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/Intrinsics.h"
24 #include "llvm/Module.h"
25 #include "llvm/Pass.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 // Loop through the basic blocks that have return instructions. Convert this:
110 // %1 = load __stack_chk_guard
111 // %2 = load <stored stack guard>
112 // %3 = cmp i1 %1, %2
113 // br i1 %3, label %SP_return, label %CallStackCheckFailBlk
118 // CallStackCheckFailBlk:
119 // call void @__stack_chk_fail()
122 BasicBlock *FailBB = 0; // The basic block to jump to if check fails.
123 AllocaInst *AI = 0; // Place on stack that stores the stack guard.
124 Constant *StackGuardVar = 0; // The stack guard variable.
126 for (Function::iterator I = F->begin(), E = F->end(); I != E; ) {
129 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
131 // Insert code into the entry block that stores the __stack_chk_guard
132 // variable onto the stack.
133 PointerType *PtrTy = PointerType::getUnqual(Type::Int8Ty);
134 StackGuardVar = M->getOrInsertGlobal("__stack_chk_guard", PtrTy);
136 BasicBlock &Entry = F->getEntryBlock();
137 Instruction *InsPt = &Entry.front();
139 AI = new AllocaInst(PtrTy, "StackGuardSlot", InsPt);
140 LoadInst *LI = new LoadInst(StackGuardVar, "StackGuard", false, InsPt);
142 Value *Args[] = { LI, AI };
144 Create(Intrinsic::getDeclaration(M, Intrinsic::stackprotector_create),
145 &Args[0], array_endof(Args), "", InsPt);
147 // Create the basic block to jump to when the guard check fails.
148 FailBB = CreateFailBB();
151 ++I; // Skip to the next block so that we don't resplit the return block.
153 // Split the basic block before the return instruction.
154 BasicBlock *NewBB = BB->splitBasicBlock(RI, "SP_return");
156 // Move the newly created basic block to the point right after the old
157 // basic block so that it's in the "fall through" position.
158 NewBB->removeFromParent();
159 F->getBasicBlockList().insert(I, NewBB);
161 // Generate the stack protector instructions in the old basic block.
162 LoadInst *LI1 = new LoadInst(StackGuardVar, "", false, BB);
163 CallInst *CI = CallInst::
164 Create(Intrinsic::getDeclaration(M, Intrinsic::stackprotector_check),
166 ICmpInst *Cmp = new ICmpInst(CmpInst::ICMP_EQ, CI, LI1, "", BB);
167 BranchInst::Create(NewBB, FailBB, Cmp, BB);
173 // Return if we didn't modify any basic blocks. I.e., there are no return
174 // statements in the function.
175 if (!FailBB) return false;
180 /// CreateFailBB - Create a basic block to jump to when the stack protector
182 BasicBlock *StackProtector::CreateFailBB() {
183 BasicBlock *FailBB = BasicBlock::Create("CallStackCheckFailBlk", F);
184 Constant *StackChkFail =
185 M->getOrInsertFunction("__stack_chk_fail", Type::VoidTy, NULL);
186 CallInst::Create(StackChkFail, "", FailBB);
187 new UnreachableInst(FailBB);
191 /// RequiresStackProtector - Check whether or not this function needs a stack
192 /// protector based upon the stack protector level. The heuristic we use is to
193 /// add a guard variable to functions that call alloca, and functions with
194 /// buffers larger than 8 bytes.
195 bool StackProtector::RequiresStackProtector() const {
197 default: return false;
198 case SSP::ALL: return true;
200 const TargetData *TD = TLI->getTargetData();
202 for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I) {
205 for (BasicBlock::iterator
206 II = BB->begin(), IE = BB->end(); II != IE; ++II)
207 if (AllocaInst *AI = dyn_cast<AllocaInst>(II)) {
208 if (AI->isArrayAllocation())
209 // This is a call to alloca with a variable size. Emit stack
213 if (const ArrayType *AT = dyn_cast<ArrayType>(AI->getAllocatedType()))
214 // If an array has more than 8 bytes of allocated space, then we
215 // emit stack protectors.
216 if (SSPBufferSize <= TD->getABITypeSize(AT))