forked from OSchip/llvm-project
617 lines
24 KiB
C++
617 lines
24 KiB
C++
//===- StackProtector.cpp - Stack Protector Insertion ---------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This pass inserts stack protectors into functions which need them. A variable
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// with a random value in it is stored onto the stack before the local variables
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// are allocated. Upon exiting the block, the stored value is checked. If it's
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// changed, then there was some sort of violation and the program aborts.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/CodeGen/StackProtector.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Analysis/BranchProbabilityInfo.h"
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#include "llvm/Analysis/EHPersonalities.h"
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#include "llvm/Analysis/MemoryLocation.h"
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#include "llvm/Analysis/OptimizationRemarkEmitter.h"
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#include "llvm/CodeGen/Passes.h"
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#include "llvm/CodeGen/TargetLowering.h"
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#include "llvm/CodeGen/TargetPassConfig.h"
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#include "llvm/CodeGen/TargetSubtargetInfo.h"
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#include "llvm/IR/Attributes.h"
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#include "llvm/IR/BasicBlock.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/DataLayout.h"
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#include "llvm/IR/DebugInfo.h"
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#include "llvm/IR/DebugLoc.h"
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#include "llvm/IR/DerivedTypes.h"
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#include "llvm/IR/Dominators.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/IRBuilder.h"
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#include "llvm/IR/Instruction.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/IntrinsicInst.h"
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#include "llvm/IR/Intrinsics.h"
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#include "llvm/IR/MDBuilder.h"
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#include "llvm/IR/Module.h"
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#include "llvm/IR/Type.h"
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#include "llvm/IR/User.h"
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#include "llvm/InitializePasses.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/Casting.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Target/TargetMachine.h"
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#include "llvm/Target/TargetOptions.h"
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#include <utility>
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using namespace llvm;
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#define DEBUG_TYPE "stack-protector"
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STATISTIC(NumFunProtected, "Number of functions protected");
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STATISTIC(NumAddrTaken, "Number of local variables that have their address"
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" taken.");
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static cl::opt<bool> EnableSelectionDAGSP("enable-selectiondag-sp",
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cl::init(true), cl::Hidden);
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char StackProtector::ID = 0;
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StackProtector::StackProtector() : FunctionPass(ID), SSPBufferSize(8) {
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initializeStackProtectorPass(*PassRegistry::getPassRegistry());
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}
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INITIALIZE_PASS_BEGIN(StackProtector, DEBUG_TYPE,
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"Insert stack protectors", false, true)
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INITIALIZE_PASS_DEPENDENCY(TargetPassConfig)
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INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
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INITIALIZE_PASS_END(StackProtector, DEBUG_TYPE,
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"Insert stack protectors", false, true)
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FunctionPass *llvm::createStackProtectorPass() { return new StackProtector(); }
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void StackProtector::getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequired<TargetPassConfig>();
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AU.addPreserved<DominatorTreeWrapperPass>();
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}
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bool StackProtector::runOnFunction(Function &Fn) {
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F = &Fn;
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M = F->getParent();
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DominatorTreeWrapperPass *DTWP =
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getAnalysisIfAvailable<DominatorTreeWrapperPass>();
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DT = DTWP ? &DTWP->getDomTree() : nullptr;
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TM = &getAnalysis<TargetPassConfig>().getTM<TargetMachine>();
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Trip = TM->getTargetTriple();
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TLI = TM->getSubtargetImpl(Fn)->getTargetLowering();
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HasPrologue = false;
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HasIRCheck = false;
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Attribute Attr = Fn.getFnAttribute("stack-protector-buffer-size");
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if (Attr.isStringAttribute() &&
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Attr.getValueAsString().getAsInteger(10, SSPBufferSize))
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return false; // Invalid integer string
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if (!RequiresStackProtector())
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return false;
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// TODO(etienneb): Functions with funclets are not correctly supported now.
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// Do nothing if this is funclet-based personality.
