1//===- SafeStack.cpp - Safe Stack Insertion -------------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This pass splits the stack into the safe stack (kept as-is for LLVM backend)
10// and the unsafe stack (explicitly allocated and managed through the runtime
11// support library).
12//
13// http://clang.llvm.org/docs/SafeStack.html
14//
15//===----------------------------------------------------------------------===//
16
17#include "SafeStackLayout.h"
18#include "llvm/ADT/APInt.h"
19#include "llvm/ADT/ArrayRef.h"
20#include "llvm/ADT/BitVector.h"
21#include "llvm/ADT/SmallPtrSet.h"
22#include "llvm/ADT/SmallVector.h"
23#include "llvm/ADT/Statistic.h"
24#include "llvm/Analysis/AssumptionCache.h"
25#include "llvm/Analysis/BranchProbabilityInfo.h"
26#include "llvm/Analysis/InlineCost.h"
27#include "llvm/Analysis/LoopInfo.h"
28#include "llvm/Analysis/ScalarEvolution.h"
29#include "llvm/Analysis/ScalarEvolutionExpressions.h"
30#include "llvm/Analysis/StackLifetime.h"
31#include "llvm/Analysis/TargetLibraryInfo.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/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// Disabled by default due to PR32143.
100static cl::opt<bool> ClColoring("safe-stack-coloring",
101                                cl::desc("enable safe stack coloring"),
102                                cl::Hidden, cl::init(false));
103
104namespace {
105
106/// Rewrite an SCEV expression for a memory access address to an expression that
107/// represents offset from the given alloca.
108///
109/// The implementation simply replaces all mentions of the alloca with zero.
110class AllocaOffsetRewriter : public SCEVRewriteVisitor<AllocaOffsetRewriter> {
111  const Value *AllocaPtr;
112
113public:
114  AllocaOffsetRewriter(ScalarEvolution &SE, const Value *AllocaPtr)
115      : SCEVRewriteVisitor(SE), AllocaPtr(AllocaPtr) {}
116
117  const SCEV *visitUnknown(const SCEVUnknown *Expr) {
118    if (Expr->getValue() == AllocaPtr)
119      return SE.getZero(Expr->getType());
120    return Expr;
121  }
122};
123
124/// The SafeStack pass splits the stack of each function into the safe
125/// stack, which is only accessed through memory safe dereferences (as
126/// determined statically), and the unsafe stack, which contains all
127/// local variables that are accessed in ways that we can't prove to
128/// be safe.
129class SafeStack {
130  Function &F;
131  const TargetLoweringBase &TL;
132  const DataLayout &DL;
133  ScalarEvolution &SE;
134
135  Type *StackPtrTy;
136  Type *IntPtrTy;
137  Type *Int32Ty;
138  Type *Int8Ty;
139
140  Value *UnsafeStackPtr = nullptr;
141
142  /// Unsafe stack alignment. Each stack frame must ensure that the stack is
143  /// aligned to this value. We need to re-align the unsafe stack if the
144  /// alignment of any object on the stack exceeds this value.
145  ///
146  /// 16 seems like a reasonable upper bound on the alignment of objects that we
147  /// might expect to appear on the stack on most common targets.
148  enum { StackAlignment = 16 };
149
150  /// Return the value of the stack canary.
151  Value *getStackGuard(IRBuilder<> &IRB, Function &F);
152
153  /// Load stack guard from the frame and check if it has changed.
154  void checkStackGuard(IRBuilder<> &IRB, Function &F, ReturnInst &RI,
155                       AllocaInst *StackGuardSlot, Value *StackGuard);
156
157  /// Find all static allocas, dynamic allocas, return instructions and
158  /// stack restore points (exception unwind blocks and setjmp calls) in the
159  /// given function and append them to the respective vectors.
160  void findInsts(Function &F, SmallVectorImpl<AllocaInst *> &StaticAllocas,
161                 SmallVectorImpl<AllocaInst *> &DynamicAllocas,
162                 SmallVectorImpl<Argument *> &ByValArguments,
163                 SmallVectorImpl<ReturnInst *> &Returns,
164                 SmallVectorImpl<Instruction *> &StackRestorePoints);
165
166  /// Calculate the allocation size of a given alloca. Returns 0 if the
167  /// size can not be statically determined.
168  uint64_t getStaticAllocaAllocationSize(const AllocaInst* AI);
169
170  /// Allocate space for all static allocas in \p StaticAllocas,
171  /// replace allocas with pointers into the unsafe stack and generate code to
172  /// restore the stack pointer before all return instructions in \p Returns.
173  ///
174  /// \returns A pointer to the top of the unsafe stack after all unsafe static
175  /// allocas are allocated.
