llvm-6502/lib/CodeGen/StackProtector.cpp
Josh Magee 18ebd48960 [stackprotector] Refactor the StackProtector pass from a single .cpp file into StackProtector.h and StackProtector.cpp.
No functionality change.  Future patches will add analysis which will be used
in other passes (PEI, StackSlot).  The end goal is to support ssp-strong stack
layout rules.

WIP.

Differential Revision: http://llvm-reviews.chandlerc.com/D1521


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191570 91177308-0d34-0410-b5e6-96231b3b80d8
2013-09-27 21:58:43 +00:00

436 lines
16 KiB
C++

//===-- 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.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "stack-protector"
#include "llvm/CodeGen/StackProtector.h"
#include "llvm/CodeGen/Analysis.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/Attributes.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/GlobalValue.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/Module.h"
#include "llvm/Support/CommandLine.h"
#include <cstdlib>
using namespace llvm;
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, false)
FunctionPass *llvm::createStackProtectorPass(const TargetMachine *TM) {
return new StackProtector(TM);
}
bool StackProtector::runOnFunction(Function &Fn) {
F = &Fn;
M = F->getParent();
DT = getAnalysisIfAvailable<DominatorTree>();
TLI = TM->getTargetLowering();
if (!RequiresStackProtector()) return false;
Attribute Attr =
Fn.getAttributes().getAttribute(AttributeSet::FunctionIndex,
"stack-protector-buffer-size");
if (Attr.isStringAttribute())
Attr.getValueAsString().getAsInteger(10, SSPBufferSize);
++NumFunProtected;
return InsertStackProtectors();
}
/// ContainsProtectableArray - Check whether the type either is an array or
/// contains a char array of sufficient size so that we need stack protectors
/// for it.
bool StackProtector::ContainsProtectableArray(Type *Ty, bool Strong,
bool InStruct) const {
if (!Ty) return false;
if (ArrayType *AT = dyn_cast<ArrayType>(Ty)) {
// In strong mode any array, regardless of type and size, triggers a
// protector
if (Strong)
return true;
if (!AT->getElementType()->isIntegerTy(8)) {
// If we're on a non-Darwin platform or we're inside of a structure, don't
// add stack protectors unless the array is a character array.
if (InStruct || !Trip.isOSDarwin())
return false;
}
// If an array has more than SSPBufferSize bytes of allocated space, then we
// emit stack protectors.
if (SSPBufferSize <= TLI->getDataLayout()->getTypeAllocSize(AT))
return true;
}
const StructType *ST = dyn_cast<StructType>(Ty);
if (!ST) return false;
for (StructType::element_iterator I = ST->element_begin(),
E = ST->element_end(); I != E; ++I)
if (ContainsProtectableArray(*I, Strong, true))
return true;
return false;
}
bool StackProtector::HasAddressTaken(const Instruction *AI) {
for (Value::const_use_iterator UI = AI->use_begin(), UE = AI->use_end();
UI != UE; ++UI) {
const User *U = *UI;
if (const StoreInst *SI = dyn_cast<StoreInst>(U)) {
if (AI == SI->getValueOperand())
return true;
} else if (const PtrToIntInst *SI = dyn_cast<PtrToIntInst>(U)) {
if (AI == SI->getOperand(0))
return true;
} else if (isa<CallInst>(U)) {
return true;
} else if (isa<InvokeInst>(U)) {
return true;
} else if (const SelectInst *SI = dyn_cast<SelectInst>(U)) {
if (HasAddressTaken(SI))
return true;
} else if (const PHINode *PN = dyn_cast<PHINode>(U)) {
// Keep track of what PHI nodes we have already visited to ensure
// they are only visited once.
if (VisitedPHIs.insert(PN))
if (HasAddressTaken(PN))
return true;
} else if (const GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) {
if (HasAddressTaken(GEP))
return true;
} else if (const BitCastInst *BI = dyn_cast<BitCastInst>(U)) {
if (HasAddressTaken(BI))
return true;
}
}
return false;
}
/// \brief Check whether or not this function needs a stack protector based
/// upon the stack protector level.
///
/// We use two heuristics: a standard (ssp) and strong (sspstrong).
/// The standard heuristic which will add a guard variable to functions that
/// call alloca with a either a variable size or a size >= SSPBufferSize,
/// functions with character buffers larger than SSPBufferSize, and functions
/// with aggregates containing character buffers larger than SSPBufferSize. The
/// strong heuristic will add a guard variables to functions that call alloca
/// regardless of size, functions with any buffer regardless of type and size,
/// functions with aggregates that contain any buffer regardless of type and
/// size, and functions that contain stack-based variables that have had their
/// address taken.
bool StackProtector::RequiresStackProtector() {
bool Strong = false;
if (F->getAttributes().hasAttribute(AttributeSet::FunctionIndex,
Attribute::StackProtectReq))
return true;
else if (F->getAttributes().hasAttribute(AttributeSet::FunctionIndex,
Attribute::StackProtectStrong))