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if (Fn.hasPersonalityFn()) {
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EHPersonality Personality = classifyEHPersonality(Fn.getPersonalityFn());
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if (isFuncletEHPersonality(Personality))
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return false;
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}
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++NumFunProtected;
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return InsertStackProtectors();
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}
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/// \param [out] IsLarge is set to true if a protectable array is found and
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/// it is "large" ( >= ssp-buffer-size). In the case of a structure with
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/// multiple arrays, this gets set if any of them is large.
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bool StackProtector::ContainsProtectableArray(Type *Ty, bool &IsLarge,
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bool Strong,
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bool InStruct) const {
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if (!Ty)
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return false;
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if (ArrayType *AT = dyn_cast<ArrayType>(Ty)) {
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if (!AT->getElementType()->isIntegerTy(8)) {
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// If we're on a non-Darwin platform or we're inside of a structure, don't
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// add stack protectors unless the array is a character array.
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// However, in strong mode any array, regardless of type and size,
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// triggers a protector.
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if (!Strong && (InStruct || !Trip.isOSDarwin()))
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return false;
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}
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// If an array has more than SSPBufferSize bytes of allocated space, then we
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// emit stack protectors.
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if (SSPBufferSize <= M->getDataLayout().getTypeAllocSize(AT)) {
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IsLarge = true;
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return true;
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}
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if (Strong)
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// Require a protector for all arrays in strong mode
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return true;
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}
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const StructType *ST = dyn_cast<StructType>(Ty);
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if (!ST)
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return false;
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bool NeedsProtector = false;
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for (StructType::element_iterator I = ST->element_begin(),
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E = ST->element_end();
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I != E; ++I)
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if (ContainsProtectableArray(*I, IsLarge, Strong, true)) {
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// If the element is a protectable array and is large (>= SSPBufferSize)
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// then we are done. If the protectable array is not large, then
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// keep looking in case a subsequent element is a large array.
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if (IsLarge)
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return true;
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NeedsProtector = true;
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}
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return NeedsProtector;
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}
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bool StackProtector::HasAddressTaken(const Instruction *AI,
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uint64_t AllocSize) {
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const DataLayout &DL = M->getDataLayout();
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for (const User *U : AI->users()) {
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const auto *I = cast<Instruction>(U);
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// If this instruction accesses memory make sure it doesn't access beyond
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// the bounds of the allocated object.
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Optional<MemoryLocation> MemLoc = MemoryLocation::getOrNone(I);
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if (MemLoc.hasValue() && MemLoc->Size.hasValue() &&
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MemLoc->Size.getValue() > AllocSize)
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return true;
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switch (I->getOpcode()) {
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case Instruction::Store:
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if (AI == cast<StoreInst>(I)->getValueOperand())
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return true;
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break;
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case Instruction::AtomicCmpXchg:
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// cmpxchg conceptually includes both a load and store from the same
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// location. So, like store, the value being stored is what matters.
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if (AI == cast<AtomicCmpXchgInst>(I)->getNewValOperand())
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return true;
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break;
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case Instruction::PtrToInt:
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if (AI == cast<PtrToIntInst>(I)->getOperand(0))
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return true;
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break;
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case Instruction::Call: {
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// Ignore intrinsics that do not become real instructions.
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// TODO: Narrow this to intrinsics that have store-like effects.
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const auto *CI = cast<CallInst>(I);
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if (!CI->isDebugOrPseudoInst() && !CI->isLifetimeStartOrEnd())
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return true;
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break;
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}
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case Instruction::Invoke:
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return true;
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case Instruction::GetElementPtr: {
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// If the GEP offset is out-of-bounds, or is non-constant and so has to be
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// assumed to be potentially out-of-bounds, then any memory access that
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// would use it could also be out-of-bounds meaning stack protection is
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// required.
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const GetElementPtrInst *GEP = cast<GetElementPtrInst>(I);
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unsigned TypeSize = DL.getIndexTypeSizeInBits(I->getType());
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APInt Offset(TypeSize, 0);
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APInt MaxOffset(TypeSize, AllocSize);
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if (!GEP->accumulateConstantOffset(DL, Offset) || Offset.ugt(MaxOffset))
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return true;
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// Adjust AllocSize to be the space remaining after this offset.
