xref: /freebsd/contrib/llvm-project/llvm/lib/CodeGen/SafeStack.cpp (revision a90b9d0159070121c221b966469c3e36d912bf82)
1 //===- SafeStack.cpp - Safe Stack Insertion -------------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This pass splits the stack into the safe stack (kept as-is for LLVM backend)
10 // and the unsafe stack (explicitly allocated and managed through the runtime
11 // support library).
12 //
13 // http://clang.llvm.org/docs/SafeStack.html
14 //
15 //===----------------------------------------------------------------------===//
16 
17 #include "llvm/CodeGen/SafeStack.h"
18 #include "SafeStackLayout.h"
19 #include "llvm/ADT/APInt.h"
20 #include "llvm/ADT/ArrayRef.h"
21 #include "llvm/ADT/SmallPtrSet.h"
22 #include "llvm/ADT/SmallVector.h"
23 #include "llvm/ADT/Statistic.h"
24 #include "llvm/Analysis/AssumptionCache.h"
25 #include "llvm/Analysis/BranchProbabilityInfo.h"
26 #include "llvm/Analysis/DomTreeUpdater.h"
27 #include "llvm/Analysis/InlineCost.h"
28 #include "llvm/Analysis/LoopInfo.h"
29 #include "llvm/Analysis/ScalarEvolution.h"
30 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
31 #include "llvm/Analysis/StackLifetime.h"
32 #include "llvm/Analysis/TargetLibraryInfo.h"
33 #include "llvm/CodeGen/TargetLowering.h"
34 #include "llvm/CodeGen/TargetPassConfig.h"
35 #include "llvm/CodeGen/TargetSubtargetInfo.h"
36 #include "llvm/IR/Argument.h"
37 #include "llvm/IR/Attributes.h"
38 #include "llvm/IR/ConstantRange.h"
39 #include "llvm/IR/Constants.h"
40 #include "llvm/IR/DIBuilder.h"
41 #include "llvm/IR/DataLayout.h"
42 #include "llvm/IR/DerivedTypes.h"
43 #include "llvm/IR/Dominators.h"
44 #include "llvm/IR/Function.h"
45 #include "llvm/IR/IRBuilder.h"
46 #include "llvm/IR/InstIterator.h"
47 #include "llvm/IR/Instruction.h"
48 #include "llvm/IR/Instructions.h"
49 #include "llvm/IR/IntrinsicInst.h"
50 #include "llvm/IR/Intrinsics.h"
51 #include "llvm/IR/MDBuilder.h"
52 #include "llvm/IR/Metadata.h"
53 #include "llvm/IR/Module.h"
54 #include "llvm/IR/Type.h"
55 #include "llvm/IR/Use.h"
56 #include "llvm/IR/Value.h"
57 #include "llvm/InitializePasses.h"
58 #include "llvm/Pass.h"
59 #include "llvm/Support/Casting.h"
60 #include "llvm/Support/Debug.h"
61 #include "llvm/Support/ErrorHandling.h"
62 #include "llvm/Support/MathExtras.h"
63 #include "llvm/Support/raw_ostream.h"
64 #include "llvm/Target/TargetMachine.h"
65 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
66 #include "llvm/Transforms/Utils/Cloning.h"
67 #include "llvm/Transforms/Utils/Local.h"
68 #include <algorithm>
69 #include <cassert>
70 #include <cstdint>
71 #include <optional>
72 #include <string>
73 #include <utility>
74 
75 using namespace llvm;
76 using namespace llvm::safestack;
77 
78 #define DEBUG_TYPE "safe-stack"
79 
80 namespace llvm {
81 
82 STATISTIC(NumFunctions, "Total number of functions");
83 STATISTIC(NumUnsafeStackFunctions, "Number of functions with unsafe stack");
84 STATISTIC(NumUnsafeStackRestorePointsFunctions,
85           "Number of functions that use setjmp or exceptions");
86 
87 STATISTIC(NumAllocas, "Total number of allocas");
88 STATISTIC(NumUnsafeStaticAllocas, "Number of unsafe static allocas");
89 STATISTIC(NumUnsafeDynamicAllocas, "Number of unsafe dynamic allocas");
90 STATISTIC(NumUnsafeByValArguments, "Number of unsafe byval arguments");
91 STATISTIC(NumUnsafeStackRestorePoints, "Number of setjmps and landingpads");
92 
93 } // namespace llvm
94 
95 /// Use __safestack_pointer_address even if the platform has a faster way of
96 /// access safe stack pointer.
97 static cl::opt<bool>
98     SafeStackUsePointerAddress("safestack-use-pointer-address",
99                                   cl::init(false), cl::Hidden);
100 
101 static cl::opt<bool> ClColoring("safe-stack-coloring",
102                                 cl::desc("enable safe stack coloring"),
103                                 cl::Hidden, cl::init(true));
104 
105 namespace {
106 
107 /// The SafeStack pass splits the stack of each function into the safe
108 /// stack, which is only accessed through memory safe dereferences (as
109 /// determined statically), and the unsafe stack, which contains all
110 /// local variables that are accessed in ways that we can't prove to
111 /// be safe.
