1 //===- SafeStack.cpp - Safe Stack Insertion -------------------------------===//
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
7 //===----------------------------------------------------------------------===//
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
13 // http://clang.llvm.org/docs/SafeStack.html
15 //===----------------------------------------------------------------------===//
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"
74 using namespace llvm::safestack;
76 #define DEBUG_TYPE "safe-stack"
80 STATISTIC(NumFunctions, "Total number of functions");
81 STATISTIC(NumUnsafeStackFunctions, "Number of functions with unsafe stack");
82 STATISTIC(NumUnsafeStackRestorePointsFunctions,
83 "Number of functions that use setjmp or exceptions");
85 STATISTIC(NumAllocas, "Total number of allocas");
86 STATISTIC(NumUnsafeStaticAllocas, "Number of unsafe static allocas");
87 STATISTIC(NumUnsafeDynamicAllocas, "Number of unsafe dynamic allocas");
88 STATISTIC(NumUnsafeByValArguments, "Number of unsafe byval arguments");
89 STATISTIC(NumUnsafeStackRestorePoints, "Number of setjmps and landingpads");
93 /// Use __safestack_pointer_address even if the platform has a faster way of
94 /// access safe stack pointer.
96 SafeStackUsePointerAddress("safestack-use-pointer-address",
97 cl::init(false), cl::Hidden);
102 /// Rewrite an SCEV expression for a memory access address to an expression that
103 /// represents offset from the given alloca.
105 /// The implementation simply replaces all mentions of the alloca with zero.
106 class AllocaOffsetRewriter : public SCEVRewriteVisitor<AllocaOffsetRewriter> {
107 const Value *AllocaPtr;
110 AllocaOffsetRewriter(ScalarEvolution &SE, const Value *AllocaPtr)
111 : SCEVRewriteVisitor(SE), AllocaPtr(AllocaPtr) {}
113 const SCEV *visitUnknown(const SCEVUnknown *Expr) {
114 if (Expr->getValue() == AllocaPtr)
115 return SE.getZero(Expr->getType());
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
127 const TargetLoweringBase &TL;
128 const DataLayout &DL;
136 Value *UnsafeStackPtr = nullptr;
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.
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 };
146 /// Return the value of the stack canary.
147 Value *getStackGuard(IRBuilder<> &IRB, Function &F);
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);
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);
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);
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.
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);
179 /// Generate code to restore the stack after all stack restore points
180 /// in \p StackRestorePoints.
182 /// \returns A local variable in which to maintain the dynamic top of the
183 /// unsafe stack if needed.
185 createStackRestorePoints(IRBuilder<> &IRB, Function &F,
186 ArrayRef<Instruction *> StackRestorePoints,
187 Value *StaticTop, bool NeedDynamicTop);
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);
196 bool IsSafeStackAlloca(const Value *AllocaPtr, uint64_t AllocaSize);
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);
203 bool ShouldInlinePointerAddress(CallSite &CS);
204 void TryInlinePointerAddress();
207 SafeStack(Function &F, const TargetLoweringBase &TL, const DataLayout &DL,
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())) {}
215 // Run the transformation on the associated function.
216 // Returns whether the function was changed.
