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 // SSPBufferSize - The lower bound for a buffer to be considered for stack
32 // smashing protection.
33 static cl::opt<unsigned>
34 SSPBufferSize("stack-protector-buffer-size", cl::init(8),
35 cl::desc("The lower bound for a buffer to be considered for "
36 "stack smashing protection."));
39 class VISIBILITY_HIDDEN StackProtector : public FunctionPass {
40 /// Level - The level of stack protection.
41 SSP::StackProtectorLevel Level;
43 /// TLI - Keep a pointer of a TargetLowering to consult for determining
44 /// target type sizes.
45 const TargetLowering *TLI;
50 /// InsertStackProtectors - Insert code into the prologue and epilogue of
53 /// - The prologue code loads and stores the stack guard onto the stack.
54 /// - The epilogue checks the value stored in the prologue against the
55 /// original value. It calls __stack_chk_fail if they differ.
56 bool InsertStackProtectors();
58 /// CreateFailBB - Create a basic block to jump to when the stack protector
60 BasicBlock *CreateFailBB();
62 /// RequiresStackProtector - Check whether or not this function needs a
63 /// stack protector based upon the stack protector level.
64 bool RequiresStackProtector() const;
66 static char ID; // Pass identification, replacement for typeid.
67 StackProtector() : FunctionPass(&ID), Level(SSP::OFF), TLI(0) {}
68 StackProtector(SSP::StackProtectorLevel lvl, const TargetLowering *tli)
69 : FunctionPass(&ID), Level(lvl), TLI(tli) {}
71 virtual bool runOnFunction(Function &Fn);
73 } // end anonymous namespace
75 char StackProtector::ID = 0;
76 static RegisterPass<StackProtector>
77 X("stack-protector", "Insert stack protectors");
79 FunctionPass *llvm::createStackProtectorPass(SSP::StackProtectorLevel lvl,
80 const TargetLowering *tli) {
81 return new StackProtector(lvl, tli);
84 bool StackProtector::runOnFunction(Function &Fn) {
88 if (!RequiresStackProtector()) return false;
90 return InsertStackProtectors();
93 /// InsertStackProtectors - Insert code into the prologue and epilogue of the
96 /// - The prologue code loads and stores the stack guard onto the stack.
97 /// - The epilogue checks the value stored in the prologue against the original
98 /// value. It calls __stack_chk_fail if they differ.
99 bool StackProtector::InsertStackProtectors() {
100 std::vector<BasicBlock*> ReturnBBs;
102 for (Function::iterator I = F->begin(); I != F->end(); ++I)
103 if (isa<ReturnInst>(I->getTerminator()))
104 ReturnBBs.push_back(I);
106 // If this function doesn't return, don't bother with stack protectors.
107 if (ReturnBBs.empty()) return false;
109 // Insert code into the entry block that stores the __stack_chk_guard variable
111 BasicBlock &Entry = F->getEntryBlock();
112 Instruction *InsertPt = &Entry.front();
113 const PointerType *GuardTy = PointerType::getUnqual(Type::Int8Ty);
115 // The global variable for the stack guard.
116 Constant *StackGuardVar = M->getOrInsertGlobal("__stack_chk_guard", GuardTy);
118 // The place on the stack that the stack protector guard is kept.
119 AllocaInst *StackProtFrameSlot =
120 new AllocaInst(GuardTy, "StackProt_Frame", InsertPt);
121 LoadInst *LI = new LoadInst(StackGuardVar, "StackGuard", false, InsertPt);
122 new StoreInst(LI, StackProtFrameSlot, false, InsertPt);
124 // Create the basic block to jump to when the guard check fails.
125 BasicBlock *FailBB = CreateFailBB();
127 // Loop through the basic blocks that have return instructions. Convert this:
137 // %1 = load __stack_chk_guard
138 // %2 = load <stored stack guard>
139 // %3 = cmp i1 %1, %2
140 // br i1 %3, label %SPRet, label %CallStackCheckFailBlk
145 // CallStackCheckFailBlk:
146 // call void @__stack_chk_fail()
149 for (std::vector<BasicBlock*>::iterator
150 I = ReturnBBs.begin(), E = ReturnBBs.end(); I != E; ++I) {
152 ReturnInst *RI = cast<ReturnInst>(BB->getTerminator());
153 Function::iterator InsPt = BB; ++InsPt; // Insertion point for new BB.
155 // Split the basic block before the return instruction.
156 BasicBlock *NewBB = BB->splitBasicBlock(RI, "SP_return");
158 // Move the newly created basic block to the point right after the old basic
159 // block so that it's in the "fall through" position.
160 NewBB->removeFromParent();
161 F->getBasicBlockList().insert(InsPt, NewBB);
163 // Generate the stack protector instructions in the old basic block.
164 LoadInst *LI2 = new LoadInst(StackGuardVar, "", false, BB);
165 LoadInst *LI1 = new LoadInst(StackProtFrameSlot, "", true, BB);
166 ICmpInst *Cmp = new ICmpInst(CmpInst::ICMP_EQ, LI1, LI2, "", BB);
167 BranchInst::Create(NewBB, FailBB, Cmp, BB);
173 /// CreateFailBB - Create a basic block to jump to when the stack protector
175 BasicBlock *StackProtector::CreateFailBB() {
176 BasicBlock *FailBB = BasicBlock::Create("CallStackCheckFailBlk", F);
177 std::vector<const Type*> Params;
178 Constant *StackChkFail =
179 M->getOrInsertFunction("__stack_chk_fail", Type::VoidTy, NULL);
180 CallInst::Create(StackChkFail, "", FailBB);
181 new UnreachableInst(FailBB);
185 /// RequiresStackProtector - Check whether or not this function needs a stack
186 /// protector based upon the stack protector level.
187 bool StackProtector::RequiresStackProtector() const {
189 default: return false;
190 case SSP::ALL: return true;
192 // If the size of the local variables allocated on the stack is greater than
193 // SSPBufferSize, then we require a stack protector.
194 uint64_t StackSize = 0;
195 const TargetData *TD = TLI->getTargetData();
197 for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I) {
200 for (BasicBlock::iterator
201 II = BB->begin(), IE = BB->end(); II != IE; ++II)
202 if (AllocaInst *AI = dyn_cast<AllocaInst>(II)) {
203 if (ConstantInt *CI = dyn_cast<ConstantInt>(AI->getArraySize())) {
204 uint64_t Bytes = TD->getTypeSizeInBits(AI->getAllocatedType()) / 8;
205 const APInt &Size = CI->getValue();
206 StackSize += Bytes * Size.getZExtValue();
208 if (SSPBufferSize <= StackSize)