AccessRange = AccessStartRange.add(SizeRange);
 237   ConstantRange AllocaRange =
 238       ConstantRange(APInt(BitWidth, 0), APInt(BitWidth, AllocaSize));
 239   bool Safe = AllocaRange.contains(AccessRange);
 240
 241   LLVM_DEBUG(
 242       dbgs() << "[SafeStack] "
 243              << (isa<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")
 244              << *AllocaPtr << "\n"
 245              << "            Access " << *Addr << "\n"
 246              << "            SCEV " << *Expr
 247              << " U: " << SE.getUnsignedRange(Expr)
 248              << ", S: " << SE.getSignedRange(Expr) << "\n"
 249              << "            Range " << AccessRange << "\n"
 250              << "            AllocaRange " << AllocaRange << "\n"
 251              << "            " << (Safe ? "safe" : "unsafe") << "\n");
 252
 253   return Safe;
 254 }
 255
 256 bool SafeStack::IsMemIntrinsicSafe(const MemIntrinsic *MI, const Use &U,
 257                                    const Value *AllocaPtr,
 258                                    uint64_t AllocaSize) {
 259   if (auto MTI = dyn_cast<MemTransferInst>(MI)) {
 260     if (MTI->getRawSource() != U && MTI->getRawDest() != U)
 261       return true;
 262   } else {
 263     if (MI->getRawDest() != U)
 264       return true;
 265   }
 266
 267   const auto *Len = dyn_cast<ConstantInt>(MI->getLength());
 268   // Non-constant size => unsafe. FIXME: try SCEV getRange.
 269   if (!Len) return false;
 270   return IsAccessSafe(U, Len->getZExtValue(), AllocaPtr, AllocaSize);
 271 }
 272
 273 /// Check whether a given allocation must be put on the safe
 274 /// stack or not. The function analyzes all uses of AI and checks whether it is
 275 /// only accessed in a memory safe way (as decided statically).
 276 bool SafeStack::IsSafeStackAlloca(const Value *AllocaPtr, uint64_t AllocaSize) {
 277   // Go through all uses of this alloca and check whether all accesses to the
 278   // allocated object are statically known to be memory safe and, hence, the
 279   // object can be placed on the safe stack.
 280   SmallPtrSet<const Value *, 16> Visited;
 281   SmallVector<const Value *, 8> WorkList;
 282   WorkList.push_back(AllocaPtr);
 283
 284   // A DFS search through all uses of the alloca in bitcasts/PHI/GEPs/etc.
 285   while (!WorkList.empty()) {
 286     const Value *V = WorkList.pop_back_val();
 287     for (const Use &UI : V->uses()) {
 288       auto I = cast<const Instruction>(UI.getUser());
 289       assert(V == UI.get());
 290
 291       switch (I->getOpcode()) {
 292       case Instruction::Load:
 293         if (!IsAccessSafe(UI, DL.getTypeStoreSize(I->getType()), AllocaPtr,
 294                           AllocaSize))
 295           return false;
 296         break;
 297
 298       case Instruction::VAArg:
 299         // "va-arg" from a pointer is safe.
 300         break;
 301       case Instruction::Store:
 302         if (V == I->getOperand(0)) {
 303           // Stored the pointer - conservatively assume it may be unsafe.
 304           LLVM_DEBUG(dbgs()
 305                      << "[SafeStack] Unsafe alloca: " << *AllocaPtr
 306                      << "\n            store of address: " << *I << "\n");
 307           return false;
 308         }
 309
 310         if (!IsAccessSafe(UI, DL.getTypeStoreSize(I->getOperand(0)->getType()),
 311                           AllocaPtr, AllocaSize))
 312           return false;
 313         break;
 314
 315       case Instruction::Ret:
 316         // Information leak.
 317         return false;
 318
 319       case Instruction::Call:
 320       case Instruction::Invoke: {
 321         const CallBase &CS = *cast<CallBase>(I);
 322
 323         if (I->isLifetimeStartOrEnd())
 324           continue;
 325
 326         if (const MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) {
 327           if (!IsMemIntrinsicSafe(MI, UI, AllocaPtr, AllocaSize)) {
 328             LLVM_DEBUG(dbgs()
 329                        << "[SafeStack] Unsafe alloca: " << *AllocaPtr
 330                        << "\n            unsafe memintrinsic: " << *I << "\n");
 331             return false;
 332           }
 333           continue;
 334         }
 335
 336         // LLVM 'nocapture' attribute is only set for arguments whose address
 337         // is not stored, passed around, or used in any other non-trivial way.
