SafeStack.cpp revision 360784 
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/CodeGen/TargetLowering.h"
32#include "llvm/CodeGen/TargetPassConfig.h"
33#include "llvm/CodeGen/TargetSubtargetInfo.h"
34#include "llvm/IR/Argument.h"
35#include "llvm/IR/Attributes.h"
36#include "llvm/IR/CallSite.h"
37#include "llvm/IR/ConstantRange.h"
38#include "llvm/IR/Constants.h"
39#include "llvm/IR/DIBuilder.h"
40#include "llvm/IR/DataLayout.h"
41#include "llvm/IR/DerivedTypes.h"
42#include "llvm/IR/Dominators.h"
43#include "llvm/IR/Function.h"
44#include "llvm/IR/IRBuilder.h"
45#include "llvm/IR/InstIterator.h"
46#include "llvm/IR/Instruction.h"
47#include "llvm/IR/Instructions.h"
48#include "llvm/IR/IntrinsicInst.h"
49#include "llvm/IR/Intrinsics.h"
50#include "llvm/IR/MDBuilder.h"
51#include "llvm/IR/Module.h"
52#include "llvm/IR/Type.h"
53#include "llvm/IR/Use.h"
54#include "llvm/IR/User.h"
55#include "llvm/IR/Value.h"
56#include "llvm/InitializePasses.h"
57#include "llvm/Pass.h"
58#include "llvm/Support/Casting.h"
59#include "llvm/Support/Debug.h"
60#include "llvm/Support/ErrorHandling.h"
61#include "llvm/Support/MathExtras.h"
62#include "llvm/Support/raw_ostream.h"
63#include "llvm/Target/TargetMachine.h"
64#include "llvm/Transforms/Utils/BasicBlockUtils.h"
65#include "llvm/Transforms/Utils/Cloning.h"
66#include "llvm/Transforms/Utils/Local.h"
67#include <algorithm>
68#include <cassert>
69#include <cstdint>
70#include <string>
71#include <utility>
72
73using namespace llvm;
74using namespace llvm::safestack;
75
76#define DEBUG_TYPE "safe-stack"
77
78namespace llvm {
79
80STATISTIC(NumFunctions, "Total number of functions");
81STATISTIC(NumUnsafeStackFunctions, "Number of functions with unsafe stack");
82STATISTIC(NumUnsafeStackRestorePointsFunctions,
83          "Number of functions that use setjmp or exceptions");
84
85STATISTIC(NumAllocas, "Total number of allocas");
86STATISTIC(NumUnsafeStaticAllocas, "Number of unsafe static allocas");
87STATISTIC(NumUnsafeDynamicAllocas, "Number of unsafe dynamic allocas");
88STATISTIC(NumUnsafeByValArguments, "Number of unsafe byval arguments");
89STATISTIC(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.
95static cl::opt<bool>
96    SafeStackUsePointerAddress("safestack-use-pointer-address",
97                                  cl::init(false), cl::Hidden);
98
99
100namespace {
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.
106class AllocaOffsetRewriter : public SCEVRewriteVisitor<AllocaOffsetRewriter> {
107  const Value *AllocaPtr;
108
109public:
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.
125class 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
206public:
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
220uint64_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
231bool 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
260bool 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).
280bool 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 (I->isLifetimeStartOrEnd())
328          continue;
329
330        if (const MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) {
331          if (!IsMemIntrinsicSafe(MI, UI, AllocaPtr, AllocaSize)) {
332            LLVM_DEBUG(dbgs()
333                       << "[SafeStack] Unsafe alloca: " << *AllocaPtr
334                       << "\n            unsafe memintrinsic: " << *I << "\n");
335            return false;
336          }
337          continue;
338        }
339
340        // LLVM 'nocapture' attribute is only set for arguments whose address
341        // is not stored, passed around, or used in any other non-trivial way.
342        // We assume that passing a pointer to an object as a 'nocapture
343        // readnone' argument is safe.
