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 "llvm/CodeGen/SafeStack.h"
  18 #include "SafeStackLayout.h"
  19 #include "llvm/ADT/APInt.h"
  20 #include "llvm/ADT/ArrayRef.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/Metadata.h"
  53 #include "llvm/IR/Module.h"
  54 #include "llvm/IR/Type.h"
  55 #include "llvm/IR/Use.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/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
 122   Value *UnsafeStackPtr = nullptr;
 123
 124   /// Unsafe stack alignment. Each stack frame must ensure that the stack is
 125   /// aligned to this value. We need to re-align the unsafe stack if the
 126   /// alignment of any object on the stack exceeds this value.
 127   ///
 128   /// 16 seems like a reasonable upper bound on the alignment of objects that we
 129   /// might expect to appear on the stack on most common targets.
 130   static constexpr Align StackAlignment = Align::Constant<16>();
 131
 132   /// Return the value of the stack canary.
 133   Value *getStackGuard(IRBuilder<> &IRB, Function &F);
 134
 135   /// Load stack guard from the frame and check if it has changed.
 136   void checkStackGuard(IRBuilder<> &IRB, Function &F, Instruction &RI,
 137                        AllocaInst *StackGuardSlot, Value *StackGuard);
 138
 139   /// Find all static allocas, dynamic allocas, return instructions and
 140   /// stack restore points (exception unwind blocks and setjmp calls) in the
 141   /// given function and append them to the respective vectors.
 142   void findInsts(Function &F, SmallVectorImpl<AllocaInst *> &StaticAllocas,
 143                  SmallVectorImpl<AllocaInst *> &DynamicAllocas,
 144                  SmallVectorImpl<Argument *> &ByValArguments,
 145                  SmallVectorImpl<Instruction *> &Returns,
 146                  SmallVectorImpl<Instruction *> &StackRestorePoints);
 147
 148   /// Calculate the allocation size of a given alloca. Returns 0 if the
 149   /// size can not be statically determined.
 150   uint64_t getStaticAllocaAllocationSize(const AllocaInst* AI);
 151
 152   /// Allocate space for all static allocas in \p StaticAllocas,
 153   /// replace allocas with pointers into the unsafe stack.
 154   ///
 155   /// \returns A pointer to the top of the unsafe stack after all unsafe static
 156   /// allocas are allocated.
 157   Value *moveStaticAllocasToUnsafeStack(IRBuilder<> &IRB, Function &F,
 158                                         ArrayRef<AllocaInst *> StaticAllocas,
 159                                         ArrayRef<Argument *> ByValArguments,
 160                                         Instruction *BasePointer,
 161                                         AllocaInst *StackGuardSlot);
 162
 163   /// Generate code to restore the stack after all stack restore points
 164   /// in \p StackRestorePoints.
 165   ///
 166   /// \returns A local variable in which to maintain the dynamic top of the
 167   /// unsafe stack if needed.
 168   AllocaInst *
 169   createStackRestorePoints(IRBuilder<> &IRB, Function &F,
 170                            ArrayRef<Instruction *> StackRestorePoints,
 171                            Value *StaticTop, bool NeedDynamicTop);
 172
 173   /// Replace all allocas in \p DynamicAllocas with code to allocate
 174   /// space dynamically on the unsafe stack and store the dynamic unsafe stack
 175   /// top to \p DynamicTop if non-null.
 176   void moveDynamicAllocasToUnsafeStack(Function &F, Value *UnsafeStackPtr,
 177                                        AllocaInst *DynamicTop,
 178                                        ArrayRef<AllocaInst *> DynamicAllocas);
 179
 180   bool IsSafeStackAlloca(const Value *AllocaPtr, uint64_t AllocaSize);
 181
 182   bool IsMemIntrinsicSafe(const MemIntrinsic *MI, const Use &U,
 183                           const Value *AllocaPtr, uint64_t AllocaSize);
 184   bool IsAccessSafe(Value *Addr, uint64_t Size, const Value *AllocaPtr,
 185                     uint64_t AllocaSize);
 186
 187   bool ShouldInlinePointerAddress(CallInst &CI);
 188   void TryInlinePointerAddress();
 189
 190 public:
 191   SafeStack(Function &F, const TargetLoweringBase &TL, const DataLayout &DL,
 192             DomTreeUpdater *DTU, ScalarEvolution &SE)
 193       : F(F), TL(TL), DL(DL), DTU(DTU), SE(SE),
 194         StackPtrTy(DL.getAllocaPtrType(F.getContext())),
 195         IntPtrTy(DL.getIntPtrType(F.getContext())),
 196         Int32Ty(Type::getInt32Ty(F.getContext())) {}
 197
 198   // Run the transformation on the associated function.
 199   // Returns whether the function was changed.