112 class SafeStack {
113   Function &F;
114   const TargetLoweringBase &TL;
115   const DataLayout &DL;
116   DomTreeUpdater *DTU;
117   ScalarEvolution &SE;
118 
119   Type *StackPtrTy;
120   Type *IntPtrTy;
121   Type *Int32Ty;
122 
123   Value *UnsafeStackPtr = nullptr;
124 
125   /// Unsafe stack alignment. Each stack frame must ensure that the stack is
126   /// aligned to this value. We need to re-align the unsafe stack if the
127   /// alignment of any object on the stack exceeds this value.
128   ///
129   /// 16 seems like a reasonable upper bound on the alignment of objects that we
130   /// might expect to appear on the stack on most common targets.
131   static constexpr Align StackAlignment = Align::Constant<16>();
132 
133   /// Return the value of the stack canary.
134   Value *getStackGuard(IRBuilder<> &IRB, Function &F);
135 
136   /// Load stack guard from the frame and check if it has changed.
137   void checkStackGuard(IRBuilder<> &IRB, Function &F, Instruction &RI,
138                        AllocaInst *StackGuardSlot, Value *StackGuard);
139 
140   /// Find all static allocas, dynamic allocas, return instructions and
141   /// stack restore points (exception unwind blocks and setjmp calls) in the
142   /// given function and append them to the respective vectors.
143   void findInsts(Function &F, SmallVectorImpl<AllocaInst *> &StaticAllocas,
144                  SmallVectorImpl<AllocaInst *> &DynamicAllocas,
145                  SmallVectorImpl<Argument *> &ByValArguments,
146                  SmallVectorImpl<Instruction *> &Returns,
147                  SmallVectorImpl<Instruction *> &StackRestorePoints);
148 
149   /// Calculate the allocation size of a given alloca. Returns 0 if the
150   /// size can not be statically determined.
151   uint64_t getStaticAllocaAllocationSize(const AllocaInst* AI);
152 
153   /// Allocate space for all static allocas in \p StaticAllocas,
154   /// replace allocas with pointers into the unsafe stack.
155   ///
156   /// \returns A pointer to the top of the unsafe stack after all unsafe static
157   /// allocas are allocated.
158   Value *moveStaticAllocasToUnsafeStack(IRBuilder<> &IRB, Function &F,
159                                         ArrayRef<AllocaInst *> StaticAllocas,
160                                         ArrayRef<Argument *> ByValArguments,
161                                         Instruction *BasePointer,
162                                         AllocaInst *StackGuardSlot);
163 
164   /// Generate code to restore the stack after all stack restore points
165   /// in \p StackRestorePoints.
166   ///
167   /// \returns A local variable in which to maintain the dynamic top of the
168   /// unsafe stack if needed.
169   AllocaInst *
170   createStackRestorePoints(IRBuilder<> &IRB, Function &F,
171                            ArrayRef<Instruction *> StackRestorePoints,
172                            Value *StaticTop, bool NeedDynamicTop);
173 
174   /// Replace all allocas in \p DynamicAllocas with code to allocate
175   /// space dynamically on the unsafe stack and store the dynamic unsafe stack
176   /// top to \p DynamicTop if non-null.
177   void moveDynamicAllocasToUnsafeStack(Function &F, Value *UnsafeStackPtr,
178                                        AllocaInst *DynamicTop,
179                                        ArrayRef<AllocaInst *> DynamicAllocas);
180 
181   bool IsSafeStackAlloca(const Value *AllocaPtr, uint64_t AllocaSize);
182 
183   bool IsMemIntrinsicSafe(const MemIntrinsic *MI, const Use &U,
184                           const Value *AllocaPtr, uint64_t AllocaSize);
185   bool IsAccessSafe(Value *Addr, uint64_t Size, const Value *AllocaPtr,
186                     uint64_t AllocaSize);
187 
188   bool ShouldInlinePointerAddress(CallInst &CI);
189   void TryInlinePointerAddress();
190 
191 public:
192   SafeStack(Function &F, const TargetLoweringBase &TL, const DataLayout &DL,
193             DomTreeUpdater *DTU, ScalarEvolution &SE)
194       : F(F), TL(TL), DL(DL), DTU(DTU), SE(SE),
195         StackPtrTy(PointerType::getUnqual(F.getContext())),
196         IntPtrTy(DL.getIntPtrType(F.getContext())),
197         Int32Ty(Type::getInt32Ty(F.getContext())) {}
198 
199   // Run the transformation on the associated function.
200   // Returns whether the function was changed.