176  Value *moveStaticAllocasToUnsafeStack(IRBuilder<> &IRB, Function &F,
177                                        ArrayRef<AllocaInst *> StaticAllocas,
178                                        ArrayRef<Argument *> ByValArguments,
179                                        ArrayRef<ReturnInst *> Returns,
180                                        Instruction *BasePointer,
181                                        AllocaInst *StackGuardSlot);
182
183  /// Generate code to restore the stack after all stack restore points
184  /// in \p StackRestorePoints.
185  ///
186  /// \returns A local variable in which to maintain the dynamic top of the
187  /// unsafe stack if needed.
188  AllocaInst *
189  createStackRestorePoints(IRBuilder<> &IRB, Function &F,
190                           ArrayRef<Instruction *> StackRestorePoints,
191                           Value *StaticTop, bool NeedDynamicTop);
192
193  /// Replace all allocas in \p DynamicAllocas with code to allocate
194  /// space dynamically on the unsafe stack and store the dynamic unsafe stack
195  /// top to \p DynamicTop if non-null.
196  void moveDynamicAllocasToUnsafeStack(Function &F, Value *UnsafeStackPtr,
197                                       AllocaInst *DynamicTop,
198                                       ArrayRef<AllocaInst *> DynamicAllocas);
199
200  bool IsSafeStackAlloca(const Value *AllocaPtr, uint64_t AllocaSize);
201
202  bool IsMemIntrinsicSafe(const MemIntrinsic *MI, const Use &U,
203                          const Value *AllocaPtr, uint64_t AllocaSize);
204  bool IsAccessSafe(Value *Addr, uint64_t Size, const Value *AllocaPtr,
205                    uint64_t AllocaSize);
206
207  bool ShouldInlinePointerAddress(CallInst &CI);
208  void TryInlinePointerAddress();
209
210public:
211  SafeStack(Function &F, const TargetLoweringBase &TL, const DataLayout &DL,
212            ScalarEvolution &SE)
213      : F(F), TL(TL), DL(DL), SE(SE),
214        StackPtrTy(Type::getInt8PtrTy(F.getContext())),
215        IntPtrTy(DL.getIntPtrType(F.getContext())),
216        Int32Ty(Type::getInt32Ty(F.getContext())),
217        Int8Ty(Type::getInt8Ty(F.getContext())) {}
218
219  // Run the transformation on the associated function.
220  // Returns whether the function was changed.
221  bool run();
222};
223
224uint64_t SafeStack::getStaticAllocaAllocationSize(const AllocaInst* AI) {
225  uint64_t Size = DL.getTypeAllocSize(AI->getAllocatedType());
226  if (AI->isArrayAllocation()) {
227    auto C = dyn_cast<ConstantInt>(AI->getArraySize());
228    if (!C)
229      return 0;
230    Size *= C->getZExtValue();
231  }
232  return Size;
233}
234
235bool SafeStack::IsAccessSafe(Value *Addr, uint64_t AccessSize,
236                             const Value *AllocaPtr, uint64_t AllocaSize) {
237  AllocaOffsetRewriter Rewriter(SE, AllocaPtr);
238  const SCEV *Expr = Rewriter.visit(SE.getSCEV(Addr));
239
240  uint64_t BitWidth = SE.getTypeSizeInBits(Expr->getType());
241  ConstantRange AccessStartRange = SE.getUnsignedRange(Expr);
242  ConstantRange SizeRange =
243      ConstantRange(APInt(BitWidth, 0), APInt(BitWidth, AccessSize));
244  ConstantRange AccessRange = AccessStartRange.add(SizeRange);
245  ConstantRange AllocaRange =
246      ConstantRange(APInt(BitWidth, 0), APInt(BitWidth, AllocaSize));
247  bool Safe = AllocaRange.contains(AccessRange);
248
249  LLVM_DEBUG(
250      dbgs() << "[SafeStack] "
251             << (isa<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")
252             << *AllocaPtr << "\n"
253             << "            Access " << *Addr << "\n"
254             << "            SCEV " << *Expr
255             << " U: " << SE.getUnsignedRange(Expr)
256             << ", S: " << SE.getSignedRange(Expr) << "\n"
257             << "            Range " << AccessRange << "\n"
258             << "            AllocaRange " << AllocaRange << "\n"
259             << "            " << (Safe ? "safe" : "unsafe") << "\n");
260
261  return Safe;
262}
263
264bool SafeStack::IsMemIntrinsicSafe(const MemIntrinsic *MI, const Use &U,
265                                   const Value *AllocaPtr,
266                                   uint64_t AllocaSize) {
267  if (auto MTI = dyn_cast<MemTransferInst>(MI)) {
268    if (MTI->getRawSource() != U && MTI->getRawDest() != U)
269      return true;
270  } else {
271    if (MI->getRawDest() != U)
272      return true;
273  }
274
275  const auto *Len = dyn_cast<ConstantInt>(MI->getLength());
276  // Non-constant size => unsafe. FIXME: try SCEV getRange.
