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1 : //===- SafeStack.cpp - Safe Stack Insertion -------------------------------===//
2 : //
3 : // The LLVM Compiler Infrastructure
4 : //
5 : // This file is distributed under the University of Illinois Open Source
6 : // License. See LICENSE.TXT for details.
7 : //
8 : //===----------------------------------------------------------------------===//
9 : //
10 : // This pass splits the stack into the safe stack (kept as-is for LLVM backend)
11 : // and the unsafe stack (explicitly allocated and managed through the runtime
12 : // support library).
13 : //
14 : // http://clang.llvm.org/docs/SafeStack.html
15 : //
16 : //===----------------------------------------------------------------------===//
17 :
18 : #include "SafeStackColoring.h"
19 : #include "SafeStackLayout.h"
20 : #include "llvm/ADT/APInt.h"
21 : #include "llvm/ADT/ArrayRef.h"
22 : #include "llvm/ADT/SmallPtrSet.h"
23 : #include "llvm/ADT/SmallVector.h"
24 : #include "llvm/ADT/Statistic.h"
25 : #include "llvm/Analysis/AssumptionCache.h"
26 : #include "llvm/Analysis/BranchProbabilityInfo.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/TargetLibraryInfo.h"
32 : #include "llvm/Transforms/Utils/Local.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/CallSite.h"
39 : #include "llvm/IR/ConstantRange.h"
40 : #include "llvm/IR/Constants.h"
41 : #include "llvm/IR/DIBuilder.h"
42 : #include "llvm/IR/DataLayout.h"
43 : #include "llvm/IR/DerivedTypes.h"
44 : #include "llvm/IR/Dominators.h"
45 : #include "llvm/IR/Function.h"
46 : #include "llvm/IR/IRBuilder.h"
47 : #include "llvm/IR/InstIterator.h"
48 : #include "llvm/IR/Instruction.h"
49 : #include "llvm/IR/Instructions.h"
50 : #include "llvm/IR/IntrinsicInst.h"
51 : #include "llvm/IR/Intrinsics.h"
52 : #include "llvm/IR/MDBuilder.h"
53 : #include "llvm/IR/Module.h"
54 : #include "llvm/IR/Type.h"
55 : #include "llvm/IR/Use.h"
56 : #include "llvm/IR/User.h"
57 : #include "llvm/IR/Value.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 <algorithm>
68 : #include <cassert>
69 : #include <cstdint>
70 : #include <string>
71 : #include <utility>
72 :
73 : using namespace llvm;
74 : using namespace llvm::safestack;
75 :
76 : #define DEBUG_TYPE "safe-stack"
77 :
78 : namespace llvm {
79 :
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");
84 :
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");
90 :
91 : } // namespace llvm
92 :
93 : /// Use __safestack_pointer_address even if the platform has a faster way of
94 : /// access safe stack pointer.
95 : static cl::opt<bool>
96 : SafeStackUsePointerAddress("safestack-use-pointer-address",
97 : cl::init(false), cl::Hidden);
98 :
99 :
100 : namespace {
101 :
102 : /// Rewrite an SCEV expression for a memory access address to an expression that
103 : /// represents offset from the given alloca.
104 : ///
105 : /// The implementation simply replaces all mentions of the alloca with zero.
106 : class AllocaOffsetRewriter : public SCEVRewriteVisitor<AllocaOffsetRewriter> {
107 : const Value *AllocaPtr;
108 :
109 : public:
110 : AllocaOffsetRewriter(ScalarEvolution &SE, const Value *AllocaPtr)
111 0 : : SCEVRewriteVisitor(SE), AllocaPtr(AllocaPtr) {}
112 :
113 0 : const SCEV *visitUnknown(const SCEVUnknown *Expr) {
114 122 : if (Expr->getValue() == AllocaPtr)
115 0 : return SE.getZero(Expr->getType());
116 11 : return Expr;
117 : }
118 : };
119 :
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
124 : /// be safe.
125 : class SafeStack {
126 : Function &F;
127 : const TargetLoweringBase &TL;
128 : const DataLayout &DL;
129 : ScalarEvolution &SE;
130 :
131 : Type *StackPtrTy;
132 : Type *IntPtrTy;
133 : Type *Int32Ty;
134 : Type *Int8Ty;
135 :
136 : Value *UnsafeStackPtr = nullptr;
137 :
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.
141 : ///
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 };
145 :
146 : /// Return the value of the stack canary.
147 : Value *getStackGuard(IRBuilder<> &IRB, Function &F);
148 :
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);
152 :
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);
161 :
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);
165 :
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.
169 : ///
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);
178 :
179 : /// Generate code to restore the stack after all stack restore points
180 : /// in \p StackRestorePoints.
181 : ///
182 : /// \returns A local variable in which to maintain the dynamic top of the
183 : /// unsafe stack if needed.
