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 "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"
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);
99 // Disabled by default due to PR32143.
100 static cl::opt<bool> ClColoring("safe-stack-coloring",
101 cl::desc("enable safe stack coloring"),
102 cl::Hidden, cl::init(false));
106 /// Rewrite an SCEV expression for a memory access address to an expression that
107 /// represents offset from the given alloca.
109 /// The implementation simply replaces all mentions of the alloca with zero.
110 class AllocaOffsetRewriter : public SCEVRewriteVisitor<AllocaOffsetRewriter> {
111 const Value *AllocaPtr;
114 AllocaOffsetRewriter(ScalarEvolution &SE, const Value *AllocaPtr)
115 : SCEVRewriteVisitor(SE), AllocaPtr(AllocaPtr) {}
117 const SCEV *visitUnknown(const SCEVUnknown *Expr) {
118 if (Expr->getValue() == AllocaPtr)
119 return SE.getZero(Expr->getType());
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
131 const TargetLoweringBase &TL;
132 const DataLayout &DL;
140 Value *UnsafeStackPtr = nullptr;
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.
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 };
150 /// Return the value of the stack canary.
151 Value *getStackGuard(IRBuilder<> &IRB, Function &F);
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);
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);
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);
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.
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);
183 /// Generate code to restore the stack after all stack restore points
184 /// in \p StackRestorePoints.
186 /// \returns A local variable in which to maintain the dynamic top of the
187 /// unsafe stack if needed.
189 createStackRestorePoints(IRBuilder<> &IRB, Function &F,
190 ArrayRef<Instruction *> StackRestorePoints,
191 Value *StaticTop, bool NeedDynamicTop);
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);
200 bool IsSafeStackAlloca(const Value *AllocaPtr, uint64_t AllocaSize);
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);
207 bool ShouldInlinePointerAddress(CallInst &CI);
208 void TryInlinePointerAddress();
211 SafeStack(Function &F, const TargetLoweringBase &TL, const DataLayout &DL,
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())) {}
219 // Run the transformation on the associated function.
220 // Returns whether the function was changed.
224 uint64_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());
230 Size *= C->getZExtValue();
235 bool 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));
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);
250 dbgs() << "[SafeStack] "
251 << (isa<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")
252 << *AllocaPtr << "\n"
253 << " Access " << *Addr << "\n"
255 << " U: " << SE.getUnsignedRange(Expr)
256 << ", S: " << SE.getSignedRange(Expr) << "\n"
257 << " Range " << AccessRange << "\n"
258 << " AllocaRange " << AllocaRange << "\n"
259 << " " << (Safe ? "safe" : "unsafe") << "\n");
264 bool 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)
271 if (MI->getRawDest() != U)
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);
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).
284 bool 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);
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());
299 switch (I->getOpcode()) {
300 case Instruction::Load:
301 if (!IsAccessSafe(UI, DL.getTypeStoreSize(I->getType()), AllocaPtr,
306 case Instruction::VAArg:
307 // "va-arg" from a pointer is safe.
309 case Instruction::Store:
310 if (V == I->getOperand(0)) {
311 // Stored the pointer - conservatively assume it may be unsafe.
313 << "[SafeStack] Unsafe alloca: " << *AllocaPtr
314 << "\n store of address: " << *I << "\n");
318 if (!IsAccessSafe(UI, DL.getTypeStoreSize(I->getOperand(0)->getType()),
319 AllocaPtr, AllocaSize))
323 case Instruction::Ret:
327 case Instruction::Call:
328 case Instruction::Invoke: {
329 const CallBase &CS = *cast<CallBase>(I);
331 if (I->isLifetimeStartOrEnd())
334 if (const MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) {
335 if (!IsMemIntrinsicSafe(MI, UI, AllocaPtr, AllocaSize)) {
337 << "[SafeStack] Unsafe alloca: " << *AllocaPtr
338 << "\n unsafe memintrinsic: " << *I << "\n");
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)
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");
364 if (Visited.insert(I).second)
365 WorkList.push_back(cast<const Instruction>(I));
370 // All uses of the alloca are safe, we can place it on the safe stack.