201   bool run();
202 };
203 
204 constexpr Align SafeStack::StackAlignment;
205 
206 uint64_t SafeStack::getStaticAllocaAllocationSize(const AllocaInst* AI) {
207   uint64_t Size = DL.getTypeAllocSize(AI->getAllocatedType());
208   if (AI->isArrayAllocation()) {
209     auto C = dyn_cast<ConstantInt>(AI->getArraySize());
210     if (!C)
211       return 0;
212     Size *= C->getZExtValue();
213   }
214   return Size;
215 }
216 
217 bool SafeStack::IsAccessSafe(Value *Addr, uint64_t AccessSize,
218                              const Value *AllocaPtr, uint64_t AllocaSize) {
219   const SCEV *AddrExpr = SE.getSCEV(Addr);
220   const auto *Base = dyn_cast<SCEVUnknown>(SE.getPointerBase(AddrExpr));
221   if (!Base || Base->getValue() != AllocaPtr) {
222     LLVM_DEBUG(
223         dbgs() << "[SafeStack] "
224                << (isa<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")
225                << *AllocaPtr << "\n"
226                << "SCEV " << *AddrExpr << " not directly based on alloca\n");
227     return false;
228   }
229 
230   const SCEV *Expr = SE.removePointerBase(AddrExpr);
231   uint64_t BitWidth = SE.getTypeSizeInBits(Expr->getType());
232   ConstantRange AccessStartRange = SE.getUnsignedRange(Expr);
233   ConstantRange SizeRange =
234       ConstantRange(APInt(BitWidth, 0), APInt(BitWidth, AccessSize));
235   ConstantRange AccessRange = AccessStartRange.add(SizeRange);
236   ConstantRange AllocaRange =
237       ConstantRange(APInt(BitWidth, 0), APInt(BitWidth, AllocaSize));
238   bool Safe = AllocaRange.contains(AccessRange);
239 
240   LLVM_DEBUG(
241       dbgs() << "[SafeStack] "
242              << (isa<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")
243              << *AllocaPtr << "\n"
244              << "            Access " << *Addr << "\n"
245              << "            SCEV " << *Expr
246              << " U: " << SE.getUnsignedRange(Expr)
247              << ", S: " << SE.getSignedRange(Expr) << "\n"
248              << "            Range " << AccessRange << "\n"
249              << "            AllocaRange " << AllocaRange << "\n"
250              << "            " << (Safe ? "safe" : "unsafe") << "\n");
251 
252   return Safe;
253 }
254 
255 bool SafeStack::IsMemIntrinsicSafe(const MemIntrinsic *MI, const Use &U,
256                                    const Value *AllocaPtr,
257                                    uint64_t AllocaSize) {
258   if (auto MTI = dyn_cast<MemTransferInst>(MI)) {
259     if (MTI->getRawSource() != U && MTI->getRawDest() != U)
260       return true;
261   } else {
262     if (MI->getRawDest() != U)
263       return true;
264   }
265 
266   const auto *Len = dyn_cast<ConstantInt>(MI->getLength());
267   // Non-constant size => unsafe. FIXME: try SCEV getRange.
268   if (!Len) return false;
269   return IsAccessSafe(U, Len->getZExtValue(), AllocaPtr, AllocaSize);
270 }
271 
272 /// Check whether a given allocation must be put on the safe
273 /// stack or not. The function analyzes all uses of AI and checks whether it is
274 /// only accessed in a memory safe way (as decided statically).
275 bool SafeStack::IsSafeStackAlloca(const Value *AllocaPtr, uint64_t AllocaSize) {
276   // Go through all uses of this alloca and check whether all accesses to the
277   // allocated object are statically known to be memory safe and, hence, the
278   // object can be placed on the safe stack.
279   SmallPtrSet<const Value *, 16> Visited;
280   SmallVector<const Value *, 8> WorkList;
281   WorkList.push_back(AllocaPtr);
282 
283   // A DFS search through all uses of the alloca in bitcasts/PHI/GEPs/etc.
284   while (!WorkList.empty()) {
285     const Value *V = WorkList.pop_back_val();
286     for (const Use &UI : V->uses()) {
287       auto I = cast<const Instruction>(UI.getUser());
288       assert(V == UI.get());
289 
290       switch (I->getOpcode()) {
291       case Instruction::Load:
292         if (!IsAccessSafe(UI, DL.getTypeStoreSize(I->getType()), AllocaPtr,
293                           AllocaSize))
294           return false;
295         break;
296 
297       case Instruction::VAArg:
298         // "va-arg" from a pointer is safe.
299         break;
300       case Instruction::Store:
301         if (V == I->getOperand(0)) {
302           // Stored the pointer - conservatively assume it may be unsafe.
303           LLVM_DEBUG(dbgs()
304                      << "[SafeStack] Unsafe alloca: " << *AllocaPtr
305                      << "\n            store of address: " << *I << "\n");
306           return false;
307         }
308 
309         if (!IsAccessSafe(UI, DL.getTypeStoreSize(I->getOperand(0)->getType()),
310                           AllocaPtr, AllocaSize))
311           return false;
312         break;
313 
314       case Instruction::Ret:
315         // Information leak.
316         return false;
317 
318       case Instruction::Call:
319       case Instruction::Invoke: {
320         const CallBase &CS = *cast<CallBase>(I);
321 
322         if (I->isLifetimeStartOrEnd())
323           continue;
324 
325         if (const MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) {
326           if (!IsMemIntrinsicSafe(MI, UI, AllocaPtr, AllocaSize)) {
327             LLVM_DEBUG(dbgs()
328                        << "[SafeStack] Unsafe alloca: " << *AllocaPtr
329                        << "\n            unsafe memintrinsic: " << *I << "\n");
330             return false;
331           }
332           continue;
333         }
334 
335         // LLVM 'nocapture' attribute is only set for arguments whose address
336         // is not stored, passed around, or used in any other non-trivial way.
337         // We assume that passing a pointer to an object as a 'nocapture
338         // readnone' argument is safe.
339         // FIXME: a more precise solution would require an interprocedural
340         // analysis here, which would look at all uses of an argument inside
341         // the function being called.
342         auto B = CS.arg_begin(), E = CS.arg_end();
343         for (const auto *A = B; A != E; ++A)
344           if (A->get() == V)
345             if (!(CS.doesNotCapture(A - B) && (CS.doesNotAccessMemory(A - B) ||
346                                                CS.doesNotAccessMemory()))) {
347               LLVM_DEBUG(dbgs() << "[SafeStack] Unsafe alloca: " << *AllocaPtr
348                                 << "\n            unsafe call: " << *I << "\n");
349               return false;
350             }
351         continue;
352       }
353 
354       default:
355         if (Visited.insert(I).second)
356           WorkList.push_back(cast<const Instruction>(I));
357       }
358     }
359   }
360 
361   // All uses of the alloca are safe, we can place it on the safe stack.
