1 //===- SafeStack.cpp - Safe Stack Insertion -------------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This pass splits the stack into the safe stack (kept as-is for LLVM backend)
10 // and the unsafe stack (explicitly allocated and managed through the runtime
11 // support library).
12 //
13 // http://clang.llvm.org/docs/SafeStack.html
14 //
15 //===----------------------------------------------------------------------===//
16
17 #include "SafeStackLayout.h"
18 #include "llvm/ADT/APInt.h"
19 #include "llvm/ADT/ArrayRef.h"
20 #include "llvm/ADT/BitVector.h"
21 #include "llvm/ADT/SmallPtrSet.h"
22 #include "llvm/ADT/SmallVector.h"
23 #include "llvm/ADT/Statistic.h"
24 #include "llvm/Analysis/AssumptionCache.h"
25 #include "llvm/Analysis/BranchProbabilityInfo.h"
26 #include "llvm/Analysis/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/Module.h"
53 #include "llvm/IR/Type.h"
54 #include "llvm/IR/Use.h"
55 #include "llvm/IR/User.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 <string>
72 #include <utility>
73
74 using namespace llvm;
75 using namespace llvm::safestack;
76
77 #define DEBUG_TYPE "safe-stack"
78
79 namespace llvm {
80
81 STATISTIC(NumFunctions, "Total number of functions");
82 STATISTIC(NumUnsafeStackFunctions, "Number of functions with unsafe stack");
83 STATISTIC(NumUnsafeStackRestorePointsFunctions,
84 "Number of functions that use setjmp or exceptions");
85
86 STATISTIC(NumAllocas, "Total number of allocas");
87 STATISTIC(NumUnsafeStaticAllocas, "Number of unsafe static allocas");
88 STATISTIC(NumUnsafeDynamicAllocas, "Number of unsafe dynamic allocas");
89 STATISTIC(NumUnsafeByValArguments, "Number of unsafe byval arguments");
90 STATISTIC(NumUnsafeStackRestorePoints, "Number of setjmps and landingpads");
91
92 } // namespace llvm
93
94 /// Use __safestack_pointer_address even if the platform has a faster way of
95 /// access safe stack pointer.
96 static cl::opt<bool>
97 SafeStackUsePointerAddress("safestack-use-pointer-address",
98 cl::init(false), cl::Hidden);
99
100 // Disabled by default due to PR32143.
101 static cl::opt<bool> ClColoring("safe-stack-coloring",
102 cl::desc("enable safe stack coloring"),
103 cl::Hidden, cl::init(false));
104
105 namespace {
106
107 /// Rewrite an SCEV expression for a memory access address to an expression that
108 /// represents offset from the given alloca.
109 ///
110 /// The implementation simply replaces all mentions of the alloca with zero.
111 class AllocaOffsetRewriter : public SCEVRewriteVisitor<AllocaOffsetRewriter> {
112 const Value *AllocaPtr;
113
114 public:
AllocaOffsetRewriter(ScalarEvolution & SE,const Value * AllocaPtr)115 AllocaOffsetRewriter(ScalarEvolution &SE, const Value *AllocaPtr)
116 : SCEVRewriteVisitor(SE), AllocaPtr(AllocaPtr) {}
117
visitUnknown(const SCEVUnknown * Expr)118 const SCEV *visitUnknown(const SCEVUnknown *Expr) {
119 if (Expr->getValue() == AllocaPtr)
120 return SE.getZero(Expr->getType());
121 return Expr;
122 }
123 };
124
125 /// The SafeStack pass splits the stack of each function into the safe
126 /// stack, which is only accessed through memory safe dereferences (as
127 /// determined statically), and the unsafe stack, which contains all
128 /// local variables that are accessed in ways that we can't prove to
129 /// be safe.
130 class SafeStack {
131 Function &F;
132 const TargetLoweringBase &TL;
133 const DataLayout &DL;
134 DomTreeUpdater *DTU;
135 ScalarEvolution &SE;
136
137 Type *StackPtrTy;
138 Type *IntPtrTy;
139 Type *Int32Ty;
140 Type *Int8Ty;
141
142 Value *UnsafeStackPtr = nullptr;
143
144 /// Unsafe stack alignment. Each stack frame must ensure that the stack is
145 /// aligned to this value. We need to re-align the unsafe stack if the
146 /// alignment of any object on the stack exceeds this value.
147 ///
148 /// 16 seems like a reasonable upper bound on the alignment of objects that we
149 /// might expect to appear on the stack on most common targets.
150 enum { StackAlignment = 16 };
151
152 /// Return the value of the stack canary.
153 Value *getStackGuard(IRBuilder<> &IRB, Function &F);
154
155 /// Load stack guard from the frame and check if it has changed.
156 void checkStackGuard(IRBuilder<> &IRB, Function &F, Instruction &RI,
157 AllocaInst *StackGuardSlot, Value *StackGuard);
158
159 /// Find all static allocas, dynamic allocas, return instructions and
160 /// stack restore points (exception unwind blocks and setjmp calls) in the
161 /// given function and append them to the respective vectors.