344        // FIXME: a more precise solution would require an interprocedural
345        // analysis here, which would look at all uses of an argument inside
346        // the function being called.
347        ImmutableCallSite::arg_iterator B = CS.arg_begin(), E = CS.arg_end();
348        for (ImmutableCallSite::arg_iterator A = B; A != E; ++A)
349          if (A->get() == V)
350            if (!(CS.doesNotCapture(A - B) && (CS.doesNotAccessMemory(A - B) ||
351                                               CS.doesNotAccessMemory()))) {
352              LLVM_DEBUG(dbgs() << "[SafeStack] Unsafe alloca: " << *AllocaPtr
353                                << "\n            unsafe call: " << *I << "\n");
354              return false;
355            }
356        continue;
357      }
358
359      default:
360        if (Visited.insert(I).second)
361          WorkList.push_back(cast<const Instruction>(I));
362      }
363    }
364  }
365
366  // All uses of the alloca are safe, we can place it on the safe stack.
367  return true;
368}
369
370Value *SafeStack::getStackGuard(IRBuilder<> &IRB, Function &F) {
371  Value *StackGuardVar = TL.getIRStackGuard(IRB);
372  if (!StackGuardVar)
373    StackGuardVar =
374        F.getParent()->getOrInsertGlobal("__stack_chk_guard", StackPtrTy);
375  return IRB.CreateLoad(StackPtrTy, StackGuardVar, "StackGuard");
376}
377
378void SafeStack::findInsts(Function &F,
379                          SmallVectorImpl<AllocaInst *> &StaticAllocas,
380                          SmallVectorImpl<AllocaInst *> &DynamicAllocas,
381                          SmallVectorImpl<Argument *> &ByValArguments,
382                          SmallVectorImpl<ReturnInst *> &Returns,
383                          SmallVectorImpl<Instruction *> &StackRestorePoints) {
384  for (Instruction &I : instructions(&F)) {
385    if (auto AI = dyn_cast<AllocaInst>(&I)) {
386      ++NumAllocas;
387
388      uint64_t Size = getStaticAllocaAllocationSize(AI);
389      if (IsSafeStackAlloca(AI, Size))
390        continue;
391
392      if (AI->isStaticAlloca()) {
393        ++NumUnsafeStaticAllocas;
394        StaticAllocas.push_back(AI);
395      } else {
396        ++NumUnsafeDynamicAllocas;
397        DynamicAllocas.push_back(AI);
398      }
399    } else if (auto RI = dyn_cast<ReturnInst>(&I)) {
400      Returns.push_back(RI);
401    } else if (auto CI = dyn_cast<CallInst>(&I)) {
402      // setjmps require stack restore.
403      if (CI->getCalledFunction() && CI->canReturnTwice())
404        StackRestorePoints.push_back(CI);
405    } else if (auto LP = dyn_cast<LandingPadInst>(&I)) {
406      // Exception landing pads require stack restore.
407      StackRestorePoints.push_back(LP);
408    } else if (auto II = dyn_cast<IntrinsicInst>(&I)) {
409      if (II->getIntrinsicID() == Intrinsic::gcroot)
410        report_fatal_error(
411            "gcroot intrinsic not compatible with safestack attribute");
412    }
413  }
414  for (Argument &Arg : F.args()) {
415    if (!Arg.hasByValAttr())
416      continue;
417    uint64_t Size =
418        DL.getTypeStoreSize(Arg.getType()->getPointerElementType());
419    if (IsSafeStackAlloca(&Arg, Size))
420      continue;
421
422    ++NumUnsafeByValArguments;
423    ByValArguments.push_back(&Arg);
424  }
425}
426
427AllocaInst *
428SafeStack::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
464void SafeStack::checkStackGuard(IRBuilder<> &IRB, Function &F, ReturnInst &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,
476                                /* Unreachable */ true, Weights);
477  IRBuilder<> IRBFail(CheckTerm);
478  // FIXME: respect -fsanitize-trap / -ftrap-function here?
