lib/CodeGen/SafeStack.cpp

   1 //===- SafeStack.cpp - Safe Stack Insertion -------------------------------===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is distributed under the University of Illinois Open Source
   6 // License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9 //
  10 // This pass splits the stack into the safe stack (kept as-is for LLVM backend)
  11 // and the unsafe stack (explicitly allocated and managed through the runtime
  12 // support library).
  13 //
  14 // http://clang.llvm.org/docs/SafeStack.html
  15 //
  16 //===----------------------------------------------------------------------===//
  17
  18 #include "SafeStackColoring.h"
  19 #include "SafeStackLayout.h"
  20 #include "llvm/ADT/APInt.h"
  21 #include "llvm/ADT/ArrayRef.h"
  22 #include "llvm/ADT/SmallPtrSet.h"
  23 #include "llvm/ADT/SmallVector.h"
  24 #include "llvm/ADT/Statistic.h"
  25 #include "llvm/Analysis/AssumptionCache.h"
  26 #include "llvm/Analysis/BranchProbabilityInfo.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/TargetLibraryInfo.h"
  32 #include "llvm/Transforms/Utils/Local.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/CallSite.h"
  39 #include "llvm/IR/ConstantRange.h"
  40 #include "llvm/IR/Constants.h"
  41 #include "llvm/IR/DIBuilder.h"
  42 #include "llvm/IR/DataLayout.h"
  43 #include "llvm/IR/DerivedTypes.h"
  44 #include "llvm/IR/Dominators.h"
  45 #include "llvm/IR/Function.h"
  46 #include "llvm/IR/IRBuilder.h"
  47 #include "llvm/IR/InstIterator.h"
  48 #include "llvm/IR/Instruction.h"
  49 #include "llvm/IR/Instructions.h"
  50 #include "llvm/IR/IntrinsicInst.h"
  51 #include "llvm/IR/Intrinsics.h"
  52 #include "llvm/IR/MDBuilder.h"
  53 #include "llvm/IR/Module.h"
  54 #include "llvm/IR/Type.h"
  55 #include "llvm/IR/Use.h"
  56 #include "llvm/IR/User.h"
  57 #include "llvm/IR/Value.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 <algorithm>
  68 #include <cassert>
  69 #include <cstdint>
  70 #include <string>
  71 #include <utility>
  72
  73 using namespace llvm;
  74 using namespace llvm::safestack;
  75
  76 #define DEBUG_TYPE "safe-stack"
  77
  78 namespace llvm {
  79
  80 STATISTIC(NumFunctions, "Total number of functions");
  81 STATISTIC(NumUnsafeStackFunctions, "Number of functions with unsafe stack");
  82 STATISTIC(NumUnsafeStackRestorePointsFunctions,
  83           "Number of functions that use setjmp or exceptions");
  84
  85 STATISTIC(NumAllocas, "Total number of allocas");
  86 STATISTIC(NumUnsafeStaticAllocas, "Number of unsafe static allocas");
  87 STATISTIC(NumUnsafeDynamicAllocas, "Number of unsafe dynamic allocas");
  88 STATISTIC(NumUnsafeByValArguments, "Number of unsafe byval arguments");
  89 STATISTIC(NumUnsafeStackRestorePoints, "Number of setjmps and landingpads");
  90
  91 } // namespace llvm
  92
  93 /// Use __safestack_pointer_address even if the platform has a faster way of
  94 /// access safe stack pointer.
  95 static cl::opt<bool>
  96     SafeStackUsePointerAddress("safestack-use-pointer-address",
  97                                   cl::init(false), cl::Hidden);
  98
  99
 100 namespace {
 101
 102 /// Rewrite an SCEV expression for a memory access address to an expression that
 103 /// represents offset from the given alloca.
 104 ///
 105 /// The implementation simply replaces all mentions of the alloca with zero.
 106 class AllocaOffsetRewriter : public SCEVRewriteVisitor<AllocaOffsetRewriter> {
 107   const Value *AllocaPtr;
 108
 109 public:
 110   AllocaOffsetRewriter(ScalarEvolution &SE, const Value *AllocaPtr)
 111       : SCEVRewriteVisitor(SE), AllocaPtr(AllocaPtr) {}
 112
 113   const SCEV *visitUnknown(const SCEVUnknown *Expr) {
 114     if (Expr->getValue() == AllocaPtr)
 115       return SE.getZero(Expr->getType());
 116     return Expr;
 117   }
 118 };
 119
 120 /// The SafeStack pass splits the stack of each function into the safe
 121 /// stack, which is only accessed through memory safe dereferences (as
 122 /// determined statically), and the unsafe stack, which contains all
 123 /// local variables that are accessed in ways that we can't prove to
 124 /// be safe.
 125 class SafeStack {
 126   Function &F;
 127   const TargetLoweringBase &TL;
 128   const DataLayout &DL;
 129   ScalarEvolution &SE;
 130
 131   Type *StackPtrTy;
 132   Type *IntPtrTy;
 133   Type *Int32Ty;
 134   Type *Int8Ty;
 135
 136   Value *UnsafeStackPtr = nullptr;
 137
 138   /// Unsafe stack alignment. Each stack frame must ensure that the stack is
 139   /// aligned to this value. We need to re-align the unsafe stack if the
 140   /// alignment of any object on the stack exceeds this value.