374 Value *SafeStack::getStackGuard(IRBuilder<> &IRB, Function &F) {
375 Value *StackGuardVar = TL.getIRStackGuard(IRB);
378 F.getParent()->getOrInsertGlobal("__stack_chk_guard", StackPtrTy);
379 return IRB.CreateLoad(StackPtrTy, StackGuardVar, "StackGuard");
382 void 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)) {
392 uint64_t Size = getStaticAllocaAllocationSize(AI);
393 if (IsSafeStackAlloca(AI, Size))
396 if (AI->isStaticAlloca()) {
397 ++NumUnsafeStaticAllocas;
398 StaticAllocas.push_back(AI);
400 ++NumUnsafeDynamicAllocas;
401 DynamicAllocas.push_back(AI);
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)
415 "gcroot intrinsic not compatible with safestack attribute");
418 for (Argument &Arg : F.args()) {
419 if (!Arg.hasByValAttr())
422 DL.getTypeStoreSize(Arg.getType()->getPointerElementType());
423 if (IsSafeStackAlloca(&Arg, Size))
426 ++NumUnsafeByValArguments;
427 ByValArguments.push_back(&Arg);
432 SafeStack::createStackRestorePoints(IRBuilder<> &IRB, Function &F,
433 ArrayRef<Instruction *> StackRestorePoints,
434 Value *StaticTop, bool NeedDynamicTop) {
435 assert(StaticTop && "The stack top isn't set.");
437 if (StackRestorePoints.empty())
440 // We need the current value of the shadow stack pointer to restore
441 // after longjmp or exception catching.
443 // FIXME: On some platforms this could be handled by the longjmp/exception
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);
455 // Restore current stack pointer after longjmp/exception catch.
456 for (Instruction *I : StackRestorePoints) {
457 ++NumUnsafeStackRestorePoints;
459 IRB.SetInsertPoint(I->getNextNode());
461 DynamicTop ? IRB.CreateLoad(StackPtrTy, DynamicTop) : StaticTop;
462 IRB.CreateStore(CurrentTop, UnsafeStackPtr);
468 void 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);
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, {});
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.
491 Value *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())
498 DIBuilder DIB(*F.getParent());
500 StackLifetime SSC(F, StaticAllocas, StackLifetime::LivenessType::May);
501 static const StackLifetime::LiveRange NoColoringRange(1, true);
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();
513 // Unsafe stack always grows down.
514 StackLayout SSL(StackAlignment);
515 if (StackGuardSlot) {
516 Type *Ty = StackGuardSlot->getAllocatedType();
518 std::max(DL.getPrefTypeAlignment(Ty), StackGuardSlot->getAlignment());
519 SSL.addObject(StackGuardSlot, getStaticAllocaAllocationSize(StackGuardSlot),
520 Align, SSC.getFullLiveRange());
523 for (Argument *Arg : ByValArguments) {
524 Type *Ty = Arg->getType()->getPointerElementType();
525 uint64_t Size = DL.getTypeStoreSize(Ty);
527 Size = 1; // Don't create zero-sized stack objects.
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());
535 for (AllocaInst *AI : StaticAllocas) {
536 Type *Ty = AI->getAllocatedType();
537 uint64_t Size = getStaticAllocaAllocationSize(AI);
539 Size = 1; // Don't create zero-sized stack objects.
541 // Ensure the object is properly aligned.
543 std::max((unsigned)DL.getPrefTypeAlignment(Ty), AI->getAlignment());
545 SSL.addObject(AI, Size, Align,
546 ClColoring ? SSC.getLiveRange(AI) : NoColoringRange);
550 unsigned FrameAlignment = SSL.getFrameAlignment();
552 // FIXME: tell SSL that we start at a less-then-MaxAlignment aligned location
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))),
564 IRB.SetInsertPoint(BasePointer->getNextNode());
566 if (StackGuardSlot) {
567 unsigned Offset = SSL.getObjectOffset(StackGuardSlot);
568 Value *Off = IRB.CreateGEP(Int8Ty, BasePointer, // BasePointer is i8*
569 ConstantInt::get(Int32Ty, -Offset));
571 IRB.CreateBitCast(Off, StackGuardSlot->getType(), "StackGuardSlot");
573 // Replace alloc with the new location.