 200   bool run();
 201 };
 202
 203 constexpr Align SafeStack::StackAlignment;
 204
 205 uint64_t SafeStack::getStaticAllocaAllocationSize(const AllocaInst* AI) {
 206   uint64_t Size = DL.getTypeAllocSize(AI->getAllocatedType());
 207   if (AI->isArrayAllocation()) {
 208     auto C = dyn_cast<ConstantInt>(AI->getArraySize());
 209     if (!C)
 210       return 0;
 211     Size *= C->getZExtValue();
 212   }
 213   return Size;
 214 }
 215
 216 bool SafeStack::IsAccessSafe(Value *Addr, uint64_t AccessSize,
 217                              const Value *AllocaPtr, uint64_t AllocaSize) {
 218   const SCEV *AddrExpr = SE.getSCEV(Addr);
 219   const auto *Base = dyn_cast<SCEVUnknown>(SE.getPointerBase(AddrExpr));
 220   if (!Base || Base->getValue() != AllocaPtr) {
 221     LLVM_DEBUG(
 222         dbgs() << "[SafeStack] "
 223                << (isa<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")
 224                << *AllocaPtr << "\n"
 225                << "SCEV " << *AddrExpr << " not directly based on alloca\n");
 226     return false;
 227   }
 228
 229   const SCEV *Expr = SE.removePointerBase(AddrExpr);
 230   uint64_t BitWidth = SE.getTypeSizeInBits(Expr->getType());
 231   ConstantRange AccessStartRange = SE.getUnsignedRange(Expr);
 232   ConstantRange SizeRange =
 233       ConstantRange(APInt(BitWidth, 0), APInt(BitWidth, AccessSize));
 234   ConstantRange AccessRange = AccessStartRange.add(SizeRange);
 235   ConstantRange AllocaRange =
 236       ConstantRange(APInt(BitWidth, 0), APInt(BitWidth, AllocaSize));
 237   bool Safe = AllocaRange.contains(AccessRange);
 238
 239   LLVM_DEBUG(
 240       dbgs() << "[SafeStack] "
 241              << (isa<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")
 242              << *AllocaPtr << "\n"
 243              << "            Access " << *Addr << "\n"
 244              << "            SCEV " << *Expr
 245              << " U: " << SE.getUnsignedRange(Expr)
 246              << ", S: " << SE.getSignedRange(Expr) << "\n"
 247              << "            Range " << AccessRange << "\n"
 248              << "            AllocaRange " << AllocaRange << "\n"
 249              << "            " << (Safe ? "safe" : "unsafe") << "\n");
 250
 251   return Safe;
 252 }
 253
 254 bool SafeStack::IsMemIntrinsicSafe(const MemIntrinsic *MI, const Use &U,
 255                                    const Value *AllocaPtr,
 256                                    uint64_t AllocaSize) {
 257   if (auto MTI = dyn_cast<MemTransferInst>(MI)) {
 258     if (MTI->getRawSource() != U && MTI->getRawDest() != U)
 259       return true;
 260   } else {
 261     if (MI->getRawDest() != U)
 262       return true;
 263   }
 264
 265   const auto *Len = dyn_cast<ConstantInt>(MI->getLength());
 266   // Non-constant size => unsafe. FIXME: try SCEV getRange.
 267   if (!Len) return false;
 268   return IsAccessSafe(U, Len->getZExtValue(), AllocaPtr, AllocaSize);
 269 }
 270
 271 /// Check whether a given allocation must be put on the safe
 272 /// stack or not. The function analyzes all uses of AI and checks whether it is
 273 /// only accessed in a memory safe way (as decided statically).
 274 bool SafeStack::IsSafeStackAlloca(const Value *AllocaPtr, uint64_t AllocaSize) {
 275   // Go through all uses of this alloca and check whether all accesses to the
 276   // allocated object are statically known to be memory safe and, hence, the
 277   // object can be placed on the safe stack.
 278   SmallPtrSet<const Value *, 16> Visited;
 279   SmallVector<const Value *, 8> WorkList;
 280   WorkList.push_back(AllocaPtr);
 281
 282   // A DFS search through all uses of the alloca in bitcasts/PHI/GEPs/etc.
 283   while (!WorkList.empty()) {
 284     const Value *V = WorkList.pop_back_val();
 285     for (const Use &UI : V->uses()) {
 286       auto I = cast<const Instruction>(UI.getUser());
 287       assert(V == UI.get());
 288
 289       switch (I->getOpcode()) {
 290       case Instruction::Load:
 291         if (!IsAccessSafe(UI, DL.getTypeStoreSize(I->getType()), AllocaPtr,
 292                           AllocaSize))
 293           return false;
 294         break;
 295
 296       case Instruction::VAArg:
 297         // "va-arg" from a pointer is safe.
 298         break;
 299       case Instruction::Store:
 300         if (V == I->getOperand(0)) {
 301           // Stored the pointer - conservatively assume it may be unsafe.
 302           LLVM_DEBUG(dbgs()
 303                      << "[SafeStack] Unsafe alloca: " << *AllocaPtr
 304                      << "\n            store of address: " << *I << "\n");
 305           return false;
 306         }
 307
 308         if (!IsAccessSafe(UI, DL.getTypeStoreSize(I->getOperand(0)->getType()),
 309                           AllocaPtr, AllocaSize))
 310           return false;
 311         break;
 312
 313       case Instruction::Ret:
 314         // Information leak.