 338         // We assume that passing a pointer to an object as a 'nocapture
 339         // readnone' argument is safe.
 340         // FIXME: a more precise solution would require an interprocedural
 341         // analysis here, which would look at all uses of an argument inside
 342         // the function being called.
 343         auto B = CS.arg_begin(), E = CS.arg_end();
 344         for (const auto *A = B; A != E; ++A)
 345           if (A->get() == V)
 346             if (!(CS.doesNotCapture(A - B) && (CS.doesNotAccessMemory(A - B) ||
 347                                                CS.doesNotAccessMemory()))) {
 348               LLVM_DEBUG(dbgs() << "[SafeStack] Unsafe alloca: " << *AllocaPtr
 349                                 << "\n            unsafe call: " << *I << "\n");
 350               return false;
 351             }
 352         continue;
 353       }
 354
 355       default:
 356         if (Visited.insert(I).second)
 357           WorkList.push_back(cast<const Instruction>(I));
 358       }
 359     }
 360   }
 361
 362   // All uses of the alloca are safe, we can place it on the safe stack.
 363   return true;
 364 }
 365
 366 Value *SafeStack::getStackGuard(IRBuilder<> &IRB, Function &F) {
 367   Value *StackGuardVar = TL.getIRStackGuard(IRB);
 368   Module *M = F.getParent();
 369
 370   if (!StackGuardVar) {
 371     TL.insertSSPDeclarations(*M);
 372     return IRB.CreateCall(Intrinsic::getDeclaration(M, Intrinsic::stackguard));
 373   }
 374
 375   return IRB.CreateLoad(StackPtrTy, StackGuardVar, "StackGuard");
 376 }
 377
 378 void SafeStack::findInsts(Function &F,
 379                           SmallVectorImpl<AllocaInst *> &StaticAllocas,
 380                           SmallVectorImpl<AllocaInst *> &DynamicAllocas,
 381                           SmallVectorImpl<Argument *> &ByValArguments,
 382                           SmallVectorImpl<Instruction *> &Returns,
 383                           SmallVectorImpl<Instruction *> &StackRestorePoints) {
 384   for (Instruction &I : instructions(&F)) {
 385     if (auto AI = dyn_cast<AllocaInst>(&I)) {
 386       ++NumAllocas;
 387
 388       uint64_t Size = getStaticAllocaAllocationSize(AI);
 389       if (IsSafeStackAlloca(AI, Size))
 390         continue;
 391
 392       if (AI->isStaticAlloca()) {
 393         ++NumUnsafeStaticAllocas;
 394         StaticAllocas.push_back(AI);
 395       } else {
 396         ++NumUnsafeDynamicAllocas;
 397         DynamicAllocas.push_back(AI);
 398       }
 399     } else if (auto RI = dyn_cast<ReturnInst>(&I)) {
 400       if (CallInst *CI = I.getParent()->getTerminatingMustTailCall())
 401         Returns.push_back(CI);
 402       else
 403         Returns.push_back(RI);
 404     } else if (auto CI = dyn_cast<CallInst>(&I)) {
 405       // setjmps require stack restore.
 406       if (CI->getCalledFunction() && CI->canReturnTwice())
 407         StackRestorePoints.push_back(CI);
 408     } else if (auto LP = dyn_cast<LandingPadInst>(&I)) {
 409       // Exception landing pads require stack restore.
