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+//===- StackProtector.cpp - Stack Protector Insertion ---------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// 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.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/CodeGen/StackProtector.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/BranchProbabilityInfo.h"
+#include "llvm/Analysis/EHPersonalities.h"
+#include "llvm/Analysis/OptimizationRemarkEmitter.h"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/CodeGen/TargetLowering.h"
+#include "llvm/CodeGen/TargetPassConfig.h"
+#include "llvm/CodeGen/TargetSubtargetInfo.h"
+#include "llvm/IR/Attributes.h"
+#include "llvm/IR/BasicBlock.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/DebugInfo.h"
+#include "llvm/IR/DebugLoc.h"
+#include "llvm/IR/DerivedTypes.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/Instruction.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/Intrinsics.h"
+#include "llvm/IR/MDBuilder.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/Type.h"
+#include "llvm/IR/User.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/Casting.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Target/TargetMachine.h"
+#include "llvm/Target/TargetOptions.h"
+#include <utility>
+
+using namespace llvm;
+
+#define DEBUG_TYPE "stack-protector"
+
+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);
+
+char StackProtector::ID = 0;
+
+INITIALIZE_PASS_BEGIN(StackProtector, DEBUG_TYPE,
+ "Insert stack protectors", false, true)
+INITIALIZE_PASS_DEPENDENCY(TargetPassConfig)
+INITIALIZE_PASS_END(StackProtector, DEBUG_TYPE,
+ "Insert stack protectors", false, true)
+
+FunctionPass *llvm::createStackProtectorPass() { return new StackProtector(); }
+
+void StackProtector::getAnalysisUsage(AnalysisUsage &AU) const {
+ AU.addRequired<TargetPassConfig>();
+ AU.addPreserved<DominatorTreeWrapperPass>();
+}
+
+bool StackProtector::runOnFunction(Function &Fn) {
+ F = &Fn;
+ M = F->getParent();
+ DominatorTreeWrapperPass *DTWP =
+ getAnalysisIfAvailable<DominatorTreeWrapperPass>();
+ DT = DTWP ? &DTWP->getDomTree() : nullptr;
+ TM = &getAnalysis<TargetPassConfig>().getTM<TargetMachine>();
+ Trip = TM->getTargetTriple();
+ TLI = TM->getSubtargetImpl(Fn)->getTargetLowering();
+ HasPrologue = false;
+ HasIRCheck = false;
+
+ Attribute Attr = Fn.getFnAttribute("stack-protector-buffer-size");
+ if (Attr.isStringAttribute() &&
+ Attr.getValueAsString().getAsInteger(10, SSPBufferSize))
+ return false; // Invalid integer string
+
+ if (!RequiresStackProtector())
+ return false;
+
+ // TODO(etienneb): Functions with funclets are not correctly supported now.
+ // Do nothing if this is funclet-based personality.
+ if (Fn.hasPersonalityFn()) {
+ EHPersonality Personality = classifyEHPersonality(Fn.getPersonalityFn());
+ if (isFuncletEHPersonality(Personality))
+ return false;
+ }
+
+ ++NumFunProtected;
+ return InsertStackProtectors();
+}
+
+/// \param [out] IsLarge is set to true if a protectable array is found and
+/// it is "large" ( >= ssp-buffer-size). In the case of a structure with
+/// multiple arrays, this gets set if any of them is large.
+bool StackProtector::ContainsProtectableArray(Type *Ty, bool &IsLarge,
+ bool Strong,
+ bool InStruct) const {
+ if (!Ty)
+ return false;
+ if (ArrayType *AT = dyn_cast<ArrayType>(Ty)) {
+ 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.
+ // However, in strong mode any array, regardless of type and size,
+ // triggers a protector.
+ if (!Strong && (InStruct || !Trip.isOSDarwin()))
+ return false;
+ }
+
+ // If an array has more than SSPBufferSize bytes of allocated space, then we
+ // emit stack protectors.
+ if (SSPBufferSize <= M->getDataLayout().getTypeAllocSize(AT)) {
+ IsLarge = true;
+ return true;
+ }
+
+ if (Strong)
+ // Require a protector for all arrays in strong mode
+ return true;
+ }
+
+ const StructType *ST = dyn_cast<StructType>(Ty);
+ if (!ST)
+ return false;
+
+ bool NeedsProtector = false;
+ for (StructType::element_iterator I = ST->element_begin(),
+ E = ST->element_end();
+ I != E; ++I)
+ if (ContainsProtectableArray(*I, IsLarge, Strong, true)) {
+ // If the element is a protectable array and is large (>= SSPBufferSize)
+ // then we are done. If the protectable array is not large, then
+ // keep looking in case a subsequent element is a large array.