362   return true;
363 }
364 
365 Value *SafeStack::getStackGuard(IRBuilder<> &IRB, Function &F) {
366   Value *StackGuardVar = TL.getIRStackGuard(IRB);
367   Module *M = F.getParent();
368 
369   if (!StackGuardVar) {
370     TL.insertSSPDeclarations(*M);
371     return IRB.CreateCall(Intrinsic::getDeclaration(M, Intrinsic::stackguard));
372   }
373 
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<Instruction *> &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       if (CallInst *CI = I.getParent()->getTerminatingMustTailCall())
400         Returns.push_back(CI);
401       else
402         Returns.push_back(RI);
403     } else if (auto CI = dyn_cast<CallInst>(&I)) {
404       // setjmps require stack restore.
405       if (CI->getCalledFunction() && CI->canReturnTwice())
406         StackRestorePoints.push_back(CI);
407     } else if (auto LP = dyn_cast<LandingPadInst>(&I)) {
408       // Exception landing pads require stack restore.
409       StackRestorePoints.push_back(LP);
410     } else if (auto II = dyn_cast<IntrinsicInst>(&I)) {
411       if (II->getIntrinsicID() == Intrinsic::gcroot)
412         report_fatal_error(
413             "gcroot intrinsic not compatible with safestack attribute");
414     }
415   }
416   for (Argument &Arg : F.args()) {
417     if (!Arg.hasByValAttr())
418       continue;
419     uint64_t Size = DL.getTypeStoreSize(Arg.getParamByValType());
420     if (IsSafeStackAlloca(&Arg, Size))
421       continue;
422 
423     ++NumUnsafeByValArguments;
424     ByValArguments.push_back(&Arg);
425   }
426 }
427 
428 AllocaInst *
429 SafeStack::createStackRestorePoints(IRBuilder<> &IRB, Function &F,
430                                     ArrayRef<Instruction *> StackRestorePoints,
431                                     Value *StaticTop, bool NeedDynamicTop) {
432   assert(StaticTop && "The stack top isn't set.");
433 
434   if (StackRestorePoints.empty())
435     return nullptr;
436 
437   // We need the current value of the shadow stack pointer to restore
438   // after longjmp or exception catching.
439 
440   // FIXME: On some platforms this could be handled by the longjmp/exception
441   // runtime itself.
442 
443   AllocaInst *DynamicTop = nullptr;
444   if (NeedDynamicTop) {
445     // If we also have dynamic alloca's, the stack pointer value changes
446     // throughout the function. For now we store it in an alloca.
447     DynamicTop = IRB.CreateAlloca(StackPtrTy, /*ArraySize=*/nullptr,
448                                   "unsafe_stack_dynamic_ptr");
449     IRB.CreateStore(StaticTop, DynamicTop);
450   }
451 
452   // Restore current stack pointer after longjmp/exception catch.
453   for (Instruction *I : StackRestorePoints) {
454     ++NumUnsafeStackRestorePoints;
455 
456     IRB.SetInsertPoint(I->getNextNode());
457     Value *CurrentTop =
458         DynamicTop ? IRB.CreateLoad(StackPtrTy, DynamicTop) : StaticTop;
459     IRB.CreateStore(CurrentTop, UnsafeStackPtr);
460   }
461 
462   return DynamicTop;
463 }
464 
465 void SafeStack::checkStackGuard(IRBuilder<> &IRB, Function &F, Instruction &RI,
466                                 AllocaInst *StackGuardSlot, Value *StackGuard) {
467   Value *V = IRB.CreateLoad(StackPtrTy, StackGuardSlot);
468   Value *Cmp = IRB.CreateICmpNE(StackGuard, V);
469 
470   auto SuccessProb = BranchProbabilityInfo::getBranchProbStackProtector(true);
471   auto FailureProb = BranchProbabilityInfo::getBranchProbStackProtector(false);
472   MDNode *Weights = MDBuilder(F.getContext())
473                         .createBranchWeights(SuccessProb.getNumerator(),
474                                              FailureProb.getNumerator());
475   Instruction *CheckTerm =
476       SplitBlockAndInsertIfThen(Cmp, &RI, /* Unreachable */ true, Weights, DTU);
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.
487 Value *SafeStack::moveStaticAllocasToUnsafeStack(
488     IRBuilder<> &IRB, Function &F, ArrayRef<AllocaInst *> StaticAllocas,
489     ArrayRef<Argument *> ByValArguments, Instruction *BasePointer,
490     AllocaInst *StackGuardSlot) {
491   if (StaticAllocas.empty() && ByValArguments.empty())
492     return BasePointer;
493 
494   DIBuilder DIB(*F.getParent());
495 
496   StackLifetime SSC(F, StaticAllocas, StackLifetime::LivenessType::May);
497   static const StackLifetime::LiveRange NoColoringRange(1, true);
498   if (ClColoring)
499     SSC.run();
500 
501   for (const auto *I : SSC.getMarkers()) {
502     auto *Op = dyn_cast<Instruction>(I->getOperand(1));
503     const_cast<IntrinsicInst *>(I)->eraseFromParent();
504     // Remove the operand bitcast, too, if it has no more uses left.
