//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "stack-protector"
+#include "llvm/CodeGen/Analysis.h"
#include "llvm/CodeGen/Passes.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/ADT/SmallPtrSet.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/ADT/Triple.h"
+#include "llvm/Analysis/Dominators.h"
+#include "llvm/Analysis/ValueTracking.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/IntrinsicInst.h"
+#include "llvm/IR/Intrinsics.h"
+#include "llvm/IR/Module.h"
#include "llvm/Pass.h"
#include "llvm/Support/CommandLine.h"
-#include "llvm/Target/TargetData.h"
#include "llvm/Target/TargetLowering.h"
+#include <cstdlib>
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"));
+STATISTIC(NumFunProtected, "Number of functions protected");
+STATISTIC(NumAddrTaken, "Number of local variables that have their address"
+ " taken.");
+
+static cl::opt<bool>
+EnableSelectionDAGSP("enable-selectiondag-sp", cl::init(true),
+ cl::Hidden);
namespace {
class StackProtector : public FunctionPass {
+ const TargetMachine *TM;
+
/// TLI - Keep a pointer of a TargetLowering to consult for determining
/// target type sizes.
- const TargetLowering *TLI;
+ 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.
///
/// 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() const;
+ bool RequiresStackProtector();
public:
static char ID; // Pass identification, replacement for typeid.
- StackProtector() : FunctionPass(&ID), TLI(0) {}
- StackProtector(const TargetLowering *tli)
- : FunctionPass(&ID), TLI(tli) {}
+ 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);
};
char StackProtector::ID = 0;
INITIALIZE_PASS(StackProtector, "stack-protector",
- "Insert stack protectors", false, false);
+ "Insert stack protectors", false, false)
-FunctionPass *llvm::createStackProtectorPass(const TargetLowering *tli) {
- return new StackProtector(tli);
+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();
}
-/// 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;
+/// 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 (!F->hasFnAttr(Attribute::StackProtect))
- 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 TargetData *TD = TLI->getTargetData();
+ 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)
+ 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 (const ArrayType *AT = dyn_cast<ArrayType>(AI->getAllocatedType())) {
- // We apparently only care about character arrays.
- if (!AT->getElementType()->isIntegerTy(8))
- continue;
+ if (AI->isArrayAllocation()) {
+ // SSP-Strong: Enable protectors for any call to alloca, regardless
+ // of size.
+ if (Strong)
+ return true;
- // If an array has more than SSPBufferSize bytes of allocated space,
- // then we emit stack protectors.
- if (SSPBufferSize <= TD->getTypeAllocSize(AT))
+ 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;
}
+static bool InstructionWillNotHaveChain(const Instruction *I) {
+ return !I->mayHaveSideEffects() && !I->mayReadFromMemory() &&
+ isSafeToSpeculativelyExecute(I);
+}
+
+/// Identify if RI has a previous instruction in the "Tail Position" and return
+/// it. Otherwise return 0.
+///
+/// This is based off of the code in llvm::isInTailCallPosition
+static CallInst *FindPotentialTailCall(BasicBlock *BB, ReturnInst *RI,
+ const TargetLoweringBase *TLI) {
+ // Establish a reasonable upper bound on the maximum amount of instructions we
+ // will look through to find a tail call.
+ unsigned SearchCounter = 0;
+ const unsigned MaxSearch = 4;
+ bool NoInterposingChain = true;
+
+ for (BasicBlock::reverse_iterator I = llvm::next(BB->rbegin()), E = BB->rend();
+ I != E && SearchCounter < MaxSearch; ++I) {
+ Instruction *Inst = &*I;
+
+ // Skip over debug intrinsics and do not allow them to affect our MaxSearch
+ // counter.
+ if (isa<DbgInfoIntrinsic>(Inst))
+ continue;
+
+ // If we find a call and the following conditions are satisifed, then we
+ // have found a tail call that satisfies at least the target independent
+ // requirements of a tail call:
+ //
+ // 1. The call site has the tail marker.