 410       StackRestorePoints.push_back(LP);
 411     } else if (auto II = dyn_cast<IntrinsicInst>(&I)) {
 412       if (II->getIntrinsicID() == Intrinsic::gcroot)
 413         report_fatal_error(
 414             "gcroot intrinsic not compatible with safestack attribute");
 415     }
 416   }
 417   for (Argument &Arg : F.args()) {
 418     if (!Arg.hasByValAttr())
 419       continue;
 420     uint64_t Size = DL.getTypeStoreSize(Arg.getParamByValType());
 421     if (IsSafeStackAlloca(&Arg, Size))
 422       continue;
 423
 424     ++NumUnsafeByValArguments;
 425     ByValArguments.push_back(&Arg);
 426   }
 427 }
 428
 429 AllocaInst *
 430 SafeStack::createStackRestorePoints(IRBuilder<> &IRB, Function &F,
 431                                     ArrayRef<Instruction *> StackRestorePoints,
 432                                     Value *StaticTop, bool NeedDynamicTop) {
 433   assert(StaticTop && "The stack top isn't set.");
 434
 435   if (StackRestorePoints.empty())
 436     return nullptr;
 437
 438   // We need the current value of the shadow stack pointer to restore
 439   // after longjmp or exception catching.
 440
 441   // FIXME: On some platforms this could be handled by the longjmp/exception
 442   // runtime itself.
 443
 444   AllocaInst *DynamicTop = nullptr;
 445   if (NeedDynamicTop) {
 446     // If we also have dynamic alloca's, the stack pointer value changes
 447     // throughout the function. For now we store it in an alloca.
 448     DynamicTop = IRB.CreateAlloca(StackPtrTy, /*ArraySize=*/nullptr,
 449                                   "unsafe_stack_dynamic_ptr");
 450     IRB.CreateStore(StaticTop, DynamicTop);
 451   }
 452
 453   // Restore current stack pointer after longjmp/exception catch.
 454   for (Instruction *I : StackRestorePoints) {
 455     ++NumUnsafeStackRestorePoints;
 456
 457     IRB.SetInsertPoint(I->getNextNode());
 458     Value *CurrentTop =
 459         DynamicTop ? IRB.CreateLoad(StackPtrTy, DynamicTop) : StaticTop;
 460     IRB.CreateStore(CurrentTop, UnsafeStackPtr);
 461   }
 462
 463   return DynamicTop;
 464 }
 465
 466 void SafeStack::checkStackGuard(IRBuilder<> &IRB, Function &F, Instruction &RI,
 467                                 AllocaInst *StackGuardSlot, Value *StackGuard) {
 468   Value *V = IRB.CreateLoad(StackPtrTy, StackGuardSlot);
 469   Value *Cmp = IRB.CreateICmpNE(StackGuard, V);
 470
 471   auto SuccessProb = BranchProbabilityInfo::getBranchProbStackProtector(true);
 472   auto FailureProb = BranchProbabilityInfo::getBranchProbStackProtector(false);
 473   MDNode *Weights = MDBuilder(F.getContext())
 474                         .createBranchWeights(SuccessProb.getNumerator(),
 475                                              FailureProb.getNumerator());
 476   Instruction *CheckTerm =
 477       SplitBlockAndInsertIfThen(Cmp, &RI, /* Unreachable */ true, Weights, DTU);
 478   IRBuilder<> IRBFail(CheckTerm);
 479   // FIXME: respect -fsanitize-trap / -ftrap-function here?
 480   FunctionCallee StackChkFail =
 481       F.getParent()->getOrInsertFunction("__stack_chk_fail", IRB.getVoidTy());
 482   IRBFail.CreateCall(StackChkFail, {});
 483 }
 484
 485 /// We explicitly compute and set the unsafe stack layout for all unsafe
 486 /// static alloca instructions. We save the unsafe "base pointer" in the
 487 /// prologue into a local variable and restore it in the epilogue.
 488 Value *SafeStack::moveStaticAllocasToUnsafeStack(
 489     IRBuilder<> &IRB, Function &F, ArrayRef<AllocaInst *> StaticAllocas,
 490     ArrayRef<Argument *> ByValArguments, Instruction *BasePointer,
 491     AllocaInst *StackGuardSlot) {
 492   if (StaticAllocas.empty() && ByValArguments.empty())
 493     return BasePointer;
 494
 495   DIBuilder DIB(*F.getParent());
 496
 497   StackLifetime SSC(F, StaticAllocas, StackLifetime::LivenessType::May);
 498   static const StackLifetime::LiveRange NoColoringRange(1, true);
 499   if (ClColoring)
 500     SSC.run();
 501
 502   for (const auto *I : SSC.getMarkers()) {
 503     auto *Op = dyn_cast<Instruction>(I->getOperand(1));
 504     const_cast<IntrinsicInst *>(I)->eraseFromParent();
 505     // Remove the operand bitcast, too, if it has no more uses left.