277  if (!Len) return false;
278  return IsAccessSafe(U, Len->getZExtValue(), AllocaPtr, AllocaSize);
279}
280
281/// Check whether a given allocation must be put on the safe
282/// stack or not. The function analyzes all uses of AI and checks whether it is
283/// only accessed in a memory safe way (as decided statically).
284bool SafeStack::IsSafeStackAlloca(const Value *AllocaPtr, uint64_t AllocaSize) {
285  // Go through all uses of this alloca and check whether all accesses to the
286  // allocated object are statically known to be memory safe and, hence, the
287  // object can be placed on the safe stack.
288  SmallPtrSet<const Value *, 16> Visited;
289  SmallVector<const Value *, 8> WorkList;
290  WorkList.push_back(AllocaPtr);
291
292  // A DFS search through all uses of the alloca in bitcasts/PHI/GEPs/etc.
293  while (!WorkList.empty()) {
294    const Value *V = WorkList.pop_back_val();
295    for (const Use &UI : V->uses()) {
296      auto I = cast<const Instruction>(UI.getUser());
297      assert(V == UI.get());
298
299      switch (I->getOpcode()) {
300      case Instruction::Load:
301        if (!IsAccessSafe(UI, DL.getTypeStoreSize(I->getType()), AllocaPtr,
302                          AllocaSize))
303          return false;
304        break;
305
306      case Instruction::VAArg:
307        // "va-arg" from a pointer is safe.
308        break;
309      case Instruction::Store:
310        if (V == I->getOperand(0)) {
311          // Stored the pointer - conservatively assume it may be unsafe.
312          LLVM_DEBUG(dbgs()
313                     << "[SafeStack] Unsafe alloca: " << *AllocaPtr
314                     << "\n            store of address: " << *I << "\n");
315          return false;
316        }
317
318        if (!IsAccessSafe(UI, DL.getTypeStoreSize(I->getOperand(0)->getType()),
319                          AllocaPtr, AllocaSize))
320          return false;
321        break;
322
323      case Instruction::Ret:
324        // Information leak.
325        return false;
326
327      case Instruction::Call:
328      case Instruction::Invoke: {
329        const CallBase &CS = *cast<CallBase>(I);
330
331        if (I->isLifetimeStartOrEnd())
332          continue;
333
334        if (const MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) {
335          if (!IsMemIntrinsicSafe(MI, UI, AllocaPtr, AllocaSize)) {
336            LLVM_DEBUG(dbgs()
337                       << "[SafeStack] Unsafe alloca: " << *AllocaPtr
338                       << "\n            unsafe memintrinsic: " << *I << "\n");
339            return false;
340          }
341          continue;
342        }
343
344        // LLVM 'nocapture' attribute is only set for arguments whose address
345        // is not stored, passed around, or used in any other non-trivial way.
346        // We assume that passing a pointer to an object as a 'nocapture
347        // readnone' argument is safe.
348        // FIXME: a more precise solution would require an interprocedural
349        // analysis here, which would look at all uses of an argument inside
350        // the function being called.
351        auto B = CS.arg_begin(), E = CS.arg_end();
352        for (auto A = B; A != E; ++A)
353          if (A->get() == V)
354            if (!(CS.doesNotCapture(A - B) && (CS.doesNotAccessMemory(A - B) ||
355                                               CS.doesNotAccessMemory()))) {
356              LLVM_DEBUG(dbgs() << "[SafeStack] Unsafe alloca: " << *AllocaPtr
357                                << "\n            unsafe call: " << *I << "\n");
358              return false;
359            }
360        continue;
361      }
362
363      default:
364        if (Visited.insert(I).second)
365          WorkList.push_back(cast<const Instruction>(I));
366      }
367    }
368  }
369
370  // All uses of the alloca are safe, we can place it on the safe stack.
371  return true;
372}
373
374Value *SafeStack::getStackGuard(IRBuilder<> &IRB, Function &F) {
375  Value *StackGuardVar = TL.getIRStackGuard(IRB);
376  if (!StackGuardVar)
377    StackGuardVar =
378        F.getParent()->getOrInsertGlobal("__stack_chk_guard", StackPtrTy);
379  return IRB.CreateLoad(StackPtrTy, StackGuardVar, "StackGuard");
380}
381
382void SafeStack::findInsts(Function &F,
383                          SmallVectorImpl<AllocaInst *> &StaticAllocas,
384                          SmallVectorImpl<AllocaInst *> &DynamicAllocas,
385                          SmallVectorImpl<Argument *> &ByValArguments,
386                          SmallVectorImpl<ReturnInst *> &Returns,
387                          SmallVectorImpl<Instruction *> &StackRestorePoints) {
388  for (Instruction &I : instructions(&F)) {
389    if (auto AI = dyn_cast<AllocaInst>(&I)) {
390      ++NumAllocas;
391
392      uint64_t Size = getStaticAllocaAllocationSize(AI);
393      if (IsSafeStackAlloca(AI, Size))
394        continue;
395
396      if (AI->isStaticAlloca()) {
397        ++NumUnsafeStaticAllocas;
398        StaticAllocas.push_back(AI);
399      } else {
400        ++NumUnsafeDynamicAllocas;
401        DynamicAllocas.push_back(AI);
402      }
403    } else if (auto RI = dyn_cast<ReturnInst>(&I)) {
404      Returns.push_back(RI);
405    } else if (auto CI = dyn_cast<CallInst>(&I)) {
406      // setjmps require stack restore.