162 void findInsts(Function &F, SmallVectorImpl<AllocaInst *> &StaticAllocas,
163 SmallVectorImpl<AllocaInst *> &DynamicAllocas,
164 SmallVectorImpl<Argument *> &ByValArguments,
165 SmallVectorImpl<Instruction *> &Returns,
166 SmallVectorImpl<Instruction *> &StackRestorePoints);
167
168 /// Calculate the allocation size of a given alloca. Returns 0 if the
169 /// size can not be statically determined.
170 uint64_t getStaticAllocaAllocationSize(const AllocaInst* AI);
171
172 /// Allocate space for all static allocas in \p StaticAllocas,
173 /// replace allocas with pointers into the unsafe stack.
174 ///
175 /// \returns A pointer to the top of the unsafe stack after all unsafe static
176 /// allocas are allocated.
177 Value *moveStaticAllocasToUnsafeStack(IRBuilder<> &IRB, Function &F,
178 ArrayRef<AllocaInst *> StaticAllocas,
179 ArrayRef<Argument *> ByValArguments,
180 Instruction *BasePointer,
181 AllocaInst *StackGuardSlot);
182
183 /// Generate code to restore the stack after all stack restore points
184 /// in \p StackRestorePoints.
185 ///
186 /// \returns A local variable in which to maintain the dynamic top of the
187 /// unsafe stack if needed.
188 AllocaInst *
189 createStackRestorePoints(IRBuilder<> &IRB, Function &F,
190 ArrayRef<Instruction *> StackRestorePoints,
191 Value *StaticTop, bool NeedDynamicTop);
192
193 /// Replace all allocas in \p DynamicAllocas with code to allocate
194 /// space dynamically on the unsafe stack and store the dynamic unsafe stack
195 /// top to \p DynamicTop if non-null.
196 void moveDynamicAllocasToUnsafeStack(Function &F, Value *UnsafeStackPtr,
197 AllocaInst *DynamicTop,
198 ArrayRef<AllocaInst *> DynamicAllocas);
199
200 bool IsSafeStackAlloca(const Value *AllocaPtr, uint64_t AllocaSize);
201
202 bool IsMemIntrinsicSafe(const MemIntrinsic *MI, const Use &U,
203 const Value *AllocaPtr, uint64_t AllocaSize);
204 bool IsAccessSafe(Value *Addr, uint64_t Size, const Value *AllocaPtr,
205 uint64_t AllocaSize);
206
207 bool ShouldInlinePointerAddress(CallInst &CI);
208 void TryInlinePointerAddress();
209
210 public:
SafeStack(Function & F,const TargetLoweringBase & TL,const DataLayout & DL,DomTreeUpdater * DTU,ScalarEvolution & SE)211 SafeStack(Function &F, const TargetLoweringBase &TL, const DataLayout &DL,
212 DomTreeUpdater *DTU, ScalarEvolution &SE)
213 : F(F), TL(TL), DL(DL), DTU(DTU), SE(SE),
214 StackPtrTy(Type::getInt8PtrTy(F.getContext())),
215 IntPtrTy(DL.getIntPtrType(F.getContext())),
216 Int32Ty(Type::getInt32Ty(F.getContext())),
217 Int8Ty(Type::getInt8Ty(F.getContext())) {}
218
219 // Run the transformation on the associated function.
220 // Returns whether the function was changed.
221 bool run();
222 };
223
getStaticAllocaAllocationSize(const AllocaInst * AI)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());
228 if (!C)
229 return 0;
230 Size *= C->getZExtValue();
231 }
232 return Size;
233 }
234
IsAccessSafe(Value * Addr,uint64_t AccessSize,const Value * AllocaPtr,uint64_t AllocaSize)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));
239
240 uint64_t BitWidth = SE.getTypeSizeInBits(Expr->getType());
241 ConstantRange AccessStartRange = SE.getUnsignedRange(Expr);
242 ConstantRange SizeRange =
243 ConstantRange(APInt(BitWidth, 0), APInt(BitWidth, AccessSize));
244 ConstantRange AccessRange = AccessStartRange.add(SizeRange);
245 ConstantRange AllocaRange =
246 ConstantRange(APInt(BitWidth, 0), APInt(BitWidth, AllocaSize));
247 bool Safe = AllocaRange.contains(AccessRange);
248
249 LLVM_DEBUG(
250 dbgs() << "[SafeStack] "
251 << (isa<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")
252 << *AllocaPtr << "\n"
253 << " Access " << *Addr << "\n"
254 << " SCEV " << *Expr
255 << " U: " << SE.getUnsignedRange(Expr)
256 << ", S: " << SE.getSignedRange(Expr) << "\n"
257 << " Range " << AccessRange << "\n"
258 << " AllocaRange " << AllocaRange << "\n"
259 << " " << (Safe ? "safe" : "unsafe") << "\n");
260
261 return Safe;
262 }
263
IsMemIntrinsicSafe(const MemIntrinsic * MI,const Use & U,const Value * AllocaPtr,uint64_t AllocaSize)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)
269 return true;
270 } else {
271 if (MI->getRawDest() != U)
272 return true;
273 }
274
275 const auto *Len = dyn_cast<ConstantInt>(MI->getLength());
276 // Non-constant size => unsafe. FIXME: try SCEV getRange.
