LLVM  16.0.0git
BoundsChecking.cpp
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1 //===- BoundsChecking.cpp - Instrumentation for run-time bounds checking --===//
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 
10 #include "llvm/ADT/Statistic.h"
11 #include "llvm/ADT/Twine.h"
16 #include "llvm/IR/BasicBlock.h"
17 #include "llvm/IR/Constants.h"
18 #include "llvm/IR/DataLayout.h"
19 #include "llvm/IR/Function.h"
20 #include "llvm/IR/IRBuilder.h"
21 #include "llvm/IR/InstIterator.h"
22 #include "llvm/IR/Instruction.h"
23 #include "llvm/IR/Instructions.h"
24 #include "llvm/IR/Intrinsics.h"
25 #include "llvm/IR/Value.h"
26 #include "llvm/InitializePasses.h"
27 #include "llvm/Pass.h"
28 #include "llvm/Support/Casting.h"
30 #include "llvm/Support/Debug.h"
32 #include <cstdint>
33 #include <utility>
34 
35 using namespace llvm;
36 
37 #define DEBUG_TYPE "bounds-checking"
38 
39 static cl::opt<bool> SingleTrapBB("bounds-checking-single-trap",
40  cl::desc("Use one trap block per function"));
41 
42 STATISTIC(ChecksAdded, "Bounds checks added");
43 STATISTIC(ChecksSkipped, "Bounds checks skipped");
44 STATISTIC(ChecksUnable, "Bounds checks unable to add");
45 
47 
48 /// Gets the conditions under which memory accessing instructions will overflow.
49 ///
50 /// \p Ptr is the pointer that will be read/written, and \p InstVal is either
51 /// the result from the load or the value being stored. It is used to determine
52 /// the size of memory block that is touched.
53 ///
54 /// Returns the condition under which the access will overflow.
55 static Value *getBoundsCheckCond(Value *Ptr, Value *InstVal,
56  const DataLayout &DL, TargetLibraryInfo &TLI,
57  ObjectSizeOffsetEvaluator &ObjSizeEval,
58  BuilderTy &IRB, ScalarEvolution &SE) {
59  uint64_t NeededSize = DL.getTypeStoreSize(InstVal->getType());
60  LLVM_DEBUG(dbgs() << "Instrument " << *Ptr << " for " << Twine(NeededSize)
61  << " bytes\n");
62 
63  SizeOffsetEvalType SizeOffset = ObjSizeEval.compute(Ptr);
64 
65  if (!ObjSizeEval.bothKnown(SizeOffset)) {
66  ++ChecksUnable;
67  return nullptr;
68  }
69 
70  Value *Size = SizeOffset.first;
71  Value *Offset = SizeOffset.second;
72  ConstantInt *SizeCI = dyn_cast<ConstantInt>(Size);
73 
74  Type *IntTy = DL.getIntPtrType(Ptr->getType());
75  Value *NeededSizeVal = ConstantInt::get(IntTy, NeededSize);
76 
77  auto SizeRange = SE.getUnsignedRange(SE.getSCEV(Size));
78  auto OffsetRange = SE.getUnsignedRange(SE.getSCEV(Offset));
79  auto NeededSizeRange = SE.getUnsignedRange(SE.getSCEV(NeededSizeVal));
80 
81  // three checks are required to ensure safety:
82  // . Offset >= 0 (since the offset is given from the base ptr)
83  // . Size >= Offset (unsigned)
84  // . Size - Offset >= NeededSize (unsigned)
85  //
86  // optimization: if Size >= 0 (signed), skip 1st check
87  // FIXME: add NSW/NUW here? -- we dont care if the subtraction overflows
88  Value *ObjSize = IRB.CreateSub(Size, Offset);
89  Value *Cmp2 = SizeRange.getUnsignedMin().uge(OffsetRange.getUnsignedMax())
90  ? ConstantInt::getFalse(Ptr->getContext())
91  : IRB.CreateICmpULT(Size, Offset);
92  Value *Cmp3 = SizeRange.sub(OffsetRange)
93  .getUnsignedMin()
94  .uge(NeededSizeRange.getUnsignedMax())
95  ? ConstantInt::getFalse(Ptr->getContext())
96  : IRB.CreateICmpULT(ObjSize, NeededSizeVal);
97  Value *Or = IRB.CreateOr(Cmp2, Cmp3);
98  if ((!SizeCI || SizeCI->getValue().slt(0)) &&
99  !SizeRange.getSignedMin().isNonNegative()) {
100  Value *Cmp1 = IRB.CreateICmpSLT(Offset, ConstantInt::get(IntTy, 0));
101  Or = IRB.CreateOr(Cmp1, Or);
102  }
103 
104  return Or;
105 }
106 
107 /// Adds run-time bounds checks to memory accessing instructions.