+ if (IsLarge)
+ return true;
+ NeedsProtector = true;
+ }
+
+ return NeedsProtector;
+}
+
+bool StackProtector::HasAddressTaken(const Instruction *AI) {
+ for (const User *U : AI->users()) {
+ const auto *I = cast<Instruction>(U);
+ switch (I->getOpcode()) {
+ case Instruction::Store:
+ if (AI == cast<StoreInst>(I)->getValueOperand())
+ return true;
+ break;
+ case Instruction::AtomicCmpXchg:
+ // cmpxchg conceptually includes both a load and store from the same
+ // location. So, like store, the value being stored is what matters.
+ if (AI == cast<AtomicCmpXchgInst>(I)->getNewValOperand())
+ return true;
+ break;
+ case Instruction::PtrToInt:
+ if (AI == cast<PtrToIntInst>(I)->getOperand(0))
+ return true;
+ break;
+ case Instruction::Call: {
+ // Ignore intrinsics that do not become real instructions.
+ // TODO: Narrow this to intrinsics that have store-like effects.
+ const auto *CI = cast<CallInst>(I);
+ if (!isa<DbgInfoIntrinsic>(CI) && !CI->isLifetimeStartOrEnd())
+ return true;
+ break;
+ }
+ case Instruction::Invoke:
+ return true;
+ case Instruction::BitCast:
+ case Instruction::GetElementPtr:
+ case Instruction::Select:
+ case Instruction::AddrSpaceCast:
+ if (HasAddressTaken(I))
+ return true;
+ break;
+ case Instruction::PHI: {
+ // Keep track of what PHI nodes we have already visited to ensure
+ // they are only visited once.
+ const auto *PN = cast<PHINode>(I);
+ if (VisitedPHIs.insert(PN).second)
+ if (HasAddressTaken(PN))
+ return true;
+ break;
+ }
+ case Instruction::Load:
+ case Instruction::AtomicRMW:
+ case Instruction::Ret:
+ // These instructions take an address operand, but have load-like or
+ // other innocuous behavior that should not trigger a stack protector.
+ // atomicrmw conceptually has both load and store semantics, but the
+ // value being stored must be integer; so if a pointer is being stored,
+ // we'll catch it in the PtrToInt case above.
+ break;
+ default:
+ // Conservatively return true for any instruction that takes an address
+ // operand, but is not handled above.
+ return true;
+ }
+ }
+ return false;
+}
+
+/// Search for the first call to the llvm.stackprotector intrinsic and return it
+/// if present.
+static const CallInst *findStackProtectorIntrinsic(Function &F) {
+ for (const BasicBlock &BB : F)
+ for (const Instruction &I : BB)
+ if (const CallInst *CI = dyn_cast<CallInst>(&I))
+ if (CI->getCalledFunction() ==
+ Intrinsic::getDeclaration(F.getParent(), Intrinsic::stackprotector))
+ return CI;
+ return nullptr;
+}
+
+/// 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;
+ bool NeedsProtector = false;
+ HasPrologue = findStackProtectorIntrinsic(*F);
+
+ if (F->hasFnAttribute(Attribute::SafeStack))
+ return false;
+
+ // We are constructing the OptimizationRemarkEmitter on the fly rather than
+ // using the analysis pass to avoid building DominatorTree and LoopInfo which
+ // are not available this late in the IR pipeline.
+ OptimizationRemarkEmitter ORE(F);
+
+ if (F->hasFnAttribute(Attribute::StackProtectReq)) {
+ ORE.emit([&]() {
+ return OptimizationRemark(DEBUG_TYPE, "StackProtectorRequested", F)
+ << "Stack protection applied to function "
+ << ore::NV("Function", F)
+ << " due to a function attribute or command-line switch";
+ });
+ NeedsProtector = true;
+ Strong = true; // Use the same heuristic as strong to determine SSPLayout
+ } else if (F->hasFnAttribute(Attribute::StackProtectStrong))
+ Strong = true;
+ else if (HasPrologue)
+ NeedsProtector = true;
+ else if (!F->hasFnAttribute(Attribute::StackProtect))
+ return false;
+
+ for (const BasicBlock &BB : *F) {
+ for (const Instruction &I : BB) {
+ if (const AllocaInst *AI = dyn_cast<AllocaInst>(&I)) {
+ if (AI->isArrayAllocation()) {
+ auto RemarkBuilder = [&]() {
+ return OptimizationRemark(DEBUG_TYPE, "StackProtectorAllocaOrArray",
+ &I)
+ << "Stack protection applied to function "
+ << ore::NV("Function", F)
+ << " due to a call to alloca or use of a variable length "
+ "array";
+ };
+ if (const auto *CI = dyn_cast<ConstantInt>(AI->getArraySize())) {
+ if (CI->getLimitedValue(SSPBufferSize) >= SSPBufferSize) {
+ // A call to alloca with size >= SSPBufferSize requires
+ // stack protectors.