277 if (!Len) return false;
278 return IsAccessSafe(U, Len->getZExtValue(), AllocaPtr, AllocaSize);
279 }
280
281 /// Check whether a given allocation must be put on the safe
282 /// stack or not. The function analyzes all uses of AI and checks whether it is
283 /// only accessed in a memory safe way (as decided statically).
IsSafeStackAlloca(const Value * AllocaPtr,uint64_t AllocaSize)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);
291
292 // A DFS search through all uses of the alloca in bitcasts/PHI/GEPs/etc.
293 while (!WorkList.empty()) {
294 const Value *V = WorkList.pop_back_val();
295 for (const Use &UI : V->uses()) {
296 auto I = cast<const Instruction>(UI.getUser());
297 assert(V == UI.get());
298
299 switch (I->getOpcode()) {
300 case Instruction::Load:
301 if (!IsAccessSafe(UI, DL.getTypeStoreSize(I->getType()), AllocaPtr,
302 AllocaSize))
303 return false;
304 break;
305
306 case Instruction::VAArg:
307 // "va-arg" from a pointer is safe.
308 break;
309 case Instruction::Store:
310 if (V == I->getOperand(0)) {
311 // Stored the pointer - conservatively assume it may be unsafe.
312 LLVM_DEBUG(dbgs()
313 << "[SafeStack] Unsafe alloca: " << *AllocaPtr
314 << "\n store of address: " << *I << "\n");
315 return false;
316 }
317
318 if (!IsAccessSafe(UI, DL.getTypeStoreSize(I->getOperand(0)->getType()),
319 AllocaPtr, AllocaSize))
320 return false;
321 break;
322
323 case Instruction::Ret:
324 // Information leak.
325 return false;
326
327 case Instruction::Call:
328 case Instruction::Invoke: {
329 const CallBase &CS = *cast<CallBase>(I);
330
331 if (I->isLifetimeStartOrEnd())
332 continue;
333
334 if (const MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) {
335 if (!IsMemIntrinsicSafe(MI, UI, AllocaPtr, AllocaSize)) {
336 LLVM_DEBUG(dbgs()
337 << "[SafeStack] Unsafe alloca: " << *AllocaPtr
338 << "\n unsafe memintrinsic: " << *I << "\n");
339 return false;
340 }
341 continue;
342 }
343
344 // LLVM 'nocapture' attribute is only set for arguments whose address
345 // is not stored, passed around, or used in any other non-trivial way.
346 // We assume that passing a pointer to an object as a 'nocapture
347 // readnone' argument is safe.
348 // FIXME: a more precise solution would require an interprocedural
349 // analysis here, which would look at all uses of an argument inside
350 // the function being called.
351 auto B = CS.arg_begin(), E = CS.arg_end();
352 for (auto A = B; A != E; ++A)
353 if (A->get() == V)
354 if (!(CS.doesNotCapture(A - B) && (CS.doesNotAccessMemory(A - B) ||
355 CS.doesNotAccessMemory()))) {
356 LLVM_DEBUG(dbgs() << "[SafeStack] Unsafe alloca: " << *AllocaPtr
357 << "\n unsafe call: " << *I << "\n");
358 return false;
359 }
360 continue;
361 }
362
363 default:
364 if (Visited.insert(I).second)
365 WorkList.push_back(cast<const Instruction>(I));
366 }
367 }
368 }
369
370 // All uses of the alloca are safe, we can place it on the safe stack.
371 return true;
372 }
373
getStackGuard(IRBuilder<> & IRB,Function & F)374 Value *SafeStack::getStackGuard(IRBuilder<> &IRB, Function &F) {
375 Value *StackGuardVar = TL.getIRStackGuard(IRB);
376 if (!StackGuardVar)
377 StackGuardVar =
378 F.getParent()->getOrInsertGlobal("__stack_chk_guard", StackPtrTy);
379 return IRB.CreateLoad(StackPtrTy, StackGuardVar, "StackGuard");
380 }
381
findInsts(Function & F,SmallVectorImpl<AllocaInst * > & StaticAllocas,SmallVectorImpl<AllocaInst * > & DynamicAllocas,SmallVectorImpl<Argument * > & ByValArguments,SmallVectorImpl<Instruction * > & Returns,SmallVectorImpl<Instruction * > & StackRestorePoints)382 void SafeStack::findInsts(Function &F,
383 SmallVectorImpl<AllocaInst *> &StaticAllocas,
384 SmallVectorImpl<AllocaInst *> &DynamicAllocas,
385 SmallVectorImpl<Argument *> &ByValArguments,
386 SmallVectorImpl<Instruction *> &Returns,
387 SmallVectorImpl<Instruction *> &StackRestorePoints) {
388 for (Instruction &I : instructions(&F)) {
389 if (auto AI = dyn_cast<AllocaInst>(&I)) {
390 ++NumAllocas;
391
392 uint64_t Size = getStaticAllocaAllocationSize(AI);
393 if (IsSafeStackAlloca(AI, Size))
394 continue;
395
396 if (AI->isStaticAlloca()) {
397 ++NumUnsafeStaticAllocas;
398 StaticAllocas.push_back(AI);
399 } else {
400 ++NumUnsafeDynamicAllocas;
401 DynamicAllocas.push_back(AI);
402 }
403 } else if (auto RI = dyn_cast<ReturnInst>(&I)) {
404 if (CallInst *CI = I.getParent()->getTerminatingMustTailCall())
405 Returns.push_back(CI);
406 else
407 Returns.push_back(RI);
408 } else if (auto CI = dyn_cast<CallInst>(&I)) {
409 // setjmps require stack restore.