 315         return false;
 316
 317       case Instruction::Call:
 318       case Instruction::Invoke: {
 319         const CallBase &CS = *cast<CallBase>(I);
 320
 321         if (I->isLifetimeStartOrEnd())
 322           continue;
 323
 324         if (const MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) {
 325           if (!IsMemIntrinsicSafe(MI, UI, AllocaPtr, AllocaSize)) {
 326             LLVM_DEBUG(dbgs()
 327                        << "[SafeStack] Unsafe alloca: " << *AllocaPtr
 328                        << "\n            unsafe memintrinsic: " << *I << "\n");
 329             return false;
 330           }
 331           continue;
 332         }
 333
 334         // LLVM 'nocapture' attribute is only set for arguments whose address
 335         // is not stored, passed around, or used in any other non-trivial way.
 336         // We assume that passing a pointer to an object as a 'nocapture
 337         // readnone' argument is safe.
 338         // FIXME: a more precise solution would require an interprocedural
 339         // analysis here, which would look at all uses of an argument inside
 340         // the function being called.
 341         auto B = CS.arg_begin(), E = CS.arg_end();
 342         for (const auto *A = B; A != E; ++A)
 343           if (A->get() == V)
 344             if (!(CS.doesNotCapture(A - B) && (CS.doesNotAccessMemory(A - B) ||
 345                                                CS.doesNotAccessMemory()))) {
 346               LLVM_DEBUG(dbgs() << "[SafeStack] Unsafe alloca: " << *AllocaPtr
 347                                 << "\n            unsafe call: " << *I << "\n");
 348               return false;
 349             }
 350         continue;
 351       }
 352
 353       default:
 354         if (Visited.insert(I).second)
 355           WorkList.push_back(cast<const Instruction>(I));
 356       }
 357     }
 358   }
 359
 360   // All uses of the alloca are safe, we can place it on the safe stack.
 361   return true;
 362 }
 363
 364 Value *SafeStack::getStackGuard(IRBuilder<> &IRB, Function &F) {
 365   Value *StackGuardVar = TL.getIRStackGuard(IRB);
 366   Module *M = F.getParent();
 367
 368   if (!StackGuardVar) {
 369     TL.insertSSPDeclarations(*M);
 370     return IRB.CreateIntrinsic(Intrinsic::stackguard, {}, {});
 371   }
 372
 373   return IRB.CreateLoad(StackPtrTy, StackGuardVar, "StackGuard");
 374 }
 375
 376 void SafeStack::findInsts(Function &F,
 377                           SmallVectorImpl<AllocaInst *> &StaticAllocas,
 378                           SmallVectorImpl<AllocaInst *> &DynamicAllocas,
 379                           SmallVectorImpl<Argument *> &ByValArguments,
 380                           SmallVectorImpl<Instruction *> &Returns,
 381                           SmallVectorImpl<Instruction *> &StackRestorePoints) {
 382   for (Instruction &I : instructions(&F)) {
 383     if (auto AI = dyn_cast<AllocaInst>(&I)) {
 384       ++NumAllocas;
 385
 386       uint64_t Size = getStaticAllocaAllocationSize(AI);
 387       if (IsSafeStackAlloca(AI, Size))
 388         continue;
 389
 390       if (AI->isStaticAlloca()) {
 391         ++NumUnsafeStaticAllocas;
 392         StaticAllocas.push_back(AI);
 393       } else {
 394         ++NumUnsafeDynamicAllocas;
 395         DynamicAllocas.push_back(AI);
 396       }
 397     } else if (auto RI = dyn_cast<ReturnInst>(&I)) {
 398       if (CallInst *CI = I.getParent()->getTerminatingMustTailCall())
 399         Returns.push_back(CI);
 400       else
 401         Returns.push_back(RI);
 402     } else if (auto CI = dyn_cast<CallInst>(&I)) {
 403       // setjmps require stack restore.
 404       if (CI->getCalledFunction() && CI->canReturnTwice())
 405         StackRestorePoints.push_back(CI);
 406     } else if (auto LP = dyn_cast<LandingPadInst>(&I)) {
 407       // Exception landing pads require stack restore.
 408       StackRestorePoints.push_back(LP);
 409     } else if (auto II = dyn_cast<IntrinsicInst>(&I)) {
 410       if (II->getIntrinsicID() == Intrinsic::gcroot)
 411         report_fatal_error(
 412             "gcroot intrinsic not compatible with safestack attribute");
 413     }
 414   }
 415   for (Argument &Arg : F.args()) {
 416     if (!Arg.hasByValAttr())
 417       continue;
 418     uint64_t Size = DL.getTypeStoreSize(Arg.getParamByValType());
 419     if (IsSafeStackAlloca(&Arg, Size))
 420       continue;
 421
 422     ++NumUnsafeByValArguments;
 423     ByValArguments.push_back(&Arg);
 424   }
 425 }
 426
 427 AllocaInst *
 428 SafeStack::createStackRestorePoints(IRBuilder<> &IRB, Function &F,
 429                                     ArrayRef<Instruction *> StackRestorePoints,
 430                                     Value *StaticTop, bool NeedDynamicTop) {
 431   assert(StaticTop && "The stack top isn't set.");
 432
 433   if (StackRestorePoints.empty())
 434     return nullptr;
 435
 436   // We need the current value of the shadow stack pointer to restore
 437   // after longjmp or exception catching.
 438
 439   // FIXME: On some platforms this could be handled by the longjmp/exception
 440   // runtime itself.