479  FunctionCallee StackChkFail =
480      F.getParent()->getOrInsertFunction("__stack_chk_fail", IRB.getVoidTy());
481  IRBFail.CreateCall(StackChkFail, {});
482}
483
484/// We explicitly compute and set the unsafe stack layout for all unsafe
485/// static alloca instructions. We save the unsafe "base pointer" in the
486/// prologue into a local variable and restore it in the epilogue.
487Value *SafeStack::moveStaticAllocasToUnsafeStack(
488    IRBuilder<> &IRB, Function &F, ArrayRef<AllocaInst *> StaticAllocas,
489    ArrayRef<Argument *> ByValArguments, ArrayRef<ReturnInst *> Returns,
490    Instruction *BasePointer, AllocaInst *StackGuardSlot) {
491  if (StaticAllocas.empty() && ByValArguments.empty())
492    return BasePointer;
493
494  DIBuilder DIB(*F.getParent());
495
496  StackColoring SSC(F, StaticAllocas);
497  SSC.run();
498  SSC.removeAllMarkers();
499
500  // Unsafe stack always grows down.
501  StackLayout SSL(StackAlignment);
502  if (StackGuardSlot) {
503    Type *Ty = StackGuardSlot->getAllocatedType();
504    unsigned Align =
505        std::max(DL.getPrefTypeAlignment(Ty), StackGuardSlot->getAlignment());
506    SSL.addObject(StackGuardSlot, getStaticAllocaAllocationSize(StackGuardSlot),
507                  Align, SSC.getFullLiveRange());
508  }
509
510  for (Argument *Arg : ByValArguments) {
511    Type *Ty = Arg->getType()->getPointerElementType();
512    uint64_t Size = DL.getTypeStoreSize(Ty);
513    if (Size == 0)
514      Size = 1; // Don't create zero-sized stack objects.
515
516    // Ensure the object is properly aligned.
517    unsigned Align = std::max((unsigned)DL.getPrefTypeAlignment(Ty),
518                              Arg->getParamAlignment());
519    SSL.addObject(Arg, Size, Align, SSC.getFullLiveRange());
520  }
521
522  for (AllocaInst *AI : StaticAllocas) {
523    Type *Ty = AI->getAllocatedType();
524    uint64_t Size = getStaticAllocaAllocationSize(AI);
525    if (Size == 0)
526      Size = 1; // Don't create zero-sized stack objects.
527
528    // Ensure the object is properly aligned.
529    unsigned Align =
530        std::max((unsigned)DL.getPrefTypeAlignment(Ty), AI->getAlignment());
531
532    SSL.addObject(AI, Size, Align, SSC.getLiveRange(AI));
533  }
534
535  SSL.computeLayout();
536  unsigned FrameAlignment = SSL.getFrameAlignment();
537
538  // FIXME: tell SSL that we start at a less-then-MaxAlignment aligned location
539  // (AlignmentSkew).
540  if (FrameAlignment > StackAlignment) {
541    // Re-align the base pointer according to the max requested alignment.
542    assert(isPowerOf2_32(FrameAlignment));
543    IRB.SetInsertPoint(BasePointer->getNextNode());
544    BasePointer = cast<Instruction>(IRB.CreateIntToPtr(
545        IRB.CreateAnd(IRB.CreatePtrToInt(BasePointer, IntPtrTy),
546                      ConstantInt::get(IntPtrTy, ~uint64_t(FrameAlignment - 1))),
547        StackPtrTy));
548  }
549
550  IRB.SetInsertPoint(BasePointer->getNextNode());
551
552  if (StackGuardSlot) {
553    unsigned Offset = SSL.getObjectOffset(StackGuardSlot);
554    Value *Off = IRB.CreateGEP(Int8Ty, BasePointer, // BasePointer is i8*
555                               ConstantInt::get(Int32Ty, -Offset));
556    Value *NewAI =
557        IRB.CreateBitCast(Off, StackGuardSlot->getType(), "StackGuardSlot");
558
559    // Replace alloc with the new location.