184 : AllocaInst *
185 : createStackRestorePoints(IRBuilder<> &IRB, Function &F,
186 : ArrayRef<Instruction *> StackRestorePoints,
187 : Value *StaticTop, bool NeedDynamicTop);
188 :
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);
195 :
196 : bool IsSafeStackAlloca(const Value *AllocaPtr, uint64_t AllocaSize);
197 :
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);
202 :
203 : bool ShouldInlinePointerAddress(CallSite &CS);
204 : void TryInlinePointerAddress();
205 :
206 : public:
207 190 : SafeStack(Function &F, const TargetLoweringBase &TL, const DataLayout &DL,
208 : ScalarEvolution &SE)
209 190 : : F(F), TL(TL), DL(DL), SE(SE),
210 190 : StackPtrTy(Type::getInt8PtrTy(F.getContext())),
211 190 : IntPtrTy(DL.getIntPtrType(F.getContext())),
212 190 : Int32Ty(Type::getInt32Ty(F.getContext())),
213 760 : Int8Ty(Type::getInt8Ty(F.getContext())) {}
214 :
215 : // Run the transformation on the associated function.
216 : // Returns whether the function was changed.
217 : bool run();
218 : };
219 :
220 0 : uint64_t SafeStack::getStaticAllocaAllocationSize(const AllocaInst* AI) {
221 0 : uint64_t Size = DL.getTypeAllocSize(AI->getAllocatedType());
222 0 : if (AI->isArrayAllocation()) {
223 : auto C = dyn_cast<ConstantInt>(AI->getArraySize());
224 : if (!C)
225 0 : return 0;
226 0 : Size *= C->getZExtValue();
227 : }
228 : return Size;
229 : }
230 :
231 0 : bool SafeStack::IsAccessSafe(Value *Addr, uint64_t AccessSize,
232 : const Value *AllocaPtr, uint64_t AllocaSize) {
233 0 : AllocaOffsetRewriter Rewriter(SE, AllocaPtr);
234 0 : const SCEV *Expr = Rewriter.visit(SE.getSCEV(Addr));
235 :
236 0 : uint64_t BitWidth = SE.getTypeSizeInBits(Expr->getType());
237 0 : ConstantRange AccessStartRange = SE.getUnsignedRange(Expr);
238 : ConstantRange SizeRange =
239 0 : ConstantRange(APInt(BitWidth, 0), APInt(BitWidth, AccessSize));
240 0 : ConstantRange AccessRange = AccessStartRange.add(SizeRange);
241 : ConstantRange AllocaRange =
242 0 : ConstantRange(APInt(BitWidth, 0), APInt(BitWidth, AllocaSize));
243 0 : bool Safe = AllocaRange.contains(AccessRange);
244 :
245 : LLVM_DEBUG(
246 : dbgs() << "[SafeStack] "
247 : << (isa<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")
248 : << *AllocaPtr << "\n"
249 : << " Access " << *Addr << "\n"
250 : << " SCEV " << *Expr
251 : << " U: " << SE.getUnsignedRange(Expr)
252 : << ", S: " << SE.getSignedRange(Expr) << "\n"
253 : << " Range " << AccessRange << "\n"
254 : << " AllocaRange " << AllocaRange << "\n"
255 : << " " << (Safe ? "safe" : "unsafe") << "\n");
256 :
257 0 : return Safe;
258 : }
259 :
260 11 : 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 3 : if (MTI->getRawSource() != U && MTI->getRawDest() != U)
265 : return true;
266 : } else {
267 8 : if (MI->getRawDest() != U)
268 : return true;
269 : }
270 :
271 : const auto *Len = dyn_cast<ConstantInt>(MI->getLength());
272 : // Non-constant size => unsafe. FIXME: try SCEV getRange.
273 : if (!Len) return false;
274 9 : return IsAccessSafe(U, Len->getZExtValue(), AllocaPtr, AllocaSize);
275 : }
276 :
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).
280 315 : 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;
286 315 : WorkList.push_back(AllocaPtr);
287 :
288 : // A DFS search through all uses of the alloca in bitcasts/PHI/GEPs/etc.
289 522 : while (!WorkList.empty()) {
290 : const Value *V = WorkList.pop_back_val();
291 699 : for (const Use &UI : V->uses()) {
292 492 : auto I = cast<const Instruction>(UI.getUser());
293 : assert(V == UI.get());
294 :
295 492 : switch (I->getOpcode()) {
296 53 : case Instruction::Load:
297 53 : if (!IsAccessSafe(UI, DL.getTypeStoreSize(I->getType()), AllocaPtr,
298 : AllocaSize))
299 : return false;
300 : break;
301 :
302 : case Instruction::VAArg:
303 : // "va-arg" from a pointer is safe.
304 : break;
305 63 : case Instruction::Store:
306 126 : if (V == I->getOperand(0)) {
307 : // Stored the pointer - conservatively assume it may be unsafe.
308 : LLVM_DEBUG(dbgs()
309 : << "[SafeStack] Unsafe alloca: " << *AllocaPtr
310 : << "\n store of address: " << *I << "\n");
311 : return false;
312 : }
313 :
314 102 : if (!IsAccessSafe(UI, DL.getTypeStoreSize(I->getOperand(0)->getType()),
315 : AllocaPtr, AllocaSize))
316 : return false;
317 : break;
318 :
319 : case Instruction::Ret:
320 : // Information leak.