220 uint64_t SafeStack::getStaticAllocaAllocationSize(const AllocaInst* AI) {
221 uint64_t Size = DL.getTypeAllocSize(AI->getAllocatedType());
222 if (AI->isArrayAllocation()) {
223 auto C = dyn_cast<ConstantInt>(AI->getArraySize());
226 Size *= C->getZExtValue();
231 bool SafeStack::IsAccessSafe(Value *Addr, uint64_t AccessSize,
232 const Value *AllocaPtr, uint64_t AllocaSize) {
233 AllocaOffsetRewriter Rewriter(SE, AllocaPtr);
234 const SCEV *Expr = Rewriter.visit(SE.getSCEV(Addr));
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);
246 dbgs() << "[SafeStack] "
247 << (isa<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")
248 << *AllocaPtr << "\n"
249 << " Access " << *Addr << "\n"
251 << " U: " << SE.getUnsignedRange(Expr)
252 << ", S: " << SE.getSignedRange(Expr) << "\n"
253 << " Range " << AccessRange << "\n"
254 << " AllocaRange " << AllocaRange << "\n"
255 << " " << (Safe ? "safe" : "unsafe") << "\n");
260 bool SafeStack::IsMemIntrinsicSafe(const MemIntrinsic *MI, const Use &U,
261 const Value *AllocaPtr,
262 uint64_t AllocaSize) {
263 if (auto MTI = dyn_cast<MemTransferInst>(MI)) {
264 if (MTI->getRawSource() != U && MTI->getRawDest() != U)
267 if (MI->getRawDest() != U)
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);
277 /// Check whether a given allocation must be put on the safe
278 /// stack or not. The function analyzes all uses of AI and checks whether it is
279 /// only accessed in a memory safe way (as decided statically).
280 bool SafeStack::IsSafeStackAlloca(const Value *AllocaPtr, uint64_t AllocaSize) {
281 // Go through all uses of this alloca and check whether all accesses to the
282 // allocated object are statically known to be memory safe and, hence, the
283 // object can be placed on the safe stack.
284 SmallPtrSet<const Value *, 16> Visited;
285 SmallVector<const Value *, 8> WorkList;
286 WorkList.push_back(AllocaPtr);
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());
295 switch (I->getOpcode()) {
296 case Instruction::Load:
297 if (!IsAccessSafe(UI, DL.getTypeStoreSize(I->getType()), AllocaPtr,
302 case Instruction::VAArg:
303 // "va-arg" from a pointer is safe.
305 case Instruction::Store:
306 if (V == I->getOperand(0)) {
307 // Stored the pointer - conservatively assume it may be unsafe.
309 << "[SafeStack] Unsafe alloca: " << *AllocaPtr
310 << "\n store of address: " << *I << "\n");
314 if (!IsAccessSafe(UI, DL.getTypeStoreSize(I->getOperand(0)->getType()),
315 AllocaPtr, AllocaSize))
319 case Instruction::Ret:
323 case Instruction::Call:
324 case Instruction::Invoke: {
325 ImmutableCallSite CS(I);
327 if (I->isLifetimeStartOrEnd())
330 if (const MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) {
331 if (!IsMemIntrinsicSafe(MI, UI, AllocaPtr, AllocaSize)) {
333 << "[SafeStack] Unsafe alloca: " << *AllocaPtr
334 << "\n unsafe memintrinsic: " << *I << "\n");
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)
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");
360 if (Visited.insert(I).second)
361 WorkList.push_back(cast<const Instruction>(I));
366 // All uses of the alloca are safe, we can place it on the safe stack.
370 Value *SafeStack::getStackGuard(IRBuilder<> &IRB, Function &F) {
371 Value *StackGuardVar = TL.getIRStackGuard(IRB);
374 F.getParent()->getOrInsertGlobal("__stack_chk_guard", StackPtrTy);
375 return IRB.CreateLoad(StackPtrTy, StackGuardVar, "StackGuard");
378 void 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)) {
388 uint64_t Size = getStaticAllocaAllocationSize(AI);
389 if (IsSafeStackAlloca(AI, Size))
392 if (AI->isStaticAlloca()) {
393 ++NumUnsafeStaticAllocas;
394 StaticAllocas.push_back(AI);
396 ++NumUnsafeDynamicAllocas;
397 DynamicAllocas.push_back(AI);
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)
411 "gcroot intrinsic not compatible with safestack attribute");
414 for (Argument &Arg : F.args()) {
415 if (!Arg.hasByValAttr())
418 DL.getTypeStoreSize(Arg.getType()->getPointerElementType());
419 if (IsSafeStackAlloca(&Arg, Size))
422 ++NumUnsafeByValArguments;
423 ByValArguments.push_back(&Arg);
428 SafeStack::createStackRestorePoints(IRBuilder<> &IRB, Function &F,
429 ArrayRef<Instruction *> StackRestorePoints,
430 Value *StaticTop, bool NeedDynamicTop) {
431 assert(StaticTop && "The stack top isn't set.");
433 if (StackRestorePoints.empty())
436 // We need the current value of the shadow stack pointer to restore
437 // after longjmp or exception catching.