410 if (CI->getCalledFunction() && CI->canReturnTwice())
411 StackRestorePoints.push_back(CI);
412 } else if (auto LP = dyn_cast<LandingPadInst>(&I)) {
413 // Exception landing pads require stack restore.
414 StackRestorePoints.push_back(LP);
415 } else if (auto II = dyn_cast<IntrinsicInst>(&I)) {
416 if (II->getIntrinsicID() == Intrinsic::gcroot)
417 report_fatal_error(
418 "gcroot intrinsic not compatible with safestack attribute");
419 }
420 }
421 for (Argument &Arg : F.args()) {
422 if (!Arg.hasByValAttr())
423 continue;
424 uint64_t Size =
425 DL.getTypeStoreSize(Arg.getType()->getPointerElementType());
426 if (IsSafeStackAlloca(&Arg, Size))
427 continue;
428
429 ++NumUnsafeByValArguments;
430 ByValArguments.push_back(&Arg);
431 }
432 }
433
434 AllocaInst *
createStackRestorePoints(IRBuilder<> & IRB,Function & F,ArrayRef<Instruction * > StackRestorePoints,Value * StaticTop,bool NeedDynamicTop)435 SafeStack::createStackRestorePoints(IRBuilder<> &IRB, Function &F,
436 ArrayRef<Instruction *> StackRestorePoints,
437 Value *StaticTop, bool NeedDynamicTop) {
438 assert(StaticTop && "The stack top isn't set.");
439
440 if (StackRestorePoints.empty())
441 return nullptr;
442
443 // We need the current value of the shadow stack pointer to restore
444 // after longjmp or exception catching.
445
446 // FIXME: On some platforms this could be handled by the longjmp/exception
447 // runtime itself.
448
449 AllocaInst *DynamicTop = nullptr;
450 if (NeedDynamicTop) {
451 // If we also have dynamic alloca's, the stack pointer value changes
452 // throughout the function. For now we store it in an alloca.
453 DynamicTop = IRB.CreateAlloca(StackPtrTy, /*ArraySize=*/nullptr,
454 "unsafe_stack_dynamic_ptr");
455 IRB.CreateStore(StaticTop, DynamicTop);
456 }
457
458 // Restore current stack pointer after longjmp/exception catch.
459 for (Instruction *I : StackRestorePoints) {
460 ++NumUnsafeStackRestorePoints;
461
462 IRB.SetInsertPoint(I->getNextNode());
463 Value *CurrentTop =
464 DynamicTop ? IRB.CreateLoad(StackPtrTy, DynamicTop) : StaticTop;
465 IRB.CreateStore(CurrentTop, UnsafeStackPtr);
466 }
467
468 return DynamicTop;
469 }
470
checkStackGuard(IRBuilder<> & IRB,Function & F,Instruction & RI,AllocaInst * StackGuardSlot,Value * StackGuard)471 void SafeStack::checkStackGuard(IRBuilder<> &IRB, Function &F, Instruction &RI,
472 AllocaInst *StackGuardSlot, Value *StackGuard) {
473 Value *V = IRB.CreateLoad(StackPtrTy, StackGuardSlot);
474 Value *Cmp = IRB.CreateICmpNE(StackGuard, V);
475
476 auto SuccessProb = BranchProbabilityInfo::getBranchProbStackProtector(true);
477 auto FailureProb = BranchProbabilityInfo::getBranchProbStackProtector(false);
478 MDNode *Weights = MDBuilder(F.getContext())
479 .createBranchWeights(SuccessProb.getNumerator(),
480 FailureProb.getNumerator());
481 Instruction *CheckTerm =
482 SplitBlockAndInsertIfThen(Cmp, &RI, /* Unreachable */ true, Weights, DTU);
483 IRBuilder<> IRBFail(CheckTerm);
484 // FIXME: respect -fsanitize-trap / -ftrap-function here?