+ Layout.insert(std::make_pair(AI,
+ MachineFrameInfo::SSPLK_LargeArray));
+ ORE.emit(RemarkBuilder);
+ NeedsProtector = true;
+ } else if (Strong) {
+ // Require protectors for all alloca calls in strong mode.
+ Layout.insert(std::make_pair(AI,
+ MachineFrameInfo::SSPLK_SmallArray));
+ ORE.emit(RemarkBuilder);
+ NeedsProtector = true;
+ }
+ } else {
+ // A call to alloca with a variable size requires protectors.
+ Layout.insert(std::make_pair(AI,
+ MachineFrameInfo::SSPLK_LargeArray));
+ ORE.emit(RemarkBuilder);
+ NeedsProtector = true;
+ }
+ continue;
+ }
+
+ bool IsLarge = false;
+ if (ContainsProtectableArray(AI->getAllocatedType(), IsLarge, Strong)) {
+ Layout.insert(std::make_pair(AI, IsLarge
+ ? MachineFrameInfo::SSPLK_LargeArray
+ : MachineFrameInfo::SSPLK_SmallArray));
+ ORE.emit([&]() {
+ return OptimizationRemark(DEBUG_TYPE, "StackProtectorBuffer", &I)
+ << "Stack protection applied to function "
+ << ore::NV("Function", F)
+ << " due to a stack allocated buffer or struct containing a "
+ "buffer";
+ });
+ NeedsProtector = true;
+ continue;
+ }
+
+ if (Strong && HasAddressTaken(AI)) {
+ ++NumAddrTaken;
+ Layout.insert(std::make_pair(AI, MachineFrameInfo::SSPLK_AddrOf));
+ ORE.emit([&]() {
+ return OptimizationRemark(DEBUG_TYPE, "StackProtectorAddressTaken",
+ &I)
+ << "Stack protection applied to function "
+ << ore::NV("Function", F)
+ << " due to the address of a local variable being taken";
+ });
+ NeedsProtector = true;
+ }
+ }
+ }
+ }
+
+ return NeedsProtector;
+}
+
+/// Create a stack guard loading and populate whether SelectionDAG SSP is
+/// supported.
+static Value *getStackGuard(const TargetLoweringBase *TLI, Module *M,
+ IRBuilder<> &B,
+ bool *SupportsSelectionDAGSP = nullptr) {
+ if (Value *Guard = TLI->getIRStackGuard(B))
+ return B.CreateLoad(B.getInt8PtrTy(), Guard, true, "StackGuard");
+
+ // Use SelectionDAG SSP handling, since there isn't an IR guard.
+ //
+ // This is more or less weird, since we optionally output whether we
+ // should perform a SelectionDAG SP here. The reason is that it's strictly
+ // defined as !TLI->getIRStackGuard(B), where getIRStackGuard is also
+ // mutating. There is no way to get this bit without mutating the IR, so
+ // getting this bit has to happen in this right time.
+ //
+ // We could have define a new function TLI::supportsSelectionDAGSP(), but that
+ // will put more burden on the backends' overriding work, especially when it
+ // actually conveys the same information getIRStackGuard() already gives.
+ if (SupportsSelectionDAGSP)
+ *SupportsSelectionDAGSP = true;
+ TLI->insertSSPDeclarations(*M);
+ return B.CreateCall(Intrinsic::getDeclaration(M, Intrinsic::stackguard));
+}
+
+/// Insert code into the entry block that stores the stack guard
+/// variable onto the stack:
+///
+/// entry:
+/// StackGuardSlot = alloca i8*
+/// StackGuard = <stack guard>
+/// call void @llvm.stackprotector(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, AllocaInst *&AI) {
+ bool SupportsSelectionDAGSP = false;
+ IRBuilder<> B(&F->getEntryBlock().front());
+ PointerType *PtrTy = Type::getInt8PtrTy(RI->getContext());
+ AI = B.CreateAlloca(PtrTy, nullptr, "StackGuardSlot");
+
+ Value *GuardSlot = getStackGuard(TLI, M, B, &SupportsSelectionDAGSP);
+ B.CreateCall(Intrinsic::getDeclaration(M, Intrinsic::stackprotector),
+ {GuardSlot, AI});
+ return SupportsSelectionDAGSP;
+}
+
+/// 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() {
+ // If the target wants to XOR the frame pointer into the guard value, it's
+ // impossible to emit the check in IR, so the target *must* support stack
+ // protection in SDAG.
+ bool SupportsSelectionDAGSP =
+ TLI->useStackGuardXorFP() ||
+ (EnableSelectionDAGSP && !TM->Options.EnableFastISel &&
+ !TM->Options.EnableGlobalISel);
+ AllocaInst *AI = nullptr; // Place on stack that stores the stack guard.