574 StackGuardSlot->replaceAllUsesWith(NewAI);
575 StackGuardSlot->eraseFromParent();
578 for (Argument *Arg : ByValArguments) {
579 unsigned Offset = SSL.getObjectOffset(Arg);
580 MaybeAlign Align(SSL.getObjectAlignment(Arg));
581 Type *Ty = Arg->getType()->getPointerElementType();
583 uint64_t Size = DL.getTypeStoreSize(Ty);
585 Size = 1; // Don't create zero-sized stack objects.
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");
592 // Replace alloc with the new location.
593 replaceDbgDeclare(Arg, BasePointer, DIB, DIExpression::ApplyOffset,
595 Arg->replaceAllUsesWith(NewArg);
596 IRB.SetInsertPoint(cast<Instruction>(NewArg)->getNextNode());
597 IRB.CreateMemCpy(Off, Align, Arg, Arg->getParamAlign(), Size);
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);
605 replaceDbgDeclare(AI, BasePointer, DIB, DIExpression::ApplyOffset, -Offset);
606 replaceDbgValueForAlloca(AI, BasePointer, DIB, -Offset);
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());
615 Instruction *InsertBefore;
616 if (auto *PHI = dyn_cast<PHINode>(User))
617 InsertBefore = PHI->getIncomingBlock(U)->getTerminator();
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);
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);
634 AI->eraseFromParent();
637 // Re-align BasePointer so that our callees would see it aligned as
639 // FIXME: no need to update BasePointer in leaf functions.
640 unsigned FrameSize = alignTo(SSL.getFrameSize(), StackAlignment);
642 // Update shadow stack pointer in the function epilogue.
643 IRB.SetInsertPoint(BasePointer->getNextNode());
646 IRB.CreateGEP(Int8Ty, BasePointer, ConstantInt::get(Int32Ty, -FrameSize),
647 "unsafe_stack_static_top");
648 IRB.CreateStore(StaticTop, UnsafeStackPtr);
652 void SafeStack::moveDynamicAllocasToUnsafeStack(
653 Function &F, Value *UnsafeStackPtr, AllocaInst *DynamicTop,
654 ArrayRef<AllocaInst *> DynamicAllocas) {
655 DIBuilder DIB(*F.getParent());
657 for (AllocaInst *AI : DynamicAllocas) {
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);
665 Type *Ty = AI->getAllocatedType();
666 uint64_t TySize = DL.getTypeAllocSize(Ty);
667 Value *Size = IRB.CreateMul(ArraySize, ConstantInt::get(IntPtrTy, TySize));
669 Value *SP = IRB.CreatePtrToInt(IRB.CreateLoad(StackPtrTy, UnsafeStackPtr),
671 SP = IRB.CreateSub(SP, Size);
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);
678 assert(isPowerOf2_32(Align));
679 Value *NewTop = IRB.CreateIntToPtr(
680 IRB.CreateAnd(SP, ConstantInt::get(IntPtrTy, ~uint64_t(Align - 1))),
683 // Save the stack pointer.
684 IRB.CreateStore(NewTop, UnsafeStackPtr);
686 IRB.CreateStore(NewTop, DynamicTop);
688 Value *NewAI = IRB.CreatePointerCast(NewTop, AI->getType());
689 if (AI->hasName() && isa<Instruction>(NewAI))
692 replaceDbgDeclare(AI, NewAI, DIB, DIExpression::ApplyOffset, 0);
693 AI->replaceAllUsesWith(NewAI);
694 AI->eraseFromParent();
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);
705 if (II->getIntrinsicID() == Intrinsic::stacksave) {
707 Instruction *LI = IRB.CreateLoad(StackPtrTy, UnsafeStackPtr);
709 II->replaceAllUsesWith(LI);
710 II->eraseFromParent();
711 } else if (II->getIntrinsicID() == Intrinsic::stackrestore) {
713 Instruction *SI = IRB.CreateStore(II->getArgOperand(0), UnsafeStackPtr);
715 assert(II->use_empty());
716 II->eraseFromParent();
722 bool SafeStack::ShouldInlinePointerAddress(CallInst &CI) {
723 Function *Callee = CI.getCalledFunction();
724 if (CI.hasFnAttr(Attribute::AlwaysInline) &&
725 isInlineViable(*Callee).isSuccess())
727 if (Callee->isInterposable() || Callee->hasFnAttribute(Attribute::NoInline) ||
733 void SafeStack::TryInlinePointerAddress() {
734 auto *CI = dyn_cast<CallInst>(UnsafeStackPtr);
741 Function *Callee = CI->getCalledFunction();
742 if (!Callee || Callee->isDeclaration())
745 if (!ShouldInlinePointerAddress(*CI))
748 InlineFunctionInfo IFI;
749 InlineFunction(*CI, IFI);
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");
759 SmallVector<AllocaInst *, 16> StaticAllocas;
760 SmallVector<AllocaInst *, 4> DynamicAllocas;
761 SmallVector<Argument *, 4> ByValArguments;
762 SmallVector<ReturnInst *, 4> Returns;
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;
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,
776 if (StaticAllocas.empty() && DynamicAllocas.empty() &&
777 ByValArguments.empty() && StackRestorePoints.empty())
778 return false; // Nothing to do in this function.