439 // FIXME: On some platforms this could be handled by the longjmp/exception
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);
451 // Restore current stack pointer after longjmp/exception catch.
452 for (Instruction *I : StackRestorePoints) {
453 ++NumUnsafeStackRestorePoints;
455 IRB.SetInsertPoint(I->getNextNode());
457 DynamicTop ? IRB.CreateLoad(StackPtrTy, DynamicTop) : StaticTop;
458 IRB.CreateStore(CurrentTop, UnsafeStackPtr);
464 void 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);
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, {});
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, ArrayRef<ReturnInst *> Returns,
490 Instruction *BasePointer, AllocaInst *StackGuardSlot) {
491 if (StaticAllocas.empty() && ByValArguments.empty())
494 DIBuilder DIB(*F.getParent());
496 StackColoring SSC(F, StaticAllocas);
498 SSC.removeAllMarkers();
500 // Unsafe stack always grows down.
501 StackLayout SSL(StackAlignment);
502 if (StackGuardSlot) {
503 Type *Ty = StackGuardSlot->getAllocatedType();
505 std::max(DL.getPrefTypeAlignment(Ty), StackGuardSlot->getAlignment());
506 SSL.addObject(StackGuardSlot, getStaticAllocaAllocationSize(StackGuardSlot),
507 Align, SSC.getFullLiveRange());
510 for (Argument *Arg : ByValArguments) {
511 Type *Ty = Arg->getType()->getPointerElementType();
512 uint64_t Size = DL.getTypeStoreSize(Ty);
514 Size = 1; // Don't create zero-sized stack objects.
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());
522 for (AllocaInst *AI : StaticAllocas) {
523 Type *Ty = AI->getAllocatedType();
524 uint64_t Size = getStaticAllocaAllocationSize(AI);
526 Size = 1; // Don't create zero-sized stack objects.
528 // Ensure the object is properly aligned.
530 std::max((unsigned)DL.getPrefTypeAlignment(Ty), AI->getAlignment());
532 SSL.addObject(AI, Size, Align, SSC.getLiveRange(AI));
536 unsigned FrameAlignment = SSL.getFrameAlignment();
538 // FIXME: tell SSL that we start at a less-then-MaxAlignment aligned location
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))),
550 IRB.SetInsertPoint(BasePointer->getNextNode());
552 if (StackGuardSlot) {
553 unsigned Offset = SSL.getObjectOffset(StackGuardSlot);
554 Value *Off = IRB.CreateGEP(Int8Ty, BasePointer, // BasePointer is i8*
555 ConstantInt::get(Int32Ty, -Offset));
557 IRB.CreateBitCast(Off, StackGuardSlot->getType(), "StackGuardSlot");
559 // Replace alloc with the new location.
560 StackGuardSlot->replaceAllUsesWith(NewAI);
561 StackGuardSlot->eraseFromParent();
564 for (Argument *Arg : ByValArguments) {
565 unsigned Offset = SSL.getObjectOffset(Arg);
566 MaybeAlign Align(SSL.getObjectAlignment(Arg));
567 Type *Ty = Arg->getType()->getPointerElementType();
569 uint64_t Size = DL.getTypeStoreSize(Ty);
571 Size = 1; // Don't create zero-sized stack objects.
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");
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);
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);
591 replaceDbgDeclareForAlloca(AI, BasePointer, DIB, DIExpression::ApplyOffset,
593 replaceDbgValueForAlloca(AI, BasePointer, DIB, -Offset);
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());
602 Instruction *InsertBefore;
603 if (auto *PHI = dyn_cast<PHINode>(User))
604 InsertBefore = PHI->getIncomingBlock(U)->getTerminator();
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);
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);
621 AI->eraseFromParent();
624 // Re-align BasePointer so that our callees would see it aligned as
626 // FIXME: no need to update BasePointer in leaf functions.
