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/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   static constexpr uint64_t 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 constexpr uint64_t SafeStack::StackAlignment;
 225
 226 uint64_t SafeStack::getStaticAllocaAllocationSize(const AllocaInst* AI) {
 227   uint64_t Size = DL.getTypeAllocSize(AI->getAllocatedType());
 228   if (AI->isArrayAllocation()) {
 229     auto C = dyn_cast<ConstantInt>(AI->getArraySize());
 230     if (!C)
 231       return 0;
 232     Size *= C->getZExtValue();
 233   }
 234   return Size;
 235 }
 236
 237 bool SafeStack::IsAccessSafe(Value *Addr, uint64_t AccessSize,
 238                              const Value *AllocaPtr, uint64_t AllocaSize) {
 239   AllocaOffsetRewriter Rewriter(SE, AllocaPtr);
 240   const SCEV *Expr = Rewriter.visit(SE.getSCEV(Addr));
 241
 242   uint64_t BitWidth = SE.getTypeSizeInBits(Expr->getType());
 243   ConstantRange AccessStartRange = SE.getUnsignedRange(Expr);
 244   ConstantRange SizeRange =
 245       ConstantRange(APInt(BitWidth, 0), APInt(BitWidth, AccessSize));
 246   ConstantRange AccessRange = AccessStartRange.add(SizeRange);
 247   ConstantRange AllocaRange =
 248       ConstantRange(APInt(BitWidth, 0), APInt(BitWidth, AllocaSize));
 249   bool Safe = AllocaRange.contains(AccessRange);
 250
 251   LLVM_DEBUG(
 252       dbgs() << "[SafeStack] "
 253              << (isa<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")
 254              << *AllocaPtr << "\n"
 255              << "            Access " << *Addr << "\n"
 256              << "            SCEV " << *Expr
 257              << " U: " << SE.getUnsignedRange(Expr)
 258              << ", S: " << SE.getSignedRange(Expr) << "\n"
 259              << "            Range " << AccessRange << "\n"
 260              << "            AllocaRange " << AllocaRange << "\n"
 261              << "            " << (Safe ? "safe" : "unsafe") << "\n");
 262
 263   return Safe;
 264 }
 265
 266 bool SafeStack::IsMemIntrinsicSafe(const MemIntrinsic *MI, const Use &U,
 267                                    const Value *AllocaPtr,
 268                                    uint64_t AllocaSize) {
 269   if (auto MTI = dyn_cast<MemTransferInst>(MI)) {
 270     if (MTI->getRawSource() != U && MTI->getRawDest() != U)
 271       return true;
 272   } else {
 273     if (MI->getRawDest() != U)
 274       return true;
 275   }
 276
 277   const auto *Len = dyn_cast<ConstantInt>(MI->getLength());
 278   // Non-constant size => unsafe. FIXME: try SCEV getRange.
 279   if (!Len) return false;
 280   return IsAccessSafe(U, Len->getZExtValue(), AllocaPtr, AllocaSize);
 281 }
 282
 283 /// Check whether a given allocation must be put on the safe
 284 /// stack or not. The function analyzes all uses of AI and checks whether it is
 285 /// only accessed in a memory safe way (as decided statically).
 286 bool SafeStack::IsSafeStackAlloca(const Value *AllocaPtr, uint64_t AllocaSize) {
 287   // Go through all uses of this alloca and check whether all accesses to the
 288   // allocated object are statically known to be memory safe and, hence, the
 289   // object can be placed on the safe stack.
 290   SmallPtrSet<const Value *, 16> Visited;
 291   SmallVector<const Value *, 8> WorkList;
 292   WorkList.push_back(AllocaPtr);
 293
 294   // A DFS search through all uses of the alloca in bitcasts/PHI/GEPs/etc.
