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llvm-project/llvm/lib/CodeGen/StackProtector.cpp

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//===-- 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/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/Triple.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/IR/Attributes.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/GlobalValue.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/Module.h"
#include "llvm/Pass.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Target/TargetLowering.h"
#include <cstdlib>
using namespace llvm;
STATISTIC(NumFunProtected, "Number of functions protected");
STATISTIC(NumAddrTaken, "Number of local variables that have their address"
" taken.");
namespace {
class StackProtector : public FunctionPass {
const TargetMachine *TM;
/// TLI - Keep a pointer of a TargetLowering to consult for determining
/// target type sizes.
const TargetLoweringBase *TLI;
const Triple Trip;
Function *F;
Module *M;
DominatorTree *DT;
/// \brief The minimum size of buffers that will receive stack smashing
/// protection when -fstack-protection is used.
unsigned SSPBufferSize;
/// VisitedPHIs - The set of PHI nodes visited when determining
/// if a variable's reference has been taken. This set
/// is maintained to ensure we don't visit the same PHI node multiple
/// times.
SmallPtrSet<const PHINode*, 16> VisitedPHIs;
/// 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();
/// ContainsProtectableArray - Check whether the type either is an array or
/// contains an array of sufficient size so that we need stack protectors
/// for it.
bool ContainsProtectableArray(Type *Ty, bool Strong = false,
bool InStruct = false) const;
/// \brief Check whether a stack allocation has its address taken.
bool HasAddressTaken(const Instruction *AI);
/// RequiresStackProtector - Check whether or not this function needs a
/// stack protector based upon the stack protector level.
bool RequiresStackProtector();
public:
static char ID; // Pass identification, replacement for typeid.
StackProtector() : FunctionPass(ID), TM(0), TLI(0), SSPBufferSize(0) {
initializeStackProtectorPass(*PassRegistry::getPassRegistry());
}
StackProtector(const TargetMachine *TM)
: FunctionPass(ID), TM(TM), TLI(0), Trip(TM->getTargetTriple()),
SSPBufferSize(8) {
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 TargetMachine *TM) {
return new StackProtector(TM);
}
bool StackProtector::runOnFunction(Function &Fn) {
F = &Fn;
M = F->getParent();
DT = getAnalysisIfAvailable<DominatorTree>();
TLI = TM->getTargetLowering();
if (!RequiresStackProtector()) return false;
Attribute Attr =
Fn.getAttributes().getAttribute(AttributeSet::FunctionIndex,
"stack-protector-buffer-size");
if (Attr.isStringAttribute())
SSPBufferSize = atoi(Attr.getValueAsString().data());
++NumFunProtected;
return InsertStackProtectors();
}
/// ContainsProtectableArray - Check whether the type either is an array or
/// contains a char array of sufficient size so that we need stack protectors
/// for it.
bool StackProtector::ContainsProtectableArray(Type *Ty, bool Strong,
bool InStruct) const {
if (!Ty) return false;
if (ArrayType *AT = dyn_cast<ArrayType>(Ty)) {
// In strong mode any array, regardless of type and size, triggers a
// protector
if (Strong)
return true;
if (!AT->getElementType()->isIntegerTy(8)) {
// If we're on a non-Darwin platform or we're inside of a structure, don't
// add stack protectors unless the array is a character array.
if (InStruct || !Trip.isOSDarwin())
return false;
}
// If an array has more than SSPBufferSize bytes of allocated space, then we
// emit stack protectors.
if (SSPBufferSize <= TLI->getDataLayout()->getTypeAllocSize(AT))
return true;
}
const StructType *ST = dyn_cast<StructType>(Ty);
if (!ST) return false;
for (StructType::element_iterator I = ST->element_begin(),
E = ST->element_end(); I != E; ++I)
if (ContainsProtectableArray(*I, Strong, true))
return true;
return false;
}
bool StackProtector::HasAddressTaken(const Instruction *AI) {
for (Value::const_use_iterator UI = AI->use_begin(), UE = AI->use_end();
UI != UE; ++UI) {
const User *U = *UI;
if (const StoreInst *SI = dyn_cast<StoreInst>(U)) {
if (AI == SI->getValueOperand())
return true;
} else if (const PtrToIntInst *SI = dyn_cast<PtrToIntInst>(U)) {
if (AI == SI->getOperand(0))
return true;
} else if (isa<CallInst>(U)) {
return true;
} else if (isa<InvokeInst>(U)) {
return true;
} else if (const SelectInst *SI = dyn_cast<SelectInst>(U)) {
if (HasAddressTaken(SI))
return true;
} else if (const PHINode *PN = dyn_cast<PHINode>(U)) {
// Keep track of what PHI nodes we have already visited to ensure
// they are only visited once.