627 unsigned FrameSize = alignTo(SSL.getFrameSize(), StackAlignment);
629 // Update shadow stack pointer in the function epilogue.
630 IRB.SetInsertPoint(BasePointer->getNextNode());
633 IRB.CreateGEP(Int8Ty, BasePointer, ConstantInt::get(Int32Ty, -FrameSize),
634 "unsafe_stack_static_top");
635 IRB.CreateStore(StaticTop, UnsafeStackPtr);
639 void SafeStack::moveDynamicAllocasToUnsafeStack(
640 Function &F, Value *UnsafeStackPtr, AllocaInst *DynamicTop,
641 ArrayRef<AllocaInst *> DynamicAllocas) {
642 DIBuilder DIB(*F.getParent());
644 for (AllocaInst *AI : DynamicAllocas) {
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);
652 Type *Ty = AI->getAllocatedType();
653 uint64_t TySize = DL.getTypeAllocSize(Ty);
654 Value *Size = IRB.CreateMul(ArraySize, ConstantInt::get(IntPtrTy, TySize));
656 Value *SP = IRB.CreatePtrToInt(IRB.CreateLoad(StackPtrTy, UnsafeStackPtr),
658 SP = IRB.CreateSub(SP, Size);
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);
665 assert(isPowerOf2_32(Align));
666 Value *NewTop = IRB.CreateIntToPtr(
667 IRB.CreateAnd(SP, ConstantInt::get(IntPtrTy, ~uint64_t(Align - 1))),
670 // Save the stack pointer.
671 IRB.CreateStore(NewTop, UnsafeStackPtr);
673 IRB.CreateStore(NewTop, DynamicTop);
675 Value *NewAI = IRB.CreatePointerCast(NewTop, AI->getType());
676 if (AI->hasName() && isa<Instruction>(NewAI))
679 replaceDbgDeclareForAlloca(AI, NewAI, DIB, DIExpression::ApplyOffset, 0);
680 AI->replaceAllUsesWith(NewAI);
681 AI->eraseFromParent();
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);
692 if (II->getIntrinsicID() == Intrinsic::stacksave) {
694 Instruction *LI = IRB.CreateLoad(StackPtrTy, UnsafeStackPtr);
696 II->replaceAllUsesWith(LI);
697 II->eraseFromParent();
698 } else if (II->getIntrinsicID() == Intrinsic::stackrestore) {
700 Instruction *SI = IRB.CreateStore(II->getArgOperand(0), UnsafeStackPtr);
702 assert(II->use_empty());
703 II->eraseFromParent();
709 bool SafeStack::ShouldInlinePointerAddress(CallSite &CS) {
710 Function *Callee = CS.getCalledFunction();
711 if (CS.hasFnAttr(Attribute::AlwaysInline) && isInlineViable(*Callee))
713 if (Callee->isInterposable() || Callee->hasFnAttribute(Attribute::NoInline) ||
719 void SafeStack::TryInlinePointerAddress() {
720 if (!isa<CallInst>(UnsafeStackPtr))
726 CallSite CS(UnsafeStackPtr);
727 Function *Callee = CS.getCalledFunction();
728 if (!Callee || Callee->isDeclaration())
731 if (!ShouldInlinePointerAddress(CS))
734 InlineFunctionInfo IFI;
735 InlineFunction(CS, IFI);
738 bool 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");
745 SmallVector<AllocaInst *, 16> StaticAllocas;
746 SmallVector<AllocaInst *, 4> DynamicAllocas;
747 SmallVector<Argument *, 4> ByValArguments;
748 SmallVector<ReturnInst *, 4> Returns;
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;
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,
762 if (StaticAllocas.empty() && DynamicAllocas.empty() &&
763 ByValArguments.empty() && StackRestorePoints.empty())
764 return false; // Nothing to do in this function.