407      if (CI->getCalledFunction() && CI->canReturnTwice())
408        StackRestorePoints.push_back(CI);
409    } else if (auto LP = dyn_cast<LandingPadInst>(&I)) {
410      // Exception landing pads require stack restore.
411      StackRestorePoints.push_back(LP);
412    } else if (auto II = dyn_cast<IntrinsicInst>(&I)) {
413      if (II->getIntrinsicID() == Intrinsic::gcroot)
414        report_fatal_error(
415            "gcroot intrinsic not compatible with safestack attribute");
416    }
417  }
418  for (Argument &Arg : F.args()) {
419    if (!Arg.hasByValAttr())
420      continue;
421    uint64_t Size =
422        DL.getTypeStoreSize(Arg.getType()->getPointerElementType());
423    if (IsSafeStackAlloca(&Arg, Size))
424      continue;
425
426    ++NumUnsafeByValArguments;
427    ByValArguments.push_back(&Arg);
428  }
429}
430
431AllocaInst *
432SafeStack::createStackRestorePoints(IRBuilder<> &IRB, Function &F,
433                                    ArrayRef<Instruction *> StackRestorePoints,
434                                    Value *StaticTop, bool NeedDynamicTop) {
435  assert(StaticTop && "The stack top isn't set.");
436
437  if (StackRestorePoints.empty())
438    return nullptr;
439
440  // We need the current value of the shadow stack pointer to restore
441  // after longjmp or exception catching.
442
443  // FIXME: On some platforms this could be handled by the longjmp/exception
444  // runtime itself.
445
446  AllocaInst *DynamicTop = nullptr;
447  if (NeedDynamicTop) {
448    // If we also have dynamic alloca's, the stack pointer value changes
449    // throughout the function. For now we store it in an alloca.
450    DynamicTop = IRB.CreateAlloca(StackPtrTy, /*ArraySize=*/nullptr,
451                                  "unsafe_stack_dynamic_ptr");
452    IRB.CreateStore(StaticTop, DynamicTop);
453  }
454
455  // Restore current stack pointer after longjmp/exception catch.
456  for (Instruction *I : StackRestorePoints) {
457    ++NumUnsafeStackRestorePoints;
458
459    IRB.SetInsertPoint(I->getNextNode());
460    Value *CurrentTop =
461        DynamicTop ? IRB.CreateLoad(StackPtrTy, DynamicTop) : StaticTop;
462    IRB.CreateStore(CurrentTop, UnsafeStackPtr);
463  }
464
465  return DynamicTop;
466}
467
468void SafeStack::checkStackGuard(IRBuilder<> &IRB, Function &F, ReturnInst &RI,
469                                AllocaInst *StackGuardSlot, Value *StackGuard) {
470  Value *V = IRB.CreateLoad(StackPtrTy, StackGuardSlot);
471  Value *Cmp = IRB.CreateICmpNE(StackGuard, V);
472
473  auto SuccessProb = BranchProbabilityInfo::getBranchProbStackProtector(true);
474  auto FailureProb = BranchProbabilityInfo::getBranchProbStackProtector(false);
475  MDNode *Weights = MDBuilder(F.getContext())
476                        .createBranchWeights(SuccessProb.getNumerator(),
477                                             FailureProb.getNumerator());
478  Instruction *CheckTerm =
479      SplitBlockAndInsertIfThen(Cmp, &RI,
480                                /* Unreachable */ true, Weights);
481  IRBuilder<> IRBFail(CheckTerm);
482  // FIXME: respect -fsanitize-trap / -ftrap-function here?
483  FunctionCallee StackChkFail =
484      F.getParent()->getOrInsertFunction("__stack_chk_fail", IRB.getVoidTy());
485  IRBFail.CreateCall(StackChkFail, {});
486}
487
488/// We explicitly compute and set the unsafe stack layout for all unsafe
489/// static alloca instructions. We save the unsafe "base pointer" in the
490/// prologue into a local variable and restore it in the epilogue.
