lib/CodeGen/StackProtector.cpp - llvm - Git at Google

 //===-- StackProtector.cpp - Stack Protector Insertion --------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This pass inserts stack protectors into functions which need them. A variable
 // with a random value in it is stored onto the stack before the local variables
 // are allocated. Upon exiting the block, the stored value is checked. If it's
 // changed, then there was some sort of violation and the program aborts.
 //
 //===----------------------------------------------------------------------===//

 #define DEBUG_TYPE "stack-protector"
 #include "llvm/CodeGen/Passes.h"
 #include "llvm/Analysis/Dominators.h"
 #include "llvm/Attributes.h"
 #include "llvm/Constants.h"
 #include "llvm/DerivedTypes.h"
 #include "llvm/Function.h"
 #include "llvm/Instructions.h"
 #include "llvm/Intrinsics.h"
 #include "llvm/Module.h"
 #include "llvm/Pass.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Target/TargetData.h"
 #include "llvm/Target/TargetLowering.h"
 using namespace llvm;

 // SSPBufferSize - The lower bound for a buffer to be considered for stack
 // smashing protection.
 static cl::opt<unsigned>
 SSPBufferSize("stack-protector-buffer-size", cl::init(8),
               cl::desc("Lower bound for a buffer to be considered for "
                        "stack protection"));

 namespace {
   class StackProtector : public FunctionPass {
     /// TLI - Keep a pointer of a TargetLowering to consult for determining
     /// target type sizes.
     const TargetLowering *TLI;

     Function *F;
     Module *M;

     DominatorTree* DT;

     /// InsertStackProtectors - Insert code into the prologue and epilogue of
     /// the function.
     ///
     ///  - The prologue code loads and stores the stack guard onto the stack.
     ///  - The epilogue checks the value stored in the prologue against the
     ///    original value. It calls __stack_chk_fail if they differ.
     bool InsertStackProtectors();

     /// CreateFailBB - Create a basic block to jump to when the stack protector
     /// check fails.
     BasicBlock *CreateFailBB();

     /// RequiresStackProtector - Check whether or not this function needs a
     /// stack protector based upon the stack protector level.
     bool RequiresStackProtector() const;
   public:
     static char ID;             // Pass identification, replacement for typeid.
     StackProtector() : FunctionPass(ID), TLI(0) {
       initializeStackProtectorPass(*PassRegistry::getPassRegistry());
     }
     StackProtector(const TargetLowering *tli)
       : FunctionPass(ID), TLI(tli) {
         initializeStackProtectorPass(*PassRegistry::getPassRegistry());
       }

     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
       AU.addPreserved<DominatorTree>();
     }

     virtual bool runOnFunction(Function &Fn);
   };
 } // end anonymous namespace

 char StackProtector::ID = 0;
 INITIALIZE_PASS(StackProtector, "stack-protector",
                 "Insert stack protectors", false, false)

 FunctionPass *llvm::createStackProtectorPass(const TargetLowering *tli) {
   return new StackProtector(tli);
 }

 bool StackProtector::runOnFunction(Function &Fn) {
   F = &Fn;
   M = F->getParent();
   DT = getAnalysisIfAvailable<DominatorTree>();

   if (!RequiresStackProtector()) return false;

   return InsertStackProtectors();
 }

 /// RequiresStackProtector - Check whether or not this function needs a stack
 /// protector based upon the stack protector level. The heuristic we use is to
 /// add a guard variable to functions that call alloca, and functions with
 /// buffers larger than SSPBufferSize bytes.
 bool StackProtector::RequiresStackProtector() const {
   if (F->hasFnAttr(Attribute::StackProtectReq))
     return true;

   if (!F->hasFnAttr(Attribute::StackProtect))
     return false;

   const TargetData *TD = TLI->getTargetData();

   for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I) {
     BasicBlock *BB = I;

     for (BasicBlock::iterator
            II = BB->begin(), IE = BB->end(); II != IE; ++II)
       if (AllocaInst *AI = dyn_cast<AllocaInst>(II)) {
         if (AI->isArrayAllocation())
           // This is a call to alloca with a variable size. Emit stack
           // protectors.
           return true;

         if (ArrayType *AT = dyn_cast<ArrayType>(AI->getAllocatedType())) {
           // We apparently only care about character arrays.
           if (!AT->getElementType()->isIntegerTy(8))
             continue;