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if (HasAddressTaken(I, AllocSize - Offset.getLimitedValue()))
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return true;
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break;
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}
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case Instruction::BitCast:
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case Instruction::Select:
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case Instruction::AddrSpaceCast:
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if (HasAddressTaken(I, AllocSize))
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return true;
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break;
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case Instruction::PHI: {
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// Keep track of what PHI nodes we have already visited to ensure
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// they are only visited once.
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const auto *PN = cast<PHINode>(I);
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if (VisitedPHIs.insert(PN).second)
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if (HasAddressTaken(PN, AllocSize))
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return true;
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break;
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}
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case Instruction::Load:
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case Instruction::AtomicRMW:
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case Instruction::Ret:
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// These instructions take an address operand, but have load-like or
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// other innocuous behavior that should not trigger a stack protector.
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// atomicrmw conceptually has both load and store semantics, but the
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// value being stored must be integer; so if a pointer is being stored,
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// we'll catch it in the PtrToInt case above.
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break;
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default:
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// Conservatively return true for any instruction that takes an address
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// operand, but is not handled above.
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return true;
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}
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}
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return false;
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}
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/// Search for the first call to the llvm.stackprotector intrinsic and return it
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/// if present.
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static const CallInst *findStackProtectorIntrinsic(Function &F) {
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for (const BasicBlock &BB : F)
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for (const Instruction &I : BB)
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if (const auto *II = dyn_cast<IntrinsicInst>(&I))
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if (II->getIntrinsicID() == Intrinsic::stackprotector)
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return II;
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return nullptr;
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}
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/// Check whether or not this function needs a stack protector based
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/// upon the stack protector level.
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///
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/// We use two heuristics: a standard (ssp) and strong (sspstrong).
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/// The standard heuristic which will add a guard variable to functions that
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/// call alloca with a either a variable size or a size >= SSPBufferSize,
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/// functions with character buffers larger than SSPBufferSize, and functions
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/// with aggregates containing character buffers larger than SSPBufferSize. The
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/// strong heuristic will add a guard variables to functions that call alloca
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/// regardless of size, functions with any buffer regardless of type and size,
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/// functions with aggregates that contain any buffer regardless of type and
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/// size, and functions that contain stack-based variables that have had their
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/// address taken.
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bool StackProtector::RequiresStackProtector() {
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bool Strong = false;
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bool NeedsProtector = false;
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if (F->hasFnAttribute(Attribute::SafeStack))
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return false;
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// We are constructing the OptimizationRemarkEmitter on the fly rather than
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// using the analysis pass to avoid building DominatorTree and LoopInfo which
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// are not available this late in the IR pipeline.
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OptimizationRemarkEmitter ORE(F);
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if (F->hasFnAttribute(Attribute::StackProtectReq)) {
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ORE.emit([&]() {
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return OptimizationRemark(DEBUG_TYPE, "StackProtectorRequested", F)
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<< "Stack protection applied to function "
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<< ore::NV("Function", F)
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<< " due to a function attribute or command-line switch";
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});
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NeedsProtector = true;
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Strong = true; // Use the same heuristic as strong to determine SSPLayout
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} else if (F->hasFnAttribute(Attribute::StackProtectStrong))
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Strong = true;
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else if (!F->hasFnAttribute(Attribute::StackProtect))
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return false;
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for (const BasicBlock &BB : *F) {
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for (const Instruction &I : BB) {
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if (const AllocaInst *AI = dyn_cast<AllocaInst>(&I)) {
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if (AI->isArrayAllocation()) {
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auto RemarkBuilder = [&]() {
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return OptimizationRemark(DEBUG_TYPE, "StackProtectorAllocaOrArray",
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&I)
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<< "Stack protection applied to function "
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<< ore::NV("Function", F)
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<< " due to a call to alloca or use of a variable length "
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"array";
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};
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if (const auto *CI = dyn_cast<ConstantInt>(AI->getArraySize())) {
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if (CI->getLimitedValue(SSPBufferSize) >= SSPBufferSize) {
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// A call to alloca with size >= SSPBufferSize requires
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// stack protectors.