505     if (Op && Op->use_empty())
506       Op->eraseFromParent();
507   }
508 
509   // Unsafe stack always grows down.
510   StackLayout SSL(StackAlignment);
511   if (StackGuardSlot) {
512     Type *Ty = StackGuardSlot->getAllocatedType();
513     Align Align = std::max(DL.getPrefTypeAlign(Ty), StackGuardSlot->getAlign());
514     SSL.addObject(StackGuardSlot, getStaticAllocaAllocationSize(StackGuardSlot),
515                   Align, SSC.getFullLiveRange());
516   }
517 
518   for (Argument *Arg : ByValArguments) {
519     Type *Ty = Arg->getParamByValType();
520     uint64_t Size = DL.getTypeStoreSize(Ty);
521     if (Size == 0)
522       Size = 1; // Don't create zero-sized stack objects.
523 
524     // Ensure the object is properly aligned.
525     Align Align = DL.getPrefTypeAlign(Ty);
526     if (auto A = Arg->getParamAlign())
527       Align = std::max(Align, *A);
528     SSL.addObject(Arg, Size, Align, SSC.getFullLiveRange());
529   }
530 
531   for (AllocaInst *AI : StaticAllocas) {
532     Type *Ty = AI->getAllocatedType();
533     uint64_t Size = getStaticAllocaAllocationSize(AI);
534     if (Size == 0)
535       Size = 1; // Don't create zero-sized stack objects.
536 
537     // Ensure the object is properly aligned.
538     Align Align = std::max(DL.getPrefTypeAlign(Ty), AI->getAlign());
539 
540     SSL.addObject(AI, Size, Align,
541                   ClColoring ? SSC.getLiveRange(AI) : NoColoringRange);
542   }
543 
544   SSL.computeLayout();
545   Align FrameAlignment = SSL.getFrameAlignment();
546 
547   // FIXME: tell SSL that we start at a less-then-MaxAlignment aligned location
548   // (AlignmentSkew).
549   if (FrameAlignment > StackAlignment) {
550     // Re-align the base pointer according to the max requested alignment.
551     IRB.SetInsertPoint(BasePointer->getNextNode());
552     BasePointer = cast<Instruction>(IRB.CreateIntToPtr(
553         IRB.CreateAnd(
554             IRB.CreatePtrToInt(BasePointer, IntPtrTy),
555             ConstantInt::get(IntPtrTy, ~(FrameAlignment.value() - 1))),
556         StackPtrTy));
557   }
558 
559   IRB.SetInsertPoint(BasePointer->getNextNode());
560 
561   if (StackGuardSlot) {
562     unsigned Offset = SSL.getObjectOffset(StackGuardSlot);
563     Value *Off =
564         IRB.CreatePtrAdd(BasePointer, ConstantInt::get(Int32Ty, -Offset));
565     Value *NewAI =
566         IRB.CreateBitCast(Off, StackGuardSlot->getType(), "StackGuardSlot");
567 
568     // Replace alloc with the new location.
569     StackGuardSlot->replaceAllUsesWith(NewAI);
570     StackGuardSlot->eraseFromParent();
571   }
572 
573   for (Argument *Arg : ByValArguments) {
574     unsigned Offset = SSL.getObjectOffset(Arg);
575     MaybeAlign Align(SSL.getObjectAlignment(Arg));
576     Type *Ty = Arg->getParamByValType();
577 
578     uint64_t Size = DL.getTypeStoreSize(Ty);
579     if (Size == 0)
580       Size = 1; // Don't create zero-sized stack objects.
581 
582     Value *Off =
583         IRB.CreatePtrAdd(BasePointer, ConstantInt::get(Int32Ty, -Offset));
584     Value *NewArg = IRB.CreateBitCast(Off, Arg->getType(),
585                                       Arg->getName() + ".unsafe-byval");
586 
587     // Replace alloc with the new location.
588     replaceDbgDeclare(Arg, BasePointer, DIB, DIExpression::ApplyOffset,
589                       -Offset);
590     Arg->replaceAllUsesWith(NewArg);
591     IRB.SetInsertPoint(cast<Instruction>(NewArg)->getNextNode());
592     IRB.CreateMemCpy(Off, Align, Arg, Arg->getParamAlign(), Size);
593   }
594 
595   // Allocate space for every unsafe static AllocaInst on the unsafe stack.
596   for (AllocaInst *AI : StaticAllocas) {
597     IRB.SetInsertPoint(AI);
598     unsigned Offset = SSL.getObjectOffset(AI);
599 
600     replaceDbgDeclare(AI, BasePointer, DIB, DIExpression::ApplyOffset, -Offset);
601     replaceDbgValueForAlloca(AI, BasePointer, DIB, -Offset);
602 
603     // Replace uses of the alloca with the new location.
604     // Insert address calculation close to each use to work around PR27844.