560    StackGuardSlot->replaceAllUsesWith(NewAI);
561    StackGuardSlot->eraseFromParent();
562  }
563
564  for (Argument *Arg : ByValArguments) {
565    unsigned Offset = SSL.getObjectOffset(Arg);
566    MaybeAlign Align(SSL.getObjectAlignment(Arg));
567    Type *Ty = Arg->getType()->getPointerElementType();
568
569    uint64_t Size = DL.getTypeStoreSize(Ty);
570    if (Size == 0)
571      Size = 1; // Don't create zero-sized stack objects.
572
573    Value *Off = IRB.CreateGEP(Int8Ty, BasePointer, // BasePointer is i8*
574                               ConstantInt::get(Int32Ty, -Offset));
575    Value *NewArg = IRB.CreateBitCast(Off, Arg->getType(),
576                                     Arg->getName() + ".unsafe-byval");
577
578    // Replace alloc with the new location.
579    replaceDbgDeclare(Arg, BasePointer, BasePointer->getNextNode(), DIB,
580                      DIExpression::ApplyOffset, -Offset);
581    Arg->replaceAllUsesWith(NewArg);
582    IRB.SetInsertPoint(cast<Instruction>(NewArg)->getNextNode());
583    IRB.CreateMemCpy(Off, Align, Arg, Arg->getParamAlign(), Size);
584  }
585
586  // Allocate space for every unsafe static AllocaInst on the unsafe stack.
587  for (AllocaInst *AI : StaticAllocas) {
588    IRB.SetInsertPoint(AI);
589    unsigned Offset = SSL.getObjectOffset(AI);
590
591    replaceDbgDeclareForAlloca(AI, BasePointer, DIB, DIExpression::ApplyOffset,
592                               -Offset);
593    replaceDbgValueForAlloca(AI, BasePointer, DIB, -Offset);
594
595    // Replace uses of the alloca with the new location.
596    // Insert address calculation close to each use to work around PR27844.
597    std::string Name = std::string(AI->getName()) + ".unsafe";
598    while (!AI->use_empty()) {
599      Use &U = *AI->use_begin();
600      Instruction *User = cast<Instruction>(U.getUser());
601
602      Instruction *InsertBefore;
603      if (auto *PHI = dyn_cast<PHINode>(User))
604        InsertBefore = PHI->getIncomingBlock(U)->getTerminator();
605      else
606        InsertBefore = User;
607
608      IRBuilder<> IRBUser(InsertBefore);
609      Value *Off = IRBUser.CreateGEP(Int8Ty, BasePointer, // BasePointer is i8*
610                                     ConstantInt::get(Int32Ty, -Offset));
611      Value *Replacement = IRBUser.CreateBitCast(Off, AI->getType(), Name);
612
613      if (auto *PHI = dyn_cast<PHINode>(User))
614        // PHI nodes may have multiple incoming edges from the same BB (why??),
615        // all must be updated at once with the same incoming value.
616        PHI->setIncomingValueForBlock(PHI->getIncomingBlock(U), Replacement);
617      else
618        U.set(Replacement);
619    }
620
621    AI->eraseFromParent();
622  }
623
624  // Re-align BasePointer so that our callees would see it aligned as
625  // expected.
626  // FIXME: no need to update BasePointer in leaf functions.
627  unsigned FrameSize = alignTo(SSL.getFrameSize(), StackAlignment);
628
629  // Update shadow stack pointer in the function epilogue.
630  IRB.SetInsertPoint(BasePointer->getNextNode());
631
632  Value *StaticTop =
633      IRB.CreateGEP(Int8Ty, BasePointer, ConstantInt::get(Int32Ty, -FrameSize),
634                    "unsafe_stack_static_top");
635  IRB.CreateStore(StaticTop, UnsafeStackPtr);
636  return StaticTop;
637}
638
639void SafeStack::moveDynamicAllocasToUnsafeStack(
640    Function &F, Value *UnsafeStackPtr, AllocaInst *DynamicTop,
641    ArrayRef<AllocaInst *> DynamicAllocas) {
642  DIBuilder DIB(*F.getParent());
643
644  for (AllocaInst *AI : DynamicAllocas) {
645    IRBuilder<> IRB(AI);
646
647    // Compute the new SP value (after AI).