 506     if (Op && Op->use_empty())
 507       Op->eraseFromParent();
 508   }
 509
 510   // Unsafe stack always grows down.
 511   StackLayout SSL(StackAlignment);
 512   if (StackGuardSlot) {
 513     Type *Ty = StackGuardSlot->getAllocatedType();
 514     Align Align = std::max(DL.getPrefTypeAlign(Ty), StackGuardSlot->getAlign());
 515     SSL.addObject(StackGuardSlot, getStaticAllocaAllocationSize(StackGuardSlot),
 516                   Align, SSC.getFullLiveRange());
 517   }
 518
 519   for (Argument *Arg : ByValArguments) {
 520     Type *Ty = Arg->getParamByValType();
 521     uint64_t Size = DL.getTypeStoreSize(Ty);
 522     if (Size == 0)
 523       Size = 1; // Don't create zero-sized stack objects.
 524
 525     // Ensure the object is properly aligned.
 526     Align Align = DL.getPrefTypeAlign(Ty);
 527     if (auto A = Arg->getParamAlign())
 528       Align = std::max(Align, *A);
 529     SSL.addObject(Arg, Size, Align, SSC.getFullLiveRange());
 530   }
 531
 532   for (AllocaInst *AI : StaticAllocas) {
 533     Type *Ty = AI->getAllocatedType();
 534     uint64_t Size = getStaticAllocaAllocationSize(AI);
 535     if (Size == 0)
 536       Size = 1; // Don't create zero-sized stack objects.
 537
 538     // Ensure the object is properly aligned.
 539     Align Align = std::max(DL.getPrefTypeAlign(Ty), AI->getAlign());
 540
 541     SSL.addObject(AI, Size, Align,
 542                   ClColoring ? SSC.getLiveRange(AI) : NoColoringRange);
 543   }
 544
 545   SSL.computeLayout();
 546   Align FrameAlignment = SSL.getFrameAlignment();
 547
 548   // FIXME: tell SSL that we start at a less-then-MaxAlignment aligned location
 549   // (AlignmentSkew).
 550   if (FrameAlignment > StackAlignment) {
 551     // Re-align the base pointer according to the max requested alignment.
 552     IRB.SetInsertPoint(BasePointer->getNextNode());
 553     BasePointer = cast<Instruction>(IRB.CreateIntToPtr(
 554         IRB.CreateAnd(
 555             IRB.CreatePtrToInt(BasePointer, IntPtrTy),
 556             ConstantInt::get(IntPtrTy, ~(FrameAlignment.value() - 1))),
 557         StackPtrTy));
 558   }
 559
 560   IRB.SetInsertPoint(BasePointer->getNextNode());
 561
 562   if (StackGuardSlot) {
 563     unsigned Offset = SSL.getObjectOffset(StackGuardSlot);
 564     Value *Off = IRB.CreateGEP(Int8Ty, BasePointer, // BasePointer is i8*
 565                                ConstantInt::get(Int32Ty, -Offset));
 566     Value *NewAI =
 567         IRB.CreateBitCast(Off, StackGuardSlot->getType(), "StackGuardSlot");
 568
 569     // Replace alloc with the new location.
 570     StackGuardSlot->replaceAllUsesWith(NewAI);
 571     StackGuardSlot->eraseFromParent();
 572   }
 573
 574   for (Argument *Arg : ByValArguments) {
 575     unsigned Offset = SSL.getObjectOffset(Arg);
 576     MaybeAlign Align(SSL.getObjectAlignment(Arg));
 577     Type *Ty = Arg->getParamByValType();
 578
 579     uint64_t Size = DL.getTypeStoreSize(Ty);
 580     if (Size == 0)
 581       Size = 1; // Don't create zero-sized stack objects.
 582
 583     Value *Off = IRB.CreateGEP(Int8Ty, BasePointer, // BasePointer is i8*
 584                                ConstantInt::get(Int32Ty, -Offset));
 585     Value *NewArg = IRB.CreateBitCast(Off, Arg->getType(),
 586                                      Arg->getName() + ".unsafe-byval");
 587
 588     // Replace alloc with the new location.