 441
 442   AllocaInst *DynamicTop = nullptr;
 443   if (NeedDynamicTop) {
 444     // If we also have dynamic alloca's, the stack pointer value changes
 445     // throughout the function. For now we store it in an alloca.
 446     DynamicTop = IRB.CreateAlloca(StackPtrTy, /*ArraySize=*/nullptr,
 447                                   "unsafe_stack_dynamic_ptr");
 448     IRB.CreateStore(StaticTop, DynamicTop);
 449   }
 450
 451   // Restore current stack pointer after longjmp/exception catch.
 452   for (Instruction *I : StackRestorePoints) {
 453     ++NumUnsafeStackRestorePoints;
 454
 455     IRB.SetInsertPoint(I->getNextNode());
 456     Value *CurrentTop =
 457         DynamicTop ? IRB.CreateLoad(StackPtrTy, DynamicTop) : StaticTop;
 458     IRB.CreateStore(CurrentTop, UnsafeStackPtr);
 459   }
 460
 461   return DynamicTop;
 462 }
 463
 464 void SafeStack::checkStackGuard(IRBuilder<> &IRB, Function &F, Instruction &RI,
 465                                 AllocaInst *StackGuardSlot, Value *StackGuard) {
 466   Value *V = IRB.CreateLoad(StackPtrTy, StackGuardSlot);
 467   Value *Cmp = IRB.CreateICmpNE(StackGuard, V);
 468
 469   auto SuccessProb = BranchProbabilityInfo::getBranchProbStackProtector(true);
 470   auto FailureProb = BranchProbabilityInfo::getBranchProbStackProtector(false);
 471   MDNode *Weights = MDBuilder(F.getContext())
 472                         .createBranchWeights(SuccessProb.getNumerator(),
 473                                              FailureProb.getNumerator());
 474   Instruction *CheckTerm =
 475       SplitBlockAndInsertIfThen(Cmp, &RI, /* Unreachable */ true, Weights, DTU);
 476   IRBuilder<> IRBFail(CheckTerm);
 477   // FIXME: respect -fsanitize-trap / -ftrap-function here?
 478   FunctionCallee StackChkFail =
 479       F.getParent()->getOrInsertFunction("__stack_chk_fail", IRB.getVoidTy());
 480   IRBFail.CreateCall(StackChkFail, {});
 481 }
 482
 483 /// We explicitly compute and set the unsafe stack layout for all unsafe
 484 /// static alloca instructions. We save the unsafe "base pointer" in the
 485 /// prologue into a local variable and restore it in the epilogue.
 486 Value *SafeStack::moveStaticAllocasToUnsafeStack(
 487     IRBuilder<> &IRB, Function &F, ArrayRef<AllocaInst *> StaticAllocas,
 488     ArrayRef<Argument *> ByValArguments, Instruction *BasePointer,
 489     AllocaInst *StackGuardSlot) {
 490   if (StaticAllocas.empty() && ByValArguments.empty())
 491     return BasePointer;
 492
 493   DIBuilder DIB(*F.getParent());
 494
 495   StackLifetime SSC(F, StaticAllocas, StackLifetime::LivenessType::May);
 496   static const StackLifetime::LiveRange NoColoringRange(1, true);
 497   if (ClColoring)
 498     SSC.run();
 499
 500   for (const auto *I : SSC.getMarkers()) {
 501     auto *Op = dyn_cast<Instruction>(I->getOperand(1));
 502     const_cast<IntrinsicInst *>(I)->eraseFromParent();
 503     // Remove the operand bitcast, too, if it has no more uses left.
 504     if (Op && Op->use_empty())
 505       Op->eraseFromParent();
 506   }
 507
 508   // Unsafe stack always grows down.
 509   StackLayout SSL(StackAlignment);
 510   if (StackGuardSlot) {
 511     Type *Ty = StackGuardSlot->getAllocatedType();
 512     Align Align = std::max(DL.getPrefTypeAlign(Ty), StackGuardSlot->getAlign());
 513     SSL.addObject(StackGuardSlot, getStaticAllocaAllocationSize(StackGuardSlot),
 514                   Align, SSC.getFullLiveRange());
 515   }
 516
 517   for (Argument *Arg : ByValArguments) {
 518     Type *Ty = Arg->getParamByValType();
 519     uint64_t Size = DL.getTypeStoreSize(Ty);
 520     if (Size == 0)
 521       Size = 1; // Don't create zero-sized stack objects.
 522
 523     // Ensure the object is properly aligned.
 524     Align Align = DL.getPrefTypeAlign(Ty);
 525     if (auto A = Arg->getParamAlign())
 526       Align = std::max(Align, *A);
 527     SSL.addObject(Arg, Size, Align, SSC.getFullLiveRange());
 528   }
 529
 530   for (AllocaInst *AI : StaticAllocas) {
 531     Type *Ty = AI->getAllocatedType();
 532     uint64_t Size = getStaticAllocaAllocationSize(AI);
 533     if (Size == 0)
 534       Size = 1; // Don't create zero-sized stack objects.
 535
 536     // Ensure the object is properly aligned.