648    Value *ArraySize = AI->getArraySize();
649    if (ArraySize->getType() != IntPtrTy)
650      ArraySize = IRB.CreateIntCast(ArraySize, IntPtrTy, false);
651
652    Type *Ty = AI->getAllocatedType();
653    uint64_t TySize = DL.getTypeAllocSize(Ty);
654    Value *Size = IRB.CreateMul(ArraySize, ConstantInt::get(IntPtrTy, TySize));
655
656    Value *SP = IRB.CreatePtrToInt(IRB.CreateLoad(StackPtrTy, UnsafeStackPtr),
657                                   IntPtrTy);
658    SP = IRB.CreateSub(SP, Size);
659
660    // Align the SP value to satisfy the AllocaInst, type and stack alignments.
661    unsigned Align = std::max(
662        std::max((unsigned)DL.getPrefTypeAlignment(Ty), AI->getAlignment()),
663        (unsigned)StackAlignment);
664
665    assert(isPowerOf2_32(Align));
666    Value *NewTop = IRB.CreateIntToPtr(
667        IRB.CreateAnd(SP, ConstantInt::get(IntPtrTy, ~uint64_t(Align - 1))),
668        StackPtrTy);
669
670    // Save the stack pointer.
671    IRB.CreateStore(NewTop, UnsafeStackPtr);
672    if (DynamicTop)
673      IRB.CreateStore(NewTop, DynamicTop);
674
675    Value *NewAI = IRB.CreatePointerCast(NewTop, AI->getType());
676    if (AI->hasName() && isa<Instruction>(NewAI))
677      NewAI->takeName(AI);
678
679    replaceDbgDeclareForAlloca(AI, NewAI, DIB, DIExpression::ApplyOffset, 0);
680    AI->replaceAllUsesWith(NewAI);
681    AI->eraseFromParent();
682  }
683
684  if (!DynamicAllocas.empty()) {
685    // Now go through the instructions again, replacing stacksave/stackrestore.
686    for (inst_iterator It = inst_begin(&F), Ie = inst_end(&F); It != Ie;) {
687      Instruction *I = &*(It++);
688      auto II = dyn_cast<IntrinsicInst>(I);
689      if (!II)
690        continue;
691
692      if (II->getIntrinsicID() == Intrinsic::stacksave) {
693        IRBuilder<> IRB(II);
694        Instruction *LI = IRB.CreateLoad(StackPtrTy, UnsafeStackPtr);
695        LI->takeName(II);
696        II->replaceAllUsesWith(LI);
697        II->eraseFromParent();
698      } else if (II->getIntrinsicID() == Intrinsic::stackrestore) {
699        IRBuilder<> IRB(II);
700        Instruction *SI = IRB.CreateStore(II->getArgOperand(0), UnsafeStackPtr);
701        SI->takeName(II);
702        assert(II->use_empty());
703        II->eraseFromParent();
704      }
705    }
706  }
707}
708
709bool SafeStack::ShouldInlinePointerAddress(CallSite &CS) {
710  Function *Callee = CS.getCalledFunction();
711  if (CS.hasFnAttr(Attribute::AlwaysInline) && isInlineViable(*Callee))
712    return true;
713  if (Callee->isInterposable() || Callee->hasFnAttribute(Attribute::NoInline) ||
714      CS.isNoInline())
715    return false;
716  return true;
717}
718
719void SafeStack::TryInlinePointerAddress() {
720  if (!isa<CallInst>(UnsafeStackPtr))
721    return;
722
723  if(F.hasOptNone())
724    return;
725
726  CallSite CS(UnsafeStackPtr);
727  Function *Callee = CS.getCalledFunction();
728  if (!Callee || Callee->isDeclaration())
729    return;
730
731  if (!ShouldInlinePointerAddress(CS))
732    return;
733
734  InlineFunctionInfo IFI;
735  InlineFunction(CS, IFI);
736}
737
738bool SafeStack::run() {
739  assert(F.hasFnAttribute(Attribute::SafeStack) &&
740         "Can't run SafeStack on a function without the attribute");
741  assert(!F.isDeclaration() && "Can't run SafeStack on a function declaration");
742
743  ++NumFunctions;
744
745  SmallVector<AllocaInst *, 16> StaticAllocas;
746  SmallVector<AllocaInst *, 4> DynamicAllocas;
747  SmallVector<Argument *, 4> ByValArguments;
748  SmallVector<ReturnInst *, 4> Returns;
749
750  // Collect all points where stack gets unwound and needs to be restored
751  // This is only necessary because the runtime (setjmp and unwind code) is
752  // not aware of the unsafe stack and won't unwind/restore it properly.