605     std::string Name = std::string(AI->getName()) + ".unsafe";
606     while (!AI->use_empty()) {
607       Use &U = *AI->use_begin();
608       Instruction *User = cast<Instruction>(U.getUser());
609 
610       Instruction *InsertBefore;
611       if (auto *PHI = dyn_cast<PHINode>(User))
612         InsertBefore = PHI->getIncomingBlock(U)->getTerminator();
613       else
614         InsertBefore = User;
615 
616       IRBuilder<> IRBUser(InsertBefore);
617       Value *Off =
618           IRBUser.CreatePtrAdd(BasePointer, ConstantInt::get(Int32Ty, -Offset));
619       Value *Replacement = IRBUser.CreateBitCast(Off, AI->getType(), Name);
620 
621       if (auto *PHI = dyn_cast<PHINode>(User))
622         // PHI nodes may have multiple incoming edges from the same BB (why??),
623         // all must be updated at once with the same incoming value.
624         PHI->setIncomingValueForBlock(PHI->getIncomingBlock(U), Replacement);
625       else
626         U.set(Replacement);
627     }
628 
629     AI->eraseFromParent();
630   }
631 
632   // Re-align BasePointer so that our callees would see it aligned as
633   // expected.
634   // FIXME: no need to update BasePointer in leaf functions.
635   unsigned FrameSize = alignTo(SSL.getFrameSize(), StackAlignment);
636 
637   MDBuilder MDB(F.getContext());
638   SmallVector<Metadata *, 2> Data;
639   Data.push_back(MDB.createString("unsafe-stack-size"));
640   Data.push_back(MDB.createConstant(ConstantInt::get(Int32Ty, FrameSize)));
641   MDNode *MD = MDTuple::get(F.getContext(), Data);
642   F.setMetadata(LLVMContext::MD_annotation, MD);
643 
644   // Update shadow stack pointer in the function epilogue.
645   IRB.SetInsertPoint(BasePointer->getNextNode());
646 
647   Value *StaticTop =
648       IRB.CreatePtrAdd(BasePointer, ConstantInt::get(Int32Ty, -FrameSize),
649                        "unsafe_stack_static_top");
650   IRB.CreateStore(StaticTop, UnsafeStackPtr);
651   return StaticTop;
652 }
653 
654 void SafeStack::moveDynamicAllocasToUnsafeStack(
655     Function &F, Value *UnsafeStackPtr, AllocaInst *DynamicTop,
656     ArrayRef<AllocaInst *> DynamicAllocas) {
657   DIBuilder DIB(*F.getParent());
658 
659   for (AllocaInst *AI : DynamicAllocas) {
660     IRBuilder<> IRB(AI);
661 
662     // Compute the new SP value (after AI).
663     Value *ArraySize = AI->getArraySize();
664     if (ArraySize->getType() != IntPtrTy)
665       ArraySize = IRB.CreateIntCast(ArraySize, IntPtrTy, false);
666 
667     Type *Ty = AI->getAllocatedType();
668     uint64_t TySize = DL.getTypeAllocSize(Ty);
669     Value *Size = IRB.CreateMul(ArraySize, ConstantInt::get(IntPtrTy, TySize));
670 
671     Value *SP = IRB.CreatePtrToInt(IRB.CreateLoad(StackPtrTy, UnsafeStackPtr),
672                                    IntPtrTy);
673     SP = IRB.CreateSub(SP, Size);
674 
675     // Align the SP value to satisfy the AllocaInst, type and stack alignments.
676     auto Align = std::max(std::max(DL.getPrefTypeAlign(Ty), AI->getAlign()),
677                           StackAlignment);
678 
679     Value *NewTop = IRB.CreateIntToPtr(
680         IRB.CreateAnd(SP,
681                       ConstantInt::get(IntPtrTy, ~uint64_t(Align.value() - 1))),
682         StackPtrTy);
683 
684     // Save the stack pointer.
685     IRB.CreateStore(NewTop, UnsafeStackPtr);
686     if (DynamicTop)
687       IRB.CreateStore(NewTop, DynamicTop);
688 
689     Value *NewAI = IRB.CreatePointerCast(NewTop, AI->getType());
690     if (AI->hasName() && isa<Instruction>(NewAI))
691       NewAI->takeName(AI);
692 
693     replaceDbgDeclare(AI, NewAI, DIB, DIExpression::ApplyOffset, 0);
694     AI->replaceAllUsesWith(NewAI);
695     AI->eraseFromParent();
696   }
697 
698   if (!DynamicAllocas.empty()) {
699     // Now go through the instructions again, replacing stacksave/stackrestore.