321 : return false;
322 :
323 : case Instruction::Call:
324 : case Instruction::Invoke: {
325 : ImmutableCallSite CS(I);
326 :
327 : if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
328 21 : if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
329 : II->getIntrinsicID() == Intrinsic::lifetime_end)
330 17 : continue;
331 : }
332 :
333 : if (const MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) {
334 11 : if (!IsMemIntrinsicSafe(MI, UI, AllocaPtr, AllocaSize)) {
335 : LLVM_DEBUG(dbgs()
336 : << "[SafeStack] Unsafe alloca: " << *AllocaPtr
337 : << "\n unsafe memintrinsic: " << *I << "\n");
338 211 : return false;
339 : }
340 : continue;
341 : }
342 :
343 : // LLVM 'nocapture' attribute is only set for arguments whose address
344 : // is not stored, passed around, or used in any other non-trivial way.
345 : // We assume that passing a pointer to an object as a 'nocapture
346 : // readnone' argument is safe.
347 : // FIXME: a more precise solution would require an interprocedural
348 : // analysis here, which would look at all uses of an argument inside
349 : // the function being called.
350 207 : ImmutableCallSite::arg_iterator B = CS.arg_begin(), E = CS.arg_end();
351 227 : for (ImmutableCallSite::arg_iterator A = B; A != E; ++A)
352 223 : if (A->get() == V)
353 229 : if (!(CS.doesNotCapture(A - B) && (CS.doesNotAccessMemory(A - B) ||
354 10 : CS.doesNotAccessMemory()))) {
355 : LLVM_DEBUG(dbgs() << "[SafeStack] Unsafe alloca: " << *AllocaPtr
356 : << "\n unsafe call: " << *I << "\n");
357 203 : return false;
358 : }
359 : continue;
360 : }
361 :
362 146 : default:
363 146 : if (Visited.insert(I).second)
364 144 : WorkList.push_back(cast<const Instruction>(I));
365 : }
366 : }
367 : }
368 :
369 : // All uses of the alloca are safe, we can place it on the safe stack.
370 : return true;
371 : }
372 :
373 0 : Value *SafeStack::getStackGuard(IRBuilder<> &IRB, Function &F) {
374 0 : Value *StackGuardVar = TL.getIRStackGuard(IRB);
375 0 : if (!StackGuardVar)
376 : StackGuardVar =
377 0 : F.getParent()->getOrInsertGlobal("__stack_chk_guard", StackPtrTy);
378 0 : return IRB.CreateLoad(StackGuardVar, "StackGuard");
379 : }
380 :
381 190 : void SafeStack::findInsts(Function &F,
382 : SmallVectorImpl<AllocaInst *> &StaticAllocas,
383 : SmallVectorImpl<AllocaInst *> &DynamicAllocas,
384 : SmallVectorImpl<Argument *> &ByValArguments,
385 : SmallVectorImpl<ReturnInst *> &Returns,
386 : SmallVectorImpl<Instruction *> &StackRestorePoints) {
387 1418 : for (Instruction &I : instructions(&F)) {
388 1418 : if (auto AI = dyn_cast<AllocaInst>(&I)) {
389 : ++NumAllocas;
390 :
391 305 : uint64_t Size = getStaticAllocaAllocationSize(AI);
392 305 : if (IsSafeStackAlloca(AI, Size))
393 64 : continue;
394 :
395 241 : if (AI->isStaticAlloca()) {
396 : ++NumUnsafeStaticAllocas;
397 232 : StaticAllocas.push_back(AI);
398 : } else {
399 : ++NumUnsafeDynamicAllocas;
400 9 : DynamicAllocas.push_back(AI);
401 : }
402 1113 : } else if (auto RI = dyn_cast<ReturnInst>(&I)) {
403 200 : Returns.push_back(RI);
404 : } else if (auto CI = dyn_cast<CallInst>(&I)) {
405 : // setjmps require stack restore.
406 441 : if (CI->getCalledFunction() && CI->canReturnTwice())
407 5 : StackRestorePoints.push_back(CI);
408 : } else if (auto LP = dyn_cast<LandingPadInst>(&I)) {
409 : // Exception landing pads require stack restore.
410 4 : StackRestorePoints.push_back(LP);
411 : } else if (auto II = dyn_cast<IntrinsicInst>(&I)) {
412 0 : if (II->getIntrinsicID() == Intrinsic::gcroot)
413 0 : report_fatal_error(
414 : "gcroot intrinsic not compatible with safestack attribute");
415 : }
416 : }
417 270 : for (Argument &Arg : F.args()) {
418 80 : if (!Arg.hasByValAttr())
419 : continue;
420 : uint64_t Size =
421 10 : DL.getTypeStoreSize(Arg.getType()->getPointerElementType());
422 10 : if (IsSafeStackAlloca(&Arg, Size))
423 : continue;
424 :
425 : ++NumUnsafeByValArguments;
426 7 : ByValArguments.push_back(&Arg);
427 : }
428 190 : }
429 :
430 : AllocaInst *
431 161 : SafeStack::createStackRestorePoints(IRBuilder<> &IRB, Function &F,
432 : ArrayRef<Instruction *> StackRestorePoints,
433 : Value *StaticTop, bool NeedDynamicTop) {
434 : assert(StaticTop && "The stack top isn't set.");
435 :
436 161 : if (StackRestorePoints.empty())
437 : return nullptr;
438 :
439 : // We need the current value of the shadow stack pointer to restore
440 : // after longjmp or exception catching.