766 if (!StaticAllocas.empty() || !DynamicAllocas.empty() ||
767 !ByValArguments.empty())
768 ++NumUnsafeStackFunctions; // This function has the unsafe stack.
770 if (!StackRestorePoints.empty())
771 ++NumUnsafeStackRestorePointsFunctions;
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);
783 UnsafeStackPtr = TL.getSafeStackPointerLocation(IRB);
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);
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);
801 for (ReturnInst *RI : Returns) {
802 IRBuilder<> IRBRet(RI);
803 checkStackGuard(IRBRet, F, *RI, StackGuardSlot, StackGuard);
807 // The top of the unsafe stack after all unsafe static allocas are
810 moveStaticAllocasToUnsafeStack(IRB, F, StaticAllocas, ByValArguments,
811 Returns, BasePointer, StackGuardSlot);
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());
822 // Handle dynamic allocas.
823 moveDynamicAllocasToUnsafeStack(F, UnsafeStackPtr, DynamicTop,
826 // Restore the unsafe stack pointer before each return.
827 for (ReturnInst *RI : Returns) {
828 IRB.SetInsertPoint(RI);
829 IRB.CreateStore(BasePointer, UnsafeStackPtr);
832 TryInlinePointerAddress();
834 LLVM_DEBUG(dbgs() << "[SafeStack] safestack applied\n");
838 class SafeStackLegacyPass : public FunctionPass {
839 const TargetMachine *TM = nullptr;
842 static char ID; // Pass identification, replacement for typeid..
844 SafeStackLegacyPass() : FunctionPass(ID) {
845 initializeSafeStackLegacyPassPass(*PassRegistry::getPassRegistry());
848 void getAnalysisUsage(AnalysisUsage &AU) const override {
849 AU.addRequired<TargetPassConfig>();
850 AU.addRequired<TargetLibraryInfoWrapperPass>();
851 AU.addRequired<AssumptionCacheTracker>();
854 bool runOnFunction(Function &F) override {
855 LLVM_DEBUG(dbgs() << "[SafeStack] Function: " << F.getName() << "\n");
857 if (!F.hasFnAttribute(Attribute::SafeStack)) {
858 LLVM_DEBUG(dbgs() << "[SafeStack] safestack is not requested"
859 " for this function\n");
863 if (F.isDeclaration()) {
864 LLVM_DEBUG(dbgs() << "[SafeStack] function definition"
865 " is not available\n");
869 TM = &getAnalysis<TargetPassConfig>().getTM<TargetMachine>();
870 auto *TL = TM->getSubtargetImpl(F)->getTargetLowering();
872 report_fatal_error("TargetLowering instance is required");
874 auto *DL = &F.getParent()->getDataLayout();
875 auto &TLI = getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F);
876 auto &ACT = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
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.
887 ScalarEvolution SE(F, TLI, ACT, DT, LI);
889 return SafeStack(F, *TL, *DL, SE).run();
893 } // end anonymous namespace
895 char SafeStackLegacyPass::ID = 0;
897 INITIALIZE_PASS_BEGIN(SafeStackLegacyPass, DEBUG_TYPE,
898 "Safe Stack instrumentation pass", false, false)
899 INITIALIZE_PASS_DEPENDENCY(TargetPassConfig)
900 INITIALIZE_PASS_END(SafeStackLegacyPass, DEBUG_TYPE,
901 "Safe Stack instrumentation pass", false, false)
903 FunctionPass *llvm::createSafeStackPass() { return new SafeStackLegacyPass(); }