485 FunctionCallee StackChkFail =
486 F.getParent()->getOrInsertFunction("__stack_chk_fail", IRB.getVoidTy());
487 IRBFail.CreateCall(StackChkFail, {});
488 }
489
490 /// We explicitly compute and set the unsafe stack layout for all unsafe
491 /// static alloca instructions. We save the unsafe "base pointer" in the
492 /// prologue into a local variable and restore it in the epilogue.
moveStaticAllocasToUnsafeStack(IRBuilder<> & IRB,Function & F,ArrayRef<AllocaInst * > StaticAllocas,ArrayRef<Argument * > ByValArguments,Instruction * BasePointer,AllocaInst * StackGuardSlot)493 Value *SafeStack::moveStaticAllocasToUnsafeStack(
494 IRBuilder<> &IRB, Function &F, ArrayRef<AllocaInst *> StaticAllocas,
495 ArrayRef<Argument *> ByValArguments, Instruction *BasePointer,
496 AllocaInst *StackGuardSlot) {
497 if (StaticAllocas.empty() && ByValArguments.empty())
498 return BasePointer;
499
500 DIBuilder DIB(*F.getParent());
501
502 StackLifetime SSC(F, StaticAllocas, StackLifetime::LivenessType::May);
503 static const StackLifetime::LiveRange NoColoringRange(1, true);
504 if (ClColoring)
505 SSC.run();
506
507 for (auto *I : SSC.getMarkers()) {
508 auto *Op = dyn_cast<Instruction>(I->getOperand(1));
509 const_cast<IntrinsicInst *>(I)->eraseFromParent();
510 // Remove the operand bitcast, too, if it has no more uses left.
511 if (Op && Op->use_empty())
512 Op->eraseFromParent();
513 }
514
515 // Unsafe stack always grows down.
516 StackLayout SSL(StackAlignment);
517 if (StackGuardSlot) {
518 Type *Ty = StackGuardSlot->getAllocatedType();
519 unsigned Align =
520 std::max(DL.getPrefTypeAlignment(Ty), StackGuardSlot->getAlignment());
521 SSL.addObject(StackGuardSlot, getStaticAllocaAllocationSize(StackGuardSlot),
522 Align, SSC.getFullLiveRange());
523 }
524
525 for (Argument *Arg : ByValArguments) {
526 Type *Ty = Arg->getType()->getPointerElementType();
527 uint64_t Size = DL.getTypeStoreSize(Ty);
528 if (Size == 0)
529 Size = 1; // Don't create zero-sized stack objects.
530
531 // Ensure the object is properly aligned.
532 unsigned Align = std::max((unsigned)DL.getPrefTypeAlignment(Ty),
533 Arg->getParamAlignment());
534 SSL.addObject(Arg, Size, Align, SSC.getFullLiveRange());
535 }
536
537 for (AllocaInst *AI : StaticAllocas) {
538 Type *Ty = AI->getAllocatedType();
539 uint64_t Size = getStaticAllocaAllocationSize(AI);
540 if (Size == 0)
541 Size = 1; // Don't create zero-sized stack objects.
542
543 // Ensure the object is properly aligned.
544 unsigned Align =
545 std::max((unsigned)DL.getPrefTypeAlignment(Ty), AI->getAlignment());
546
547 SSL.addObject(AI, Size, Align,
548 ClColoring ? SSC.getLiveRange(AI) : NoColoringRange);
549 }
550
551 SSL.computeLayout();
552 unsigned FrameAlignment = SSL.getFrameAlignment();
553
554 // FIXME: tell SSL that we start at a less-then-MaxAlignment aligned location
555 // (AlignmentSkew).
556 if (FrameAlignment > StackAlignment) {
557 // Re-align the base pointer according to the max requested alignment.
558 assert(isPowerOf2_32(FrameAlignment));
559 IRB.SetInsertPoint(BasePointer->getNextNode());
560 BasePointer = cast<Instruction>(IRB.CreateIntToPtr(
561 IRB.CreateAnd(IRB.CreatePtrToInt(BasePointer, IntPtrTy),
562 ConstantInt::get(IntPtrTy, ~uint64_t(FrameAlignment - 1))),
563 StackPtrTy));
564 }
565
566 IRB.SetInsertPoint(BasePointer->getNextNode());
567
568 if (StackGuardSlot) {
569 unsigned Offset = SSL.getObjectOffset(StackGuardSlot);
570 Value *Off = IRB.CreateGEP(Int8Ty, BasePointer, // BasePointer is i8*
571 ConstantInt::get(Int32Ty, -Offset));
572 Value *NewAI =
573 IRB.CreateBitCast(Off, StackGuardSlot->getType(), "StackGuardSlot");
574
575 // Replace alloc with the new location.
576 StackGuardSlot->replaceAllUsesWith(NewAI);
577 StackGuardSlot->eraseFromParent();
578 }
579
580 for (Argument *Arg : ByValArguments) {
581 unsigned Offset = SSL.getObjectOffset(Arg);
582 MaybeAlign Align(SSL.getObjectAlignment(Arg));
583 Type *Ty = Arg->getType()->getPointerElementType();
584
585 uint64_t Size = DL.getTypeStoreSize(Ty);
586 if (Size == 0)
587 Size = 1; // Don't create zero-sized stack objects.
588
589 Value *Off = IRB.CreateGEP(Int8Ty, BasePointer, // BasePointer is i8*
590 ConstantInt::get(Int32Ty, -Offset));
591 Value *NewArg = IRB.CreateBitCast(Off, Arg->getType(),
592 Arg->getName() + ".unsafe-byval");
593
594 // Replace alloc with the new location.