+
+ for (Function::iterator I = F->begin(), E = F->end(); I != E;) {
+ BasicBlock *BB = &*I++;
+ ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator());
+ if (!RI)
+ continue;
+
+ // Generate prologue instrumentation if not already generated.
+ if (!HasPrologue) {
+ HasPrologue = true;
+ SupportsSelectionDAGSP &= CreatePrologue(F, M, RI, TLI, AI);
+ }
+
+ // SelectionDAG based code generation. Nothing else needs to be done here.
+ // The epilogue instrumentation is postponed to SelectionDAG.
+ if (SupportsSelectionDAGSP)
+ break;
+
+ // Find the stack guard slot if the prologue was not created by this pass
+ // itself via a previous call to CreatePrologue().
+ if (!AI) {
+ const CallInst *SPCall = findStackProtectorIntrinsic(*F);
+ assert(SPCall && "Call to llvm.stackprotector is missing");
+ AI = cast<AllocaInst>(SPCall->getArgOperand(1));
+ }
+
+ // Set HasIRCheck to true, so that SelectionDAG will not generate its own
+ // version. SelectionDAG called 'shouldEmitSDCheck' to check whether
+ // instrumentation has already been generated.
+ HasIRCheck = true;
+
+ // Generate epilogue instrumentation. The epilogue intrumentation can be
+ // function-based or inlined depending on which mechanism the target is
+ // providing.
+ if (Function *GuardCheck = TLI->getSSPStackGuardCheck(*M)) {
+ // Generate the function-based epilogue instrumentation.
+ // The target provides a guard check function, generate a call to it.
+ IRBuilder<> B(RI);
+ LoadInst *Guard = B.CreateLoad(B.getInt8PtrTy(), AI, true, "Guard");
+ CallInst *Call = B.CreateCall(GuardCheck, {Guard});
+ Call->setAttributes(GuardCheck->getAttributes());
+ Call->setCallingConv(GuardCheck->getCallingConv());
+ } else {
+ // Generate the epilogue with inline instrumentation.
+ // 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 = <stack 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->getIterator(), "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();
+
+ // 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.
+ IRBuilder<> B(BB);
+ Value *Guard = getStackGuard(TLI, M, B);
+ LoadInst *LI2 = B.CreateLoad(B.getInt8PtrTy(), AI, true);
+ Value *Cmp = B.CreateICmpEQ(Guard, LI2);
+ auto SuccessProb =
+ BranchProbabilityInfo::getBranchProbStackProtector(true);
+ auto FailureProb =
+ BranchProbabilityInfo::getBranchProbStackProtector(false);
+ MDNode *Weights = MDBuilder(F->getContext())
+ .createBranchWeights(SuccessProb.getNumerator(),
+ FailureProb.getNumerator());
+ B.CreateCondBr(Cmp, NewBB, FailBB, Weights);
+ }
+ }
+
+ // Return if we didn't modify any basic blocks. i.e., there are no return
+ // statements in the function.
+ return HasPrologue;
+}
+
+/// 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);
+ IRBuilder<> B(FailBB);
+ B.SetCurrentDebugLocation(DebugLoc::get(0, 0, F->getSubprogram()));
+ if (Trip.isOSOpenBSD()) {
+ FunctionCallee StackChkFail = M->getOrInsertFunction(
+ "__stack_smash_handler", Type::getVoidTy(Context),
+ Type::getInt8PtrTy(Context));
+
+ B.CreateCall(StackChkFail, B.CreateGlobalStringPtr(F->getName(), "SSH"));
+ } else {
+ FunctionCallee StackChkFail =
+ M->getOrInsertFunction("__stack_chk_fail", Type::getVoidTy(Context));
+
+ B.CreateCall(StackChkFail, {});
+ }
+ B.CreateUnreachable();
+ return FailBB;
+}
+
+bool StackProtector::shouldEmitSDCheck(const BasicBlock &BB) const {
+ return HasPrologue && !HasIRCheck && isa<ReturnInst>(BB.getTerminator());
+}
+
+void StackProtector::copyToMachineFrameInfo(MachineFrameInfo &MFI) const {
+ if (Layout.empty())
+ return;
+
+ for (int I = 0, E = MFI.getObjectIndexEnd(); I != E; ++I) {
+ if (MFI.isDeadObjectIndex(I))
+ continue;
+
+ const AllocaInst *AI = MFI.getObjectAllocation(I);
+ if (!AI)
+ continue;
+
+ SSPLayoutMap::const_iterator LI = Layout.find(AI);
+ if (LI == Layout.end())
+ continue;
+
+ MFI.setObjectSSPLayout(I, LI->second);
+ }
+}
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