467 lines
18 KiB
C++
467 lines
18 KiB
C++
//===-- StackProtector.cpp - Stack Protector Insertion --------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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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/ValueTracking.h"
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#include "llvm/CodeGen/Passes.h"
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#include "llvm/IR/Attributes.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/DerivedTypes.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/GlobalValue.h"
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#include "llvm/IR/GlobalVariable.h"
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#include "llvm/IR/IRBuilder.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/Support/CommandLine.h"
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#include "llvm/Target/TargetSubtargetInfo.h"
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#include <cstdlib>
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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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INITIALIZE_TM_PASS(StackProtector, "stack-protector", "Insert stack protectors",
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false, true)
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FunctionPass *llvm::createStackProtectorPass(const TargetMachine *TM) {
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return new StackProtector(TM);
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}
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StackProtector::SSPLayoutKind
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StackProtector::getSSPLayout(const AllocaInst *AI) const {
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return AI ? Layout.lookup(AI) : SSPLK_None;
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}
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void StackProtector::adjustForColoring(const AllocaInst *From,
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const AllocaInst *To) {
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// When coloring replaces one alloca with another, transfer the SSPLayoutKind
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// tag from the remapped to the target alloca. The remapped alloca should
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// have a size smaller than or equal to the replacement alloca.
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SSPLayoutMap::iterator I = Layout.find(From);
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if (I != Layout.end()) {
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SSPLayoutKind Kind = I->second;
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Layout.erase(I);
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// Transfer the tag, but make sure that SSPLK_AddrOf does not overwrite
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// SSPLK_SmallArray or SSPLK_LargeArray, and make sure that
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// SSPLK_SmallArray does not overwrite SSPLK_LargeArray.
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I = Layout.find(To);
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if (I == Layout.end())
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Layout.insert(std::make_pair(To, Kind));
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else if (I->second != SSPLK_LargeArray && Kind != SSPLK_AddrOf)
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I->second = Kind;
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}
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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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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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for (const User *U : AI->users()) {
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if (const StoreInst *SI = dyn_cast<StoreInst>(U)) {
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if (AI == SI->getValueOperand())
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return true;
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} else if (const PtrToIntInst *SI = dyn_cast<PtrToIntInst>(U)) {
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if (AI == SI->getOperand(0))
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return true;
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} else if (isa<CallInst>(U)) {
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return true;
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} else if (isa<InvokeInst>(U)) {
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return true;
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} else if (const SelectInst *SI = dyn_cast<SelectInst>(U)) {
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if (HasAddressTaken(SI))
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return true;
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} else if (const PHINode *PN = dyn_cast<PHINode>(U)) {
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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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if (VisitedPHIs.insert(PN).second)
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if (HasAddressTaken(PN))
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return true;
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} else if (const GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) {
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if (HasAddressTaken(GEP))
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return true;
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} else if (const BitCastInst *BI = dyn_cast<BitCastInst>(U)) {
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if (HasAddressTaken(BI))
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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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/// \brief 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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for (const BasicBlock &BB : *F)
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for (const Instruction &I : BB)
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if (const CallInst *CI = dyn_cast<CallInst>(&I))
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if (CI->getCalledFunction() ==
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Intrinsic::getDeclaration(F->getParent(),
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Intrinsic::stackprotector))
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HasPrologue = true;
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if (F->hasFnAttribute(Attribute::SafeStack))
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return false;
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if (F->hasFnAttribute(Attribute::StackProtectReq)) {
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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 (HasPrologue)
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NeedsProtector = 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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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, SSPLK_LargeArray));
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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, SSPLK_SmallArray));
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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, SSPLK_LargeArray));
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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 ? SSPLK_LargeArray
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: SSPLK_SmallArray));
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NeedsProtector = true;
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continue;
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}
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if (Strong && HasAddressTaken(AI)) {
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++NumAddrTaken;
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Layout.insert(std::make_pair(AI, SSPLK_AddrOf));
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NeedsProtector = true;
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}
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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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if (Value *Guard = TLI->getIRStackGuard(B))
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return B.CreateLoad(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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bool SupportsSelectionDAGSP =
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EnableSelectionDAGSP && !TM->Options.EnableFastISel;
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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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// 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;
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// Generate epilogue instrumentation. The epilogue intrumentation can be
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// function-based or inlined depending on which mechanism the target is
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// providing.