108 ///
109 /// \p Or is the condition that should guard the trap.
110 ///
111 /// \p GetTrapBB is a callable that returns the trap BB to use on failure.
112 template <typename GetTrapBBT>
113 static void insertBoundsCheck(Value *Or, BuilderTy &IRB, GetTrapBBT GetTrapBB) {
114  // check if the comparison is always false
115  ConstantInt *C = dyn_cast_or_null<ConstantInt>(Or);
116  if (C) {
117  ++ChecksSkipped;
118  // If non-zero, nothing to do.
119  if (!C->getZExtValue())
120  return;
121  }
122  ++ChecksAdded;
123 
124  BasicBlock::iterator SplitI = IRB.GetInsertPoint();
125  BasicBlock *OldBB = SplitI->getParent();
126  BasicBlock *Cont = OldBB->splitBasicBlock(SplitI);
127  OldBB->getTerminator()->eraseFromParent();
128 
129  if (C) {
130  // If we have a constant zero, unconditionally branch.
131  // FIXME: We should really handle this differently to bypass the splitting
132  // the block.
133  BranchInst::Create(GetTrapBB(IRB), OldBB);
134  return;
135  }
136 
137  // Create the conditional branch.
138  BranchInst::Create(GetTrapBB(IRB), Cont, Or, OldBB);
139 }
140 
142  ScalarEvolution &SE) {
143  if (F.hasFnAttribute(Attribute::NoSanitizeBounds))
144  return false;
145 
146  const DataLayout &DL = F.getParent()->getDataLayout();
147  ObjectSizeOpts EvalOpts;
148  EvalOpts.RoundToAlign = true;
150  ObjectSizeOffsetEvaluator ObjSizeEval(DL, &TLI, F.getContext(), EvalOpts);
151 
152  // check HANDLE_MEMORY_INST in include/llvm/Instruction.def for memory
153  // touching instructions
155  for (Instruction &I : instructions(F)) {
156  Value *Or = nullptr;
157  BuilderTy IRB(I.getParent(), BasicBlock::iterator(&I), TargetFolder(DL));
158  if (LoadInst *LI = dyn_cast<LoadInst>(&I)) {
159  if (!LI->isVolatile())
160  Or = getBoundsCheckCond(LI->getPointerOperand(), LI, DL, TLI,
161  ObjSizeEval, IRB, SE);
162  } else if (StoreInst *SI = dyn_cast<StoreInst>(&I)) {
163  if (!SI->isVolatile())
164  Or = getBoundsCheckCond(SI->getPointerOperand(), SI->getValueOperand(),
165  DL, TLI, ObjSizeEval, IRB, SE);
166  } else if (AtomicCmpXchgInst *AI = dyn_cast<AtomicCmpXchgInst>(&I)) {
167  if (!AI->isVolatile())
168  Or =
169  getBoundsCheckCond(AI->getPointerOperand(), AI->getCompareOperand(),
170  DL, TLI, ObjSizeEval, IRB, SE);
171  } else if (AtomicRMWInst *AI = dyn_cast<AtomicRMWInst>(&I)) {
172  if (!AI->isVolatile())
173  Or = getBoundsCheckCond(AI->getPointerOperand(), AI->getValOperand(),
174  DL, TLI, ObjSizeEval, IRB, SE);
175  }
176  if (Or)
177  TrapInfo.push_back(std::make_pair(&I, Or));
178  }
179 
180  // Create a trapping basic block on demand using a callback. Depending on
181  // flags, this will either create a single block for the entire function or
182  // will create a fresh block every time it is called.
183  BasicBlock *TrapBB = nullptr;
184  auto GetTrapBB = [&TrapBB](BuilderTy &IRB) {
185  if (TrapBB && SingleTrapBB)
186  return TrapBB;
187 
188  Function *Fn = IRB.GetInsertBlock()->getParent();
189  // FIXME: This debug location doesn't make a lot of sense in the
190  // `SingleTrapBB` case.