 295   while (!WorkList.empty()) {
 296     const Value *V = WorkList.pop_back_val();
 297     for (const Use &UI : V->uses()) {
 298       auto I = cast<const Instruction>(UI.getUser());
 299       assert(V == UI.get());
 300
 301       switch (I->getOpcode()) {
 302       case Instruction::Load:
 303         if (!IsAccessSafe(UI, DL.getTypeStoreSize(I->getType()), AllocaPtr,
 304                           AllocaSize))
 305           return false;
 306         break;
 307
 308       case Instruction::VAArg:
 309         // "va-arg" from a pointer is safe.
 310         break;
 311       case Instruction::Store:
 312         if (V == I->getOperand(0)) {
 313           // Stored the pointer - conservatively assume it may be unsafe.
 314           LLVM_DEBUG(dbgs()
 315                      << "[SafeStack] Unsafe alloca: " << *AllocaPtr
 316                      << "\n            store of address: " << *I << "\n");
 317           return false;
 318         }
 319
 320         if (!IsAccessSafe(UI, DL.getTypeStoreSize(I->getOperand(0)->getType()),
 321                           AllocaPtr, AllocaSize))
 322           return false;
 323         break;
 324
 325       case Instruction::Ret:
 326         // Information leak.
 327         return false;
 328
 329       case Instruction::Call:
 330       case Instruction::Invoke: {
 331         const CallBase &CS = *cast<CallBase>(I);
 332
 333         if (I->isLifetimeStartOrEnd())
 334           continue;
 335
 336         if (const MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) {
 337           if (!IsMemIntrinsicSafe(MI, UI, AllocaPtr, AllocaSize)) {
 338             LLVM_DEBUG(dbgs()
 339                        << "[SafeStack] Unsafe alloca: " << *AllocaPtr
 340                        << "\n            unsafe memintrinsic: " << *I << "\n");
 341             return false;
 342           }
 343           continue;
 344         }
 345
 346         // LLVM 'nocapture' attribute is only set for arguments whose address
 347         // is not stored, passed around, or used in any other non-trivial way.
 348         // We assume that passing a pointer to an object as a 'nocapture
 349         // readnone' argument is safe.
 350         // FIXME: a more precise solution would require an interprocedural
 351         // analysis here, which would look at all uses of an argument inside
 352         // the function being called.
 353         auto B = CS.arg_begin(), E = CS.arg_end();
 354         for (auto A = B; A != E; ++A)
 355           if (A->get() == V)
 356             if (!(CS.doesNotCapture(A - B) && (CS.doesNotAccessMemory(A - B) ||
 357                                                CS.doesNotAccessMemory()))) {
 358               LLVM_DEBUG(dbgs() << "[SafeStack] Unsafe alloca: " << *AllocaPtr
 359                                 << "\n            unsafe call: " << *I << "\n");
 360               return false;
 361             }
 362         continue;
 363       }
 364
 365       default:
 366         if (Visited.insert(I).second)
 367           WorkList.push_back(cast<const Instruction>(I));
 368       }
 369     }
 370   }
 371
 372   // All uses of the alloca are safe, we can place it on the safe stack.
 373   return true;
 374 }
 375
 376 Value *SafeStack::getStackGuard(IRBuilder<> &IRB, Function &F) {
 377   Value *StackGuardVar = TL.getIRStackGuard(IRB);
 378   Module *M = F.getParent();
 379
 380   if (!StackGuardVar) {
 381     TL.insertSSPDeclarations(*M);
 382     return IRB.CreateCall(Intrinsic::getDeclaration(M, Intrinsic::stackguard));
 383   }
 384
 385   return IRB.CreateLoad(StackPtrTy, StackGuardVar, "StackGuard");
 386 }
 387
 388 void SafeStack::findInsts(Function &F,
 389                           SmallVectorImpl<AllocaInst *> &StaticAllocas,
 390                           SmallVectorImpl<AllocaInst *> &DynamicAllocas,
 391                           SmallVectorImpl<Argument *> &ByValArguments,
 392                           SmallVectorImpl<Instruction *> &Returns,
 393                           SmallVectorImpl<Instruction *> &StackRestorePoints) {
 394   for (Instruction &I : instructions(&F)) {
 395     if (auto AI = dyn_cast<AllocaInst>(&I)) {
 396       ++NumAllocas;
 397
 398       uint64_t Size = getStaticAllocaAllocationSize(AI);
 399       if (IsSafeStackAlloca(AI, Size))
 400         continue;
 401
 402       if (AI->isStaticAlloca()) {
 403         ++NumUnsafeStaticAllocas;
 404         StaticAllocas.push_back(AI);
 405       } else {
 406         ++NumUnsafeDynamicAllocas;
 407         DynamicAllocas.push_back(AI);
 408       }
 409     } else if (auto RI = dyn_cast<ReturnInst>(&I)) {
 410       if (CallInst *CI = I.getParent()->getTerminatingMustTailCall())
 411         Returns.push_back(CI);
 412       else
 413         Returns.push_back(RI);
 414     } else if (auto CI = dyn_cast<CallInst>(&I)) {
 415       // setjmps require stack restore.