491Value *SafeStack::moveStaticAllocasToUnsafeStack(
492    IRBuilder<> &IRB, Function &F, ArrayRef<AllocaInst *> StaticAllocas,
493    ArrayRef<Argument *> ByValArguments, ArrayRef<ReturnInst *> Returns,
494    Instruction *BasePointer, AllocaInst *StackGuardSlot) {
495  if (StaticAllocas.empty() && ByValArguments.empty())
496    return BasePointer;
497
498  DIBuilder DIB(*F.getParent());
499
500  StackLifetime SSC(F, StaticAllocas, StackLifetime::LivenessType::May);
501  static const StackLifetime::LiveRange NoColoringRange(1, true);
502  if (ClColoring)
503    SSC.run();
504
505  for (auto *I : SSC.getMarkers()) {
506    auto *Op = dyn_cast<Instruction>(I->getOperand(1));
507    const_cast<IntrinsicInst *>(I)->eraseFromParent();
508    // Remove the operand bitcast, too, if it has no more uses left.
509    if (Op && Op->use_empty())
510      Op->eraseFromParent();
511  }
512
513  // Unsafe stack always grows down.
514  StackLayout SSL(StackAlignment);
515  if (StackGuardSlot) {
516    Type *Ty = StackGuardSlot->getAllocatedType();
517    unsigned Align =
518        std::max(DL.getPrefTypeAlignment(Ty), StackGuardSlot->getAlignment());
519    SSL.addObject(StackGuardSlot, getStaticAllocaAllocationSize(StackGuardSlot),
520                  Align, SSC.getFullLiveRange());
521  }
522
523  for (Argument *Arg : ByValArguments) {
524    Type *Ty = Arg->getType()->getPointerElementType();
525    uint64_t Size = DL.getTypeStoreSize(Ty);
526    if (Size == 0)
527      Size = 1; // Don't create zero-sized stack objects.
528
529    // Ensure the object is properly aligned.
530    unsigned Align = std::max((unsigned)DL.getPrefTypeAlignment(Ty),
531                              Arg->getParamAlignment());
532    SSL.addObject(Arg, Size, Align, SSC.getFullLiveRange());
533  }
534
535  for (AllocaInst *AI : StaticAllocas) {
536    Type *Ty = AI->getAllocatedType();
537    uint64_t Size = getStaticAllocaAllocationSize(AI);
538    if (Size == 0)
539      Size = 1; // Don't create zero-sized stack objects.
540
541    // Ensure the object is properly aligned.
542    unsigned Align =
543        std::max((unsigned)DL.getPrefTypeAlignment(Ty), AI->getAlignment());
544
545    SSL.addObject(AI, Size, Align,
546                  ClColoring ? SSC.getLiveRange(AI) : NoColoringRange);
547  }
548
549  SSL.computeLayout();
550  unsigned FrameAlignment = SSL.getFrameAlignment();
551
552  // FIXME: tell SSL that we start at a less-then-MaxAlignment aligned location
553  // (AlignmentSkew).
554  if (FrameAlignment > StackAlignment) {
555    // Re-align the base pointer according to the max requested alignment.
556    assert(isPowerOf2_32(FrameAlignment));
557    IRB.SetInsertPoint(BasePointer->getNextNode());
558    BasePointer = cast<Instruction>(IRB.CreateIntToPtr(
559        IRB.CreateAnd(IRB.CreatePtrToInt(BasePointer, IntPtrTy),
560                      ConstantInt::get(IntPtrTy, ~uint64_t(FrameAlignment - 1))),
561        StackPtrTy));
562  }
563
564  IRB.SetInsertPoint(BasePointer->getNextNode());
565
566  if (StackGuardSlot) {
567    unsigned Offset = SSL.getObjectOffset(StackGuardSlot);
568    Value *Off = IRB.CreateGEP(Int8Ty, BasePointer, // BasePointer is i8*
569                               ConstantInt::get(Int32Ty, -Offset));
570    Value *NewAI =
571        IRB.CreateBitCast(Off, StackGuardSlot->getType(), "StackGuardSlot");
572
573    // Replace alloc with the new location.
574    StackGuardSlot->replaceAllUsesWith(NewAI);
575    StackGuardSlot->eraseFromParent();
576  }
577
578  for (Argument *Arg : ByValArguments) {
579    unsigned Offset = SSL.getObjectOffset(Arg);
580    MaybeAlign Align(SSL.getObjectAlignment(Arg));
581    Type *Ty = Arg->getType()->getPointerElementType();
582
583    uint64_t Size = DL.getTypeStoreSize(Ty);
584    if (Size == 0)
585      Size = 1; // Don't create zero-sized stack objects.
586
587    Value *Off = IRB.CreateGEP(Int8Ty, BasePointer, // BasePointer is i8*
588                               ConstantInt::get(Int32Ty, -Offset));
589    Value *NewArg = IRB.CreateBitCast(Off, Arg->getType(),
590                                     Arg->getName() + ".unsafe-byval");
591
592    // Replace alloc with the new location.
593    replaceDbgDeclare(Arg, BasePointer, DIB, DIExpression::ApplyOffset,
594                      -Offset);
595    Arg->replaceAllUsesWith(NewArg);
596    IRB.SetInsertPoint(cast<Instruction>(NewArg)->getNextNode());
597    IRB.CreateMemCpy(Off, Align, Arg, Arg->getParamAlign(), Size);
598  }
599
600  // Allocate space for every unsafe static AllocaInst on the unsafe stack.