441 :
442 : // FIXME: On some platforms this could be handled by the longjmp/exception
443 : // runtime itself.
444 :
445 : AllocaInst *DynamicTop = nullptr;
446 9 : if (NeedDynamicTop) {
447 : // If we also have dynamic alloca's, the stack pointer value changes
448 : // throughout the function. For now we store it in an alloca.
449 3 : DynamicTop = IRB.CreateAlloca(StackPtrTy, /*ArraySize=*/nullptr,
450 : "unsafe_stack_dynamic_ptr");
451 3 : IRB.CreateStore(StaticTop, DynamicTop);
452 : }
453 :
454 : // Restore current stack pointer after longjmp/exception catch.
455 18 : for (Instruction *I : StackRestorePoints) {
456 : ++NumUnsafeStackRestorePoints;
457 :
458 18 : IRB.SetInsertPoint(I->getNextNode());
459 9 : Value *CurrentTop = DynamicTop ? IRB.CreateLoad(DynamicTop) : StaticTop;
460 9 : IRB.CreateStore(CurrentTop, UnsafeStackPtr);
461 : }
462 :
463 : return DynamicTop;
464 : }
465 :
466 0 : void SafeStack::checkStackGuard(IRBuilder<> &IRB, Function &F, ReturnInst &RI,
467 : AllocaInst *StackGuardSlot, Value *StackGuard) {
468 0 : Value *V = IRB.CreateLoad(StackGuardSlot);
469 0 : Value *Cmp = IRB.CreateICmpNE(StackGuard, V);
470 :
471 0 : auto SuccessProb = BranchProbabilityInfo::getBranchProbStackProtector(true);
472 0 : auto FailureProb = BranchProbabilityInfo::getBranchProbStackProtector(false);
473 0 : MDNode *Weights = MDBuilder(F.getContext())
474 0 : .createBranchWeights(SuccessProb.getNumerator(),
475 : FailureProb.getNumerator());
476 : Instruction *CheckTerm =
477 0 : SplitBlockAndInsertIfThen(Cmp, &RI,
478 : /* Unreachable */ true, Weights);
479 0 : IRBuilder<> IRBFail(CheckTerm);
480 : // FIXME: respect -fsanitize-trap / -ftrap-function here?
481 0 : Constant *StackChkFail = F.getParent()->getOrInsertFunction(
482 : "__stack_chk_fail", IRB.getVoidTy());
483 0 : IRBFail.CreateCall(StackChkFail, {});
484 0 : }
485 :
486 : /// We explicitly compute and set the unsafe stack layout for all unsafe
487 : /// static alloca instructions. We save the unsafe "base pointer" in the
488 : /// prologue into a local variable and restore it in the epilogue.
489 0 : Value *SafeStack::moveStaticAllocasToUnsafeStack(
490 : IRBuilder<> &IRB, Function &F, ArrayRef<AllocaInst *> StaticAllocas,
491 : ArrayRef<Argument *> ByValArguments, ArrayRef<ReturnInst *> Returns,
492 : Instruction *BasePointer, AllocaInst *StackGuardSlot) {
493 0 : if (StaticAllocas.empty() && ByValArguments.empty())
494 0 : return BasePointer;
495 :
496 0 : DIBuilder DIB(*F.getParent());
497 :
498 0 : StackColoring SSC(F, StaticAllocas);
499 0 : SSC.run();
500 0 : SSC.removeAllMarkers();
501 :
502 : // Unsafe stack always grows down.
503 0 : StackLayout SSL(StackAlignment);
504 0 : if (StackGuardSlot) {
505 0 : Type *Ty = StackGuardSlot->getAllocatedType();
506 : unsigned Align =
507 0 : std::max(DL.getPrefTypeAlignment(Ty), StackGuardSlot->getAlignment());
508 0 : SSL.addObject(StackGuardSlot, getStaticAllocaAllocationSize(StackGuardSlot),
509 0 : Align, SSC.getFullLiveRange());
510 : }
511 :
512 0 : for (Argument *Arg : ByValArguments) {
513 0 : Type *Ty = Arg->getType()->getPointerElementType();
514 0 : uint64_t Size = DL.getTypeStoreSize(Ty);
515 0 : if (Size == 0)
516 : Size = 1; // Don't create zero-sized stack objects.
517 :
518 : // Ensure the object is properly aligned.