 416       if (CI->getCalledFunction() && CI->canReturnTwice())
 417         StackRestorePoints.push_back(CI);
 418     } else if (auto LP = dyn_cast<LandingPadInst>(&I)) {
 419       // Exception landing pads require stack restore.
 420       StackRestorePoints.push_back(LP);
 421     } else if (auto II = dyn_cast<IntrinsicInst>(&I)) {
 422       if (II->getIntrinsicID() == Intrinsic::gcroot)
 423         report_fatal_error(
 424             "gcroot intrinsic not compatible with safestack attribute");
 425     }
 426   }
 427   for (Argument &Arg : F.args()) {
 428     if (!Arg.hasByValAttr())
 429       continue;
 430     uint64_t Size = DL.getTypeStoreSize(Arg.getParamByValType());
 431     if (IsSafeStackAlloca(&Arg, Size))
 432       continue;
 433
 434     ++NumUnsafeByValArguments;
 435     ByValArguments.push_back(&Arg);
 436   }
 437 }
 438
 439 AllocaInst *
 440 SafeStack::createStackRestorePoints(IRBuilder<> &IRB, Function &F,
 441                                     ArrayRef<Instruction *> StackRestorePoints,
 442                                     Value *StaticTop, bool NeedDynamicTop) {
 443   assert(StaticTop && "The stack top isn't set.");
 444
 445   if (StackRestorePoints.empty())
 446     return nullptr;
 447
 448   // We need the current value of the shadow stack pointer to restore
 449   // after longjmp or exception catching.
 450
 451   // FIXME: On some platforms this could be handled by the longjmp/exception
 452   // runtime itself.
 453
 454   AllocaInst *DynamicTop = nullptr;
 455   if (NeedDynamicTop) {
 456     // If we also have dynamic alloca's, the stack pointer value changes
 457     // throughout the function. For now we store it in an alloca.
 458     DynamicTop = IRB.CreateAlloca(StackPtrTy, /*ArraySize=*/nullptr,
 459                                   "unsafe_stack_dynamic_ptr");
 460     IRB.CreateStore(StaticTop, DynamicTop);
 461   }
 462
 463   // Restore current stack pointer after longjmp/exception catch.
 464   for (Instruction *I : StackRestorePoints) {
 465     ++NumUnsafeStackRestorePoints;
 466
 467     IRB.SetInsertPoint(I->getNextNode());
 468     Value *CurrentTop =
 469         DynamicTop ? IRB.CreateLoad(StackPtrTy, DynamicTop) : StaticTop;
 470     IRB.CreateStore(CurrentTop, UnsafeStackPtr);
 471   }
 472
 473   return DynamicTop;
 474 }
 475
 476 void SafeStack::checkStackGuard(IRBuilder<> &IRB, Function &F, Instruction &RI,
 477                                 AllocaInst *StackGuardSlot, Value *StackGuard) {
 478   Value *V = IRB.CreateLoad(StackPtrTy, StackGuardSlot);
 479   Value *Cmp = IRB.CreateICmpNE(StackGuard, V);
 480
 481   auto SuccessProb = BranchProbabilityInfo::getBranchProbStackProtector(true);
 482   auto FailureProb = BranchProbabilityInfo::getBranchProbStackProtector(false);
 483   MDNode *Weights = MDBuilder(F.getContext())
 484                         .createBranchWeights(SuccessProb.getNumerator(),
 485                                              FailureProb.getNumerator());
 486   Instruction *CheckTerm =
 487       SplitBlockAndInsertIfThen(Cmp, &RI, /* Unreachable */ true, Weights, DTU);
 488   IRBuilder<> IRBFail(CheckTerm);
 489   // FIXME: respect -fsanitize-trap / -ftrap-function here?