           // If an array has more than SSPBufferSize bytes of allocated space,
           // then we emit stack protectors.
           if (SSPBufferSize <= TD->getTypeAllocSize(AT))
             return true;
         }
       }
   }

   return false;
 }

 /// InsertStackProtectors - Insert code into the prologue and epilogue of the
 /// function.
 ///
 ///  - The prologue code loads and stores the stack guard onto the stack.
 ///  - The epilogue checks the value stored in the prologue against the original
 ///    value. It calls __stack_chk_fail if they differ.
 bool StackProtector::InsertStackProtectors() {
   BasicBlock *FailBB = 0;       // The basic block to jump to if check fails.
   BasicBlock *FailBBDom = 0;    // FailBB's dominator.
   AllocaInst *AI = 0;           // Place on stack that stores the stack guard.
   Value *StackGuardVar = 0;  // The stack guard variable.

   for (Function::iterator I = F->begin(), E = F->end(); I != E; ) {
     BasicBlock *BB = I++;
     ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator());
     if (!RI) continue;

     if (!FailBB) {
       // Insert code into the entry block that stores the __stack_chk_guard
       // variable onto the stack:
       //
       //   entry:
       //     StackGuardSlot = alloca i8*
       //     StackGuard = load __stack_chk_guard
       //     call void @llvm.stackprotect.create(StackGuard, StackGuardSlot)
       //
       PointerType *PtrTy = Type::getInt8PtrTy(RI->getContext());
       unsigned AddressSpace, Offset;
       if (TLI->getStackCookieLocation(AddressSpace, Offset)) {
         Constant *OffsetVal =
           ConstantInt::get(Type::getInt32Ty(RI->getContext()), Offset);

         StackGuardVar = ConstantExpr::getIntToPtr(OffsetVal,
                                       PointerType::get(PtrTy, AddressSpace));
       } else {
         StackGuardVar = M->getOrInsertGlobal("__stack_chk_guard", PtrTy);
       }

       BasicBlock &Entry = F->getEntryBlock();
       Instruction *InsPt = &Entry.front();

       AI = new AllocaInst(PtrTy, "StackGuardSlot", InsPt);
       LoadInst *LI = new LoadInst(StackGuardVar, "StackGuard", false, InsPt);

       Value *Args[] = { LI, AI };
       CallInst::
         Create(Intrinsic::getDeclaration(M, Intrinsic::stackprotector),
                Args, "", InsPt);

       // Create the basic block to jump to when the guard check fails.
       FailBB = CreateFailBB();
     }

     // For each block with a return instruction, convert this:
     //
     //   return:
     //     ...
     //     ret ...
     //
     // into this:
     //
     //   return:
     //     ...
     //     %1 = load __stack_chk_guard
     //     %2 = load StackGuardSlot
     //     %3 = cmp i1 %1, %2
     //     br i1 %3, label %SP_return, label %CallStackCheckFailBlk
     //
     //   SP_return:
     //     ret ...
     //
     //   CallStackCheckFailBlk:
     //     call void @__stack_chk_fail()
     //     unreachable

     // Split the basic block before the return instruction.
     BasicBlock *NewBB = BB->splitBasicBlock(RI, "SP_return");

     if (DT && DT->isReachableFromEntry(BB)) {
       DT->addNewBlock(NewBB, BB);
       FailBBDom = FailBBDom ? DT->findNearestCommonDominator(FailBBDom, BB) :BB;
     }

     // Remove default branch instruction to the new BB.
     BB->getTerminator()->eraseFromParent();

     // Move the newly created basic block to the point right after the old basic
     // block so that it's in the "fall through" position.
     NewBB->moveAfter(BB);

     // Generate the stack protector instructions in the old basic block.
     LoadInst *LI1 = new LoadInst(StackGuardVar, "", false, BB);
     LoadInst *LI2 = new LoadInst(AI, "", true, BB);
     ICmpInst *Cmp = new ICmpInst(*BB, CmpInst::ICMP_EQ, LI1, LI2, "");
     BranchInst::Create(NewBB, FailBB, Cmp, BB);
   }

   // Return if we didn't modify any basic blocks. I.e., there are no return
   // statements in the function.
   if (!FailBB) return false;

   if (DT && FailBBDom)
     DT->addNewBlock(FailBB, FailBBDom);

   return true;
 }

 /// CreateFailBB - Create a basic block to jump to when the stack protector
 /// check fails.
 BasicBlock *StackProtector::CreateFailBB() {
   BasicBlock *FailBB = BasicBlock::Create(F->getContext(),
                                           "CallStackCheckFailBlk", F);
   Constant *StackChkFail =
     M->getOrInsertFunction("__stack_chk_fail",
                            Type::getVoidTy(F->getContext()), NULL);
   CallInst::Create(StackChkFail, "", FailBB);
   new UnreachableInst(F->getContext(), FailBB);
   return FailBB;
 }
	//===-- StackProtector.cpp - Stack Protector Insertion --------------------===//
	//
	// The LLVM Compiler Infrastructure
	//
	// This file is distributed under the University of Illinois Open Source
	// License. See LICENSE.TXT for details.
	//
	//===----------------------------------------------------------------------===//
	//
	// This pass inserts stack protectors into functions which need them. A variable
	// with a random value in it is stored onto the stack before the local variables
	// are allocated. Upon exiting the block, the stored value is checked. If it's
	// changed, then there was some sort of violation and the program aborts.
	//
	//===----------------------------------------------------------------------===//