191  auto DebugLoc = IRB.getCurrentDebugLocation();
193  TrapBB = BasicBlock::Create(Fn->getContext(), "trap", Fn);
194  IRB.SetInsertPoint(TrapBB);
195 
196  auto *F = Intrinsic::getDeclaration(Fn->getParent(), Intrinsic::trap);
197  CallInst *TrapCall = IRB.CreateCall(F, {});
198  TrapCall->setDoesNotReturn();
199  TrapCall->setDoesNotThrow();
200  TrapCall->setDebugLoc(DebugLoc);
201  IRB.CreateUnreachable();
202 
203  return TrapBB;
204  };
205 
206  // Add the checks.
207  for (const auto &Entry : TrapInfo) {
208  Instruction *Inst = Entry.first;
210  insertBoundsCheck(Entry.second, IRB, GetTrapBB);
211  }
212 
213  return !TrapInfo.empty();
214 }
215 
217  auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
218  auto &SE = AM.getResult<ScalarEvolutionAnalysis>(F);
219 
220  if (!addBoundsChecking(F, TLI, SE))
221  return PreservedAnalyses::all();
222 
223  return PreservedAnalyses::none();
224 }
llvm::PreservedAnalyses
A set of analyses that are preserved following a run of a transformation pass.
Definition: PassManager.h:152
llvm::ScalarEvolutionAnalysis
Analysis pass that exposes the ScalarEvolution for a function.
Definition: ScalarEvolution.h:2157
llvm
This is an optimization pass for GlobalISel generic memory operations.
Definition: AddressRanges.h:18
llvm::RecurKind::Or
@ Or
Bitwise or logical OR of integers.
llvm::DataLayout
A parsed version of the target data layout string in and methods for querying it.
Definition: DataLayout.h:113
llvm::BasicBlock::iterator
InstListType::iterator iterator
Instruction iterators...
Definition: BasicBlock.h:87
llvm::BasicBlock::getParent
const Function * getParent() const
Return the enclosing method, or null if none.
Definition: BasicBlock.h:104
llvm::AnalysisManager::getResult
PassT::Result & getResult(IRUnitT &IR, ExtraArgTs... ExtraArgs)
Get the result of an analysis pass for a given IR unit.
Definition: PassManager.h:774
InstIterator.h
llvm::Function
Definition: Function.h:60
TargetFolder.h
Pass.h
llvm::ConstantInt::getValue
const APInt & getValue() const
Return the constant as an APInt value reference.
Definition: Constants.h:133
llvm::SmallVector
This is a 'vector' (really, a variable-sized array), optimized for the case when the array is small.
Definition: SmallVector.h:1199
Statistic.h
llvm::ObjectSizeOffsetEvaluator::compute
SizeOffsetEvalType compute(Value *V)
Definition: MemoryBuiltins.cpp:1051
llvm::BoundsCheckingPass::run
PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM)
Definition: BoundsChecking.cpp:216
llvm::IRBuilder
This provides a uniform API for creating instructions and inserting them into a basic block: either a...
Definition: IRBuilder.h:2533
llvm::ScalarEvolution
The main scalar evolution driver.
Definition: ScalarEvolution.h:449
llvm::IRBuilderBase::CreateOr
Value * CreateOr(Value *LHS, Value *RHS, const Twine &Name="")
Definition: IRBuilder.h:1409
llvm::PreservedAnalyses::none
static PreservedAnalyses none()
Convenience factory function for the empty preserved set.
Definition: PassManager.h:155
llvm::Function::getContext
LLVMContext & getContext() const
getContext - Return a reference to the LLVMContext associated with this function.
Definition: Function.cpp:321
ScalarEvolution.h
llvm::Type
The instances of the Type class are immutable: once they are created, they are never changed.
Definition: Type.h:45
MemoryBuiltins.h
llvm::BasicBlock::splitBasicBlock
BasicBlock * splitBasicBlock(iterator I, const Twine &BBName="", bool Before=false)
Split the basic block into two basic blocks at the specified instruction.
Definition: BasicBlock.cpp:402
llvm::ObjectSizeOpts::RoundToAlign
bool RoundToAlign
Whether to round the result up to the alignment of allocas, byval arguments, and global variables.