601  for (AllocaInst *AI : StaticAllocas) {
602    IRB.SetInsertPoint(AI);
603    unsigned Offset = SSL.getObjectOffset(AI);
604
605    replaceDbgDeclare(AI, BasePointer, DIB, DIExpression::ApplyOffset, -Offset);
606    replaceDbgValueForAlloca(AI, BasePointer, DIB, -Offset);
607
608    // Replace uses of the alloca with the new location.
609    // Insert address calculation close to each use to work around PR27844.
610    std::string Name = std::string(AI->getName()) + ".unsafe";
611    while (!AI->use_empty()) {
612      Use &U = *AI->use_begin();
613      Instruction *User = cast<Instruction>(U.getUser());
614
615      Instruction *InsertBefore;
616      if (auto *PHI = dyn_cast<PHINode>(User))
617        InsertBefore = PHI->getIncomingBlock(U)->getTerminator();
618      else
619        InsertBefore = User;
620
621      IRBuilder<> IRBUser(InsertBefore);
622      Value *Off = IRBUser.CreateGEP(Int8Ty, BasePointer, // BasePointer is i8*
623                                     ConstantInt::get(Int32Ty, -Offset));
624      Value *Replacement = IRBUser.CreateBitCast(Off, AI->getType(), Name);
625
626      if (auto *PHI = dyn_cast<PHINode>(User))
627        // PHI nodes may have multiple incoming edges from the same BB (why??),
628        // all must be updated at once with the same incoming value.
629        PHI->setIncomingValueForBlock(PHI->getIncomingBlock(U), Replacement);
630      else
631        U.set(Replacement);
632    }
633
634    AI->eraseFromParent();
635  }
636
637  // Re-align BasePointer so that our callees would see it aligned as
638  // expected.
639  // FIXME: no need to update BasePointer in leaf functions.
640  unsigned FrameSize = alignTo(SSL.getFrameSize(), StackAlignment);
641
642  // Update shadow stack pointer in the function epilogue.
643  IRB.SetInsertPoint(BasePointer->getNextNode());
644
645  Value *StaticTop =
646      IRB.CreateGEP(Int8Ty, BasePointer, ConstantInt::get(Int32Ty, -FrameSize),
647                    "unsafe_stack_static_top");
648  IRB.CreateStore(StaticTop, UnsafeStackPtr);
649  return StaticTop;
650}
651
652void SafeStack::moveDynamicAllocasToUnsafeStack(
653    Function &F, Value *UnsafeStackPtr, AllocaInst *DynamicTop,
654    ArrayRef<AllocaInst *> DynamicAllocas) {
655  DIBuilder DIB(*F.getParent());
656
657  for (AllocaInst *AI : DynamicAllocas) {
658    IRBuilder<> IRB(AI);
659
660    // Compute the new SP value (after AI).
661    Value *ArraySize = AI->getArraySize();
662    if (ArraySize->getType() != IntPtrTy)
663      ArraySize = IRB.CreateIntCast(ArraySize, IntPtrTy, false);
664
665    Type *Ty = AI->getAllocatedType();
666    uint64_t TySize = DL.getTypeAllocSize(Ty);
667    Value *Size = IRB.CreateMul(ArraySize, ConstantInt::get(IntPtrTy, TySize));
668
669    Value *SP = IRB.CreatePtrToInt(IRB.CreateLoad(StackPtrTy, UnsafeStackPtr),
670                                   IntPtrTy);
671    SP = IRB.CreateSub(SP, Size);
672
673    // Align the SP value to satisfy the AllocaInst, type and stack alignments.
674    unsigned Align = std::max(
675        std::max((unsigned)DL.getPrefTypeAlignment(Ty), AI->getAlignment()),
676        (unsigned)StackAlignment);
677
678    assert(isPowerOf2_32(Align));
679    Value *NewTop = IRB.CreateIntToPtr(
680        IRB.CreateAnd(SP, ConstantInt::get(IntPtrTy, ~uint64_t(Align - 1))),
681        StackPtrTy);
682
683    // Save the stack pointer.
684    IRB.CreateStore(NewTop, UnsafeStackPtr);
685    if (DynamicTop)
686      IRB.CreateStore(NewTop, DynamicTop);
687
688    Value *NewAI = IRB.CreatePointerCast(NewTop, AI->getType());
689    if (AI->hasName() && isa<Instruction>(NewAI))
690      NewAI->takeName(AI);
691
692    replaceDbgDeclare(AI, NewAI, DIB, DIExpression::ApplyOffset, 0);
693    AI->replaceAllUsesWith(NewAI);
694    AI->eraseFromParent();
695  }
696
697  if (!DynamicAllocas.empty()) {
698    // Now go through the instructions again, replacing stacksave/stackrestore.