	#define DEBUG_TYPE "stack-protector"
	#include "llvm/CodeGen/Passes.h"
	#include "llvm/Analysis/Dominators.h"
	#include "llvm/Attributes.h"
	#include "llvm/Constants.h"
	#include "llvm/DerivedTypes.h"
	#include "llvm/Function.h"
	#include "llvm/Instructions.h"
	#include "llvm/Intrinsics.h"
	#include "llvm/Module.h"
	#include "llvm/Pass.h"
	#include "llvm/Support/CommandLine.h"
	#include "llvm/Target/TargetData.h"
	#include "llvm/Target/TargetLowering.h"
	using namespace llvm;

	// SSPBufferSize - The lower bound for a buffer to be considered for stack
	// smashing protection.
	static cl::opt<unsigned>
	SSPBufferSize("stack-protector-buffer-size", cl::init(8),
	cl::desc("Lower bound for a buffer to be considered for "
	"stack protection"));

	namespace {
	class StackProtector : public FunctionPass {
	/// TLI - Keep a pointer of a TargetLowering to consult for determining
	/// target type sizes.
	const TargetLowering *TLI;

	Function *F;
	Module *M;

	DominatorTree* DT;

	/// InsertStackProtectors - Insert code into the prologue and epilogue of
	/// the function.
	///
	/// - The prologue code loads and stores the stack guard onto the stack.
	/// - The epilogue checks the value stored in the prologue against the
	/// original value. It calls __stack_chk_fail if they differ.
	bool InsertStackProtectors();

	/// CreateFailBB - Create a basic block to jump to when the stack protector
	/// check fails.
	BasicBlock *CreateFailBB();

	/// RequiresStackProtector - Check whether or not this function needs a
	/// stack protector based upon the stack protector level.
	bool RequiresStackProtector() const;
	public:
	static char ID; // Pass identification, replacement for typeid.
	StackProtector() : FunctionPass(ID), TLI(0) {
	initializeStackProtectorPass(*PassRegistry::getPassRegistry());
	}
	StackProtector(const TargetLowering *tli)
	: FunctionPass(ID), TLI(tli) {
	initializeStackProtectorPass(*PassRegistry::getPassRegistry());
	}

	virtual void getAnalysisUsage(AnalysisUsage &AU) const {
	AU.addPreserved<DominatorTree>();
	}

	virtual bool runOnFunction(Function &Fn);
	};
	} // end anonymous namespace

	char StackProtector::ID = 0;
	INITIALIZE_PASS(StackProtector, "stack-protector",
	"Insert stack protectors", false, false)

	FunctionPass llvm::createStackProtectorPass(const TargetLowering tli) {
	return new StackProtector(tli);
	}

	bool StackProtector::runOnFunction(Function &Fn) {
	F = &Fn;
	M = F->getParent();
	DT = getAnalysisIfAvailable<DominatorTree>();

	if (!RequiresStackProtector()) return false;

	return InsertStackProtectors();
	}

	/// RequiresStackProtector - Check whether or not this function needs a stack
	/// protector based upon the stack protector level. The heuristic we use is to
	/// add a guard variable to functions that call alloca, and functions with
	/// buffers larger than SSPBufferSize bytes.
	bool StackProtector::RequiresStackProtector() const {
	if (F->hasFnAttr(Attribute::StackProtectReq))
	return true;

	if (!F->hasFnAttr(Attribute::StackProtect))
	return false;

	const TargetData *TD = TLI->getTargetData();

	for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I) {
	BasicBlock *BB = I;

	for (BasicBlock::iterator
	II = BB->begin(), IE = BB->end(); II != IE; ++II)
	if (AllocaInst *AI = dyn_cast<AllocaInst>(II)) {
	if (AI->isArrayAllocation())
	// This is a call to alloca with a variable size. Emit stack
	// protectors.
	return true;

	if (ArrayType *AT = dyn_cast<ArrayType>(AI->getAllocatedType())) {
	// We apparently only care about character arrays.
	if (!AT->getElementType()->isIntegerTy(8))
	continue;