Definition: MemoryBuiltins.h:158
llvm::CallBase::setDoesNotThrow
void setDoesNotThrow()
Definition: InstrTypes.h:1891
llvm::ObjectSizeOpts::Mode::ExactUnderlyingSizeAndOffset
@ ExactUnderlyingSizeAndOffset
All branches must be known and have the same underlying size and offset to be merged.
LLVM_DEBUG
#define LLVM_DEBUG(X)
Definition: Debug.h:101
F
#define F(x, y, z)
Definition: MD5.cpp:55
llvm::BasicBlock
LLVM Basic Block Representation.
Definition: BasicBlock.h:55
llvm::dbgs
raw_ostream & dbgs()
dbgs() - This returns a reference to a raw_ostream for debugging messages.
Definition: Debug.cpp:163
Instruction.h
CommandLine.h
llvm::ConstantInt
This is the shared class of boolean and integer constants.
Definition: Constants.h:79
llvm::CallBase::setDoesNotReturn
void setDoesNotReturn()
Definition: InstrTypes.h:1884
Constants.h
Intrinsics.h
C
(vector float) vec_cmpeq(*A, *B) C
Definition: README_ALTIVEC.txt:86
Twine.h
SI
@ SI
Definition: SIInstrInfo.cpp:7966
TargetLibraryInfo.h
insertBoundsCheck
static void insertBoundsCheck(Value *Or, BuilderTy &IRB, GetTrapBBT GetTrapBB)
Adds run-time bounds checks to memory accessing instructions.
Definition: BoundsChecking.cpp:113
llvm::Instruction
Definition: Instruction.h:42
llvm::STATISTIC
STATISTIC(NumFunctions, "Total number of functions")
llvm::ConstantInt::get
static Constant * get(Type *Ty, uint64_t V, bool IsSigned=false)
If Ty is a vector type, return a Constant with a splat of the given value.
Definition: Constants.cpp:879
llvm::ObjectSizeOffsetEvaluator
Evaluate the size and offset of an object pointed to by a Value*.
Definition: MemoryBuiltins.h:256
llvm::ScalarEvolution::getSCEV
const SCEV * getSCEV(Value *V)
Return a SCEV expression for the full generality of the specified expression.
Definition: ScalarEvolution.cpp:4442
BasicBlock.h
llvm::cl::opt< bool >
llvm::APInt::slt
bool slt(const APInt &RHS) const
Signed less than comparison.
Definition: APInt.h:1100
llvm::instructions
inst_range instructions(Function *F)
Definition: InstIterator.h:133
llvm::StoreInst
An instruction for storing to memory.
Definition: Instructions.h:298
SingleTrapBB
static cl::opt< bool > SingleTrapBB("bounds-checking-single-trap", cl::desc("Use one trap block per function"))
llvm::IRBuilderBase::GetInsertPoint
BasicBlock::iterator GetInsertPoint() const
Definition: IRBuilder.h:175
llvm::Instruction::eraseFromParent
SymbolTableList< Instruction >::iterator eraseFromParent()
This method unlinks 'this' from the containing basic block and deletes it.
Definition: Instruction.cpp:81
uint64_t
llvm::GlobalValue::getParent
Module * getParent()
Get the module that this global value is contained inside of...
Definition: GlobalValue.h:652
BoundsChecking.h
llvm::BranchInst::Create
static BranchInst * Create(BasicBlock *IfTrue, Instruction *InsertBefore=nullptr)
Definition: Instructions.h:3188
I
#define I(x, y, z)
Definition: MD5.cpp:58
llvm::Instruction::setDebugLoc
void setDebugLoc(DebugLoc Loc)
Set the debug location information for this instruction.
Definition: Instruction.h:356
llvm::ScalarEvolution::getUnsignedRange
ConstantRange getUnsignedRange(const SCEV *S)
Determine the unsigned range for a particular SCEV.
Definition: ScalarEvolution.h:957
addBoundsChecking
static bool addBoundsChecking(Function &F, TargetLibraryInfo &TLI, ScalarEvolution &SE)
Definition: BoundsChecking.cpp:141
IRBuilder.h
Ptr
@ Ptr
Definition: TargetLibraryInfo.cpp:60
llvm::IRBuilderBase::CreateICmpSLT
Value * CreateICmpSLT(Value *LHS, Value *RHS, const Twine &Name="")
Definition: IRBuilder.h:2137
DataLayout.h
llvm::Value::getType
Type * getType() const
All values are typed, get the type of this value.