 589     replaceDbgDeclare(Arg, BasePointer, DIB, DIExpression::ApplyOffset,
 590                       -Offset);
 591     Arg->replaceAllUsesWith(NewArg);
 592     IRB.SetInsertPoint(cast<Instruction>(NewArg)->getNextNode());
 593     IRB.CreateMemCpy(Off, Align, Arg, Arg->getParamAlign(), Size);
 594   }
 595
 596   // Allocate space for every unsafe static AllocaInst on the unsafe stack.
 597   for (AllocaInst *AI : StaticAllocas) {
 598     IRB.SetInsertPoint(AI);
 599     unsigned Offset = SSL.getObjectOffset(AI);
 600
 601     replaceDbgDeclare(AI, BasePointer, DIB, DIExpression::ApplyOffset, -Offset);
 602     replaceDbgValueForAlloca(AI, BasePointer, DIB, -Offset);
 603
 604     // Replace uses of the alloca with the new location.
 605     // Insert address calculation close to each use to work around PR27844.
 606     std::string Name = std::string(AI->getName()) + ".unsafe";
 607     while (!AI->use_empty()) {
 608       Use &U = *AI->use_begin();
 609       Instruction *User = cast<Instruction>(U.getUser());
 610
 611       Instruction *InsertBefore;
 612       if (auto *PHI = dyn_cast<PHINode>(User))
 613         InsertBefore = PHI->getIncomingBlock(U)->getTerminator();
 614       else
 615         InsertBefore = User;
 616
 617       IRBuilder<> IRBUser(InsertBefore);
 618       Value *Off = IRBUser.CreateGEP(Int8Ty, BasePointer, // BasePointer is i8*
 619                                      ConstantInt::get(Int32Ty, -Offset));
 620       Value *Replacement = IRBUser.CreateBitCast(Off, AI->getType(), Name);
 621
 622       if (auto *PHI = dyn_cast<PHINode>(User))
 623         // PHI nodes may have multiple incoming edges from the same BB (why??),
 624         // all must be updated at once with the same incoming value.
 625         PHI->setIncomingValueForBlock(PHI->getIncomingBlock(U), Replacement);
 626       else
 627         U.set(Replacement);
 628     }
 629
 630     AI->eraseFromParent();
 631   }
 632
 633   // Re-align BasePointer so that our callees would see it aligned as
 634   // expected.
 635   // FIXME: no need to update BasePointer in leaf functions.
 636   unsigned FrameSize = alignTo(SSL.getFrameSize(), StackAlignment);
 637
 638   MDBuilder MDB(F.getContext());
 639   SmallVector<Metadata *, 2> Data;
 640   Data.push_back(MDB.createString("unsafe-stack-size"));
 641   Data.push_back(MDB.createConstant(ConstantInt::get(Int32Ty, FrameSize)));
 642   MDNode *MD = MDTuple::get(F.getContext(), Data);
 643   F.setMetadata(LLVMContext::MD_annotation, MD);
 644
 645   // Update shadow stack pointer in the function epilogue.
 646   IRB.SetInsertPoint(BasePointer->getNextNode());
 647
 648   Value *StaticTop =
 649       IRB.CreateGEP(Int8Ty, BasePointer, ConstantInt::get(Int32Ty, -FrameSize),
 650                     "unsafe_stack_static_top");
 651   IRB.CreateStore(StaticTop, UnsafeStackPtr);
 652   return StaticTop;
 653 }
 654
 655 void SafeStack::moveDynamicAllocasToUnsafeStack(
 656     Function &F, Value *UnsafeStackPtr, AllocaInst *DynamicTop,
 657     ArrayRef<AllocaInst *> DynamicAllocas) {
 658   DIBuilder DIB(*F.getParent());
 659
 660   for (AllocaInst *AI : DynamicAllocas) {
 661     IRBuilder<> IRB(AI);
 662
 663     // Compute the new SP value (after AI).