	// If an array has more than SSPBufferSize bytes of allocated space,
	// then we emit stack protectors.
	if (SSPBufferSize <= TD->getTypeAllocSize(AT))
	return true;
	}
	}
	}

	return false;
	}

	/// InsertStackProtectors - Insert code into the prologue and epilogue of the
	/// function.
	///
	/// - The prologue code loads and stores the stack guard onto the stack.
	/// - The epilogue checks the value stored in the prologue against the original
	/// value. It calls __stack_chk_fail if they differ.
	bool StackProtector::InsertStackProtectors() {
	BasicBlock *FailBB = 0; // The basic block to jump to if check fails.
	BasicBlock *FailBBDom = 0; // FailBB's dominator.
	AllocaInst *AI = 0; // Place on stack that stores the stack guard.
	Value *StackGuardVar = 0; // The stack guard variable.

	for (Function::iterator I = F->begin(), E = F->end(); I != E; ) {
	BasicBlock *BB = I++;
	ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator());
	if (!RI) continue;

	if (!FailBB) {
	// Insert code into the entry block that stores the __stack_chk_guard
	// variable onto the stack:
	//
	// entry:
	// StackGuardSlot = alloca i8*
	// StackGuard = load __stack_chk_guard
	// call void @llvm.stackprotect.create(StackGuard, StackGuardSlot)
	//
	PointerType *PtrTy = Type::getInt8PtrTy(RI->getContext());
	unsigned AddressSpace, Offset;
	if (TLI->getStackCookieLocation(AddressSpace, Offset)) {
	Constant *OffsetVal =
	ConstantInt::get(Type::getInt32Ty(RI->getContext()), Offset);

	StackGuardVar = ConstantExpr::getIntToPtr(OffsetVal,
	PointerType::get(PtrTy, AddressSpace));
	} else {
	StackGuardVar = M->getOrInsertGlobal("__stack_chk_guard", PtrTy);
	}

	BasicBlock &Entry = F->getEntryBlock();
	Instruction *InsPt = &Entry.front();

	AI = new AllocaInst(PtrTy, "StackGuardSlot", InsPt);
	LoadInst *LI = new LoadInst(StackGuardVar, "StackGuard", false, InsPt);

	Value *Args[] = { LI, AI };
	CallInst::
	Create(Intrinsic::getDeclaration(M, Intrinsic::stackprotector),
	Args, "", InsPt);

	// Create the basic block to jump to when the guard check fails.
	FailBB = CreateFailBB();
	}

	// For each block with a return instruction, convert this:
	//
	// return:
	// ...
	// ret ...
	//
	// into this:
	//
	// return:
	// ...
	// %1 = load __stack_chk_guard
	// %2 = load StackGuardSlot
	// %3 = cmp i1 %1, %2
	// br i1 %3, label %SP_return, label %CallStackCheckFailBlk
	//
	// SP_return:
	// ret ...
	//
	// CallStackCheckFailBlk:
	// call void @__stack_chk_fail()
	// unreachable

	// Split the basic block before the return instruction.
	BasicBlock *NewBB = BB->splitBasicBlock(RI, "SP_return");

	if (DT && DT->isReachableFromEntry(BB)) {
	DT->addNewBlock(NewBB, BB);
	FailBBDom = FailBBDom ? DT->findNearestCommonDominator(FailBBDom, BB) :BB;
	}

	// Remove default branch instruction to the new BB.
	BB->getTerminator()->eraseFromParent();

	// Move the newly created basic block to the point right after the old basic
	// block so that it's in the "fall through" position.
	NewBB->moveAfter(BB);

	// Generate the stack protector instructions in the old basic block.
	LoadInst *LI1 = new LoadInst(StackGuardVar, "", false, BB);
	LoadInst *LI2 = new LoadInst(AI, "", true, BB);
	ICmpInst Cmp = new ICmpInst(BB, CmpInst::ICMP_EQ, LI1, LI2, "");
	BranchInst::Create(NewBB, FailBB, Cmp, BB);
	}

	// Return if we didn't modify any basic blocks. I.e., there are no return
	// statements in the function.
	if (!FailBB) return false;

	if (DT && FailBBDom)
	DT->addNewBlock(FailBB, FailBBDom);

	return true;
	}

	/// CreateFailBB - Create a basic block to jump to when the stack protector
	/// check fails.
	BasicBlock *StackProtector::CreateFailBB() {
	BasicBlock *FailBB = BasicBlock::Create(F->getContext(),
	"CallStackCheckFailBlk", F);
	Constant *StackChkFail =
	M->getOrInsertFunction("__stack_chk_fail",
	Type::getVoidTy(F->getContext()), NULL);
	CallInst::Create(StackChkFail, "", FailBB);
	new UnreachableInst(F->getContext(), FailBB);
	return FailBB;
	}