 141   ///
 142   /// 16 seems like a reasonable upper bound on the alignment of objects that we
 143   /// might expect to appear on the stack on most common targets.
 144   enum { StackAlignment = 16 };
 145
 146   /// Return the value of the stack canary.
 147   Value *getStackGuard(IRBuilder<> &IRB, Function &F);
 148
 149   /// Load stack guard from the frame and check if it has changed.
 150   void checkStackGuard(IRBuilder<> &IRB, Function &F, ReturnInst &RI,
 151                        AllocaInst *StackGuardSlot, Value *StackGuard);
 152
 153   /// Find all static allocas, dynamic allocas, return instructions and
 154   /// stack restore points (exception unwind blocks and setjmp calls) in the
 155   /// given function and append them to the respective vectors.
 156   void findInsts(Function &F, SmallVectorImpl<AllocaInst *> &StaticAllocas,
 157                  SmallVectorImpl<AllocaInst *> &DynamicAllocas,
 158                  SmallVectorImpl<Argument *> &ByValArguments,
 159                  SmallVectorImpl<ReturnInst *> &Returns,
 160                  SmallVectorImpl<Instruction *> &StackRestorePoints);
 161
 162   /// Calculate the allocation size of a given alloca. Returns 0 if the
 163   /// size can not be statically determined.
 164   uint64_t getStaticAllocaAllocationSize(const AllocaInst* AI);
 165
 166   /// Allocate space for all static allocas in \p StaticAllocas,
 167   /// replace allocas with pointers into the unsafe stack and generate code to
 168   /// restore the stack pointer before all return instructions in \p Returns.
 169   ///
 170   /// \returns A pointer to the top of the unsafe stack after all unsafe static
 171   /// allocas are allocated.
 172   Value *moveStaticAllocasToUnsafeStack(IRBuilder<> &IRB, Function &F,
 173                                         ArrayRef<AllocaInst *> StaticAllocas,
 174                                         ArrayRef<Argument *> ByValArguments,
 175                                         ArrayRef<ReturnInst *> Returns,
 176                                         Instruction *BasePointer,
 177                                         AllocaInst *StackGuardSlot);
 178
 179   /// Generate code to restore the stack after all stack restore points
 180   /// in \p StackRestorePoints.
 181   ///
 182   /// \returns A local variable in which to maintain the dynamic top of the
 183   /// unsafe stack if needed.
 184   AllocaInst *
 185   createStackRestorePoints(IRBuilder<> &IRB, Function &F,
 186                            ArrayRef<Instruction *> StackRestorePoints,
 187                            Value *StaticTop, bool NeedDynamicTop);
 188
 189   /// Replace all allocas in \p DynamicAllocas with code to allocate
 190   /// space dynamically on the unsafe stack and store the dynamic unsafe stack
 191   /// top to \p DynamicTop if non-null.
 192   void moveDynamicAllocasToUnsafeStack(Function &F, Value *UnsafeStackPtr,
 193                                        AllocaInst *DynamicTop,
 194                                        ArrayRef<AllocaInst *> DynamicAllocas);
 195
 196   bool IsSafeStackAlloca(const Value *AllocaPtr, uint64_t AllocaSize);
 197
 198   bool IsMemIntrinsicSafe(const MemIntrinsic *MI, const Use &U,
 199                           const Value *AllocaPtr, uint64_t AllocaSize);
 200   bool IsAccessSafe(Value *Addr, uint64_t Size, const Value *AllocaPtr,
 201                     uint64_t AllocaSize);
 202
 203   bool ShouldInlinePointerAddress(CallSite &CS);
 204   void TryInlinePointerAddress();
 205
 206 public:
 207   SafeStack(Function &F, const TargetLoweringBase &TL, const DataLayout &DL,
 208             ScalarEvolution &SE)
 209       : F(F), TL(TL), DL(DL), SE(SE),
 210         StackPtrTy(Type::getInt8PtrTy(F.getContext())),
 211         IntPtrTy(DL.getIntPtrType(F.getContext())),
 212         Int32Ty(Type::getInt32Ty(F.getContext())),
 213         Int8Ty(Type::getInt8Ty(F.getContext())) {}
 214
 215   // Run the transformation on the associated function.
 216   // Returns whether the function was changed.
