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Diffstat (limited to 'contrib/llvm/lib/CodeGen/StackProtector.cpp')
| -rw-r--r-- | contrib/llvm/lib/CodeGen/StackProtector.cpp | 495 |
1 files changed, 495 insertions, 0 deletions
diff --git a/contrib/llvm/lib/CodeGen/StackProtector.cpp b/contrib/llvm/lib/CodeGen/StackProtector.cpp new file mode 100644 index 0000000..0824d6f --- /dev/null +++ b/contrib/llvm/lib/CodeGen/StackProtector.cpp @@ -0,0 +1,495 @@ +//===-- 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. +// +//===----------------------------------------------------------------------===// + +#include "llvm/CodeGen/StackProtector.h" +#include "llvm/ADT/SmallPtrSet.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/Analysis/BranchProbabilityInfo.h" +#include "llvm/Analysis/ValueTracking.h" +#include "llvm/CodeGen/Analysis.h" +#include "llvm/CodeGen/Passes.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/IRBuilder.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/Support/CommandLine.h" +#include "llvm/Target/TargetSubtargetInfo.h" +#include <cstdlib> +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(StackProtector, "stack-protector", "Insert stack protectors", + false, true) + +FunctionPass *llvm::createStackProtectorPass(const TargetMachine *TM) { + return new StackProtector(TM); +} + +StackProtector::SSPLayoutKind +StackProtector::getSSPLayout(const AllocaInst *AI) const { + return AI ? Layout.lookup(AI) : SSPLK_None; +} + +void StackProtector::adjustForColoring(const AllocaInst *From, + const AllocaInst *To) { + // When coloring replaces one alloca with another, transfer the SSPLayoutKind + // tag from the remapped to the target alloca. The remapped alloca should + // have a size smaller than or equal to the replacement alloca. + SSPLayoutMap::iterator I = Layout.find(From); + if (I != Layout.end()) { + SSPLayoutKind Kind = I->second; + Layout.erase(I); + + // Transfer the tag, but make sure that SSPLK_AddrOf does not overwrite + // SSPLK_SmallArray or SSPLK_LargeArray, and make sure that + // SSPLK_SmallArray does not overwrite SSPLK_LargeArray. + I = Layout.find(To); + if (I == Layout.end()) + Layout.insert(std::make_pair(To, Kind)); + else if (I->second != SSPLK_LargeArray && Kind != SSPLK_AddrOf) + I->second = Kind; + } +} + +bool StackProtector::runOnFunction(Function &Fn) { + F = &Fn; + M = F->getParent(); + DominatorTreeWrapperPass *DTWP = + getAnalysisIfAvailable<DominatorTreeWrapperPass>(); + DT = DTWP ? &DTWP->getDomTree() : nullptr; + TLI = TM->getSubtargetImpl(Fn)->getTargetLowering(); + + 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; + + ++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 <= TLI->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()) { + 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).second) + 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; + bool NeedsProtector = false; + if (F->hasFnAttribute(Attribute::StackProtectReq)) { + NeedsProtector = true; + Strong = true; // Use the same heuristic as strong to determine SSPLayout + } else if (F->hasFnAttribute(Attribute::StackProtectStrong)) + Strong = 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()) { + // SSP-Strong: Enable protectors for any call to alloca, regardless + // of size. + if (Strong) + return true; + + 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, SSPLK_LargeArray)); + NeedsProtector = true; + } else if (Strong) { + // Require protectors for all alloca calls in strong mode. + Layout.insert(std::make_pair(AI, SSPLK_SmallArray)); + NeedsProtector = true; + } + } else { + // A call to alloca with a variable size requires protectors. + Layout.insert(std::make_pair(AI, SSPLK_LargeArray)); + NeedsProtector = true; + } + continue; + } + + bool IsLarge = false; + if (ContainsProtectableArray(AI->getAllocatedType(), IsLarge, Strong)) { + Layout.insert(std::make_pair(AI, IsLarge ? SSPLK_LargeArray + : SSPLK_SmallArray)); + NeedsProtector = true; + continue; + } + + if (Strong && HasAddressTaken(AI)) { + ++NumAddrTaken; + Layout.insert(std::make_pair(AI, SSPLK_AddrOf)); + NeedsProtector = true; + } + } + } + } + + return NeedsProtector; +} + +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. The difference +/// is that it inverts the first part of llvm::isInTailCallPosition since +/// isInTailCallPosition is checking if a call is in a tail call position, and +/// we are searching for an unknown tail call that might be in the tail call +/// position. Once we find the call though, the code uses the same refactored +/// code, returnTypeIsEligibleForTailCall. +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 = std::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 nullptr; +} + +/// 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 &TT, + 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 (TT.isOSOpenBSD()) { + StackGuardVar = M->getOrInsertGlobal("__guard_local", PtrTy); + cast<GlobalValue>(StackGuardVar) + ->setVisibility(GlobalValue::HiddenVisibility); + } else { + SupportsSelectionDAGSP = true; + StackGuardVar = M->getOrInsertGlobal("__stack_chk_guard", PtrTy); + } + + IRBuilder<> B(&F->getEntryBlock().front()); + AI = B.CreateAlloca(PtrTy, nullptr, "StackGuardSlot"); + LoadInst *LI = B.CreateLoad(StackGuardVar, "StackGuard"); + B.CreateCall(Intrinsic::getDeclaration(M, Intrinsic::stackprotector), + {LI, 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() { + bool HasPrologue = false; + bool SupportsSelectionDAGSP = + EnableSelectionDAGSP && !TM->Options.EnableFastISel; + AllocaInst *AI = nullptr; // Place on stack that stores the stack guard. + Value *StackGuardVar = nullptr; // 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 (!HasPrologue) { + HasPrologue = true; + SupportsSelectionDAGSP &= + CreatePrologue(F, M, RI, TLI, Trip, AI, StackGuardVar); + } + + if (SupportsSelectionDAGSP) { + // Since we have a potential tail call, insert the special stack check + // intrinsic. + Instruction *InsertionPt = nullptr; + if (CallInst *CI = FindPotentialTailCall(BB, RI, TLI)) { + InsertionPt = CI; + } else { + InsertionPt = RI; + // At this point we know that BB has a return statement so it *DOES* + // have a terminator. + assert(InsertionPt != nullptr && + "BB must have a terminator instruction at this point."); + } + + Function *Intrinsic = + Intrinsic::getDeclaration(M, Intrinsic::stackprotectorcheck); + CallInst::Create(Intrinsic, StackGuardVar, "", InsertionPt); + } 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(); + + // 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); + LoadInst *LI1 = B.CreateLoad(StackGuardVar); + LoadInst *LI2 = B.CreateLoad(AI); + Value *Cmp = B.CreateICmpEQ(LI1, LI2); + unsigned SuccessWeight = + BranchProbabilityInfo::getBranchWeightStackProtector(true); + unsigned FailureWeight = + BranchProbabilityInfo::getBranchWeightStackProtector(false); + MDNode *Weights = MDBuilder(F->getContext()) + .createBranchWeights(SuccessWeight, FailureWeight); + 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. + if (!HasPrologue) + return false; + + 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); + IRBuilder<> B(FailBB); + if (Trip.isOSOpenBSD()) { + Constant *StackChkFail = + M->getOrInsertFunction("__stack_smash_handler", + Type::getVoidTy(Context), + Type::getInt8PtrTy(Context), nullptr); + + B.CreateCall(StackChkFail, B.CreateGlobalStringPtr(F->getName(), "SSH")); + } else { + Constant *StackChkFail = + M->getOrInsertFunction("__stack_chk_fail", Type::getVoidTy(Context), + nullptr); + B.CreateCall(StackChkFail, {}); + } + B.CreateUnreachable(); + return FailBB; +} |