700     for (Instruction &I : llvm::make_early_inc_range(instructions(&F))) {
701       auto *II = dyn_cast<IntrinsicInst>(&I);
702       if (!II)
703         continue;
704 
705       if (II->getIntrinsicID() == Intrinsic::stacksave) {
706         IRBuilder<> IRB(II);
707         Instruction *LI = IRB.CreateLoad(StackPtrTy, UnsafeStackPtr);
708         LI->takeName(II);
709         II->replaceAllUsesWith(LI);
710         II->eraseFromParent();
711       } else if (II->getIntrinsicID() == Intrinsic::stackrestore) {
712         IRBuilder<> IRB(II);
713         Instruction *SI = IRB.CreateStore(II->getArgOperand(0), UnsafeStackPtr);
714         SI->takeName(II);
715         assert(II->use_empty());
716         II->eraseFromParent();
717       }
718     }
719   }
720 }
721 
722 bool SafeStack::ShouldInlinePointerAddress(CallInst &CI) {
723   Function *Callee = CI.getCalledFunction();
724   if (CI.hasFnAttr(Attribute::AlwaysInline) &&
725       isInlineViable(*Callee).isSuccess())
726     return true;
727   if (Callee->isInterposable() || Callee->hasFnAttribute(Attribute::NoInline) ||
728       CI.isNoInline())
729     return false;
730   return true;
731 }
732 
733 void SafeStack::TryInlinePointerAddress() {
734   auto *CI = dyn_cast<CallInst>(UnsafeStackPtr);
735   if (!CI)
736     return;
737 
738   if(F.hasOptNone())
739     return;
740 
741   Function *Callee = CI->getCalledFunction();
742   if (!Callee || Callee->isDeclaration())
743     return;
744 
745   if (!ShouldInlinePointerAddress(*CI))
746     return;
747 
748   InlineFunctionInfo IFI;
749   InlineFunction(*CI, IFI);
750 }
751 
752 bool SafeStack::run() {
753   assert(F.hasFnAttribute(Attribute::SafeStack) &&
754          "Can't run SafeStack on a function without the attribute");
755   assert(!F.isDeclaration() && "Can't run SafeStack on a function declaration");
756 
757   ++NumFunctions;
758 
759   SmallVector<AllocaInst *, 16> StaticAllocas;
760   SmallVector<AllocaInst *, 4> DynamicAllocas;
761   SmallVector<Argument *, 4> ByValArguments;
762   SmallVector<Instruction *, 4> Returns;
763 
764   // Collect all points where stack gets unwound and needs to be restored
765   // This is only necessary because the runtime (setjmp and unwind code) is
766   // not aware of the unsafe stack and won't unwind/restore it properly.
767   // To work around this problem without changing the runtime, we insert
768   // instrumentation to restore the unsafe stack pointer when necessary.
769   SmallVector<Instruction *, 4> StackRestorePoints;
770 
771   // Find all static and dynamic alloca instructions that must be moved to the
772   // unsafe stack, all return instructions and stack restore points.
773   findInsts(F, StaticAllocas, DynamicAllocas, ByValArguments, Returns,
774             StackRestorePoints);
775 
776   if (StaticAllocas.empty() && DynamicAllocas.empty() &&
777       ByValArguments.empty() && StackRestorePoints.empty())
778     return false; // Nothing to do in this function.
779 
780   if (!StaticAllocas.empty() || !DynamicAllocas.empty() ||
781       !ByValArguments.empty())
782     ++NumUnsafeStackFunctions; // This function has the unsafe stack.
783 
784   if (!StackRestorePoints.empty())
785     ++NumUnsafeStackRestorePointsFunctions;
786 
787   IRBuilder<> IRB(&F.front(), F.begin()->getFirstInsertionPt());
788   // Calls must always have a debug location, or else inlining breaks. So
789   // we explicitly set a artificial debug location here.
790   if (DISubprogram *SP = F.getSubprogram())
791     IRB.SetCurrentDebugLocation(
792         DILocation::get(SP->getContext(), SP->getScopeLine(), 0, SP));
793   if (SafeStackUsePointerAddress) {
794     FunctionCallee Fn = F.getParent()->getOrInsertFunction(
795         "__safestack_pointer_address", IRB.getPtrTy(0));
796     UnsafeStackPtr = IRB.CreateCall(Fn);
797   } else {
798     UnsafeStackPtr = TL.getSafeStackPointerLocation(IRB);
799   }
800 
801   // Load the current stack pointer (we'll also use it as a base pointer).
802   // FIXME: use a dedicated register for it ?
803   Instruction *BasePointer =
804       IRB.CreateLoad(StackPtrTy, UnsafeStackPtr, false, "unsafe_stack_ptr");
805   assert(BasePointer->getType() == StackPtrTy);
806 
807   AllocaInst *StackGuardSlot = nullptr;
808   // FIXME: implement weaker forms of stack protector.
809   if (F.hasFnAttribute(Attribute::StackProtect) ||
810       F.hasFnAttribute(Attribute::StackProtectStrong) ||
811       F.hasFnAttribute(Attribute::StackProtectReq)) {
812     Value *StackGuard = getStackGuard(IRB, F);
813     StackGuardSlot = IRB.CreateAlloca(StackPtrTy, nullptr);
814     IRB.CreateStore(StackGuard, StackGuardSlot);
815 
816     for (Instruction *RI : Returns) {
817       IRBuilder<> IRBRet(RI);
818       checkStackGuard(IRBRet, F, *RI, StackGuardSlot, StackGuard);
819     }
820   }
821 
822   // The top of the unsafe stack after all unsafe static allocas are
823   // allocated.
824   Value *StaticTop = moveStaticAllocasToUnsafeStack(
825       IRB, F, StaticAllocas, ByValArguments, BasePointer, StackGuardSlot);
826 
827   // Safe stack object that stores the current unsafe stack top. It is updated
828   // as unsafe dynamic (non-constant-sized) allocas are allocated and freed.
829   // This is only needed if we need to restore stack pointer after longjmp
830   // or exceptions, and we have dynamic allocations.
831   // FIXME: a better alternative might be to store the unsafe stack pointer
832   // before setjmp / invoke instructions.
833   AllocaInst *DynamicTop = createStackRestorePoints(
834       IRB, F, StackRestorePoints, StaticTop, !DynamicAllocas.empty());
835 
836   // Handle dynamic allocas.
837   moveDynamicAllocasToUnsafeStack(F, UnsafeStackPtr, DynamicTop,
838                                   DynamicAllocas);
839 
840   // Restore the unsafe stack pointer before each return.