 217   bool run();
 218 };
 219
 220 uint64_t SafeStack::getStaticAllocaAllocationSize(const AllocaInst* AI) {
 221   uint64_t Size = DL.getTypeAllocSize(AI->getAllocatedType());
 222   if (AI->isArrayAllocation()) {
 223     auto C = dyn_cast<ConstantInt>(AI->getArraySize());
 224     if (!C)
 225       return 0;
 226     Size *= C->getZExtValue();
 227   }
 228   return Size;
 229 }
 230
 231 bool SafeStack::IsAccessSafe(Value *Addr, uint64_t AccessSize,
 232                              const Value *AllocaPtr, uint64_t AllocaSize) {
 233   AllocaOffsetRewriter Rewriter(SE, AllocaPtr);
 234   const SCEV *Expr = Rewriter.visit(SE.getSCEV(Addr));
 235
 236   uint64_t BitWidth = SE.getTypeSizeInBits(Expr->getType());
 237   ConstantRange AccessStartRange = SE.getUnsignedRange(Expr);
 238   ConstantRange SizeRange =
 239       ConstantRange(APInt(BitWidth, 0), APInt(BitWidth, AccessSize));
 240   ConstantRange AccessRange = AccessStartRange.add(SizeRange);
 241   ConstantRange AllocaRange =
 242       ConstantRange(APInt(BitWidth, 0), APInt(BitWidth, AllocaSize));
 243   bool Safe = AllocaRange.contains(AccessRange);
 244
 245   LLVM_DEBUG(
 246       dbgs() << "[SafeStack] "
 247              << (isa<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")
 248              << *AllocaPtr << "\n"
 249              << "            Access " << *Addr << "\n"
 250              << "            SCEV " << *Expr
 251              << " U: " << SE.getUnsignedRange(Expr)
 252              << ", S: " << SE.getSignedRange(Expr) << "\n"
 253              << "            Range " << AccessRange << "\n"
 254              << "            AllocaRange " << AllocaRange << "\n"
 255              << "            " << (Safe ? "safe" : "unsafe") << "\n");
 256
 257   return Safe;
 258 }
 259
 260 bool SafeStack::IsMemIntrinsicSafe(const MemIntrinsic *MI, const Use &U,
 261                                    const Value *AllocaPtr,
 262                                    uint64_t AllocaSize) {
 263   if (auto MTI = dyn_cast<MemTransferInst>(MI)) {
 264     if (MTI->getRawSource() != U && MTI->getRawDest() != U)
 265       return true;
 266   } else {
 267     if (MI->getRawDest() != U)
 268       return true;
 269   }
 270
 271   const auto *Len = dyn_cast<ConstantInt>(MI->getLength());
 272   // Non-constant size => unsafe. FIXME: try SCEV getRange.
 273   if (!Len) return false;
 274   return IsAccessSafe(U, Len->getZExtValue(), AllocaPtr, AllocaSize);
 275 }
 276
 277 /// Check whether a given allocation must be put on the safe
 278 /// stack or not. The function analyzes all uses of AI and checks whether it is
 279 /// only accessed in a memory safe way (as decided statically).
 280 bool SafeStack::IsSafeStackAlloca(const Value *AllocaPtr, uint64_t AllocaSize) {
 281   // Go through all uses of this alloca and check whether all accesses to the
 282   // allocated object are statically known to be memory safe and, hence, the
 283   // object can be placed on the safe stack.
 284   SmallPtrSet<const Value *, 16> Visited;
 285   SmallVector<const Value *, 8> WorkList;
 286   WorkList.push_back(AllocaPtr);
 287
 288   // A DFS search through all uses of the alloca in bitcasts/PHI/GEPs/etc.
 289   while (!WorkList.empty()) {
 290     const Value *V = WorkList.pop_back_val();
 291     for (const Use &UI : V->uses()) {
 292       auto I = cast<const Instruction>(UI.getUser());
 293       assert(V == UI.get());
 294
 295       switch (I->getOpcode()) {
 296       case Instruction::Load:
 297         if (!IsAccessSafe(UI, DL.getTypeStoreSize(I->getType()), AllocaPtr,
 298                           AllocaSize))
 299           return false;
 300         break;
 301
 302       case Instruction::VAArg:
 303         // "va-arg" from a pointer is safe.
 304         break;
 305       case Instruction::Store:
 306         if (V == I->getOperand(0)) {
 307           // Stored the pointer - conservatively assume it may be unsafe.
 308           LLVM_DEBUG(dbgs()
 309                      << "[SafeStack] Unsafe alloca: " << *AllocaPtr
 310                      << "\n            store of address: " << *I << "\n");
 311           return false;
 312         }
 313
 314         if (!IsAccessSafe(UI, DL.getTypeStoreSize(I->getOperand(0)->getType()),
 315                           AllocaPtr, AllocaSize))
 316           return false;
 317         break;
 318
 319       case Instruction::Ret:
 320         // Information leak.
 321         return false;
 322
 323       case Instruction::Call:
 324       case Instruction::Invoke: {
 325         ImmutableCallSite CS(I);
 326
 327         if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
 328           if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
 329               II->getIntrinsicID() == Intrinsic::lifetime_end)
 330             continue;
 331         }
 332
 333         if (const MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) {
 334           if (!IsMemIntrinsicSafe(MI, UI, AllocaPtr, AllocaSize)) {
 335             LLVM_DEBUG(dbgs()
 336                        << "[SafeStack] Unsafe alloca: " << *AllocaPtr
 337                        << "\n            unsafe memintrinsic: " << *I << "\n");
 338             return false;
 339           }
 340           continue;
 341         }
 342
 343         // LLVM 'nocapture' attribute is only set for arguments whose address
 344         // is not stored, passed around, or used in any other non-trivial way.
 345         // We assume that passing a pointer to an object as a 'nocapture
 346         // readnone' argument is safe.
 347         // FIXME: a more precise solution would require an interprocedural
 348         // analysis here, which would look at all uses of an argument inside
 349         // the function being called.