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Layout.insert(std::make_pair(AI,
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MachineFrameInfo::SSPLK_LargeArray));
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ORE.emit(RemarkBuilder);
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NeedsProtector = true;
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} else if (Strong) {
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// Require protectors for all alloca calls in strong mode.
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Layout.insert(std::make_pair(AI,
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MachineFrameInfo::SSPLK_SmallArray));
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ORE.emit(RemarkBuilder);
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NeedsProtector = true;
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}
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} else {
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// A call to alloca with a variable size requires protectors.
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Layout.insert(std::make_pair(AI,
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MachineFrameInfo::SSPLK_LargeArray));
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ORE.emit(RemarkBuilder);
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NeedsProtector = true;
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}
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continue;
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}
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bool IsLarge = false;
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if (ContainsProtectableArray(AI->getAllocatedType(), IsLarge, Strong)) {
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Layout.insert(std::make_pair(AI, IsLarge
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? MachineFrameInfo::SSPLK_LargeArray
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: MachineFrameInfo::SSPLK_SmallArray));
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ORE.emit([&]() {
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return OptimizationRemark(DEBUG_TYPE, "StackProtectorBuffer", &I)
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<< "Stack protection applied to function "
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<< ore::NV("Function", F)
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<< " due to a stack allocated buffer or struct containing a "
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"buffer";
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});
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NeedsProtector = true;
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continue;
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}
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if (Strong && HasAddressTaken(AI, M->getDataLayout().getTypeAllocSize(
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AI->getAllocatedType()))) {
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++NumAddrTaken;
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Layout.insert(std::make_pair(AI, MachineFrameInfo::SSPLK_AddrOf));
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ORE.emit([&]() {
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return OptimizationRemark(DEBUG_TYPE, "StackProtectorAddressTaken",
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&I)
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<< "Stack protection applied to function "
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<< ore::NV("Function", F)
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<< " due to the address of a local variable being taken";
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});
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NeedsProtector = true;
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}
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// Clear any PHIs that we visited, to make sure we examine all uses of
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// any subsequent allocas that we look at.
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VisitedPHIs.clear();
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}
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}
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}
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return NeedsProtector;
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}
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/// Create a stack guard loading and populate whether SelectionDAG SSP is
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/// supported.
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static Value *getStackGuard(const TargetLoweringBase *TLI, Module *M,
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IRBuilder<> &B,
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bool *SupportsSelectionDAGSP = nullptr) {
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Value *Guard = TLI->getIRStackGuard(B);
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StringRef GuardMode = M->getStackProtectorGuard();
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if ((GuardMode == "tls" || GuardMode.empty()) && Guard)
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return B.CreateLoad(B.getInt8PtrTy(), Guard, true, "StackGuard");
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// Use SelectionDAG SSP handling, since there isn't an IR guard.
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//
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// This is more or less weird, since we optionally output whether we
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// should perform a SelectionDAG SP here. The reason is that it's strictly
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// defined as !TLI->getIRStackGuard(B), where getIRStackGuard is also
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// mutating. There is no way to get this bit without mutating the IR, so
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// getting this bit has to happen in this right time.
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//
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// We could have define a new function TLI::supportsSelectionDAGSP(), but that
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// will put more burden on the backends' overriding work, especially when it
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// actually conveys the same information getIRStackGuard() already gives.
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if (SupportsSelectionDAGSP)
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*SupportsSelectionDAGSP = true;
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TLI->insertSSPDeclarations(*M);
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return B.CreateCall(Intrinsic::getDeclaration(M, Intrinsic::stackguard));
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}
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/// Insert code into the entry block that stores the stack guard
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/// variable onto the stack:
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///
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/// entry:
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/// StackGuardSlot = alloca i8*
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/// StackGuard = <stack guard>
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/// call void @llvm.stackprotector(StackGuard, StackGuardSlot)
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///
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/// Returns true if the platform/triple supports the stackprotectorcreate pseudo
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/// node.