519 0 : unsigned Align = std::max((unsigned)DL.getPrefTypeAlignment(Ty),
520 0 : Arg->getParamAlignment());
521 0 : SSL.addObject(Arg, Size, Align, SSC.getFullLiveRange());
522 : }
523 :
524 0 : for (AllocaInst *AI : StaticAllocas) {
525 0 : Type *Ty = AI->getAllocatedType();
526 0 : uint64_t Size = getStaticAllocaAllocationSize(AI);
527 0 : if (Size == 0)
528 : Size = 1; // Don't create zero-sized stack objects.
529 :
530 : // Ensure the object is properly aligned.
531 : unsigned Align =
532 0 : std::max((unsigned)DL.getPrefTypeAlignment(Ty), AI->getAlignment());
533 :
534 0 : SSL.addObject(AI, Size, Align, SSC.getLiveRange(AI));
535 : }
536 :
537 0 : SSL.computeLayout();
538 0 : unsigned FrameAlignment = SSL.getFrameAlignment();
539 :
540 : // FIXME: tell SSL that we start at a less-then-MaxAlignment aligned location
541 : // (AlignmentSkew).
542 0 : if (FrameAlignment > StackAlignment) {
543 : // Re-align the base pointer according to the max requested alignment.
544 : assert(isPowerOf2_32(FrameAlignment));
545 0 : IRB.SetInsertPoint(BasePointer->getNextNode());
546 0 : BasePointer = cast<Instruction>(IRB.CreateIntToPtr(
547 : IRB.CreateAnd(IRB.CreatePtrToInt(BasePointer, IntPtrTy),
548 0 : ConstantInt::get(IntPtrTy, ~uint64_t(FrameAlignment - 1))),
549 : StackPtrTy));
550 : }
551 :
552 0 : IRB.SetInsertPoint(BasePointer->getNextNode());
553 :
554 0 : if (StackGuardSlot) {
555 0 : unsigned Offset = SSL.getObjectOffset(StackGuardSlot);
556 0 : Value *Off = IRB.CreateGEP(BasePointer, // BasePointer is i8*
557 0 : ConstantInt::get(Int32Ty, -Offset));
558 : Value *NewAI =
559 0 : IRB.CreateBitCast(Off, StackGuardSlot->getType(), "StackGuardSlot");
560 :
561 : // Replace alloc with the new location.
562 0 : StackGuardSlot->replaceAllUsesWith(NewAI);
563 0 : StackGuardSlot->eraseFromParent();
564 : }
565 :
566 0 : for (Argument *Arg : ByValArguments) {
567 0 : unsigned Offset = SSL.getObjectOffset(Arg);
568 0 : unsigned Align = SSL.getObjectAlignment(Arg);
569 0 : Type *Ty = Arg->getType()->getPointerElementType();
570 :
571 0 : uint64_t Size = DL.getTypeStoreSize(Ty);
572 0 : if (Size == 0)
573 : Size = 1; // Don't create zero-sized stack objects.
574 :
575 0 : Value *Off = IRB.CreateGEP(BasePointer, // BasePointer is i8*
576 0 : ConstantInt::get(Int32Ty, -Offset));
577 0 : Value *NewArg = IRB.CreateBitCast(Off, Arg->getType(),
578 0 : Arg->getName() + ".unsafe-byval");
579 :
580 : // Replace alloc with the new location.
581 0 : replaceDbgDeclare(Arg, BasePointer, BasePointer->getNextNode(), DIB,
582 : DIExpression::NoDeref, -Offset, DIExpression::NoDeref);
583 0 : Arg->replaceAllUsesWith(NewArg);
584 0 : IRB.SetInsertPoint(cast<Instruction>(NewArg)->getNextNode());
585 0 : IRB.CreateMemCpy(Off, Align, Arg, Arg->getParamAlignment(), Size);
586 : }
587 :
588 : // Allocate space for every unsafe static AllocaInst on the unsafe stack.
589 0 : for (AllocaInst *AI : StaticAllocas) {
590 0 : IRB.SetInsertPoint(AI);
591 0 : unsigned Offset = SSL.getObjectOffset(AI);
592 :
593 0 : uint64_t Size = getStaticAllocaAllocationSize(AI);
594 : if (Size == 0)
595 : Size = 1; // Don't create zero-sized stack objects.
596 :
597 0 : replaceDbgDeclareForAlloca(AI, BasePointer, DIB, DIExpression::NoDeref,
598 0 : -Offset, DIExpression::NoDeref);
599 0 : replaceDbgValueForAlloca(AI, BasePointer, DIB, -Offset);
600 :
601 : // Replace uses of the alloca with the new location.
602 : // Insert address calculation close to each use to work around PR27844.