 350         ImmutableCallSite::arg_iterator B = CS.arg_begin(), E = CS.arg_end();
 351         for (ImmutableCallSite::arg_iterator A = B; A != E; ++A)
 352           if (A->get() == V)
 353             if (!(CS.doesNotCapture(A - B) && (CS.doesNotAccessMemory(A - B) ||
 354                                                CS.doesNotAccessMemory()))) {
 355               LLVM_DEBUG(dbgs() << "[SafeStack] Unsafe alloca: " << *AllocaPtr
 356                                 << "\n            unsafe call: " << *I << "\n");
 357               return false;
 358             }
 359         continue;
 360       }
 361
 362       default:
 363         if (Visited.insert(I).second)
 364           WorkList.push_back(cast<const Instruction>(I));
 365       }
 366     }
 367   }
 368
 369   // All uses of the alloca are safe, we can place it on the safe stack.
 370   return true;
 371 }
 372
 373 Value *SafeStack::getStackGuard(IRBuilder<> &IRB, Function &F) {
 374   Value *StackGuardVar = TL.getIRStackGuard(IRB);
 375   if (!StackGuardVar)
 376     StackGuardVar =
 377         F.getParent()->getOrInsertGlobal("__stack_chk_guard", StackPtrTy);
 378   return IRB.CreateLoad(StackGuardVar, "StackGuard");
 379 }
 380
 381 void SafeStack::findInsts(Function &F,
 382                           SmallVectorImpl<AllocaInst *> &StaticAllocas,
 383                           SmallVectorImpl<AllocaInst *> &DynamicAllocas,
 384                           SmallVectorImpl<Argument *> &ByValArguments,
 385                           SmallVectorImpl<ReturnInst *> &Returns,
 386                           SmallVectorImpl<Instruction *> &StackRestorePoints) {
 387   for (Instruction &I : instructions(&F)) {
 388     if (auto AI = dyn_cast<AllocaInst>(&I)) {
 389       ++NumAllocas;
 390
 391       uint64_t Size = getStaticAllocaAllocationSize(AI);
 392       if (IsSafeStackAlloca(AI, Size))
 393         continue;
 394
 395       if (AI->isStaticAlloca()) {
 396         ++NumUnsafeStaticAllocas;
 397         StaticAllocas.push_back(AI);
 398       } else {
 399         ++NumUnsafeDynamicAllocas;
 400         DynamicAllocas.push_back(AI);
 401       }
 402     } else if (auto RI = dyn_cast<ReturnInst>(&I)) {
 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 =
 421         DL.getTypeStoreSize(Arg.getType()->getPointerElementType());
 422     if (IsSafeStackAlloca(&Arg, Size))
 423       continue;
 424
 425     ++NumUnsafeByValArguments;
 426     ByValArguments.push_back(&Arg);
 427   }
 428 }
 429
 430 AllocaInst *
 431 SafeStack::createStackRestorePoints(IRBuilder<> &IRB, Function &F,
 432                                     ArrayRef<Instruction *> StackRestorePoints,
 433                                     Value *StaticTop, bool NeedDynamicTop) {
 434   assert(StaticTop && "The stack top isn't set.");
 435
 436   if (StackRestorePoints.empty())
 437     return nullptr;
 438
 439   // We need the current value of the shadow stack pointer to restore
 440   // after longjmp or exception catching.
 441
 442   // FIXME: On some platforms this could be handled by the longjmp/exception
 443   // runtime itself.
 444
 445   AllocaInst *DynamicTop = nullptr;
 446   if (NeedDynamicTop) {
 447     // If we also have dynamic alloca's, the stack pointer value changes
 448     // throughout the function. For now we store it in an alloca.
 449     DynamicTop = IRB.CreateAlloca(StackPtrTy, /*ArraySize=*/nullptr,
 450                                   "unsafe_stack_dynamic_ptr");
 451     IRB.CreateStore(StaticTop, DynamicTop);
 452   }
 453
 454   // Restore current stack pointer after longjmp/exception catch.
 455   for (Instruction *I : StackRestorePoints) {
 456     ++NumUnsafeStackRestorePoints;
 457
 458     IRB.SetInsertPoint(I->getNextNode());
 459     Value *CurrentTop = DynamicTop ? IRB.CreateLoad(DynamicTop) : StaticTop;
 460     IRB.CreateStore(CurrentTop, UnsafeStackPtr);
 461   }
 462
 463   return DynamicTop;
 464 }
 465
 466 void SafeStack::checkStackGuard(IRBuilder<> &IRB, Function &F, ReturnInst &RI,
 467                                 AllocaInst *StackGuardSlot, Value *StackGuard) {
 468   Value *V = IRB.CreateLoad(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,
 478                                 /* Unreachable */ true, Weights);
 479   IRBuilder<> IRBFail(CheckTerm);
 480   // FIXME: respect -fsanitize-trap / -ftrap-function here?
 481   Constant *StackChkFail = F.getParent()->getOrInsertFunction(
 482       "__stack_chk_fail", IRB.getVoidTy());
 483   IRBFail.CreateCall(StackChkFail, {});
 484 }
 485
 486 /// We explicitly compute and set the unsafe stack layout for all unsafe
 487 /// static alloca instructions. We save the unsafe "base pointer" in the
 488 /// prologue into a local variable and restore it in the epilogue.