 537     Align Align = std::max(DL.getPrefTypeAlign(Ty), AI->getAlign());
 538
 539     SSL.addObject(AI, Size, Align,
 540                   ClColoring ? SSC.getLiveRange(AI) : NoColoringRange);
 541   }
 542
 543   SSL.computeLayout();
 544   Align FrameAlignment = SSL.getFrameAlignment();
 545
 546   // FIXME: tell SSL that we start at a less-then-MaxAlignment aligned location
 547   // (AlignmentSkew).
 548   if (FrameAlignment > StackAlignment) {
 549     // Re-align the base pointer according to the max requested alignment.
 550     IRB.SetInsertPoint(BasePointer->getNextNode());
 551     BasePointer = cast<Instruction>(IRB.CreateIntToPtr(
 552         IRB.CreateAnd(
 553             IRB.CreatePtrToInt(BasePointer, IntPtrTy),
 554             ConstantInt::get(IntPtrTy, ~(FrameAlignment.value() - 1))),
 555         StackPtrTy));
 556   }
 557
 558   IRB.SetInsertPoint(BasePointer->getNextNode());
 559
 560   if (StackGuardSlot) {
 561     unsigned Offset = SSL.getObjectOffset(StackGuardSlot);
 562     Value *Off =
 563         IRB.CreatePtrAdd(BasePointer, ConstantInt::get(Int32Ty, -Offset));
 564     Value *NewAI =
 565         IRB.CreateBitCast(Off, StackGuardSlot->getType(), "StackGuardSlot");
 566
 567     // Replace alloc with the new location.
 568     StackGuardSlot->replaceAllUsesWith(NewAI);
 569     StackGuardSlot->eraseFromParent();
 570   }
 571
 572   for (Argument *Arg : ByValArguments) {
 573     unsigned Offset = SSL.getObjectOffset(Arg);
 574     MaybeAlign Align(SSL.getObjectAlignment(Arg));
 575     Type *Ty = Arg->getParamByValType();
 576
 577     uint64_t Size = DL.getTypeStoreSize(Ty);
 578     if (Size == 0)
 579       Size = 1; // Don't create zero-sized stack objects.
 580
 581     Value *Off =
 582         IRB.CreatePtrAdd(BasePointer, ConstantInt::get(Int32Ty, -Offset));
 583     Value *NewArg = IRB.CreateBitCast(Off, Arg->getType(),
 584                                       Arg->getName() + ".unsafe-byval");
 585
 586     // Replace alloc with the new location.
 587     replaceDbgDeclare(Arg, BasePointer, DIB, DIExpression::ApplyOffset,
 588                       -Offset);
 589     Arg->replaceAllUsesWith(NewArg);
 590     IRB.SetInsertPoint(cast<Instruction>(NewArg)->getNextNode());
 591     IRB.CreateMemCpy(Off, Align, Arg, Arg->getParamAlign(), Size);
 592   }
 593
 594   // Allocate space for every unsafe static AllocaInst on the unsafe stack.
 595   for (AllocaInst *AI : StaticAllocas) {
 596     IRB.SetInsertPoint(AI);
 597     unsigned Offset = SSL.getObjectOffset(AI);
 598
 599     replaceDbgDeclare(AI, BasePointer, DIB, DIExpression::ApplyOffset, -Offset);
 600     replaceDbgValueForAlloca(AI, BasePointer, DIB, -Offset);
 601
 602     // Replace uses of the alloca with the new location.
 603     // Insert address calculation close to each use to work around PR27844.
 604     std::string Name = std::string(AI->getName()) + ".unsafe";
 605     while (!AI->use_empty()) {
 606       Use &U = *AI->use_begin();
 607       Instruction *User = cast<Instruction>(U.getUser());
 608
 609       Instruction *InsertBefore;
 610       if (auto *PHI = dyn_cast<PHINode>(User))
 611         InsertBefore = PHI->getIncomingBlock(U)->getTerminator();
 612       else
 613         InsertBefore = User;
 614
 615       IRBuilder<> IRBUser(InsertBefore);
 616       Value *Off =
 617           IRBUser.CreatePtrAdd(BasePointer, ConstantInt::get(Int32Ty, -Offset));
 618       Value *Replacement =
 619           IRBUser.CreateAddrSpaceCast(Off, AI->getType(), Name);
 620
 621       if (auto *PHI = dyn_cast<PHINode>(User))
 622         // PHI nodes may have multiple incoming edges from the same BB (why??),
 623         // all must be updated at once with the same incoming value.
 624         PHI->setIncomingValueForBlock(PHI->getIncomingBlock(U), Replacement);
 625       else
 626         U.set(Replacement);
 627     }
 628
 629     AI->eraseFromParent();
 630   }
 631
 632   // Re-align BasePointer so that our callees would see it aligned as
 633   // expected.
 634   // FIXME: no need to update BasePointer in leaf functions.
 635   unsigned FrameSize = alignTo(SSL.getFrameSize(), StackAlignment);
 636
 637   MDBuilder MDB(F.getContext());
 638   SmallVector<Metadata *, 2> Data;
 639   Data.push_back(MDB.createString("unsafe-stack-size"));
 640   Data.push_back(MDB.createConstant(ConstantInt::get(Int32Ty, FrameSize)));
 641   MDNode *MD = MDTuple::get(F.getContext(), Data);
 642   F.setMetadata(LLVMContext::MD_annotation, MD);
 643
 644   // Update shadow stack pointer in the function epilogue.