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static bool CreatePrologue(Function *F, Module *M, ReturnInst *RI,
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const TargetLoweringBase *TLI, AllocaInst *&AI) {
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bool SupportsSelectionDAGSP = false;
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IRBuilder<> B(&F->getEntryBlock().front());
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PointerType *PtrTy = Type::getInt8PtrTy(RI->getContext());
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AI = B.CreateAlloca(PtrTy, nullptr, "StackGuardSlot");
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Value *GuardSlot = getStackGuard(TLI, M, B, &SupportsSelectionDAGSP);
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B.CreateCall(Intrinsic::getDeclaration(M, Intrinsic::stackprotector),
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{GuardSlot, AI});
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return SupportsSelectionDAGSP;
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}
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/// InsertStackProtectors - Insert code into the prologue and epilogue of the
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/// function.
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///
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/// - The prologue code loads and stores the stack guard onto the stack.
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/// - The epilogue checks the value stored in the prologue against the original
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/// value. It calls __stack_chk_fail if they differ.
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bool StackProtector::InsertStackProtectors() {
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// If the target wants to XOR the frame pointer into the guard value, it's
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// impossible to emit the check in IR, so the target *must* support stack
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// protection in SDAG.
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bool SupportsSelectionDAGSP =
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TLI->useStackGuardXorFP() ||
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(EnableSelectionDAGSP && !TM->Options.EnableFastISel &&
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!TM->Options.EnableGlobalISel);
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AllocaInst *AI = nullptr; // Place on stack that stores the stack guard.
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for (Function::iterator I = F->begin(), E = F->end(); I != E;) {
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BasicBlock *BB = &*I++;
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ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator());
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if (!RI)
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continue;
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// Generate prologue instrumentation if not already generated.
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if (!HasPrologue) {
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HasPrologue = true;
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SupportsSelectionDAGSP &= CreatePrologue(F, M, RI, TLI, AI);
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}
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// SelectionDAG based code generation. Nothing else needs to be done here.
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// The epilogue instrumentation is postponed to SelectionDAG.
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if (SupportsSelectionDAGSP)
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break;
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// Find the stack guard slot if the prologue was not created by this pass
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// itself via a previous call to CreatePrologue().
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if (!AI) {
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const CallInst *SPCall = findStackProtectorIntrinsic(*F);
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assert(SPCall && "Call to llvm.stackprotector is missing");
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AI = cast<AllocaInst>(SPCall->getArgOperand(1));
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}
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// Set HasIRCheck to true, so that SelectionDAG will not generate its own
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// version. SelectionDAG called 'shouldEmitSDCheck' to check whether
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|
// instrumentation has already been generated.
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|
HasIRCheck = true;
|
|
|
|
// If we're instrumenting a block with a musttail call, the check has to be
|
|
// inserted before the call rather than between it and the return. The
|
|
// verifier guarantees that a musttail call is either directly before the
|
|
// return or with a single correct bitcast of the return value in between so
|
|
// we don't need to worry about many situations here.
|
|
Instruction *CheckLoc = RI;
|
|
Instruction *Prev = RI->getPrevNonDebugInstruction();
|
|
if (Prev && isa<CallInst>(Prev) && cast<CallInst>(Prev)->isMustTailCall())
|
|
CheckLoc = Prev;
|
|
else if (Prev) {
|
|
Prev = Prev->getPrevNonDebugInstruction();
|
|
if (Prev && isa<CallInst>(Prev) && cast<CallInst>(Prev)->isMustTailCall())
|
|
CheckLoc = Prev;
|
|
}
|
|
|
|
// 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(CheckLoc);
|
|
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 calls, generate IR level
|
|
// 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(CheckLoc->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);
|
|
if (F->getSubprogram())
|
|
B.SetCurrentDebugLocation(
|
|
DILocation::get(Context, 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);
|
|
}
|
|
}
|