 664     Value *ArraySize = AI->getArraySize();
 665     if (ArraySize->getType() != IntPtrTy)
 666       ArraySize = IRB.CreateIntCast(ArraySize, IntPtrTy, false);
 667
 668     Type *Ty = AI->getAllocatedType();
 669     uint64_t TySize = DL.getTypeAllocSize(Ty);
 670     Value *Size = IRB.CreateMul(ArraySize, ConstantInt::get(IntPtrTy, TySize));
 671
 672     Value *SP = IRB.CreatePtrToInt(IRB.CreateLoad(StackPtrTy, UnsafeStackPtr),
 673                                    IntPtrTy);
 674     SP = IRB.CreateSub(SP, Size);
 675
 676     // Align the SP value to satisfy the AllocaInst, type and stack alignments.
 677     auto Align = std::max(std::max(DL.getPrefTypeAlign(Ty), AI->getAlign()),
 678                           StackAlignment);
 679
 680     Value *NewTop = IRB.CreateIntToPtr(
 681         IRB.CreateAnd(SP,
 682                       ConstantInt::get(IntPtrTy, ~uint64_t(Align.value() - 1))),
 683         StackPtrTy);
 684
 685     // Save the stack pointer.
 686     IRB.CreateStore(NewTop, UnsafeStackPtr);
 687     if (DynamicTop)
 688       IRB.CreateStore(NewTop, DynamicTop);
 689
 690     Value *NewAI = IRB.CreatePointerCast(NewTop, AI->getType());
 691     if (AI->hasName() && isa<Instruction>(NewAI))
 692       NewAI->takeName(AI);
 693
 694     replaceDbgDeclare(AI, NewAI, DIB, DIExpression::ApplyOffset, 0);
 695     AI->replaceAllUsesWith(NewAI);
 696     AI->eraseFromParent();
 697   }
 698
 699   if (!DynamicAllocas.empty()) {
 700     // Now go through the instructions again, replacing stacksave/stackrestore.
 701     for (Instruction &I : llvm::make_early_inc_range(instructions(&F))) {
 702       auto *II = dyn_cast<IntrinsicInst>(&I);
 703       if (!II)
 704         continue;
 705
 706       if (II->getIntrinsicID() == Intrinsic::stacksave) {
 707         IRBuilder<> IRB(II);
 708         Instruction *LI = IRB.CreateLoad(StackPtrTy, UnsafeStackPtr);
 709         LI->takeName(II);
 710         II->replaceAllUsesWith(LI);
 711         II->eraseFromParent();
 712       } else if (II->getIntrinsicID() == Intrinsic::stackrestore) {
 713         IRBuilder<> IRB(II);
 714         Instruction *SI = IRB.CreateStore(II->getArgOperand(0), UnsafeStackPtr);
 715         SI->takeName(II);
 716         assert(II->use_empty());
 717         II->eraseFromParent();
 718       }
 719     }
 720   }
 721 }
 722
 723 bool SafeStack::ShouldInlinePointerAddress(CallInst &CI) {
 724   Function *Callee = CI.getCalledFunction();
 725   if (CI.hasFnAttr(Attribute::AlwaysInline) &&
 726       isInlineViable(*Callee).isSuccess())
 727     return true;
 728   if (Callee->isInterposable() || Callee->hasFnAttribute(Attribute::NoInline) ||
 729       CI.isNoInline())
 730     return false;
 731   return true;
 732 }
 733
 734 void SafeStack::TryInlinePointerAddress() {
 735   auto *CI = dyn_cast<CallInst>(UnsafeStackPtr);
 736   if (!CI)
 737     return;
 738
 739   if(F.hasOptNone())
 740     return;
 741
 742   Function *Callee = CI->getCalledFunction();
 743   if (!Callee || Callee->isDeclaration())
 744     return;
 745
 746   if (!ShouldInlinePointerAddress(*CI))
 747     return;
 748
 749   InlineFunctionInfo IFI;
 750   InlineFunction(*CI, IFI);
 751 }
 752
 753 bool SafeStack::run() {
 754   assert(F.hasFnAttribute(Attribute::SafeStack) &&
 755          "Can't run SafeStack on a function without the attribute");
 756   assert(!F.isDeclaration() && "Can't run SafeStack on a function declaration");
 757
 758   ++NumFunctions;
 759
 760   SmallVector<AllocaInst *, 16> StaticAllocas;
 761   SmallVector<AllocaInst *, 4> DynamicAllocas;
 762   SmallVector<Argument *, 4> ByValArguments;
 763   SmallVector<Instruction *, 4> Returns;
 764
 765   // Collect all points where stack gets unwound and needs to be restored
 766   // This is only necessary because the runtime (setjmp and unwind code) is
 767   // not aware of the unsafe stack and won't unwind/restore it properly.
