1 //===-- StackProtector.cpp - Stack Protector Insertion --------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This pass inserts stack protectors into functions which need them. A variable
11 // with a random value in it is stored onto the stack before the local variables
12 // are allocated. Upon exiting the block, the stored value is checked. If it's
13 // changed, then there was some sort of violation and the program aborts.
15 //===----------------------------------------------------------------------===//
17 #define DEBUG_TYPE "stack-protector"
18 #include "llvm/CodeGen/Passes.h"
19 #include "llvm/Constants.h"
20 #include "llvm/DerivedTypes.h"
21 #include "llvm/Function.h"
22 #include "llvm/Instructions.h"
23 #include "llvm/Module.h"
24 #include "llvm/Pass.h"
25 #include "llvm/ADT/APInt.h"
26 #include "llvm/Support/CommandLine.h"
27 #include "llvm/Target/TargetData.h"
28 #include "llvm/Target/TargetLowering.h"
31 // Enable stack protectors.
32 static cl::opt<unsigned>
33 SSPBufferSize("stack-protector-buffer-size", cl::init(8),
34 cl::desc("The lower bound for a buffer to be considered for "
35 "stack smashing protection."));
38 class VISIBILITY_HIDDEN StackProtector : public FunctionPass {
39 /// Level - The level of stack protection.
40 SSP::StackProtectorLevel Level;
42 /// TLI - Keep a pointer of a TargetLowering to consult for determining
43 /// target type sizes.
44 const TargetLowering *TLI;
49 /// InsertStackProtectors - Insert code into the prologue and epilogue of
52 /// - The prologue code loads and stores the stack guard onto the stack.
53 /// - The epilogue checks the value stored in the prologue against the
54 /// original value. It calls __stack_chk_fail if they differ.
55 bool InsertStackProtectors();
57 /// CreateFailBB - Create a basic block to jump to when the stack protector
59 BasicBlock *CreateFailBB();
61 /// RequiresStackProtector - Check whether or not this function needs a
62 /// stack protector based upon the stack protector level.
63 bool RequiresStackProtector() const;
65 static char ID; // Pass identification, replacement for typeid.
66 StackProtector() : FunctionPass(&ID), Level(SSP::OFF), TLI(0) {}
67 StackProtector(SSP::StackProtectorLevel lvl, const TargetLowering *tli)
68 : FunctionPass(&ID), Level(lvl), TLI(tli) {}
70 virtual bool runOnFunction(Function &Fn);
72 } // end anonymous namespace
74 char StackProtector::ID = 0;
75 static RegisterPass<StackProtector>
76 X("stack-protector", "Insert stack protectors");
78 FunctionPass *llvm::createStackProtectorPass(SSP::StackProtectorLevel lvl,
79 const TargetLowering *tli) {
80 return new StackProtector(lvl, tli);
83 bool StackProtector::runOnFunction(Function &Fn) {
87 if (!RequiresStackProtector()) return false;
89 return InsertStackProtectors();
92 /// InsertStackProtectors - Insert code into the prologue and epilogue of the
95 /// - The prologue code loads and stores the stack guard onto the stack.
96 /// - The epilogue checks the value stored in the prologue against the original
97 /// value. It calls __stack_chk_fail if they differ.
98 bool StackProtector::InsertStackProtectors() {
99 std::vector<BasicBlock*> ReturnBBs;
101 for (Function::iterator I = F->begin(); I != F->end(); ++I)
102 if (isa<ReturnInst>(I->getTerminator()))
103 ReturnBBs.push_back(I);
105 // If this function doesn't return, don't bother with stack protectors.
106 if (ReturnBBs.empty()) return false;
108 // Insert code into the entry block that stores the __stack_chk_guard variable
110 BasicBlock &Entry = F->getEntryBlock();
111 Instruction *InsertPt = &Entry.front();
112 const PointerType *GuardTy = PointerType::getUnqual(Type::Int8Ty);
114 // The global variable for the stack guard.
115 Constant *StackGuardVar = M->getOrInsertGlobal("__stack_chk_guard", GuardTy);
117 // The place on the stack that the stack protector guard is kept.
118 AllocaInst *StackProtFrameSlot =
119 new AllocaInst(GuardTy, "StackProt_Frame", InsertPt);
120 LoadInst *LI = new LoadInst(StackGuardVar, "StackGuard", false, InsertPt);
121 new StoreInst(LI, StackProtFrameSlot, false, InsertPt);
123 // Create the basic block to jump to when the guard check fails.
124 BasicBlock *FailBB = CreateFailBB();
126 // Loop through the basic blocks that have return instructions. Convert this:
136 // %1 = load __stack_chk_guard
137 // %2 = load <stored stack guard>
138 // %3 = cmp i1 %1, %2
139 // br i1 %3, label %SPRet, label %CallStackCheckFailBlk
144 // CallStackCheckFailBlk:
145 // call void @__stack_chk_fail()
148 for (std::vector<BasicBlock*>::iterator
149 I = ReturnBBs.begin(), E = ReturnBBs.end(); I != E; ++I) {
151 ReturnInst *RI = cast<ReturnInst>(BB->getTerminator());
152 Function::iterator InsPt = BB; ++InsPt; // Insertion point for new BB.
154 // Split the basic block before the return instruction.
155 BasicBlock *NewBB = BB->splitBasicBlock(RI, "SP_return");
157 // Move the newly created basic block to the point right after the old basic
158 // block so that it's in the "fall through" position.
159 NewBB->removeFromParent();
160 F->getBasicBlockList().insert(InsPt, NewBB);
162 // Generate the stack protector instructions in the old basic block.
163 LoadInst *LI2 = new LoadInst(StackGuardVar, "", false, BB);
164 LoadInst *LI1 = new LoadInst(StackProtFrameSlot, "", true, BB);
165 ICmpInst *Cmp = new ICmpInst(CmpInst::ICMP_EQ, LI1, LI2, "", BB);
166 BranchInst::Create(NewBB, FailBB, Cmp, BB);
172 /// CreateFailBB - Create a basic block to jump to when the stack protector
174 BasicBlock *StackProtector::CreateFailBB() {
175 BasicBlock *FailBB = BasicBlock::Create("CallStackCheckFailBlk", F);
176 std::vector<const Type*> Params;
177 Constant *StackChkFail =
178 M->getOrInsertFunction("__stack_chk_fail", Type::VoidTy, NULL);
179 CallInst::Create(StackChkFail, "", FailBB);
180 new UnreachableInst(FailBB);
184 /// RequiresStackProtector - Check whether or not this function needs a stack
185 /// protector based upon the stack protector level.
186 bool StackProtector::RequiresStackProtector() const {
188 default: return false;
189 case SSP::ALL: return true;
191 // If the size of the local variables allocated on the stack is greater than
192 // SSPBufferSize, then we require a stack protector.
193 uint64_t StackSize = 0;
194 const TargetData *TD = TLI->getTargetData();
196 for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I) {
199 for (BasicBlock::iterator
200 II = BB->begin(), IE = BB->end(); II != IE; ++II)
201 if (AllocaInst *AI = dyn_cast<AllocaInst>(II)) {
202 if (ConstantInt *CI = dyn_cast<ConstantInt>(AI->getArraySize())) {
203 uint64_t Bytes = TD->getTypeSizeInBits(AI->getAllocatedType()) / 8;
204 const APInt &Size = CI->getValue();
205 StackSize += Bytes * Size.getZExtValue();
207 if (SSPBufferSize <= StackSize)