595 replaceDbgDeclare(Arg, BasePointer, DIB, DIExpression::ApplyOffset,
596 -Offset);
597 Arg->replaceAllUsesWith(NewArg);
598 IRB.SetInsertPoint(cast<Instruction>(NewArg)->getNextNode());
599 IRB.CreateMemCpy(Off, Align, Arg, Arg->getParamAlign(), Size);
600 }
601
602 // Allocate space for every unsafe static AllocaInst on the unsafe stack.
603 for (AllocaInst *AI : StaticAllocas) {
604 IRB.SetInsertPoint(AI);
605 unsigned Offset = SSL.getObjectOffset(AI);
606
607 replaceDbgDeclare(AI, BasePointer, DIB, DIExpression::ApplyOffset, -Offset);
608 replaceDbgValueForAlloca(AI, BasePointer, DIB, -Offset);
609
610 // Replace uses of the alloca with the new location.
611 // Insert address calculation close to each use to work around PR27844.
612 std::string Name = std::string(AI->getName()) + ".unsafe";
613 while (!AI->use_empty()) {
614 Use &U = *AI->use_begin();
615 Instruction *User = cast<Instruction>(U.getUser());
616
617 Instruction *InsertBefore;
618 if (auto *PHI = dyn_cast<PHINode>(User))
619 InsertBefore = PHI->getIncomingBlock(U)->getTerminator();
620 else
621 InsertBefore = User;
622
623 IRBuilder<> IRBUser(InsertBefore);
624 Value *Off = IRBUser.CreateGEP(Int8Ty, BasePointer, // BasePointer is i8*
625 ConstantInt::get(Int32Ty, -Offset));
626 Value *Replacement = IRBUser.CreateBitCast(Off, AI->getType(), Name);
627
628 if (auto *PHI = dyn_cast<PHINode>(User))
629 // PHI nodes may have multiple incoming edges from the same BB (why??),
630 // all must be updated at once with the same incoming value.
631 PHI->setIncomingValueForBlock(PHI->getIncomingBlock(U), Replacement);
632 else
633 U.set(Replacement);
634 }
635
636 AI->eraseFromParent();
637 }
638
639 // Re-align BasePointer so that our callees would see it aligned as
640 // expected.
641 // FIXME: no need to update BasePointer in leaf functions.
642 unsigned FrameSize = alignTo(SSL.getFrameSize(), StackAlignment);
643
644 // Update shadow stack pointer in the function epilogue.
645 IRB.SetInsertPoint(BasePointer->getNextNode());
646
647 Value *StaticTop =
648 IRB.CreateGEP(Int8Ty, BasePointer, ConstantInt::get(Int32Ty, -FrameSize),
649 "unsafe_stack_static_top");
650 IRB.CreateStore(StaticTop, UnsafeStackPtr);
651 return StaticTop;
652 }
653
moveDynamicAllocasToUnsafeStack(Function & F,Value * UnsafeStackPtr,AllocaInst * DynamicTop,ArrayRef<AllocaInst * > DynamicAllocas)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 unsigned Align = std::max(
677 std::max((unsigned)DL.getPrefTypeAlignment(Ty), AI->getAlignment()),
678 (unsigned)StackAlignment);
679
680 assert(isPowerOf2_32(Align));
681 Value *NewTop = IRB.CreateIntToPtr(
682 IRB.CreateAnd(SP, ConstantInt::get(IntPtrTy, ~uint64_t(Align - 1))),
683 StackPtrTy);
684
685 // Save the stack pointer.
686 IRB.CreateStore(NewTop, UnsafeStackPtr);
687 if (DynamicTop)
688 IRB.CreateStore(NewTop, DynamicTop);
689
690 Value *NewAI = IRB.CreatePointerCast(NewTop, AI->getType());
691 if (AI->hasName() && isa<Instruction>(NewAI))
692 NewAI->takeName(AI);
693
694 replaceDbgDeclare(AI, NewAI, DIB, DIExpression::ApplyOffset, 0);
695 AI->replaceAllUsesWith(NewAI);
696 AI->eraseFromParent();
697 }
698
699 if (!DynamicAllocas.empty()) {
700 // Now go through the instructions again, replacing stacksave/stackrestore.