 490   FunctionCallee StackChkFail =
 491       F.getParent()->getOrInsertFunction("__stack_chk_fail", IRB.getVoidTy());
 492   IRBFail.CreateCall(StackChkFail, {});
 493 }
 494
 495 /// We explicitly compute and set the unsafe stack layout for all unsafe
 496 /// static alloca instructions. We save the unsafe "base pointer" in the
 497 /// prologue into a local variable and restore it in the epilogue.
 498 Value *SafeStack::moveStaticAllocasToUnsafeStack(
 499     IRBuilder<> &IRB, Function &F, ArrayRef<AllocaInst *> StaticAllocas,
 500     ArrayRef<Argument *> ByValArguments, Instruction *BasePointer,
 501     AllocaInst *StackGuardSlot) {
 502   if (StaticAllocas.empty() && ByValArguments.empty())
 503     return BasePointer;
 504
 505   DIBuilder DIB(*F.getParent());
 506
 507   StackLifetime SSC(F, StaticAllocas, StackLifetime::LivenessType::May);
 508   static const StackLifetime::LiveRange NoColoringRange(1, true);
 509   if (ClColoring)
 510     SSC.run();
 511
 512   for (auto *I : SSC.getMarkers()) {
 513     auto *Op = dyn_cast<Instruction>(I->getOperand(1));
 514     const_cast<IntrinsicInst *>(I)->eraseFromParent();
 515     // Remove the operand bitcast, too, if it has no more uses left.
 516     if (Op && Op->use_empty())
 517       Op->eraseFromParent();
 518   }
 519
 520   // Unsafe stack always grows down.
 521   StackLayout SSL(StackAlignment);
 522   if (StackGuardSlot) {
 523     Type *Ty = StackGuardSlot->getAllocatedType();
 524     Align Align = std::max(DL.getPrefTypeAlign(Ty), StackGuardSlot->getAlign());
 525     SSL.addObject(StackGuardSlot, getStaticAllocaAllocationSize(StackGuardSlot),
 526                   Align, SSC.getFullLiveRange());
 527   }
 528
 529   for (Argument *Arg : ByValArguments) {
 530     Type *Ty = Arg->getParamByValType();
 531     uint64_t Size = DL.getTypeStoreSize(Ty);
 532     if (Size == 0)
 533       Size = 1; // Don't create zero-sized stack objects.
 534
 535     // Ensure the object is properly aligned.
 536     Align Align = DL.getPrefTypeAlign(Ty);
 537     if (auto A = Arg->getParamAlign())
 538       Align = std::max(Align, *A);
 539     SSL.addObject(Arg, Size, Align, SSC.getFullLiveRange());
 540   }
 541
 542   for (AllocaInst *AI : StaticAllocas) {
 543     Type *Ty = AI->getAllocatedType();
 544     uint64_t Size = getStaticAllocaAllocationSize(AI);
 545     if (Size == 0)
 546       Size = 1; // Don't create zero-sized stack objects.
 547
 548     // Ensure the object is properly aligned.