 645   IRB.SetInsertPoint(BasePointer->getNextNode());
 646
 647   Value *StaticTop =
 648       IRB.CreatePtrAdd(BasePointer, ConstantInt::get(Int32Ty, -FrameSize),
 649                        "unsafe_stack_static_top");
 650   IRB.CreateStore(StaticTop, UnsafeStackPtr);
 651   return StaticTop;
 652 }
 653
 654 void SafeStack::moveDynamicAllocasToUnsafeStack(
 655     Function &F, Value *UnsafeStackPtr, AllocaInst *DynamicTop,
 656     ArrayRef<AllocaInst *> DynamicAllocas) {
 657   DIBuilder DIB(*F.getParent());
 658
 659   for (AllocaInst *AI : DynamicAllocas) {
 660     IRBuilder<> IRB(AI);
 661
 662     // Compute the new SP value (after AI).
 663     Value *ArraySize = AI->getArraySize();
 664     if (ArraySize->getType() != IntPtrTy)
 665       ArraySize = IRB.CreateIntCast(ArraySize, IntPtrTy, false);
 666
 667     Type *Ty = AI->getAllocatedType();
 668     uint64_t TySize = DL.getTypeAllocSize(Ty);
 669     Value *Size = IRB.CreateMul(ArraySize, ConstantInt::get(IntPtrTy, TySize));
 670
 671     Value *SP = IRB.CreatePtrToInt(IRB.CreateLoad(StackPtrTy, UnsafeStackPtr),
 672                                    IntPtrTy);
 673     SP = IRB.CreateSub(SP, Size);
 674
 675     // Align the SP value to satisfy the AllocaInst, type and stack alignments.
 676     auto Align = std::max(std::max(DL.getPrefTypeAlign(Ty), AI->getAlign()),
 677                           StackAlignment);
 678
 679     Value *NewTop = IRB.CreateIntToPtr(
 680         IRB.CreateAnd(SP,
 681                       ConstantInt::get(IntPtrTy, ~uint64_t(Align.value() - 1))),
 682         StackPtrTy);
 683
 684     // Save the stack pointer.
 685     IRB.CreateStore(NewTop, UnsafeStackPtr);
 686     if (DynamicTop)
 687       IRB.CreateStore(NewTop, DynamicTop);
 688
 689     Value *NewAI = IRB.CreatePointerCast(NewTop, AI->getType());
 690     if (AI->hasName() && isa<Instruction>(NewAI))
 691       NewAI->takeName(AI);
 692
 693     replaceDbgDeclare(AI, NewAI, DIB, DIExpression::ApplyOffset, 0);
 694     AI->replaceAllUsesWith(NewAI);
 695     AI->eraseFromParent();
 696   }
 697
 698   if (!DynamicAllocas.empty()) {
 699     // Now go through the instructions again, replacing stacksave/stackrestore.
 700     for (Instruction &I : llvm::make_early_inc_range(instructions(&F))) {
 701       auto *II = dyn_cast<IntrinsicInst>(&I);
 702       if (!II)
 703         continue;
 704
 705       if (II->getIntrinsicID() == Intrinsic::stacksave) {
 706         IRBuilder<> IRB(II);
 707         Instruction *LI = IRB.CreateLoad(StackPtrTy, UnsafeStackPtr);
 708         LI->takeName(II);
 709         II->replaceAllUsesWith(LI);
 710         II->eraseFromParent();
 711       } else if (II->getIntrinsicID() == Intrinsic::stackrestore) {
 712         IRBuilder<> IRB(II);
 713         Instruction *SI = IRB.CreateStore(II->getArgOperand(0), UnsafeStackPtr);
 714         SI->takeName(II);
 715         assert(II->use_empty());
 716         II->eraseFromParent();
 717       }
 718     }
 719   }
 720 }
 721
 722 bool SafeStack::ShouldInlinePointerAddress(CallInst &CI) {
 723   Function *Callee = CI.getCalledFunction();
 724   if (CI.hasFnAttr(Attribute::AlwaysInline) &&
 725       isInlineViable(*Callee).isSuccess())
 726     return true;
 727   if (Callee->isInterposable() || Callee->hasFnAttribute(Attribute::NoInline) ||
 728       CI.isNoInline())
 729     return false;
 730   return true;
 731 }
 732
 733 void SafeStack::TryInlinePointerAddress() {
 734   auto *CI = dyn_cast<CallInst>(UnsafeStackPtr);
 735   if (!CI)
 736     return;
 737
 738   if(F.hasOptNone())
 739     return;
 740
 741   Function *Callee = CI->getCalledFunction();
 742   if (!Callee || Callee->isDeclaration())
 743     return;
 744
 745   if (!ShouldInlinePointerAddress(*CI))
 746     return;
 747
 748   InlineFunctionInfo IFI;
 749   InlineFunction(*CI, IFI);
 750 }
 751
 752 bool SafeStack::run() {
 753   assert(F.hasFnAttribute(Attribute::SafeStack) &&
 754          "Can't run SafeStack on a function without the attribute");
 755   assert(!F.isDeclaration() && "Can't run SafeStack on a function declaration");
 756
 757   ++NumFunctions;
 758
 759   SmallVector<AllocaInst *, 16> StaticAllocas;
 760   SmallVector<AllocaInst *, 4> DynamicAllocas;
 761   SmallVector<Argument *, 4> ByValArguments;
 762   SmallVector<Instruction *, 4> Returns;
 763
 764   // Collect all points where stack gets unwound and needs to be restored
 765   // This is only necessary because the runtime (setjmp and unwind code) is
 766   // not aware of the unsafe stack and won't unwind/restore it properly.