Definition: Value.h:255
llvm::BasicBlock::Create
static BasicBlock * Create(LLVMContext &Context, const Twine &Name="", Function *Parent=nullptr, BasicBlock *InsertBefore=nullptr)
Creates a new BasicBlock.
Definition: BasicBlock.h:97
DL
MachineBasicBlock MachineBasicBlock::iterator DebugLoc DL
Definition: AArch64SLSHardening.cpp:76
llvm::ObjectSizeOpts
Various options to control the behavior of getObjectSize.
Definition: MemoryBuiltins.h:138
llvm::LoadInst
An instruction for reading from memory.
Definition: Instructions.h:174
llvm::Intrinsic::getDeclaration
Function * getDeclaration(Module *M, ID id, ArrayRef< Type * > Tys=std::nullopt)
Create or insert an LLVM Function declaration for an intrinsic, and return it.
Definition: Function.cpp:1481
llvm::AtomicRMWInst
an instruction that atomically reads a memory location, combines it with another value,...
Definition: Instructions.h:715
llvm::ConstantInt::getFalse
static ConstantInt * getFalse(LLVMContext &Context)
Definition: Constants.cpp:834
llvm::Twine
Twine - A lightweight data structure for efficiently representing the concatenation of temporary valu...
Definition: Twine.h:81
llvm::TargetFolder
TargetFolder - Create constants with target dependent folding.
Definition: TargetFolder.h:34
llvm::PreservedAnalyses::all
static PreservedAnalyses all()
Construct a special preserved set that preserves all passes.
Definition: PassManager.h:158
llvm::IRBuilderBase::CreateICmpULT
Value * CreateICmpULT(Value *LHS, Value *RHS, const Twine &Name="")
Definition: IRBuilder.h:2121
llvm::ObjectSizeOpts::EvalMode
Mode EvalMode
How we want to evaluate this object's size.
Definition: MemoryBuiltins.h:155
llvm::SizeOffsetEvalType
std::pair< Value *, Value * > SizeOffsetEvalType
Definition: MemoryBuiltins.h:252
Casting.h
Function.h
llvm::TargetLibraryInfo
Provides information about what library functions are available for the current target.
Definition: TargetLibraryInfo.h:226
getBoundsCheckCond
static Value * getBoundsCheckCond(Value *Ptr, Value *InstVal, const DataLayout &DL, TargetLibraryInfo &TLI, ObjectSizeOffsetEvaluator &ObjSizeEval, BuilderTy &IRB, ScalarEvolution &SE)
Gets the conditions under which memory accessing instructions will overflow.
Definition: BoundsChecking.cpp:55
Instructions.h
llvm::Instruction::getParent
const BasicBlock * getParent() const
Definition: Instruction.h:91
llvm::BasicBlock::getTerminator
const Instruction * getTerminator() const LLVM_READONLY
Returns the terminator instruction if the block is well formed or null if the block is not well forme...
Definition: BasicBlock.h:119
llvm::ObjectSizeOffsetEvaluator::bothKnown
bool bothKnown(SizeOffsetEvalType SizeOffset)
Definition: MemoryBuiltins.h:298
llvm::AnalysisManager
A container for analyses that lazily runs them and caches their results.
Definition: InstructionSimplify.h:42
llvm::CallInst
This class represents a function call, abstracting a target machine's calling convention.
Definition: Instructions.h:1474
llvm::IRBuilderBase::CreateSub
Value * CreateSub(Value *LHS, Value *RHS, const Twine &Name="", bool HasNUW=false, bool HasNSW=false)
Definition: IRBuilder.h:1256
llvm::DebugLoc
A debug info location.
Definition: DebugLoc.h:33
llvm::cl::desc
Definition: CommandLine.h:413
raw_ostream.h
Value.h
InitializePasses.h
llvm::Value
LLVM Value Representation.
Definition: Value.h:74
llvm::AtomicCmpXchgInst
An instruction that atomically checks whether a specified value is in a memory location,...
Definition: Instructions.h:510
Debug.h
llvm::TargetLibraryAnalysis
Analysis pass providing the TargetLibraryInfo.
Definition: TargetLibraryInfo.h:450