 549     Align Align = std::max(DL.getPrefTypeAlign(Ty), AI->getAlign());
 550
 551     SSL.addObject(AI, Size, Align,
 552                   ClColoring ? SSC.getLiveRange(AI) : NoColoringRange);
 553   }
 554
 555   SSL.computeLayout();
 556   Align FrameAlignment = SSL.getFrameAlignment();
 557
 558   // FIXME: tell SSL that we start at a less-then-MaxAlignment aligned location
 559   // (AlignmentSkew).
 560   if (FrameAlignment > StackAlignment) {
 561     // Re-align the base pointer according to the max requested alignment.
 562     IRB.SetInsertPoint(BasePointer->getNextNode());
 563     BasePointer = cast<Instruction>(IRB.CreateIntToPtr(
 564         IRB.CreateAnd(
 565             IRB.CreatePtrToInt(BasePointer, IntPtrTy),
 566             ConstantInt::get(IntPtrTy, ~(FrameAlignment.value() - 1))),
 567         StackPtrTy));
 568   }
 569
 570   IRB.SetInsertPoint(BasePointer->getNextNode());
 571
 572   if (StackGuardSlot) {
 573     unsigned Offset = SSL.getObjectOffset(StackGuardSlot);
 574     Value *Off = IRB.CreateGEP(Int8Ty, BasePointer, // BasePointer is i8*
 575                                ConstantInt::get(Int32Ty, -Offset));
 576     Value *NewAI =
 577         IRB.CreateBitCast(Off, StackGuardSlot->getType(), "StackGuardSlot");
 578
 579     // Replace alloc with the new location.
 580     StackGuardSlot->replaceAllUsesWith(NewAI);
 581     StackGuardSlot->eraseFromParent();
 582   }
 583
 584   for (Argument *Arg : ByValArguments) {
 585     unsigned Offset = SSL.getObjectOffset(Arg);
 586     MaybeAlign Align(SSL.getObjectAlignment(Arg));
 587     Type *Ty = Arg->getParamByValType();
 588
 589     uint64_t Size = DL.getTypeStoreSize(Ty);
 590     if (Size == 0)
 591       Size = 1; // Don't create zero-sized stack objects.
 592
 593     Value *Off = IRB.CreateGEP(Int8Ty, BasePointer, // BasePointer is i8*
 594                                ConstantInt::get(Int32Ty, -Offset));
 595     Value *NewArg = IRB.CreateBitCast(Off, Arg->getType(),
 596                                      Arg->getName() + ".unsafe-byval");
 597
 598     // Replace alloc with the new location.
 599     replaceDbgDeclare(Arg, BasePointer, DIB, DIExpression::ApplyOffset,
 600                       -Offset);
 601     Arg->replaceAllUsesWith(NewArg);
 602     IRB.SetInsertPoint(cast<Instruction>(NewArg)->getNextNode());
 603     IRB.CreateMemCpy(Off, Align, Arg, Arg->getParamAlign(), Size);
 604   }
 605
 606   // Allocate space for every unsafe static AllocaInst on the unsafe stack.
 607   for (AllocaInst *AI : StaticAllocas) {
 608     IRB.SetInsertPoint(AI);
 609     unsigned Offset = SSL.getObjectOffset(AI);
 610
 611     replaceDbgDeclare(AI, BasePointer, DIB, DIExpression::ApplyOffset, -Offset);
 612     replaceDbgValueForAlloca(AI, BasePointer, DIB, -Offset);
 613
 614     // Replace uses of the alloca with the new location.
 615     // Insert address calculation close to each use to work around PR27844.
 616     std::string Name = std::string(AI->getName()) + ".unsafe";
 617     while (!AI->use_empty()) {
 618       Use &U = *AI->use_begin();
 619       Instruction *User = cast<Instruction>(U.getUser());
 620
 621       Instruction *InsertBefore;
 622       if (auto *PHI = dyn_cast<PHINode>(User))
 623         InsertBefore = PHI->getIncomingBlock(U)->getTerminator();
 624       else
 625         InsertBefore = User;
 626
 627       IRBuilder<> IRBUser(InsertBefore);
 628       Value *Off = IRBUser.CreateGEP(Int8Ty, BasePointer, // BasePointer is i8*
 629                                      ConstantInt::get(Int32Ty, -Offset));
 630       Value *Replacement = IRBUser.CreateBitCast(Off, AI->getType(), Name);
 631
 632       if (auto *PHI = dyn_cast<PHINode>(User))
 633         // PHI nodes may have multiple incoming edges from the same BB (why??),
 634         // all must be updated at once with the same incoming value.