 767   // To work around this problem without changing the runtime, we insert
 768   // instrumentation to restore the unsafe stack pointer when necessary.
 769   SmallVector<Instruction *, 4> StackRestorePoints;
 770
 771   // Find all static and dynamic alloca instructions that must be moved to the
 772   // unsafe stack, all return instructions and stack restore points.
 773   findInsts(F, StaticAllocas, DynamicAllocas, ByValArguments, Returns,
 774             StackRestorePoints);
 775
 776   if (StaticAllocas.empty() && DynamicAllocas.empty() &&
 777       ByValArguments.empty() && StackRestorePoints.empty())
 778     return false; // Nothing to do in this function.
 779
 780   if (!StaticAllocas.empty() || !DynamicAllocas.empty() ||
 781       !ByValArguments.empty())
 782     ++NumUnsafeStackFunctions; // This function has the unsafe stack.
 783
 784   if (!StackRestorePoints.empty())
 785     ++NumUnsafeStackRestorePointsFunctions;
 786
 787   IRBuilder<> IRB(&F.front(), F.begin()->getFirstInsertionPt());
 788   // Calls must always have a debug location, or else inlining breaks. So
 789   // we explicitly set a artificial debug location here.
 790   if (DISubprogram *SP = F.getSubprogram())
 791     IRB.SetCurrentDebugLocation(
 792         DILocation::get(SP->getContext(), SP->getScopeLine(), 0, SP));
 793   if (SafeStackUsePointerAddress) {
 794     FunctionCallee Fn = F.getParent()->getOrInsertFunction(
 795         "__safestack_pointer_address", IRB.getPtrTy(0));
 796     UnsafeStackPtr = IRB.CreateCall(Fn);
 797   } else {
 798     UnsafeStackPtr = TL.getSafeStackPointerLocation(IRB);
 799   }
 800
 801   // Load the current stack pointer (we'll also use it as a base pointer).
 802   // FIXME: use a dedicated register for it ?
 803   Instruction *BasePointer =
 804       IRB.CreateLoad(StackPtrTy, UnsafeStackPtr, false, "unsafe_stack_ptr");
 805   assert(BasePointer->getType() == StackPtrTy);
 806
 807   AllocaInst *StackGuardSlot = nullptr;
 808   // FIXME: implement weaker forms of stack protector.
 809   if (F.hasFnAttribute(Attribute::StackProtect) ||
 810       F.hasFnAttribute(Attribute::StackProtectStrong) ||
 811       F.hasFnAttribute(Attribute::StackProtectReq)) {
 812     Value *StackGuard = getStackGuard(IRB, F);
 813     StackGuardSlot = IRB.CreateAlloca(StackPtrTy, nullptr);
 814     IRB.CreateStore(StackGuard, StackGuardSlot);
 815
 816     for (Instruction *RI : Returns) {
 817       IRBuilder<> IRBRet(RI);
 818       checkStackGuard(IRBRet, F, *RI, StackGuardSlot, StackGuard);
 819     }
 820   }
 821
 822   // The top of the unsafe stack after all unsafe static allocas are
 823   // allocated.
 824   Value *StaticTop = moveStaticAllocasToUnsafeStack(
 825       IRB, F, StaticAllocas, ByValArguments, BasePointer, StackGuardSlot);
 826
 827   // Safe stack object that stores the current unsafe stack top. It is updated
 828   // as unsafe dynamic (non-constant-sized) allocas are allocated and freed.
 829   // This is only needed if we need to restore stack pointer after longjmp
 830   // or exceptions, and we have dynamic allocations.
 831   // FIXME: a better alternative might be to store the unsafe stack pointer
 832   // before setjmp / invoke instructions.
 833   AllocaInst *DynamicTop = createStackRestorePoints(
 834       IRB, F, StackRestorePoints, StaticTop, !DynamicAllocas.empty());
 835
 836   // Handle dynamic allocas.
 837   moveDynamicAllocasToUnsafeStack(F, UnsafeStackPtr, DynamicTop,
 838                                   DynamicAllocas);
 839
 840   // Restore the unsafe stack pointer before each return.
 841   for (Instruction *RI : Returns) {
 842     IRB.SetInsertPoint(RI);
 843     IRB.CreateStore(BasePointer, UnsafeStackPtr);
 844   }
 845
 846   TryInlinePointerAddress();
 847
 848   LLVM_DEBUG(dbgs() << "[SafeStack]     safestack applied\n");
 849   return true;
 850 }
 851
 852 class SafeStackLegacyPass : public FunctionPass {
 853   const TargetMachine *TM = nullptr;
 854
 855 public:
 856   static char ID; // Pass identification, replacement for typeid..