 768   // To work around this problem without changing the runtime, we insert
 769   // instrumentation to restore the unsafe stack pointer when necessary.
 770   SmallVector<Instruction *, 4> StackRestorePoints;
 771
 772   // Find all static and dynamic alloca instructions that must be moved to the
 773   // unsafe stack, all return instructions and stack restore points.
 774   findInsts(F, StaticAllocas, DynamicAllocas, ByValArguments, Returns,
 775             StackRestorePoints);
 776
 777   if (StaticAllocas.empty() && DynamicAllocas.empty() &&
 778       ByValArguments.empty() && StackRestorePoints.empty())
 779     return false; // Nothing to do in this function.
 780
 781   if (!StaticAllocas.empty() || !DynamicAllocas.empty() ||
 782       !ByValArguments.empty())
 783     ++NumUnsafeStackFunctions; // This function has the unsafe stack.
 784
 785   if (!StackRestorePoints.empty())
 786     ++NumUnsafeStackRestorePointsFunctions;
 787
 788   IRBuilder<> IRB(&F.front(), F.begin()->getFirstInsertionPt());
 789   // Calls must always have a debug location, or else inlining breaks. So
 790   // we explicitly set a artificial debug location here.
 791   if (DISubprogram *SP = F.getSubprogram())
 792     IRB.SetCurrentDebugLocation(
 793         DILocation::get(SP->getContext(), SP->getScopeLine(), 0, SP));
 794   if (SafeStackUsePointerAddress) {
 795     FunctionCallee Fn = F.getParent()->getOrInsertFunction(
 796         "__safestack_pointer_address", StackPtrTy->getPointerTo(0));
 797     UnsafeStackPtr = IRB.CreateCall(Fn);
 798   } else {
 799     UnsafeStackPtr = TL.getSafeStackPointerLocation(IRB);
 800   }
 801
 802   // Load the current stack pointer (we'll also use it as a base pointer).
 803   // FIXME: use a dedicated register for it ?
 804   Instruction *BasePointer =
 805       IRB.CreateLoad(StackPtrTy, UnsafeStackPtr, false, "unsafe_stack_ptr");
 806   assert(BasePointer->getType() == StackPtrTy);
 807
 808   AllocaInst *StackGuardSlot = nullptr;
 809   // FIXME: implement weaker forms of stack protector.
 810   if (F.hasFnAttribute(Attribute::StackProtect) ||
 811       F.hasFnAttribute(Attribute::StackProtectStrong) ||
 812       F.hasFnAttribute(Attribute::StackProtectReq)) {
 813     Value *StackGuard = getStackGuard(IRB, F);
 814     StackGuardSlot = IRB.CreateAlloca(StackPtrTy, nullptr);
 815     IRB.CreateStore(StackGuard, StackGuardSlot);
 816
 817     for (Instruction *RI : Returns) {
 818       IRBuilder<> IRBRet(RI);
 819       checkStackGuard(IRBRet, F, *RI, StackGuardSlot, StackGuard);
 820     }
 821   }
 822
 823   // The top of the unsafe stack after all unsafe static allocas are
 824   // allocated.
 825   Value *StaticTop = moveStaticAllocasToUnsafeStack(
 826       IRB, F, StaticAllocas, ByValArguments, BasePointer, StackGuardSlot);
 827
 828   // Safe stack object that stores the current unsafe stack top. It is updated
 829   // as unsafe dynamic (non-constant-sized) allocas are allocated and freed.
 830   // This is only needed if we need to restore stack pointer after longjmp
 831   // or exceptions, and we have dynamic allocations.
 832   // FIXME: a better alternative might be to store the unsafe stack pointer
 833   // before setjmp / invoke instructions.
 834   AllocaInst *DynamicTop = createStackRestorePoints(
 835       IRB, F, StackRestorePoints, StaticTop, !DynamicAllocas.empty());
 836
 837   // Handle dynamic allocas.
 838   moveDynamicAllocasToUnsafeStack(F, UnsafeStackPtr, DynamicTop,
 839                                   DynamicAllocas);
 840
 841   // Restore the unsafe stack pointer before each return.