753  // To work around this problem without changing the runtime, we insert
754  // instrumentation to restore the unsafe stack pointer when necessary.
755  SmallVector<Instruction *, 4> StackRestorePoints;
756
757  // Find all static and dynamic alloca instructions that must be moved to the
758  // unsafe stack, all return instructions and stack restore points.
759  findInsts(F, StaticAllocas, DynamicAllocas, ByValArguments, Returns,
760            StackRestorePoints);
761
762  if (StaticAllocas.empty() && DynamicAllocas.empty() &&
763      ByValArguments.empty() && StackRestorePoints.empty())
764    return false; // Nothing to do in this function.
765
766  if (!StaticAllocas.empty() || !DynamicAllocas.empty() ||
767      !ByValArguments.empty())
768    ++NumUnsafeStackFunctions; // This function has the unsafe stack.
769
770  if (!StackRestorePoints.empty())
771    ++NumUnsafeStackRestorePointsFunctions;
772
773  IRBuilder<> IRB(&F.front(), F.begin()->getFirstInsertionPt());
774  // Calls must always have a debug location, or else inlining breaks. So
775  // we explicitly set a artificial debug location here.
776  if (DISubprogram *SP = F.getSubprogram())
777    IRB.SetCurrentDebugLocation(DebugLoc::get(SP->getScopeLine(), 0, SP));
778  if (SafeStackUsePointerAddress) {
779    FunctionCallee Fn = F.getParent()->getOrInsertFunction(
780        "__safestack_pointer_address", StackPtrTy->getPointerTo(0));
781    UnsafeStackPtr = IRB.CreateCall(Fn);
782  } else {
783    UnsafeStackPtr = TL.getSafeStackPointerLocation(IRB);
784  }
785
786  // Load the current stack pointer (we'll also use it as a base pointer).
787  // FIXME: use a dedicated register for it ?
788  Instruction *BasePointer =
789      IRB.CreateLoad(StackPtrTy, UnsafeStackPtr, false, "unsafe_stack_ptr");
790  assert(BasePointer->getType() == StackPtrTy);
791
792  AllocaInst *StackGuardSlot = nullptr;
793  // FIXME: implement weaker forms of stack protector.
794  if (F.hasFnAttribute(Attribute::StackProtect) ||
795      F.hasFnAttribute(Attribute::StackProtectStrong) ||
796      F.hasFnAttribute(Attribute::StackProtectReq)) {
797    Value *StackGuard = getStackGuard(IRB, F);
798    StackGuardSlot = IRB.CreateAlloca(StackPtrTy, nullptr);
799    IRB.CreateStore(StackGuard, StackGuardSlot);
800
801    for (ReturnInst *RI : Returns) {
802      IRBuilder<> IRBRet(RI);
803      checkStackGuard(IRBRet, F, *RI, StackGuardSlot, StackGuard);
804    }
805  }
806
807  // The top of the unsafe stack after all unsafe static allocas are
808  // allocated.