Strong = true;
else if (!F->getAttributes().hasAttribute(AttributeSet::FunctionIndex,
Attribute::StackProtect))
return false;
for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I) {
BasicBlock *BB = I;
for (BasicBlock::iterator
II = BB->begin(), IE = BB->end(); II != IE; ++II) {
if (AllocaInst *AI = dyn_cast<AllocaInst>(II)) {
if (AI->isArrayAllocation()) {
// SSP-Strong: Enable protectors for any call to alloca, regardless
// of size.
if (Strong)
return true;
if (const ConstantInt *CI =
dyn_cast<ConstantInt>(AI->getArraySize())) {
if (CI->getLimitedValue(SSPBufferSize) >= SSPBufferSize)
// A call to alloca with size >= SSPBufferSize requires
// stack protectors.
return true;
} else {
// A call to alloca with a variable size requires protectors.
return true;
}
}
if (ContainsProtectableArray(AI->getAllocatedType(), Strong))
return true;
if (Strong && HasAddressTaken(AI)) {
++NumAddrTaken;
return true;
}
}
}
}
return false;
}
static bool InstructionWillNotHaveChain(const Instruction *I) {
return !I->mayHaveSideEffects() && !I->mayReadFromMemory() &&
isSafeToSpeculativelyExecute(I);
}
/// Identify if RI has a previous instruction in the "Tail Position" and return
/// it. Otherwise return 0.
///
/// This is based off of the code in llvm::isInTailCallPosition. 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 = llvm::next(BB->rbegin()), E = BB->rend();
I != E && SearchCounter < MaxSearch; ++I) {
Instruction *Inst = &*I;
// Skip over debug intrinsics and do not allow them to affect our MaxSearch
// counter.
if (isa<DbgInfoIntrinsic>(Inst))
continue;
// If we find a call and the following conditions are satisifed, then we
// have found a tail call that satisfies at least the target independent
// requirements of a tail call:
//
// 1. The call site has the tail marker.
//
// 2. The call site either will not cause the creation of a chain or if a
// chain is necessary there are no instructions in between the callsite and
// the call which would create an interposing chain.
//
// 3. The return type of the function does not impede tail call
// optimization.
if (CallInst *CI = dyn_cast<CallInst>(Inst)) {
if (CI->isTailCall() &&
(InstructionWillNotHaveChain(CI) || NoInterposingChain) &&
returnTypeIsEligibleForTailCall(BB->getParent(), CI, RI, *TLI))
return CI;
}
// If we did not find a call see if we have an instruction that may create
// an interposing chain.
NoInterposingChain = NoInterposingChain && InstructionWillNotHaveChain(Inst);
// Increment max search.
SearchCounter++;
}
return 0;
}
/// Insert code into the entry block that stores the __stack_chk_guard
/// variable onto the stack:
///
/// entry:
/// StackGuardSlot = alloca i8*
/// StackGuard = load __stack_chk_guard
/// call void @llvm.stackprotect.create(StackGuard, StackGuardSlot)
///
/// Returns true if the platform/triple supports the stackprotectorcreate pseudo
/// node.
static bool CreatePrologue(Function *F, Module *M, ReturnInst *RI,
const TargetLoweringBase *TLI, const Triple &Trip,
AllocaInst *&AI, Value *&StackGuardVar) {
bool SupportsSelectionDAGSP = false;
PointerType *PtrTy = Type::getInt8PtrTy(RI->getContext());
unsigned AddressSpace, Offset;
if (TLI->getStackCookieLocation(AddressSpace, Offset)) {
Constant *OffsetVal =
ConstantInt::get(Type::getInt32Ty(RI->getContext()), Offset);
StackGuardVar = ConstantExpr::getIntToPtr(OffsetVal,
PointerType::get(PtrTy,
AddressSpace));
} else if (Trip.getOS() == llvm::Triple::OpenBSD) {
StackGuardVar = M->getOrInsertGlobal("__guard_local", PtrTy);
cast<GlobalValue>(StackGuardVar)
->setVisibility(GlobalValue::HiddenVisibility);
} else {
SupportsSelectionDAGSP = true;
StackGuardVar = M->getOrInsertGlobal("__stack_chk_guard", PtrTy);
}
IRBuilder<> B(&F->getEntryBlock().front());
AI = B.CreateAlloca(PtrTy, 0, "StackGuardSlot");
LoadInst *LI = B.CreateLoad(StackGuardVar, "StackGuard");
B.CreateCall2(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 = 0; // Place on stack that stores the stack guard.
Value *StackGuardVar = 0; // The stack guard variable.
for (Function::iterator I = F->begin(), E = F->end(); I != E; ) {
BasicBlock *BB = I++;
ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator());
if (!RI)
continue;
if (!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 = 0;
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 != 0 && "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);
B.CreateCondBr(Cmp, NewBB, FailBB);
}
}
// 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.getOS() == llvm::Triple::OpenBSD) {
Constant *StackChkFail = M->getOrInsertFunction(
"__stack_smash_handler", Type::getVoidTy(Context),
Type::getInt8PtrTy(Context), NULL);
B.CreateCall(StackChkFail, B.CreateGlobalStringPtr(F->getName(), "SSH"));
} else {
Constant *StackChkFail = M->getOrInsertFunction(
"__stack_chk_fail", Type::getVoidTy(Context), NULL);
B.CreateCall(StackChkFail);
}
B.CreateUnreachable();
return FailBB;
}