 842   for (Instruction *RI : Returns) {
 843     IRB.SetInsertPoint(RI);
 844     IRB.CreateStore(BasePointer, UnsafeStackPtr);
 845   }
 846
 847   TryInlinePointerAddress();
 848
 849   LLVM_DEBUG(dbgs() << "[SafeStack]     safestack applied\n");
 850   return true;
 851 }
 852
 853 class SafeStackLegacyPass : public FunctionPass {
 854   const TargetMachine *TM = nullptr;
 855
 856 public:
 857   static char ID; // Pass identification, replacement for typeid..
 858
 859   SafeStackLegacyPass() : FunctionPass(ID) {
 860     initializeSafeStackLegacyPassPass(*PassRegistry::getPassRegistry());
 861   }
 862
 863   void getAnalysisUsage(AnalysisUsage &AU) const override {
 864     AU.addRequired<TargetPassConfig>();
 865     AU.addRequired<TargetLibraryInfoWrapperPass>();
 866     AU.addRequired<AssumptionCacheTracker>();
 867     AU.addPreserved<DominatorTreeWrapperPass>();
 868   }
 869
 870   bool runOnFunction(Function &F) override {
 871     LLVM_DEBUG(dbgs() << "[SafeStack] Function: " << F.getName() << "\n");
 872
 873     if (!F.hasFnAttribute(Attribute::SafeStack)) {
 874       LLVM_DEBUG(dbgs() << "[SafeStack]     safestack is not requested"
 875                            " for this function\n");
 876       return false;
 877     }
 878
 879     if (F.isDeclaration()) {
 880       LLVM_DEBUG(dbgs() << "[SafeStack]     function definition"
 881                            " is not available\n");
 882       return false;
 883     }
 884
 885     TM = &getAnalysis<TargetPassConfig>().getTM<TargetMachine>();
 886     auto *TL = TM->getSubtargetImpl(F)->getTargetLowering();
 887     if (!TL)
 888       report_fatal_error("TargetLowering instance is required");
 889
 890     auto *DL = &F.getParent()->getDataLayout();
 891     auto &TLI = getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F);
 892     auto &ACT = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
 893
 894     // Compute DT and LI only for functions that have the attribute.
 895     // This is only useful because the legacy pass manager doesn't let us
 896     // compute analyzes lazily.
 897
 898     DominatorTree *DT;
 899     bool ShouldPreserveDominatorTree;
 900     std::optional<DominatorTree> LazilyComputedDomTree;
 901
 902     // Do we already have a DominatorTree avaliable from the previous pass?
 903     // Note that we should *NOT* require it, to avoid the case where we end up
 904     // not needing it, but the legacy PM would have computed it for us anyways.
 905     if (auto *DTWP = getAnalysisIfAvailable<DominatorTreeWrapperPass>()) {
 906       DT = &DTWP->getDomTree();
 907       ShouldPreserveDominatorTree = true;
 908     } else {
 909       // Otherwise, we need to compute it.
 910       LazilyComputedDomTree.emplace(F);
 911       DT = &*LazilyComputedDomTree;
 912       ShouldPreserveDominatorTree = false;
 913     }
 914
 915     // Likewise, lazily compute loop info.
 916     LoopInfo LI(*DT);
 917
 918     DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Lazy);
 919
 920     ScalarEvolution SE(F, TLI, ACT, *DT, LI);
 921
 922     return SafeStack(F, *TL, *DL, ShouldPreserveDominatorTree ? &DTU : nullptr,
 923                      SE)
 924         .run();
 925   }
 926 };
 927
 928 } // end anonymous namespace
 929
 930 char SafeStackLegacyPass::ID = 0;
 931
 932 INITIALIZE_PASS_BEGIN(SafeStackLegacyPass, DEBUG_TYPE,
 933                       "Safe Stack instrumentation pass", false, false)
 934 INITIALIZE_PASS_DEPENDENCY(TargetPassConfig)
 935 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
 936 INITIALIZE_PASS_END(SafeStackLegacyPass, DEBUG_TYPE,
 937                     "Safe Stack instrumentation pass", false, false)
 938
 939 FunctionPass *llvm::createSafeStackPass() { return new SafeStackLegacyPass(); }