701 for (inst_iterator It = inst_begin(&F), Ie = inst_end(&F); It != Ie;) {
702 Instruction *I = &*(It++);
703 auto II = dyn_cast<IntrinsicInst>(I);
704 if (!II)
705 continue;
706
707 if (II->getIntrinsicID() == Intrinsic::stacksave) {
708 IRBuilder<> IRB(II);
709 Instruction *LI = IRB.CreateLoad(StackPtrTy, UnsafeStackPtr);
710 LI->takeName(II);
711 II->replaceAllUsesWith(LI);
712 II->eraseFromParent();
713 } else if (II->getIntrinsicID() == Intrinsic::stackrestore) {
714 IRBuilder<> IRB(II);
715 Instruction *SI = IRB.CreateStore(II->getArgOperand(0), UnsafeStackPtr);
716 SI->takeName(II);
717 assert(II->use_empty());
718 II->eraseFromParent();
719 }
720 }
721 }
722 }
723
ShouldInlinePointerAddress(CallInst & CI)724 bool SafeStack::ShouldInlinePointerAddress(CallInst &CI) {
725 Function *Callee = CI.getCalledFunction();
726 if (CI.hasFnAttr(Attribute::AlwaysInline) &&
727 isInlineViable(*Callee).isSuccess())
728 return true;
729 if (Callee->isInterposable() || Callee->hasFnAttribute(Attribute::NoInline) ||
730 CI.isNoInline())
731 return false;
732 return true;
733 }
734
TryInlinePointerAddress()735 void SafeStack::TryInlinePointerAddress() {
736 auto *CI = dyn_cast<CallInst>(UnsafeStackPtr);
737 if (!CI)
738 return;
739
740 if(F.hasOptNone())
741 return;
742
743 Function *Callee = CI->getCalledFunction();
744 if (!Callee || Callee->isDeclaration())
745 return;
746
747 if (!ShouldInlinePointerAddress(*CI))
748 return;
749
750 InlineFunctionInfo IFI;
751 InlineFunction(*CI, IFI);
752 }
753
run()754 bool SafeStack::run() {
755 assert(F.hasFnAttribute(Attribute::SafeStack) &&
756 "Can't run SafeStack on a function without the attribute");
757 assert(!F.isDeclaration() && "Can't run SafeStack on a function declaration");
758
759 ++NumFunctions;
760
761 SmallVector<AllocaInst *, 16> StaticAllocas;
762 SmallVector<AllocaInst *, 4> DynamicAllocas;
763 SmallVector<Argument *, 4> ByValArguments;
764 SmallVector<Instruction *, 4> Returns;
765
766 // Collect all points where stack gets unwound and needs to be restored
767 // This is only necessary because the runtime (setjmp and unwind code) is
768 // not aware of the unsafe stack and won't unwind/restore it properly.
769 // To work around this problem without changing the runtime, we insert
770 // instrumentation to restore the unsafe stack pointer when necessary.
771 SmallVector<Instruction *, 4> StackRestorePoints;
772
773 // Find all static and dynamic alloca instructions that must be moved to the
774 // unsafe stack, all return instructions and stack restore points.
775 findInsts(F, StaticAllocas, DynamicAllocas, ByValArguments, Returns,
776 StackRestorePoints);
777
778 if (StaticAllocas.empty() && DynamicAllocas.empty() &&
779 ByValArguments.empty() && StackRestorePoints.empty())
780 return false; // Nothing to do in this function.
781
782 if (!StaticAllocas.empty() || !DynamicAllocas.empty() ||
783 !ByValArguments.empty())
784 ++NumUnsafeStackFunctions; // This function has the unsafe stack.
785
786 if (!StackRestorePoints.empty())
787 ++NumUnsafeStackRestorePointsFunctions;
788
789 IRBuilder<> IRB(&F.front(), F.begin()->getFirstInsertionPt());
790 // Calls must always have a debug location, or else inlining breaks. So
791 // we explicitly set a artificial debug location here.
792 if (DISubprogram *SP = F.getSubprogram())
793 IRB.SetCurrentDebugLocation(
794 DILocation::get(SP->getContext(), SP->getScopeLine(), 0, SP));
795 if (SafeStackUsePointerAddress) {
796 FunctionCallee Fn = F.getParent()->getOrInsertFunction(
797 "__safestack_pointer_address", StackPtrTy->getPointerTo(0));
798 UnsafeStackPtr = IRB.CreateCall(Fn);
799 } else {
800 UnsafeStackPtr = TL.getSafeStackPointerLocation(IRB);
801 }
802
803 // Load the current stack pointer (we'll also use it as a base pointer).
804 // FIXME: use a dedicated register for it ?
805 Instruction *BasePointer =
806 IRB.CreateLoad(StackPtrTy, UnsafeStackPtr, false, "unsafe_stack_ptr");
807 assert(BasePointer->getType() == StackPtrTy);
808
809 AllocaInst *StackGuardSlot = nullptr;
810 // FIXME: implement weaker forms of stack protector.
811 if (F.hasFnAttribute(Attribute::StackProtect) ||
812 F.hasFnAttribute(Attribute::StackProtectStrong) ||
813 F.hasFnAttribute(Attribute::StackProtectReq)) {
814 Value *StackGuard = getStackGuard(IRB, F);
815 StackGuardSlot = IRB.CreateAlloca(StackPtrTy, nullptr);
816 IRB.CreateStore(StackGuard, StackGuardSlot);
817
818 for (Instruction *RI : Returns) {
819 IRBuilder<> IRBRet(RI);
820 checkStackGuard(IRBRet, F, *RI, StackGuardSlot, StackGuard);
821 }
822 }
823
824 // The top of the unsafe stack after all unsafe static allocas are
825 // allocated.