699    for (inst_iterator It = inst_begin(&F), Ie = inst_end(&F); It != Ie;) {
700      Instruction *I = &*(It++);
701      auto II = dyn_cast<IntrinsicInst>(I);
702      if (!II)
703        continue;
704
705      if (II->getIntrinsicID() == Intrinsic::stacksave) {
706        IRBuilder<> IRB(II);
707        Instruction *LI = IRB.CreateLoad(StackPtrTy, UnsafeStackPtr);
708        LI->takeName(II);
709        II->replaceAllUsesWith(LI);
710        II->eraseFromParent();
711      } else if (II->getIntrinsicID() == Intrinsic::stackrestore) {
712        IRBuilder<> IRB(II);
713        Instruction *SI = IRB.CreateStore(II->getArgOperand(0), UnsafeStackPtr);
714        SI->takeName(II);
715        assert(II->use_empty());
716        II->eraseFromParent();
717      }
718    }
719  }
720}
721
722bool SafeStack::ShouldInlinePointerAddress(CallInst &CI) {
723  Function *Callee = CI.getCalledFunction();
724  if (CI.hasFnAttr(Attribute::AlwaysInline) &&
725      isInlineViable(*Callee).isSuccess())
726    return true;
727  if (Callee->isInterposable() || Callee->hasFnAttribute(Attribute::NoInline) ||
728      CI.isNoInline())
729    return false;
730  return true;
731}
732
733void SafeStack::TryInlinePointerAddress() {
734  auto *CI = dyn_cast<CallInst>(UnsafeStackPtr);
735  if (!CI)
736    return;
737
738  if(F.hasOptNone())
739    return;
740
741  Function *Callee = CI->getCalledFunction();
742  if (!Callee || Callee->isDeclaration())
743    return;
744
745  if (!ShouldInlinePointerAddress(*CI))
746    return;
747
748  InlineFunctionInfo IFI;
749  InlineFunction(*CI, IFI);
750}
751
752bool SafeStack::run() {
753  assert(F.hasFnAttribute(Attribute::SafeStack) &&
754         "Can't run SafeStack on a function without the attribute");
755  assert(!F.isDeclaration() && "Can't run SafeStack on a function declaration");
756
757  ++NumFunctions;
758
759  SmallVector<AllocaInst *, 16> StaticAllocas;
760  SmallVector<AllocaInst *, 4> DynamicAllocas;
761  SmallVector<Argument *, 4> ByValArguments;
762  SmallVector<ReturnInst *, 4> Returns;
763
764  // Collect all points where stack gets unwound and needs to be restored
765  // This is only necessary because the runtime (setjmp and unwind code) is
766  // not aware of the unsafe stack and won't unwind/restore it properly.
767  // To work around this problem without changing the runtime, we insert
768  // instrumentation to restore the unsafe stack pointer when necessary.
769  SmallVector<Instruction *, 4> StackRestorePoints;
770
771  // Find all static and dynamic alloca instructions that must be moved to the
772  // unsafe stack, all return instructions and stack restore points.
773  findInsts(F, StaticAllocas, DynamicAllocas, ByValArguments, Returns,
774            StackRestorePoints);
775
776  if (StaticAllocas.empty() && DynamicAllocas.empty() &&
777      ByValArguments.empty() && StackRestorePoints.empty())
778    return false; // Nothing to do in this function.
779
780  if (!StaticAllocas.empty() || !DynamicAllocas.empty() ||
781      !ByValArguments.empty())
782    ++NumUnsafeStackFunctions; // This function has the unsafe stack.
783
784  if (!StackRestorePoints.empty())
785    ++NumUnsafeStackRestorePointsFunctions;
786
787  IRBuilder<> IRB(&F.front(), F.begin()->getFirstInsertionPt());
788  // Calls must always have a debug location, or else inlining breaks. So
789  // we explicitly set a artificial debug location here.
790  if (DISubprogram *SP = F.getSubprogram())
791    IRB.SetCurrentDebugLocation(DebugLoc::get(SP->getScopeLine(), 0, SP));
792  if (SafeStackUsePointerAddress) {
793    FunctionCallee Fn = F.getParent()->getOrInsertFunction(
794        "__safestack_pointer_address", StackPtrTy->getPointerTo(0));
795    UnsafeStackPtr = IRB.CreateCall(Fn);
796  } else {
797    UnsafeStackPtr = TL.getSafeStackPointerLocation(IRB);
798  }
799
800  // Load the current stack pointer (we'll also use it as a base pointer).
801  // FIXME: use a dedicated register for it ?
802  Instruction *BasePointer =
803      IRB.CreateLoad(StackPtrTy, UnsafeStackPtr, false, "unsafe_stack_ptr");
804  assert(BasePointer->getType() == StackPtrTy);
805
806  AllocaInst *StackGuardSlot = nullptr;
807  // FIXME: implement weaker forms of stack protector.
