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