 857
 858   SafeStackLegacyPass() : FunctionPass(ID) {
 859     initializeSafeStackLegacyPassPass(*PassRegistry::getPassRegistry());
 860   }
 861
 862   void getAnalysisUsage(AnalysisUsage &AU) const override {
 863     AU.addRequired<TargetPassConfig>();
 864     AU.addRequired<TargetLibraryInfoWrapperPass>();
 865     AU.addRequired<AssumptionCacheTracker>();
 866     AU.addPreserved<DominatorTreeWrapperPass>();
 867   }
 868
 869   bool runOnFunction(Function &F) override {
 870     LLVM_DEBUG(dbgs() << "[SafeStack] Function: " << F.getName() << "\n");
 871
 872     if (!F.hasFnAttribute(Attribute::SafeStack)) {
 873       LLVM_DEBUG(dbgs() << "[SafeStack]     safestack is not requested"
 874                            " for this function\n");
 875       return false;
 876     }
 877
 878     if (F.isDeclaration()) {
 879       LLVM_DEBUG(dbgs() << "[SafeStack]     function definition"
 880                            " is not available\n");
 881       return false;
 882     }
 883
 884     TM = &getAnalysis<TargetPassConfig>().getTM<TargetMachine>();
 885     auto *TL = TM->getSubtargetImpl(F)->getTargetLowering();
 886     if (!TL)
 887       report_fatal_error("TargetLowering instance is required");
 888
 889     auto *DL = &F.getDataLayout();
 890     auto &TLI = getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F);
 891     auto &ACT = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
 892
 893     // Compute DT and LI only for functions that have the attribute.
 894     // This is only useful because the legacy pass manager doesn't let us
 895     // compute analyzes lazily.
 896
 897     DominatorTree *DT;
 898     bool ShouldPreserveDominatorTree;
 899     std::optional<DominatorTree> LazilyComputedDomTree;
 900
 901     // Do we already have a DominatorTree available from the previous pass?
 902     // Note that we should *NOT* require it, to avoid the case where we end up
 903     // not needing it, but the legacy PM would have computed it for us anyways.
 904     if (auto *DTWP = getAnalysisIfAvailable<DominatorTreeWrapperPass>()) {
 905       DT = &DTWP->getDomTree();
 906       ShouldPreserveDominatorTree = true;
 907     } else {
 908       // Otherwise, we need to compute it.
 909       LazilyComputedDomTree.emplace(F);
 910       DT = &*LazilyComputedDomTree;
 911       ShouldPreserveDominatorTree = false;
 912     }
 913
 914     // Likewise, lazily compute loop info.
 915     LoopInfo LI(*DT);
 916
 917     DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Lazy);
 918
 919     ScalarEvolution SE(F, TLI, ACT, *DT, LI);
 920
 921     return SafeStack(F, *TL, *DL, ShouldPreserveDominatorTree ? &DTU : nullptr,
 922                      SE)
 923         .run();
 924   }
 925 };
 926
 927 } // end anonymous namespace
 928
 929 PreservedAnalyses SafeStackPass::run(Function &F,
 930                                      FunctionAnalysisManager &FAM) {
 931   LLVM_DEBUG(dbgs() << "[SafeStack] Function: " << F.getName() << "\n");
 932
 933   if (!F.hasFnAttribute(Attribute::SafeStack)) {
 934     LLVM_DEBUG(dbgs() << "[SafeStack]     safestack is not requested"
 935                          " for this function\n");
 936     return PreservedAnalyses::all();
 937   }
 938
 939   if (F.isDeclaration()) {
 940     LLVM_DEBUG(dbgs() << "[SafeStack]     function definition"
 941                          " is not available\n");
 942     return PreservedAnalyses::all();
 943   }
 944
 945   auto *TL = TM->getSubtargetImpl(F)->getTargetLowering();
 946   if (!TL)
 947     report_fatal_error("TargetLowering instance is required");
 948
 949   auto &DL = F.getDataLayout();
 950
 951   // preserve DominatorTree
 952   auto &DT = FAM.getResult<DominatorTreeAnalysis>(F);
 953   auto &SE = FAM.getResult<ScalarEvolutionAnalysis>(F);
 954   DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Lazy);
 955
 956   bool Changed = SafeStack(F, *TL, DL, &DTU, SE).run();
 957
 958   if (!Changed)
 959     return PreservedAnalyses::all();
 960   PreservedAnalyses PA;
 961   PA.preserve<DominatorTreeAnalysis>();
 962   return PA;
 963 }
 964
 965 char SafeStackLegacyPass::ID = 0;
 966
 967 INITIALIZE_PASS_BEGIN(SafeStackLegacyPass, DEBUG_TYPE,
 968                       "Safe Stack instrumentation pass", false, false)
 969 INITIALIZE_PASS_DEPENDENCY(TargetPassConfig)
 970 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
 971 INITIALIZE_PASS_END(SafeStackLegacyPass, DEBUG_TYPE,
 972                     "Safe Stack instrumentation pass", false, false)
 973
 974 FunctionPass *llvm::createSafeStackPass() { return new SafeStackLegacyPass(); }