809  Value *StaticTop =
810      moveStaticAllocasToUnsafeStack(IRB, F, StaticAllocas, ByValArguments,
811                                     Returns, BasePointer, StackGuardSlot);
812
813  // Safe stack object that stores the current unsafe stack top. It is updated
814  // as unsafe dynamic (non-constant-sized) allocas are allocated and freed.
815  // This is only needed if we need to restore stack pointer after longjmp
816  // or exceptions, and we have dynamic allocations.
817  // FIXME: a better alternative might be to store the unsafe stack pointer
818  // before setjmp / invoke instructions.
819  AllocaInst *DynamicTop = createStackRestorePoints(
820      IRB, F, StackRestorePoints, StaticTop, !DynamicAllocas.empty());
821
822  // Handle dynamic allocas.
823  moveDynamicAllocasToUnsafeStack(F, UnsafeStackPtr, DynamicTop,
824                                  DynamicAllocas);
825
826  // Restore the unsafe stack pointer before each return.
827  for (ReturnInst *RI : Returns) {
828    IRB.SetInsertPoint(RI);
829    IRB.CreateStore(BasePointer, UnsafeStackPtr);
830  }
831
832  TryInlinePointerAddress();
833
834  LLVM_DEBUG(dbgs() << "[SafeStack]     safestack applied\n");
835  return true;
836}
837
838class SafeStackLegacyPass : public FunctionPass {
839  const TargetMachine *TM = nullptr;
840
841public:
842  static char ID; // Pass identification, replacement for typeid..
843
844  SafeStackLegacyPass() : FunctionPass(ID) {
845    initializeSafeStackLegacyPassPass(*PassRegistry::getPassRegistry());
846  }
847
848  void getAnalysisUsage(AnalysisUsage &AU) const override {
849    AU.addRequired<TargetPassConfig>();
850    AU.addRequired<TargetLibraryInfoWrapperPass>();
851    AU.addRequired<AssumptionCacheTracker>();
852  }
853
854  bool runOnFunction(Function &F) override {
855    LLVM_DEBUG(dbgs() << "[SafeStack] Function: " << F.getName() << "\n");
856
857    if (!F.hasFnAttribute(Attribute::SafeStack)) {
858      LLVM_DEBUG(dbgs() << "[SafeStack]     safestack is not requested"
859                           " for this function\n");
860      return false;
861    }
862
863    if (F.isDeclaration()) {
864      LLVM_DEBUG(dbgs() << "[SafeStack]     function definition"
865                           " is not available\n");
866      return false;
867    }
868
869    TM = &getAnalysis<TargetPassConfig>().getTM<TargetMachine>();
870    auto *TL = TM->getSubtargetImpl(F)->getTargetLowering();
871    if (!TL)
872      report_fatal_error("TargetLowering instance is required");
873
874    auto *DL = &F.getParent()->getDataLayout();
875    auto &TLI = getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F);
876    auto &ACT = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
877
878    // Compute DT and LI only for functions that have the attribute.
879    // This is only useful because the legacy pass manager doesn't let us
880    // compute analyzes lazily.
881    // In the backend pipeline, nothing preserves DT before SafeStack, so we
882    // would otherwise always compute it wastefully, even if there is no
883    // function with the safestack attribute.
884    DominatorTree DT(F);
885    LoopInfo LI(DT);
886
887    ScalarEvolution SE(F, TLI, ACT, DT, LI);
888
889    return SafeStack(F, *TL, *DL, SE).run();
890  }
891};
892
893} // end anonymous namespace
894
895char SafeStackLegacyPass::ID = 0;
896
897INITIALIZE_PASS_BEGIN(SafeStackLegacyPass, DEBUG_TYPE,
898                      "Safe Stack instrumentation pass", false, false)
899INITIALIZE_PASS_DEPENDENCY(TargetPassConfig)
900INITIALIZE_PASS_END(SafeStackLegacyPass, DEBUG_TYPE,
901                    "Safe Stack instrumentation pass", false, false)
902
903FunctionPass *llvm::createSafeStackPass() { return new SafeStackLegacyPass(); }
904