 635         PHI->setIncomingValueForBlock(PHI->getIncomingBlock(U), Replacement);
 636       else
 637         U.set(Replacement);
 638     }
 639
 640     AI->eraseFromParent();
 641   }
 642
 643   // Re-align BasePointer so that our callees would see it aligned as
 644   // expected.
 645   // FIXME: no need to update BasePointer in leaf functions.
 646   unsigned FrameSize = alignTo(SSL.getFrameSize(), StackAlignment);
 647
 648   // Update shadow stack pointer in the function epilogue.
 649   IRB.SetInsertPoint(BasePointer->getNextNode());
 650
 651   Value *StaticTop =
 652       IRB.CreateGEP(Int8Ty, BasePointer, ConstantInt::get(Int32Ty, -FrameSize),
 653                     "unsafe_stack_static_top");
 654   IRB.CreateStore(StaticTop, UnsafeStackPtr);
 655   return StaticTop;
 656 }
 657
 658 void SafeStack::moveDynamicAllocasToUnsafeStack(
 659     Function &F, Value *UnsafeStackPtr, AllocaInst *DynamicTop,
 660     ArrayRef<AllocaInst *> DynamicAllocas) {
 661   DIBuilder DIB(*F.getParent());
 662
 663   for (AllocaInst *AI : DynamicAllocas) {
 664     IRBuilder<> IRB(AI);
 665
 666     // Compute the new SP value (after AI).
 667     Value *ArraySize = AI->getArraySize();
 668     if (ArraySize->getType() != IntPtrTy)
 669       ArraySize = IRB.CreateIntCast(ArraySize, IntPtrTy, false);
 670
 671     Type *Ty = AI->getAllocatedType();
 672     uint64_t TySize = DL.getTypeAllocSize(Ty);
 673     Value *Size = IRB.CreateMul(ArraySize, ConstantInt::get(IntPtrTy, TySize));
 674
 675     Value *SP = IRB.CreatePtrToInt(IRB.CreateLoad(StackPtrTy, UnsafeStackPtr),
 676                                    IntPtrTy);
 677     SP = IRB.CreateSub(SP, Size);
 678
 679     // Align the SP value to satisfy the AllocaInst, type and stack alignments.
 680     uint64_t Align =
 681         std::max(std::max(DL.getPrefTypeAlignment(Ty), AI->getAlignment()),
 682                  StackAlignment);
 683
 684     assert(isPowerOf2_32(Align));
 685     Value *NewTop = IRB.CreateIntToPtr(
 686         IRB.CreateAnd(SP, ConstantInt::get(IntPtrTy, ~uint64_t(Align - 1))),
 687         StackPtrTy);
 688
 689     // Save the stack pointer.
 690     IRB.CreateStore(NewTop, UnsafeStackPtr);
 691     if (DynamicTop)
 692       IRB.CreateStore(NewTop, DynamicTop);
 693
 694     Value *NewAI = IRB.CreatePointerCast(NewTop, AI->getType());
 695     if (AI->hasName() && isa<Instruction>(NewAI))
 696       NewAI->takeName(AI);
 697
 698     replaceDbgDeclare(AI, NewAI, DIB, DIExpression::ApplyOffset, 0);
 699     AI->replaceAllUsesWith(NewAI);
 700     AI->eraseFromParent();
 701   }
 702
 703   if (!DynamicAllocas.empty()) {
 704     // Now go through the instructions again, replacing stacksave/stackrestore.
 705     for (Instruction &I : llvm::make_early_inc_range(instructions(&F))) {
 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(); }