 489 Value *SafeStack::moveStaticAllocasToUnsafeStack(
 490     IRBuilder<> &IRB, Function &F, ArrayRef<AllocaInst *> StaticAllocas,
 491     ArrayRef<Argument *> ByValArguments, ArrayRef<ReturnInst *> Returns,
 492     Instruction *BasePointer, AllocaInst *StackGuardSlot) {
 493   if (StaticAllocas.empty() && ByValArguments.empty())
 494     return BasePointer;
 495
 496   DIBuilder DIB(*F.getParent());
 497
 498   StackColoring SSC(F, StaticAllocas);
 499   SSC.run();
 500   SSC.removeAllMarkers();
 501
 502   // Unsafe stack always grows down.
 503   StackLayout SSL(StackAlignment);
 504   if (StackGuardSlot) {
 505     Type *Ty = StackGuardSlot->getAllocatedType();
 506     unsigned Align =
 507         std::max(DL.getPrefTypeAlignment(Ty), StackGuardSlot->getAlignment());
 508     SSL.addObject(StackGuardSlot, getStaticAllocaAllocationSize(StackGuardSlot),
 509                   Align, SSC.getFullLiveRange());
 510   }
 511
 512   for (Argument *Arg : ByValArguments) {
 513     Type *Ty = Arg->getType()->getPointerElementType();
 514     uint64_t Size = DL.getTypeStoreSize(Ty);
 515     if (Size == 0)
 516       Size = 1; // Don't create zero-sized stack objects.
 517
 518     // Ensure the object is properly aligned.
 519     unsigned Align = std::max((unsigned)DL.getPrefTypeAlignment(Ty),
 520                               Arg->getParamAlignment());
 521     SSL.addObject(Arg, Size, Align, SSC.getFullLiveRange());
 522   }
 523
 524   for (AllocaInst *AI : StaticAllocas) {
 525     Type *Ty = AI->getAllocatedType();
 526     uint64_t Size = getStaticAllocaAllocationSize(AI);
 527     if (Size == 0)
 528       Size = 1; // Don't create zero-sized stack objects.
 529
 530     // Ensure the object is properly aligned.
 531     unsigned Align =
 532         std::max((unsigned)DL.getPrefTypeAlignment(Ty), AI->getAlignment());
 533
 534     SSL.addObject(AI, Size, Align, SSC.getLiveRange(AI));
 535   }
 536
 537   SSL.computeLayout();
 538   unsigned FrameAlignment = SSL.getFrameAlignment();
 539
 540   // FIXME: tell SSL that we start at a less-then-MaxAlignment aligned location
 541   // (AlignmentSkew).
 542   if (FrameAlignment > StackAlignment) {
 543     // Re-align the base pointer according to the max requested alignment.
 544     assert(isPowerOf2_32(FrameAlignment));
 545     IRB.SetInsertPoint(BasePointer->getNextNode());
 546     BasePointer = cast<Instruction>(IRB.CreateIntToPtr(
 547         IRB.CreateAnd(IRB.CreatePtrToInt(BasePointer, IntPtrTy),
 548                       ConstantInt::get(IntPtrTy, ~uint64_t(FrameAlignment - 1))),
 549         StackPtrTy));
 550   }
 551
 552   IRB.SetInsertPoint(BasePointer->getNextNode());
 553
 554   if (StackGuardSlot) {
 555     unsigned Offset = SSL.getObjectOffset(StackGuardSlot);
 556     Value *Off = IRB.CreateGEP(BasePointer, // BasePointer is i8*
 557                                ConstantInt::get(Int32Ty, -Offset));
 558     Value *NewAI =
 559         IRB.CreateBitCast(Off, StackGuardSlot->getType(), "StackGuardSlot");
 560
 561     // Replace alloc with the new location.
 562     StackGuardSlot->replaceAllUsesWith(NewAI);
 563     StackGuardSlot->eraseFromParent();
 564   }
 565
 566   for (Argument *Arg : ByValArguments) {
 567     unsigned Offset = SSL.getObjectOffset(Arg);
 568     unsigned Align = SSL.getObjectAlignment(Arg);
 569     Type *Ty = Arg->getType()->getPointerElementType();
 570
 571     uint64_t Size = DL.getTypeStoreSize(Ty);
 572     if (Size == 0)
 573       Size = 1; // Don't create zero-sized stack objects.
 574
 575     Value *Off = IRB.CreateGEP(BasePointer, // BasePointer is i8*
 576                                ConstantInt::get(Int32Ty, -Offset));
 577     Value *NewArg = IRB.CreateBitCast(Off, Arg->getType(),
 578                                      Arg->getName() + ".unsafe-byval");
 579
 580     // Replace alloc with the new location.
 581     replaceDbgDeclare(Arg, BasePointer, BasePointer->getNextNode(), DIB,
 582                       DIExpression::NoDeref, -Offset, DIExpression::NoDeref);
 583     Arg->replaceAllUsesWith(NewArg);
 584     IRB.SetInsertPoint(cast<Instruction>(NewArg)->getNextNode());
 585     IRB.CreateMemCpy(Off, Align, Arg, Arg->getParamAlignment(), Size);
 586   }
 587
 588   // Allocate space for every unsafe static AllocaInst on the unsafe stack.