808  if (F.hasFnAttribute(Attribute::StackProtect) ||
809      F.hasFnAttribute(Attribute::StackProtectStrong) ||
810      F.hasFnAttribute(Attribute::StackProtectReq)) {
811    Value *StackGuard = getStackGuard(IRB, F);
812    StackGuardSlot = IRB.CreateAlloca(StackPtrTy, nullptr);
813    IRB.CreateStore(StackGuard, StackGuardSlot);
814
815    for (ReturnInst *RI : Returns) {
816      IRBuilder<> IRBRet(RI);
817      checkStackGuard(IRBRet, F, *RI, StackGuardSlot, StackGuard);
818    }
819  }
820
821  // The top of the unsafe stack after all unsafe static allocas are
822  // allocated.
823  Value *StaticTop =
824      moveStaticAllocasToUnsafeStack(IRB, F, StaticAllocas, ByValArguments,
825                                     Returns, BasePointer, StackGuardSlot);
826
827  // Safe stack object that stores the current unsafe stack top. It is updated
828  // as unsafe dynamic (non-constant-sized) allocas are allocated and freed.
829  // This is only needed if we need to restore stack pointer after longjmp
830  // or exceptions, and we have dynamic allocations.
831  // FIXME: a better alternative might be to store the unsafe stack pointer
832  // before setjmp / invoke instructions.
833  AllocaInst *DynamicTop = createStackRestorePoints(
834      IRB, F, StackRestorePoints, StaticTop, !DynamicAllocas.empty());
835
836  // Handle dynamic allocas.
837  moveDynamicAllocasToUnsafeStack(F, UnsafeStackPtr, DynamicTop,
838                                  DynamicAllocas);
839
840  // Restore the unsafe stack pointer before each return.
841  for (ReturnInst *RI : Returns) {
842    IRB.SetInsertPoint(RI);
843    IRB.CreateStore(BasePointer, UnsafeStackPtr);
844  }
845
846  TryInlinePointerAddress();
847
848  LLVM_DEBUG(dbgs() << "[SafeStack]     safestack applied\n");
849  return true;
850}
851
852class SafeStackLegacyPass : public FunctionPass {
853  const TargetMachine *TM = nullptr;
854
855public:
856  static char ID; // Pass identification, replacement for typeid..
857
858  SafeStackLegacyPass() : FunctionPass(ID) {
859    initializeSafeStackLegacyPassPass(*PassRegistry::getPassRegistry());
860  }
861
862  void getAnalysisUsage(AnalysisUsage &AU) const override {
863    AU.addRequired<TargetPassConfig>();
864    AU.addRequired<TargetLibraryInfoWrapperPass>();
865    AU.addRequired<AssumptionCacheTracker>();
866  }
867
868  bool runOnFunction(Function &F) override {
869    LLVM_DEBUG(dbgs() << "[SafeStack] Function: " << F.getName() << "\n");
870
871    if (!F.hasFnAttribute(Attribute::SafeStack)) {
872      LLVM_DEBUG(dbgs() << "[SafeStack]     safestack is not requested"
873                           " for this function\n");
874      return false;
875    }
876
877    if (F.isDeclaration()) {
878      LLVM_DEBUG(dbgs() << "[SafeStack]     function definition"
879                           " is not available\n");
880      return false;
881    }
882
883    TM = &getAnalysis<TargetPassConfig>().getTM<TargetMachine>();
884    auto *TL = TM->getSubtargetImpl(F)->getTargetLowering();
885    if (!TL)
886      report_fatal_error("TargetLowering instance is required");
887
888    auto *DL = &F.getParent()->getDataLayout();
889    auto &TLI = getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F);
890    auto &ACT = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
891
892    // Compute DT and LI only for functions that have the attribute.
893    // This is only useful because the legacy pass manager doesn't let us
894    // compute analyzes lazily.
895    // In the backend pipeline, nothing preserves DT before SafeStack, so we
896    // would otherwise always compute it wastefully, even if there is no
897    // function with the safestack attribute.
898    DominatorTree DT(F);
899    LoopInfo LI(DT);
900
901    ScalarEvolution SE(F, TLI, ACT, DT, LI);
902
903    return SafeStack(F, *TL, *DL, SE).run();
904  }
905};
906
907} // end anonymous namespace
908
909char SafeStackLegacyPass::ID = 0;
910
911INITIALIZE_PASS_BEGIN(SafeStackLegacyPass, DEBUG_TYPE,
912                      "Safe Stack instrumentation pass", false, false)
913INITIALIZE_PASS_DEPENDENCY(TargetPassConfig)
914INITIALIZE_PASS_END(SafeStackLegacyPass, DEBUG_TYPE,
915                    "Safe Stack instrumentation pass", false, false)
916
917FunctionPass *llvm::createSafeStackPass() { return new SafeStackLegacyPass(); }
918