780 if (!StaticAllocas.empty() || !DynamicAllocas.empty() ||
781 !ByValArguments.empty())
782 ++NumUnsafeStackFunctions; // This function has the unsafe stack.
784 if (!StackRestorePoints.empty())
785 ++NumUnsafeStackRestorePointsFunctions;
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);
797 UnsafeStackPtr = TL.getSafeStackPointerLocation(IRB);
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);
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);
815 for (ReturnInst *RI : Returns) {
816 IRBuilder<> IRBRet(RI);
817 checkStackGuard(IRBRet, F, *RI, StackGuardSlot, StackGuard);
821 // The top of the unsafe stack after all unsafe static allocas are
824 moveStaticAllocasToUnsafeStack(IRB, F, StaticAllocas, ByValArguments,
825 Returns, BasePointer, StackGuardSlot);
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());
836 // Handle dynamic allocas.
837 moveDynamicAllocasToUnsafeStack(F, UnsafeStackPtr, DynamicTop,
840 // Restore the unsafe stack pointer before each return.
841 for (ReturnInst *RI : Returns) {
842 IRB.SetInsertPoint(RI);
843 IRB.CreateStore(BasePointer, UnsafeStackPtr);
846 TryInlinePointerAddress();
848 LLVM_DEBUG(dbgs() << "[SafeStack] safestack applied\n");
852 class SafeStackLegacyPass : public FunctionPass {
853 const TargetMachine *TM = nullptr;
856 static char ID; // Pass identification, replacement for typeid..
858 SafeStackLegacyPass() : FunctionPass(ID) {
859 initializeSafeStackLegacyPassPass(*PassRegistry::getPassRegistry());
862 void getAnalysisUsage(AnalysisUsage &AU) const override {
863 AU.addRequired<TargetPassConfig>();
864 AU.addRequired<TargetLibraryInfoWrapperPass>();
865 AU.addRequired<AssumptionCacheTracker>();
868 bool runOnFunction(Function &F) override {
869 LLVM_DEBUG(dbgs() << "[SafeStack] Function: " << F.getName() << "\n");
871 if (!F.hasFnAttribute(Attribute::SafeStack)) {
872 LLVM_DEBUG(dbgs() << "[SafeStack] safestack is not requested"
873 " for this function\n");
877 if (F.isDeclaration()) {
878 LLVM_DEBUG(dbgs() << "[SafeStack] function definition"
879 " is not available\n");
883 TM = &getAnalysis<TargetPassConfig>().getTM<TargetMachine>();
884 auto *TL = TM->getSubtargetImpl(F)->getTargetLowering();
886 report_fatal_error("TargetLowering instance is required");
888 auto *DL = &F.getParent()->getDataLayout();
889 auto &TLI = getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F);
890 auto &ACT = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
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.
901 ScalarEvolution SE(F, TLI, ACT, DT, LI);
903 return SafeStack(F, *TL, *DL, SE).run();
907 } // end anonymous namespace
909 char SafeStackLegacyPass::ID = 0;
911 INITIALIZE_PASS_BEGIN(SafeStackLegacyPass, DEBUG_TYPE,
912 "Safe Stack instrumentation pass", false, false)
913 INITIALIZE_PASS_DEPENDENCY(TargetPassConfig)
914 INITIALIZE_PASS_END(SafeStackLegacyPass, DEBUG_TYPE,
915 "Safe Stack instrumentation pass", false, false)
917 FunctionPass *llvm::createSafeStackPass() { return new SafeStackLegacyPass(); }