 589   for (AllocaInst *AI : StaticAllocas) {
 590     IRB.SetInsertPoint(AI);
 591     unsigned Offset = SSL.getObjectOffset(AI);
 592
 593     uint64_t Size = getStaticAllocaAllocationSize(AI);
 594     if (Size == 0)
 595       Size = 1; // Don't create zero-sized stack objects.
 596
 597     replaceDbgDeclareForAlloca(AI, BasePointer, DIB, DIExpression::NoDeref,
 598                                -Offset, DIExpression::NoDeref);
 599     replaceDbgValueForAlloca(AI, BasePointer, DIB, -Offset);
 600
 601     // Replace uses of the alloca with the new location.
 602     // Insert address calculation close to each use to work around PR27844.
 603     std::string Name = std::string(AI->getName()) + ".unsafe";
 604     while (!AI->use_empty()) {
 605       Use &U = *AI->use_begin();
 606       Instruction *User = cast<Instruction>(U.getUser());
 607
 608       Instruction *InsertBefore;
 609       if (auto *PHI = dyn_cast<PHINode>(User))
 610         InsertBefore = PHI->getIncomingBlock(U)->getTerminator();
 611       else
 612         InsertBefore = User;
 613
 614       IRBuilder<> IRBUser(InsertBefore);
 615       Value *Off = IRBUser.CreateGEP(BasePointer, // BasePointer is i8*
 616                                      ConstantInt::get(Int32Ty, -Offset));
 617       Value *Replacement = IRBUser.CreateBitCast(Off, AI->getType(), Name);
 618
 619       if (auto *PHI = dyn_cast<PHINode>(User)) {
 620         // PHI nodes may have multiple incoming edges from the same BB (why??),
 621         // all must be updated at once with the same incoming value.
 622         auto *BB = PHI->getIncomingBlock(U);
 623         for (unsigned I = 0; I < PHI->getNumIncomingValues(); ++I)
 624           if (PHI->getIncomingBlock(I) == BB)
 625             PHI->setIncomingValue(I, Replacement);
 626       } else {
 627         U.set(Replacement);
 628       }
 629     }
 630
 631     AI->eraseFromParent();
 632   }
 633
 634   // Re-align BasePointer so that our callees would see it aligned as
 635   // expected.
 636   // FIXME: no need to update BasePointer in leaf functions.
 637   unsigned FrameSize = alignTo(SSL.getFrameSize(), StackAlignment);
 638
 639   // Update shadow stack pointer in the function epilogue.
 640   IRB.SetInsertPoint(BasePointer->getNextNode());
 641
 642   Value *StaticTop =
 643       IRB.CreateGEP(BasePointer, ConstantInt::get(Int32Ty, -FrameSize),
 644                     "unsafe_stack_static_top");
 645   IRB.CreateStore(StaticTop, UnsafeStackPtr);
 646   return StaticTop;
 647 }
 648
 649 void SafeStack::moveDynamicAllocasToUnsafeStack(
 650     Function &F, Value *UnsafeStackPtr, AllocaInst *DynamicTop,
 651     ArrayRef<AllocaInst *> DynamicAllocas) {
 652   DIBuilder DIB(*F.getParent());
 653
 654   for (AllocaInst *AI : DynamicAllocas) {
 655     IRBuilder<> IRB(AI);
 656
 657     // Compute the new SP value (after AI).
 658     Value *ArraySize = AI->getArraySize();
 659     if (ArraySize->getType() != IntPtrTy)
 660       ArraySize = IRB.CreateIntCast(ArraySize, IntPtrTy, false);
 661
 662     Type *Ty = AI->getAllocatedType();
 663     uint64_t TySize = DL.getTypeAllocSize(Ty);
 664     Value *Size = IRB.CreateMul(ArraySize, ConstantInt::get(IntPtrTy, TySize));
 665
 666     Value *SP = IRB.CreatePtrToInt(IRB.CreateLoad(UnsafeStackPtr), IntPtrTy);
 667     SP = IRB.CreateSub(SP, Size);
 668
 669     // Align the SP value to satisfy the AllocaInst, type and stack alignments.
 670     unsigned Align = std::max(
 671         std::max((unsigned)DL.getPrefTypeAlignment(Ty), AI->getAlignment()),
 672         (unsigned)StackAlignment);
 673
 674     assert(isPowerOf2_32(Align));
 675     Value *NewTop = IRB.CreateIntToPtr(
 676         IRB.CreateAnd(SP, ConstantInt::get(IntPtrTy, ~uint64_t(Align - 1))),
 677         StackPtrTy);
 678
 679     // Save the stack pointer.
 680     IRB.CreateStore(NewTop, UnsafeStackPtr);
 681     if (DynamicTop)
 682       IRB.CreateStore(NewTop, DynamicTop);
 683
 684     Value *NewAI = IRB.CreatePointerCast(NewTop, AI->getType());
 685     if (AI->hasName() && isa<Instruction>(NewAI))
 686       NewAI->takeName(AI);
 687
 688     replaceDbgDeclareForAlloca(AI, NewAI, DIB, DIExpression::NoDeref, 0,
 689                                DIExpression::NoDeref);
 690     AI->replaceAllUsesWith(NewAI);
 691     AI->eraseFromParent();
 692   }
 693
 694   if (!DynamicAllocas.empty()) {
 695     // Now go through the instructions again, replacing stacksave/stackrestore.