603 0 : std::string Name = std::string(AI->getName()) + ".unsafe";
604 0 : while (!AI->use_empty()) {
605 : Use &U = *AI->use_begin();
606 0 : Instruction *User = cast<Instruction>(U.getUser());
607 :
608 : Instruction *InsertBefore;
609 : if (auto *PHI = dyn_cast<PHINode>(User))
610 : InsertBefore = PHI->getIncomingBlock(U)->getTerminator();
611 : else
612 : InsertBefore = User;
613 :
614 0 : IRBuilder<> IRBUser(InsertBefore);
615 0 : Value *Off = IRBUser.CreateGEP(BasePointer, // BasePointer is i8*
616 0 : ConstantInt::get(Int32Ty, -Offset));
617 0 : Value *Replacement = IRBUser.CreateBitCast(Off, AI->getType(), Name);
618 :
619 : if (auto *PHI = dyn_cast<PHINode>(User)) {
620 : // PHI nodes may have multiple incoming edges from the same BB (why??),
621 : // all must be updated at once with the same incoming value.
622 : auto *BB = PHI->getIncomingBlock(U);
623 0 : for (unsigned I = 0; I < PHI->getNumIncomingValues(); ++I)
624 0 : if (PHI->getIncomingBlock(I) == BB)
625 : PHI->setIncomingValue(I, Replacement);
626 : } else {
627 0 : U.set(Replacement);
628 : }
629 : }
630 :
631 0 : AI->eraseFromParent();
632 : }
633 :
634 : // Re-align BasePointer so that our callees would see it aligned as
635 : // expected.
636 : // FIXME: no need to update BasePointer in leaf functions.
637 0 : unsigned FrameSize = alignTo(SSL.getFrameSize(), StackAlignment);
638 :
639 : // Update shadow stack pointer in the function epilogue.
640 0 : IRB.SetInsertPoint(BasePointer->getNextNode());
641 :
642 : Value *StaticTop =
643 0 : IRB.CreateGEP(BasePointer, ConstantInt::get(Int32Ty, -FrameSize),
644 : "unsafe_stack_static_top");
645 0 : IRB.CreateStore(StaticTop, UnsafeStackPtr);
646 : return StaticTop;
647 : }
648 :
649 161 : void SafeStack::moveDynamicAllocasToUnsafeStack(
650 : Function &F, Value *UnsafeStackPtr, AllocaInst *DynamicTop,
651 : ArrayRef<AllocaInst *> DynamicAllocas) {
652 322 : DIBuilder DIB(*F.getParent());
653 :
654 170 : for (AllocaInst *AI : DynamicAllocas) {
655 9 : IRBuilder<> IRB(AI);
656 :
657 : // Compute the new SP value (after AI).
658 : Value *ArraySize = AI->getArraySize();
659 9 : if (ArraySize->getType() != IntPtrTy)
660 6 : ArraySize = IRB.CreateIntCast(ArraySize, IntPtrTy, false);
661 :
662 9 : Type *Ty = AI->getAllocatedType();
663 9 : uint64_t TySize = DL.getTypeAllocSize(Ty);
664 9 : Value *Size = IRB.CreateMul(ArraySize, ConstantInt::get(IntPtrTy, TySize));
665 :
666 27 : Value *SP = IRB.CreatePtrToInt(IRB.CreateLoad(UnsafeStackPtr), IntPtrTy);
667 9 : SP = IRB.CreateSub(SP, Size);
668 :
669 : // Align the SP value to satisfy the AllocaInst, type and stack alignments.
670 : unsigned Align = std::max(
671 9 : std::max((unsigned)DL.getPrefTypeAlignment(Ty), AI->getAlignment()),
672 18 : (unsigned)StackAlignment);
673 :
674 : assert(isPowerOf2_32(Align));
675 9 : Value *NewTop = IRB.CreateIntToPtr(
676 9 : IRB.CreateAnd(SP, ConstantInt::get(IntPtrTy, ~uint64_t(Align - 1))),
677 : StackPtrTy);
678 :
679 : // Save the stack pointer.
680 9 : IRB.CreateStore(NewTop, UnsafeStackPtr);
681 9 : if (DynamicTop)
682 3 : IRB.CreateStore(NewTop, DynamicTop);
683 :
684 9 : Value *NewAI = IRB.CreatePointerCast(NewTop, AI->getType());
685 9 : if (AI->hasName() && isa<Instruction>(NewAI))
686 6 : NewAI->takeName(AI);
687 :
688 9 : replaceDbgDeclareForAlloca(AI, NewAI, DIB, DIExpression::NoDeref, 0,
689 : DIExpression::NoDeref);
690 9 : AI->replaceAllUsesWith(NewAI);
691 9 : AI->eraseFromParent();
692 : }
693 :
694 161 : if (!DynamicAllocas.empty()) {
695 : // Now go through the instructions again, replacing stacksave/stackrestore.