if (VisitedPHIs.insert(PN))
if (HasAddressTaken(PN))
return true;
} else if (const GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) {
if (HasAddressTaken(GEP))
return true;
} else if (const BitCastInst *BI = dyn_cast<BitCastInst>(U)) {
if (HasAddressTaken(BI))
return true;
}
}
return false;
}
/// \brief Check whether or not this function needs a stack protector based
/// upon the stack protector level.
///
/// We use two heuristics: a standard (ssp) and strong (sspstrong).
/// The standard heuristic which will add a guard variable to functions that
/// call alloca with a either a variable size or a size >= SSPBufferSize,
/// functions with character buffers larger than SSPBufferSize, and functions
/// with aggregates containing character buffers larger than SSPBufferSize. The
/// strong heuristic will add a guard variables to functions that call alloca
/// regardless of size, functions with any buffer regardless of type and size,
/// functions with aggregates that contain any buffer regardless of type and
/// size, and functions that contain stack-based variables that have had their
/// address taken.
bool StackProtector::RequiresStackProtector() {
bool Strong = false;
if (F->getAttributes().hasAttribute(AttributeSet::FunctionIndex,
Attribute::StackProtectReq))
return true;
else if (F->getAttributes().hasAttribute(AttributeSet::FunctionIndex,
Attribute::StackProtectStrong))
Strong = true;
else if (!F->getAttributes().hasAttribute(AttributeSet::FunctionIndex,
Attribute::StackProtect))
return false;
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()) {
// SSP-Strong: Enable protectors for any call to alloca, regardless
// of size.
if (Strong)
return true;
if (const ConstantInt *CI =
dyn_cast<ConstantInt>(AI->getArraySize())) {
if (CI->getLimitedValue(SSPBufferSize) >= SSPBufferSize)
// A call to alloca with size >= SSPBufferSize requires
// stack protectors.
return true;
} else {
// A call to alloca with a variable size requires protectors.
return true;
}
}
if (ContainsProtectableArray(AI->getAllocatedType(), Strong))
return true;
if (Strong && HasAddressTaken(AI)) {
++NumAddrTaken;
return true;
}
}
}
}
return false;
}
/// 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)
///
static void CreatePrologue(Function *F, Module *M, ReturnInst *RI,
const TargetLoweringBase *TLI, const Triple &Trip,
AllocaInst *&AI, Value *&StackGuardVar) {
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 if (Trip.getOS() == llvm::Triple::OpenBSD) {
StackGuardVar = M->getOrInsertGlobal("__guard_local", PtrTy);
cast<GlobalValue>(StackGuardVar)
->setVisibility(GlobalValue::HiddenVisibility);
} 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);
}
/// 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) {
CreatePrologue(F, M, RI, TLI, Trip, AI, StackGuardVar);
// 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() {
LLVMContext &Context = F->getContext();
BasicBlock *FailBB = BasicBlock::Create(Context, "CallStackCheckFailBlk", F);
if (Trip.getOS() == llvm::Triple::OpenBSD) {
Constant *StackChkFail = M->getOrInsertFunction(
"__stack_smash_handler", Type::getVoidTy(Context),
Type::getInt8PtrTy(Context), NULL);
Constant *NameStr = ConstantDataArray::getString(Context, F->getName());
Constant *FuncName =
new GlobalVariable(*M, NameStr->getType(), true,
GlobalVariable::PrivateLinkage, NameStr, "SSH");
SmallVector<Constant *, 2> IdxList;
IdxList.push_back(ConstantInt::get(Type::getInt8Ty(Context), 0));
IdxList.push_back(ConstantInt::get(Type::getInt8Ty(Context), 0));
SmallVector<Value *, 1> Args;
Args.push_back(ConstantExpr::getGetElementPtr(FuncName, IdxList));
CallInst::Create(StackChkFail, Args, "", FailBB);
} else {
Constant *StackChkFail = M->getOrInsertFunction(
"__stack_chk_fail", Type::getVoidTy(Context), NULL);
CallInst::Create(StackChkFail, "", FailBB);
}
new UnreachableInst(Context, FailBB);
return FailBB;
}
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