 696     for (inst_iterator It = inst_begin(&F), Ie = inst_end(&F); It != Ie;) {
 697       Instruction *I = &*(It++);
 698       auto II = dyn_cast<IntrinsicInst>(I);
 699       if (!II)
 700         continue;
 701
 702       if (II->getIntrinsicID() == Intrinsic::stacksave) {
 703         IRBuilder<> IRB(II);
 704         Instruction *LI = IRB.CreateLoad(UnsafeStackPtr);
 705         LI->takeName(II);
 706         II->replaceAllUsesWith(LI);
 707         II->eraseFromParent();
 708       } else if (II->getIntrinsicID() == Intrinsic::stackrestore) {
 709         IRBuilder<> IRB(II);
 710         Instruction *SI = IRB.CreateStore(II->getArgOperand(0), UnsafeStackPtr);
 711         SI->takeName(II);
 712         assert(II->use_empty());
 713         II->eraseFromParent();
 714       }
 715     }
 716   }
 717 }
 718
 719 bool SafeStack::ShouldInlinePointerAddress(CallSite &CS) {
 720   Function *Callee = CS.getCalledFunction();
 721   if (CS.hasFnAttr(Attribute::AlwaysInline) && isInlineViable(*Callee))
 722     return true;
 723   if (Callee->isInterposable() || Callee->hasFnAttribute(Attribute::NoInline) ||
 724       CS.isNoInline())
 725     return false;
 726   return true;
 727 }
 728
 729 void SafeStack::TryInlinePointerAddress() {
 730   if (!isa<CallInst>(UnsafeStackPtr))
 731     return;
 732
 733   if(F.hasFnAttribute(Attribute::OptimizeNone))
 734     return;
 735
 736   CallSite CS(UnsafeStackPtr);
 737   Function *Callee = CS.getCalledFunction();
 738   if (!Callee || Callee->isDeclaration())
 739     return;
 740
 741   if (!ShouldInlinePointerAddress(CS))
 742     return;
 743
 744   InlineFunctionInfo IFI;
 745   InlineFunction(CS, IFI);
 746 }
 747
 748 bool SafeStack::run() {
 749   assert(F.hasFnAttribute(Attribute::SafeStack) &&
 750          "Can't run SafeStack on a function without the attribute");
 751   assert(!F.isDeclaration() && "Can't run SafeStack on a function declaration");
 752
 753   ++NumFunctions;
 754
 755   SmallVector<AllocaInst *, 16> StaticAllocas;
 756   SmallVector<AllocaInst *, 4> DynamicAllocas;
 757   SmallVector<Argument *, 4> ByValArguments;
 758   SmallVector<ReturnInst *, 4> Returns;
 759
 760   // Collect all points where stack gets unwound and needs to be restored
 761   // This is only necessary because the runtime (setjmp and unwind code) is
 762   // not aware of the unsafe stack and won't unwind/restore it properly.
 763   // To work around this problem without changing the runtime, we insert
 764   // instrumentation to restore the unsafe stack pointer when necessary.
 765   SmallVector<Instruction *, 4> StackRestorePoints;
 766
 767   // Find all static and dynamic alloca instructions that must be moved to the
 768   // unsafe stack, all return instructions and stack restore points.
 769   findInsts(F, StaticAllocas, DynamicAllocas, ByValArguments, Returns,
 770             StackRestorePoints);
 771
 772   if (StaticAllocas.empty() && DynamicAllocas.empty() &&
 773       ByValArguments.empty() && StackRestorePoints.empty())
 774     return false; // Nothing to do in this function.
 775
 776   if (!StaticAllocas.empty() || !DynamicAllocas.empty() ||
 777       !ByValArguments.empty())
 778     ++NumUnsafeStackFunctions; // This function has the unsafe stack.
 779
 780   if (!StackRestorePoints.empty())
 781     ++NumUnsafeStackRestorePointsFunctions;
 782
 783   IRBuilder<> IRB(&F.front(), F.begin()->getFirstInsertionPt());
 784   // Calls must always have a debug location, or else inlining breaks. So
 785   // we explicitly set a artificial debug location here.
 786   if (DISubprogram *SP = F.getSubprogram())
 787     IRB.SetCurrentDebugLocation(DebugLoc::get(SP->getScopeLine(), 0, SP));
 788   if (SafeStackUsePointerAddress) {
 789     Value *Fn = F.getParent()->getOrInsertFunction(
 790         "__safestack_pointer_address", StackPtrTy->getPointerTo(0));
 791     UnsafeStackPtr = IRB.CreateCall(Fn);
 792   } else {
 793     UnsafeStackPtr = TL.getSafeStackPointerLocation(IRB);
 794   }
 795
 796   // Load the current stack pointer (we'll also use it as a base pointer).
 797   // FIXME: use a dedicated register for it ?
 798   Instruction *BasePointer =
 799       IRB.CreateLoad(UnsafeStackPtr, false, "unsafe_stack_ptr");
 800   assert(BasePointer->getType() == StackPtrTy);
 801
 802   AllocaInst *StackGuardSlot = nullptr;
 803   // FIXME: implement weaker forms of stack protector.