696 : for (inst_iterator It = inst_begin(&F), Ie = inst_end(&F); It != Ie;) {
697 : Instruction *I = &*(It++);
698 : auto II = dyn_cast<IntrinsicInst>(I);
699 : if (!II)
700 : continue;
701 :
702 2 : if (II->getIntrinsicID() == Intrinsic::stacksave) {
703 0 : IRBuilder<> IRB(II);
704 0 : Instruction *LI = IRB.CreateLoad(UnsafeStackPtr);
705 0 : LI->takeName(II);
706 0 : II->replaceAllUsesWith(LI);
707 0 : II->eraseFromParent();
708 2 : } else if (II->getIntrinsicID() == Intrinsic::stackrestore) {
709 0 : IRBuilder<> IRB(II);
710 0 : Instruction *SI = IRB.CreateStore(II->getArgOperand(0), UnsafeStackPtr);
711 0 : SI->takeName(II);
712 : assert(II->use_empty());
713 0 : II->eraseFromParent();
714 : }
715 : }
716 : }
717 161 : }
718 :
719 0 : bool SafeStack::ShouldInlinePointerAddress(CallSite &CS) {
720 : Function *Callee = CS.getCalledFunction();
721 0 : if (CS.hasFnAttr(Attribute::AlwaysInline) && isInlineViable(*Callee))
722 0 : return true;
723 0 : if (Callee->isInterposable() || Callee->hasFnAttribute(Attribute::NoInline) ||
724 0 : CS.isNoInline())
725 0 : return false;
726 : return true;
727 : }
728 :
729 161 : void SafeStack::TryInlinePointerAddress() {
730 161 : if (!isa<CallInst>(UnsafeStackPtr))
731 159 : return;
732 :
733 6 : if(F.hasFnAttribute(Attribute::OptimizeNone))
734 : return;
735 :
736 6 : CallSite CS(UnsafeStackPtr);
737 : Function *Callee = CS.getCalledFunction();
738 6 : if (!Callee || Callee->isDeclaration())
739 3 : return;
740 :
741 3 : if (!ShouldInlinePointerAddress(CS))
742 : return;
743 :
744 2 : InlineFunctionInfo IFI;
745 2 : InlineFunction(CS, IFI);
746 : }
747 :
748 190 : bool SafeStack::run() {
749 : assert(F.hasFnAttribute(Attribute::SafeStack) &&
750 : "Can't run SafeStack on a function without the attribute");
751 : assert(!F.isDeclaration() && "Can't run SafeStack on a function declaration");
752 :
753 : ++NumFunctions;
754 :
755 : SmallVector<AllocaInst *, 16> StaticAllocas;
756 : SmallVector<AllocaInst *, 4> DynamicAllocas;
757 : SmallVector<Argument *, 4> ByValArguments;
758 : SmallVector<ReturnInst *, 4> Returns;
759 :
760 : // Collect all points where stack gets unwound and needs to be restored
761 : // This is only necessary because the runtime (setjmp and unwind code) is
762 : // not aware of the unsafe stack and won't unwind/restore it properly.
763 : // To work around this problem without changing the runtime, we insert
764 : // instrumentation to restore the unsafe stack pointer when necessary.
765 : SmallVector<Instruction *, 4> StackRestorePoints;
766 :
767 : // Find all static and dynamic alloca instructions that must be moved to the
768 : // unsafe stack, all return instructions and stack restore points.
769 190 : findInsts(F, StaticAllocas, DynamicAllocas, ByValArguments, Returns,
770 : StackRestorePoints);
771 :
772 44 : if (StaticAllocas.empty() && DynamicAllocas.empty() &&
773 225 : ByValArguments.empty() && StackRestorePoints.empty())
774 : return false; // Nothing to do in this function.
775 :
776 : if (!StaticAllocas.empty() || !DynamicAllocas.empty() ||
777 : !ByValArguments.empty())
778 : ++NumUnsafeStackFunctions; // This function has the unsafe stack.
779 :
780 : if (!StackRestorePoints.empty())
781 : ++NumUnsafeStackRestorePointsFunctions;
782 :
783 483 : IRBuilder<> IRB(&F.front(), F.begin()->getFirstInsertionPt());
784 : // Calls must always have a debug location, or else inlining breaks. So
785 : // we explicitly set a artificial debug location here.
786 161 : if (DISubprogram *SP = F.getSubprogram())
787 8 : IRB.SetCurrentDebugLocation(DebugLoc::get(SP->getScopeLine(), 0, SP));
788 161 : if (SafeStackUsePointerAddress) {
789 4 : Value *Fn = F.getParent()->getOrInsertFunction(
790 4 : "__safestack_pointer_address", StackPtrTy->getPointerTo(0));
791 4 : UnsafeStackPtr = IRB.CreateCall(Fn);
792 : } else {
793 157 : UnsafeStackPtr = TL.getSafeStackPointerLocation(IRB);
794 : }
795 :
796 : // Load the current stack pointer (we'll also use it as a base pointer).
797 : // FIXME: use a dedicated register for it ?
798 : Instruction *BasePointer =
799 161 : IRB.CreateLoad(UnsafeStackPtr, false, "unsafe_stack_ptr");
800 : assert(BasePointer->getType() == StackPtrTy);
801 :
802 : AllocaInst *StackGuardSlot = nullptr;
803 : // FIXME: implement weaker forms of stack protector.