+ //
+ // 2. The call site either will not cause the creation of a chain or if a
+ // chain is necessary there are no instructions in between the callsite and
+ // the call which would create an interposing chain.
+ //
+ // 3. The return type of the function does not impede tail call
+ // optimization.
+ if (CallInst *CI = dyn_cast<CallInst>(Inst)) {
+ if (CI->isTailCall() &&
+ (InstructionWillNotHaveChain(CI) || NoInterposingChain) &&
+ returnTypeIsEligibleForTailCall(BB->getParent(), CI, RI, *TLI))
+ return CI;
+ }
+
+ // If we did not find a call see if we have an instruction that may create
+ // an interposing chain.
+ NoInterposingChain = NoInterposingChain && InstructionWillNotHaveChain(Inst);
+
+ // Increment max search.
+ SearchCounter++;
+ }
+
+ return 0;
+}
+
+/// 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)
+///
+/// Returns true if the platform/triple supports the stackprotectorcreate pseudo
+/// node.
+static bool CreatePrologue(Function *F, Module *M, ReturnInst *RI,
+ const TargetLoweringBase *TLI, const Triple &Trip,
+ AllocaInst *&AI, Value *&StackGuardVar) {
+ bool SupportsSelectionDAGSP = false;
+ 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 {
+ SupportsSelectionDAGSP = true;
+ 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);
+
+ return SupportsSelectionDAGSP;
+}
+
/// InsertStackProtectors - Insert code into the prologue and epilogue of the
/// function.
///
/// - 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.
+ bool HasPrologue = false;
+ bool SupportsSelectionDAGSP = false;
AllocaInst *AI = 0; // Place on stack that stores the stack guard.
- Value *StackGuardVar = 0; // The stack guard variable.
+ 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)
- //
- const 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));
+ if (!HasPrologue) {
+ HasPrologue = true;
+ SupportsSelectionDAGSP = CreatePrologue(F, M, RI, TLI, Trip, AI,
+ StackGuardVar);
+ }
+
+ if (EnableSelectionDAGSP && !TM->Options.EnableFastISel &&
+ SupportsSelectionDAGSP) {
+ // Since we have a potential tail call, insert the special stack check
+ // intrinsic.
+ Instruction *InsertionPt = 0;
+ if (CallInst *CI = FindPotentialTailCall(BB, RI, TLI)) {
+ InsertionPt = CI;
} else {
- StackGuardVar = M->getOrInsertGlobal("__stack_chk_guard", PtrTy);
+ InsertionPt = RI;
+ // At this point we know that BB has a return statement so it *DOES*
+ // have a terminator.
+ assert(InsertionPt != 0 && "BB must have a terminator instruction at "
+ "this point.");
}
- 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[0], array_endof(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
+ Function *Intrinsic =
+ Intrinsic::getDeclaration(M, Intrinsic::stackprotectorcheck);
+ Value *Args[] = { StackGuardVar };
+ CallInst::Create(Intrinsic, Args, "", InsertionPt);
- // Split the basic block before the return instruction.
- BasicBlock *NewBB = BB->splitBasicBlock(RI, "SP_return");
+ } else {
+ // If we do not support SelectionDAG based tail calls, generate IR level
+ // tail calls.
+ //
+ // 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
+
+ // Create the FailBB. We duplicate the BB every time since the MI tail
+ // merge pass will merge together all of the various BB into one including
+ // fail BB generated by the stack protector pseudo instruction.
+ BasicBlock *FailBB = CreateFailBB();
+
+ // Split the basic block before the return instruction.
+ BasicBlock *NewBB = BB->splitBasicBlock(RI, "SP_return");
+
+ // Update the dominator tree if we need to.
+ if (DT && DT->isReachableFromEntry(BB)) {
+ DT->addNewBlock(NewBB, BB);
+ DT->addNewBlock(FailBB, BB);
+ }
- // Remove default branch instruction to the new BB.
- BB->getTerminator()->eraseFromParent();
+ // 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);
+ // 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);
+ // 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 (!HasPrologue)
+ return false;
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);
+ 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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