 804   if (F.hasFnAttribute(Attribute::StackProtect) ||
 805       F.hasFnAttribute(Attribute::StackProtectStrong) ||
 806       F.hasFnAttribute(Attribute::StackProtectReq)) {
 807     Value *StackGuard = getStackGuard(IRB, F);
 808     StackGuardSlot = IRB.CreateAlloca(StackPtrTy, nullptr);
 809     IRB.CreateStore(StackGuard, StackGuardSlot);
 810
 811     for (ReturnInst *RI : Returns) {
 812       IRBuilder<> IRBRet(RI);
 813       checkStackGuard(IRBRet, F, *RI, StackGuardSlot, StackGuard);
 814     }
 815   }
 816
 817   // The top of the unsafe stack after all unsafe static allocas are
 818   // allocated.
 819   Value *StaticTop =
 820       moveStaticAllocasToUnsafeStack(IRB, F, StaticAllocas, ByValArguments,
 821                                      Returns, BasePointer, StackGuardSlot);
 822
 823   // Safe stack object that stores the current unsafe stack top. It is updated
 824   // as unsafe dynamic (non-constant-sized) allocas are allocated and freed.
 825   // This is only needed if we need to restore stack pointer after longjmp
 826   // or exceptions, and we have dynamic allocations.
 827   // FIXME: a better alternative might be to store the unsafe stack pointer
 828   // before setjmp / invoke instructions.
 829   AllocaInst *DynamicTop = createStackRestorePoints(
 830       IRB, F, StackRestorePoints, StaticTop, !DynamicAllocas.empty());
 831
 832   // Handle dynamic allocas.
 833   moveDynamicAllocasToUnsafeStack(F, UnsafeStackPtr, DynamicTop,
 834                                   DynamicAllocas);
 835
 836   // Restore the unsafe stack pointer before each return.
 837   for (ReturnInst *RI : Returns) {
 838     IRB.SetInsertPoint(RI);
 839     IRB.CreateStore(BasePointer, UnsafeStackPtr);
 840   }
 841
 842   TryInlinePointerAddress();
 843
 844   LLVM_DEBUG(dbgs() << "[SafeStack]     safestack applied\n");
 845   return true;
 846 }
 847
 848 class SafeStackLegacyPass : public FunctionPass {
 849   const TargetMachine *TM = nullptr;
 850
 851 public:
 852   static char ID; // Pass identification, replacement for typeid..
 853
 854   SafeStackLegacyPass() : FunctionPass(ID) {
 855     initializeSafeStackLegacyPassPass(*PassRegistry::getPassRegistry());
 856   }
 857
 858   void getAnalysisUsage(AnalysisUsage &AU) const override {
 859     AU.addRequired<TargetPassConfig>();
 860     AU.addRequired<TargetLibraryInfoWrapperPass>();
 861     AU.addRequired<AssumptionCacheTracker>();
 862   }
 863
 864   bool runOnFunction(Function &F) override {
 865     LLVM_DEBUG(dbgs() << "[SafeStack] Function: " << F.getName() << "\n");
 866
 867     if (!F.hasFnAttribute(Attribute::SafeStack)) {
 868       LLVM_DEBUG(dbgs() << "[SafeStack]     safestack is not requested"
 869                            " for this function\n");
 870       return false;
 871     }
 872
 873     if (F.isDeclaration()) {
 874       LLVM_DEBUG(dbgs() << "[SafeStack]     function definition"
 875                            " is not available\n");
 876       return false;
 877     }
 878
 879     TM = &getAnalysis<TargetPassConfig>().getTM<TargetMachine>();
 880     auto *TL = TM->getSubtargetImpl(F)->getTargetLowering();
 881     if (!TL)
 882       report_fatal_error("TargetLowering instance is required");
 883
 884     auto *DL = &F.getParent()->getDataLayout();
 885     auto &TLI = getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
 886     auto &ACT = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
 887
 888     // Compute DT and LI only for functions that have the attribute.
 889     // This is only useful because the legacy pass manager doesn't let us
 890     // compute analyzes lazily.
 891     // In the backend pipeline, nothing preserves DT before SafeStack, so we
 892     // would otherwise always compute it wastefully, even if there is no
 893     // function with the safestack attribute.
 894     DominatorTree DT(F);
 895     LoopInfo LI(DT);
 896
 897     ScalarEvolution SE(F, TLI, ACT, DT, LI);
 898
 899     return SafeStack(F, *TL, *DL, SE).run();
 900   }
 901 };
 902
 903 } // end anonymous namespace
 904
 905 char SafeStackLegacyPass::ID = 0;
 906
 907 INITIALIZE_PASS_BEGIN(SafeStackLegacyPass, DEBUG_TYPE,
 908                       "Safe Stack instrumentation pass", false, false)
 909 INITIALIZE_PASS_DEPENDENCY(TargetPassConfig)
 910 INITIALIZE_PASS_END(SafeStackLegacyPass, DEBUG_TYPE,
 911                     "Safe Stack instrumentation pass", false, false)
 912
 913 FunctionPass *llvm::createSafeStackPass() { return new SafeStackLegacyPass(); }