804 322 : if (F.hasFnAttribute(Attribute::StackProtect) ||
805 322 : F.hasFnAttribute(Attribute::StackProtectStrong) ||
806 161 : F.hasFnAttribute(Attribute::StackProtectReq)) {
807 13 : Value *StackGuard = getStackGuard(IRB, F);
808 13 : StackGuardSlot = IRB.CreateAlloca(StackPtrTy, nullptr);
809 13 : IRB.CreateStore(StackGuard, StackGuardSlot);
810 :
811 26 : for (ReturnInst *RI : Returns) {
812 13 : IRBuilder<> IRBRet(RI);
813 13 : checkStackGuard(IRBRet, F, *RI, StackGuardSlot, StackGuard);
814 : }
815 : }
816 :
817 : // The top of the unsafe stack after all unsafe static allocas are
818 : // allocated.
819 : Value *StaticTop =
820 161 : moveStaticAllocasToUnsafeStack(IRB, F, StaticAllocas, ByValArguments,
821 : Returns, BasePointer, StackGuardSlot);
822 :
823 : // Safe stack object that stores the current unsafe stack top. It is updated
824 : // as unsafe dynamic (non-constant-sized) allocas are allocated and freed.
825 : // This is only needed if we need to restore stack pointer after longjmp
826 : // or exceptions, and we have dynamic allocations.
827 : // FIXME: a better alternative might be to store the unsafe stack pointer
828 : // before setjmp / invoke instructions.
829 161 : AllocaInst *DynamicTop = createStackRestorePoints(
830 161 : IRB, F, StackRestorePoints, StaticTop, !DynamicAllocas.empty());
831 :
832 : // Handle dynamic allocas.
833 161 : moveDynamicAllocasToUnsafeStack(F, UnsafeStackPtr, DynamicTop,
834 : DynamicAllocas);
835 :
836 : // Restore the unsafe stack pointer before each return.
837 332 : for (ReturnInst *RI : Returns) {
838 171 : IRB.SetInsertPoint(RI);
839 171 : IRB.CreateStore(BasePointer, UnsafeStackPtr);
840 : }
841 :
842 161 : TryInlinePointerAddress();
843 :
844 : LLVM_DEBUG(dbgs() << "[SafeStack] safestack applied\n");
845 : return true;
846 : }
847 :
848 : class SafeStackLegacyPass : public FunctionPass {
849 : const TargetMachine *TM = nullptr;
850 :
851 : public:
852 : static char ID; // Pass identification, replacement for typeid..
853 :
854 27550 : SafeStackLegacyPass() : FunctionPass(ID) {
855 27550 : initializeSafeStackLegacyPassPass(*PassRegistry::getPassRegistry());
856 27550 : }
857 :
858 27421 : void getAnalysisUsage(AnalysisUsage &AU) const override {
859 : AU.addRequired<TargetPassConfig>();
860 : AU.addRequired<TargetLibraryInfoWrapperPass>();
861 : AU.addRequired<AssumptionCacheTracker>();
862 27421 : }
863 :
864 406648 : bool runOnFunction(Function &F) override {
865 : LLVM_DEBUG(dbgs() << "[SafeStack] Function: " << F.getName() << "\n");
866 :
867 406648 : if (!F.hasFnAttribute(Attribute::SafeStack)) {
868 : LLVM_DEBUG(dbgs() << "[SafeStack] safestack is not requested"
869 : " for this function\n");
870 : return false;
871 : }
872 :
873 190 : if (F.isDeclaration()) {
874 : LLVM_DEBUG(dbgs() << "[SafeStack] function definition"
875 : " is not available\n");
876 : return false;
877 : }
878 :
879 190 : TM = &getAnalysis<TargetPassConfig>().getTM<TargetMachine>();
880 190 : auto *TL = TM->getSubtargetImpl(F)->getTargetLowering();
881 190 : if (!TL)
882 0 : report_fatal_error("TargetLowering instance is required");
883 :
884 190 : auto *DL = &F.getParent()->getDataLayout();
885 190 : auto &TLI = getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
886 190 : auto &ACT = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
887 :
888 : // Compute DT and LI only for functions that have the attribute.
889 : // This is only useful because the legacy pass manager doesn't let us
890 : // compute analyzes lazily.
891 : // In the backend pipeline, nothing preserves DT before SafeStack, so we
892 : // would otherwise always compute it wastefully, even if there is no
893 : // function with the safestack attribute.
894 190 : DominatorTree DT(F);
895 190 : LoopInfo LI(DT);
896 :
897 190 : ScalarEvolution SE(F, TLI, ACT, DT, LI);
898 :
899 190 : return SafeStack(F, *TL, *DL, SE).run();
900 : }
901 : };
902 :
903 : } // end anonymous namespace
904 :
905 : char SafeStackLegacyPass::ID = 0;
906 :
907 39044 : INITIALIZE_PASS_BEGIN(SafeStackLegacyPass, DEBUG_TYPE,
908 : "Safe Stack instrumentation pass", false, false)
909 39044 : INITIALIZE_PASS_DEPENDENCY(TargetPassConfig)
910 130700 : INITIALIZE_PASS_END(SafeStackLegacyPass, DEBUG_TYPE,
911 : "Safe Stack instrumentation pass", false, false)
912 :
913 27453 : FunctionPass *llvm::createSafeStackPass() { return new SafeStackLegacyPass(); }
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