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;
46 /// FailBB - Holds the basic block to jump to when the stack protector check
50 /// StackProtFrameSlot - The place on the stack that the stack protector
52 AllocaInst *StackProtFrameSlot;
54 /// StackGuardVar - The global variable for the stack guard.
55 Constant *StackGuardVar;
60 /// InsertStackProtectorPrologue - Insert code into the entry block that
61 /// stores the __stack_chk_guard variable onto the stack.
62 void InsertStackProtectorPrologue();
64 /// InsertStackProtectorEpilogue - Insert code before the return
65 /// instructions checking the stack value that was stored in the
66 /// prologue. If it isn't the same as the original value, then call a
67 /// "failure" function.
68 void InsertStackProtectorEpilogue();
70 /// CreateFailBB - Create a basic block to jump to when the stack protector
74 /// RequiresStackProtector - Check whether or not this function needs a
75 /// stack protector based upon the stack protector level.
76 bool RequiresStackProtector() const;
78 static char ID; // Pass identification, replacement for typeid.
79 StackProtector() : FunctionPass(&ID), Level(SSP::OFF), TLI(0), FailBB(0) {}
80 StackProtector(SSP::StackProtectorLevel lvl, const TargetLowering *tli)
81 : FunctionPass(&ID), Level(lvl), TLI(tli), FailBB(0) {}
83 virtual bool runOnFunction(Function &Fn);
85 } // end anonymous namespace
87 char StackProtector::ID = 0;
88 static RegisterPass<StackProtector>
89 X("stack-protector", "Insert stack protectors");
91 FunctionPass *llvm::createStackProtectorPass(SSP::StackProtectorLevel lvl,
92 const TargetLowering *tli) {
93 return new StackProtector(lvl, tli);
96 bool StackProtector::runOnFunction(Function &Fn) {
100 if (!RequiresStackProtector()) return false;
102 InsertStackProtectorPrologue();
103 InsertStackProtectorEpilogue();
107 StackProtFrameSlot = 0;
112 /// InsertStackProtectorPrologue - Insert code into the entry block that stores
113 /// the __stack_chk_guard variable onto the stack.
114 void StackProtector::InsertStackProtectorPrologue() {
115 BasicBlock &Entry = F->getEntryBlock();
116 Instruction &InsertPt = Entry.front();
118 StackGuardVar = M->getOrInsertGlobal("__stack_chk_guard",
119 PointerType::getUnqual(Type::Int8Ty));
120 StackProtFrameSlot = new AllocaInst(PointerType::getUnqual(Type::Int8Ty),
121 "StackProt_Frame", &InsertPt);
122 LoadInst *LI = new LoadInst(StackGuardVar, "StackGuard", false, &InsertPt);
123 new StoreInst(LI, StackProtFrameSlot, false, &InsertPt);
126 /// InsertStackProtectorEpilogue - Insert code before the return instructions
127 /// checking the stack value that was stored in the prologue. If it isn't the
128 /// same as the original value, then call a "failure" function.
129 void StackProtector::InsertStackProtectorEpilogue() {
130 // Create the basic block to jump to when the guard check fails.
133 Function::iterator I = F->begin(), E = F->end();
134 std::vector<BasicBlock*> ReturnBBs;
135 ReturnBBs.reserve(F->size());
138 if (isa<ReturnInst>(I->getTerminator()))
139 ReturnBBs.push_back(I);
141 if (ReturnBBs.empty()) return; // Odd, but could happen. . .
143 // Loop through the basic blocks that have return instructions. Convert this:
153 // %1 = load __stack_chk_guard
154 // %2 = load <stored stack guard>
155 // %3 = cmp i1 %1, %2
156 // br i1 %3, label %SPRet, label %CallStackCheckFailBlk
161 // CallStackCheckFailBlk:
162 // call void @__stack_chk_fail()
165 for (std::vector<BasicBlock*>::iterator
166 II = ReturnBBs.begin(), IE = ReturnBBs.end(); II != IE; ++II) {
167 BasicBlock *BB = *II;
168 ReturnInst *RI = cast<ReturnInst>(BB->getTerminator());
169 Function::iterator InsPt = BB; ++InsPt; // Insertion point for new BB.
171 // Split the basic block before the return instruction.
172 BasicBlock *NewBB = BB->splitBasicBlock(RI, "SP_return");
174 // Move the newly created basic block to the point right after the old basic
176 NewBB->removeFromParent();
177 F->getBasicBlockList().insert(InsPt, NewBB);
179 // Generate the stack protector instructions in the old basic block.
180 LoadInst *LI2 = new LoadInst(StackGuardVar, "", false, BB);
181 LoadInst *LI1 = new LoadInst(StackProtFrameSlot, "", true, BB);
182 ICmpInst *Cmp = new ICmpInst(CmpInst::ICMP_EQ, LI1, LI2, "", BB);
183 BranchInst::Create(NewBB, FailBB, Cmp, BB);
187 /// CreateFailBB - Create a basic block to jump to when the stack protector
189 void StackProtector::CreateFailBB() {
190 assert(!FailBB && "Failure basic block already created?!");
191 FailBB = BasicBlock::Create("CallStackCheckFailBlk", F);
192 std::vector<const Type*> Params;
193 Constant *StackChkFail =
194 M->getOrInsertFunction("__stack_chk_fail", Type::VoidTy, NULL);
195 CallInst::Create(StackChkFail, "", FailBB);
196 new UnreachableInst(FailBB);
199 /// RequiresStackProtector - Check whether or not this function needs a stack
200 /// protector based upon the stack protector level.
201 bool StackProtector::RequiresStackProtector() const {
203 default: return false;
204 case SSP::ALL: return true;
206 // If the size of the local variables allocated on the stack is greater than
207 // SSPBufferSize, then we require a stack protector.
208 uint64_t StackSize = 0;
209 const TargetData *TD = TLI->getTargetData();
211 for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I) {
214 for (BasicBlock::iterator
215 II = BB->begin(), IE = BB->end(); II != IE; ++II)
216 if (AllocaInst *AI = dyn_cast<AllocaInst>(II)) {
217 if (ConstantInt *CI = dyn_cast<ConstantInt>(AI->getArraySize())) {
218 uint64_t Bytes = TD->getTypeSizeInBits(AI->getAllocatedType()) / 8;
219 const APInt &Size = CI->getValue();
220 StackSize += Bytes * Size.getZExtValue();
222 if (SSPBufferSize <= StackSize)