826 Value *StaticTop = moveStaticAllocasToUnsafeStack(
827 IRB, F, StaticAllocas, ByValArguments, BasePointer, StackGuardSlot);
828
829 // Safe stack object that stores the current unsafe stack top. It is updated
830 // as unsafe dynamic (non-constant-sized) allocas are allocated and freed.
831 // This is only needed if we need to restore stack pointer after longjmp
832 // or exceptions, and we have dynamic allocations.
833 // FIXME: a better alternative might be to store the unsafe stack pointer
834 // before setjmp / invoke instructions.
835 AllocaInst *DynamicTop = createStackRestorePoints(
836 IRB, F, StackRestorePoints, StaticTop, !DynamicAllocas.empty());
837
838 // Handle dynamic allocas.
839 moveDynamicAllocasToUnsafeStack(F, UnsafeStackPtr, DynamicTop,
840 DynamicAllocas);
841
842 // Restore the unsafe stack pointer before each return.
843 for (Instruction *RI : Returns) {
844 IRB.SetInsertPoint(RI);
845 IRB.CreateStore(BasePointer, UnsafeStackPtr);
846 }
847
848 TryInlinePointerAddress();
849
850 LLVM_DEBUG(dbgs() << "[SafeStack] safestack applied\n");
851 return true;
852 }
853
854 class SafeStackLegacyPass : public FunctionPass {
855 const TargetMachine *TM = nullptr;
856
857 public:
858 static char ID; // Pass identification, replacement for typeid..
859
SafeStackLegacyPass()860 SafeStackLegacyPass() : FunctionPass(ID) {
861 initializeSafeStackLegacyPassPass(*PassRegistry::getPassRegistry());
862 }
863
getAnalysisUsage(AnalysisUsage & AU) const864 void getAnalysisUsage(AnalysisUsage &AU) const override {
865 AU.addRequired<TargetPassConfig>();
866 AU.addRequired<TargetLibraryInfoWrapperPass>();
867 AU.addRequired<AssumptionCacheTracker>();
868 AU.addPreserved<DominatorTreeWrapperPass>();
869 }
870
runOnFunction(Function & F)871 bool runOnFunction(Function &F) override {
872 LLVM_DEBUG(dbgs() << "[SafeStack] Function: " << F.getName() << "\n");
873
874 if (!F.hasFnAttribute(Attribute::SafeStack)) {
875 LLVM_DEBUG(dbgs() << "[SafeStack] safestack is not requested"
876 " for this function\n");
877 return false;
878 }
879
880 if (F.isDeclaration()) {
881 LLVM_DEBUG(dbgs() << "[SafeStack] function definition"
882 " is not available\n");
883 return false;
884 }
885
886 TM = &getAnalysis<TargetPassConfig>().getTM<TargetMachine>();
887 auto *TL = TM->getSubtargetImpl(F)->getTargetLowering();
888 if (!TL)
889 report_fatal_error("TargetLowering instance is required");
890
891 auto *DL = &F.getParent()->getDataLayout();
892 auto &TLI = getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F);
893 auto &ACT = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
894
895 // Compute DT and LI only for functions that have the attribute.
896 // This is only useful because the legacy pass manager doesn't let us
897 // compute analyzes lazily.
898
899 DominatorTree *DT;
900 bool ShouldPreserveDominatorTree;
901 Optional<DominatorTree> LazilyComputedDomTree;
902
903 // Do we already have a DominatorTree avaliable from the previous pass?
904 // Note that we should *NOT* require it, to avoid the case where we end up
905 // not needing it, but the legacy PM would have computed it for us anyways.
906 if (auto *DTWP = getAnalysisIfAvailable<DominatorTreeWrapperPass>()) {
907 DT = &DTWP->getDomTree();
908 ShouldPreserveDominatorTree = true;
909 } else {
910 // Otherwise, we need to compute it.
911 LazilyComputedDomTree.emplace(F);
912 DT = LazilyComputedDomTree.getPointer();
913 ShouldPreserveDominatorTree = false;
914 }
915
916 // Likewise, lazily compute loop info.
917 LoopInfo LI(*DT);
918
919 DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Lazy);
920
921 ScalarEvolution SE(F, TLI, ACT, *DT, LI);
922
923 return SafeStack(F, *TL, *DL, ShouldPreserveDominatorTree ? &DTU : nullptr,
924 SE)
925 .run();
926 }
927 };
928
929 } // end anonymous namespace
930
931 char SafeStackLegacyPass::ID = 0;
932
933 INITIALIZE_PASS_BEGIN(SafeStackLegacyPass, DEBUG_TYPE,
934 "Safe Stack instrumentation pass", false, false)
INITIALIZE_PASS_DEPENDENCY(TargetPassConfig)935 INITIALIZE_PASS_DEPENDENCY(TargetPassConfig)
936 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
937 INITIALIZE_PASS_END(SafeStackLegacyPass, DEBUG_TYPE,
938 "Safe Stack instrumentation pass", false, false)
939
940 FunctionPass *llvm::createSafeStackPass() { return new SafeStackLegacyPass(); }
941