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if (Value* GuardCheck = TLI->getSSPStackGuardCheck(*M)) {
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// Generate the function-based epilogue instrumentation.
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// The target provides a guard check function, generate a call to it.
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IRBuilder<> B(RI);
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LoadInst *Guard = B.CreateLoad(AI, true, "Guard");
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CallInst *Call = B.CreateCall(GuardCheck, {Guard});
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llvm::Function *Function = cast<llvm::Function>(GuardCheck);
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Call->setAttributes(Function->getAttributes());
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Call->setCallingConv(Function->getCallingConv());
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} else {
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// Generate the epilogue with inline instrumentation.
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// If we do not support SelectionDAG based tail calls, generate IR level
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// tail calls.
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//
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// For each block with a return instruction, convert this:
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//
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// return:
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// ...
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// ret ...
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//
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// into this:
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//
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// return:
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// ...
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// %1 = <stack guard>
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// %2 = load StackGuardSlot
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// %3 = cmp i1 %1, %2
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// br i1 %3, label %SP_return, label %CallStackCheckFailBlk
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//
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// SP_return:
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// ret ...
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//
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// CallStackCheckFailBlk:
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// call void @__stack_chk_fail()
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// unreachable
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// Create the FailBB. We duplicate the BB every time since the MI tail
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// merge pass will merge together all of the various BB into one including
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// fail BB generated by the stack protector pseudo instruction.
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BasicBlock *FailBB = CreateFailBB();
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// Split the basic block before the return instruction.
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BasicBlock *NewBB = BB->splitBasicBlock(RI->getIterator(), "SP_return");
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// Update the dominator tree if we need to.
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if (DT && DT->isReachableFromEntry(BB)) {
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DT->addNewBlock(NewBB, BB);
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DT->addNewBlock(FailBB, BB);
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}
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// Remove default branch instruction to the new BB.
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BB->getTerminator()->eraseFromParent();
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// Move the newly created basic block to the point right after the old
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// basic block so that it's in the "fall through" position.
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NewBB->moveAfter(BB);
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// Generate the stack protector instructions in the old basic block.
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IRBuilder<> B(BB);
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Value *Guard = getStackGuard(TLI, M, B);
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LoadInst *LI2 = B.CreateLoad(AI, true);
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Value *Cmp = B.CreateICmpEQ(Guard, LI2);
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auto SuccessProb =
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BranchProbabilityInfo::getBranchProbStackProtector(true);
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auto FailureProb =
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BranchProbabilityInfo::getBranchProbStackProtector(false);
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MDNode *Weights = MDBuilder(F->getContext())
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.createBranchWeights(SuccessProb.getNumerator(),
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FailureProb.getNumerator());
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B.CreateCondBr(Cmp, NewBB, FailBB, Weights);
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}
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}
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// Return if we didn't modify any basic blocks. i.e., there are no return
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// statements in the function.
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return HasPrologue;
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}
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/// CreateFailBB - Create a basic block to jump to when the stack protector
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/// check fails.
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BasicBlock *StackProtector::CreateFailBB() {
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LLVMContext &Context = F->getContext();
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BasicBlock *FailBB = BasicBlock::Create(Context, "CallStackCheckFailBlk", F);
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IRBuilder<> B(FailBB);
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B.SetCurrentDebugLocation(DebugLoc::get(0, 0, F->getSubprogram()));
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if (Trip.isOSOpenBSD()) {
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Constant *StackChkFail =
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M->getOrInsertFunction("__stack_smash_handler",
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Type::getVoidTy(Context),
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Type::getInt8PtrTy(Context), nullptr);
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B.CreateCall(StackChkFail, B.CreateGlobalStringPtr(F->getName(), "SSH"));
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} else {
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Constant *StackChkFail =
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M->getOrInsertFunction("__stack_chk_fail", Type::getVoidTy(Context),
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nullptr);
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B.CreateCall(StackChkFail, {});
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}
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B.CreateUnreachable();
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return FailBB;
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}
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bool StackProtector::shouldEmitSDCheck(const BasicBlock &BB) const {
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return HasPrologue && !HasIRCheck && dyn_cast<ReturnInst>(BB.getTerminator());
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}
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