841   for (Instruction *RI : Returns) {
842     IRB.SetInsertPoint(RI);
843     IRB.CreateStore(BasePointer, UnsafeStackPtr);
844   }
845 
846   TryInlinePointerAddress();
847 
848   LLVM_DEBUG(dbgs() << "[SafeStack]     safestack applied\n");
849   return true;
850 }
851 
852 class SafeStackLegacyPass : public FunctionPass {
853   const TargetMachine *TM = nullptr;
854 
855 public:
856   static char ID; // Pass identification, replacement for typeid..
857 
858   SafeStackLegacyPass() : FunctionPass(ID) {
859     initializeSafeStackLegacyPassPass(*PassRegistry::getPassRegistry());
860   }
861 
862   void getAnalysisUsage(AnalysisUsage &AU) const override {
863     AU.addRequired<TargetPassConfig>();
864     AU.addRequired<TargetLibraryInfoWrapperPass>();
865     AU.addRequired<AssumptionCacheTracker>();
866     AU.addPreserved<DominatorTreeWrapperPass>();
867   }
868 
869   bool runOnFunction(Function &F) override {
870     LLVM_DEBUG(dbgs() << "[SafeStack] Function: " << F.getName() << "\n");
871 
872     if (!F.hasFnAttribute(Attribute::SafeStack)) {
873       LLVM_DEBUG(dbgs() << "[SafeStack]     safestack is not requested"
874                            " for this function\n");
875       return false;
876     }
877 
878     if (F.isDeclaration()) {
879       LLVM_DEBUG(dbgs() << "[SafeStack]     function definition"
880                            " is not available\n");
881       return false;
882     }
883 
884     TM = &getAnalysis<TargetPassConfig>().getTM<TargetMachine>();
885     auto *TL = TM->getSubtargetImpl(F)->getTargetLowering();
886     if (!TL)
887       report_fatal_error("TargetLowering instance is required");
888 
889     auto *DL = &F.getParent()->getDataLayout();
890     auto &TLI = getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F);
891     auto &ACT = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
892 
893     // Compute DT and LI only for functions that have the attribute.
894     // This is only useful because the legacy pass manager doesn't let us
895     // compute analyzes lazily.
896 
897     DominatorTree *DT;
898     bool ShouldPreserveDominatorTree;
899     std::optional<DominatorTree> LazilyComputedDomTree;
900 
901     // Do we already have a DominatorTree avaliable from the previous pass?
902     // Note that we should *NOT* require it, to avoid the case where we end up
903     // not needing it, but the legacy PM would have computed it for us anyways.
904     if (auto *DTWP = getAnalysisIfAvailable<DominatorTreeWrapperPass>()) {
905       DT = &DTWP->getDomTree();
906       ShouldPreserveDominatorTree = true;
907     } else {
908       // Otherwise, we need to compute it.
909       LazilyComputedDomTree.emplace(F);
910       DT = &*LazilyComputedDomTree;
911       ShouldPreserveDominatorTree = false;
912     }
913 
914     // Likewise, lazily compute loop info.
915     LoopInfo LI(*DT);
916 
917     DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Lazy);
918 
919     ScalarEvolution SE(F, TLI, ACT, *DT, LI);
920 
921     return SafeStack(F, *TL, *DL, ShouldPreserveDominatorTree ? &DTU : nullptr,
922                      SE)
923         .run();
924   }
925 };
926 
927 } // end anonymous namespace
928 
929 PreservedAnalyses SafeStackPass::run(Function &F,
930                                      FunctionAnalysisManager &FAM) {
931   LLVM_DEBUG(dbgs() << "[SafeStack] Function: " << F.getName() << "\n");
932 
933   if (!F.hasFnAttribute(Attribute::SafeStack)) {
934     LLVM_DEBUG(dbgs() << "[SafeStack]     safestack is not requested"
935                          " for this function\n");
936     return PreservedAnalyses::all();
937   }
938 
939   if (F.isDeclaration()) {
940     LLVM_DEBUG(dbgs() << "[SafeStack]     function definition"
941                          " is not available\n");
942     return PreservedAnalyses::all();
943   }
944 
945   auto *TL = TM->getSubtargetImpl(F)->getTargetLowering();
946   if (!TL)
947     report_fatal_error("TargetLowering instance is required");
948 
949   auto &DL = F.getParent()->getDataLayout();
950 
951   // preserve DominatorTree
952   auto &DT = FAM.getResult<DominatorTreeAnalysis>(F);
953   auto &SE = FAM.getResult<ScalarEvolutionAnalysis>(F);
954   DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Lazy);
955 
956   bool Changed = SafeStack(F, *TL, DL, &DTU, SE).run();
957 
958   if (!Changed)
959     return PreservedAnalyses::all();
960   PreservedAnalyses PA;
961   PA.preserve<DominatorTreeAnalysis>();
962   return PA;
963 }
964 
965 char SafeStackLegacyPass::ID = 0;
966 
967 INITIALIZE_PASS_BEGIN(SafeStackLegacyPass, DEBUG_TYPE,
968                       "Safe Stack instrumentation pass", false, false)
969 INITIALIZE_PASS_DEPENDENCY(TargetPassConfig)
970 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
971 INITIALIZE_PASS_END(SafeStackLegacyPass, DEBUG_TYPE,
972                     "Safe Stack instrumentation pass", false, false)
973 
974 FunctionPass *llvm::createSafeStackPass() { return new SafeStackLegacyPass(); }
975