llvm-6502/lib/CodeGen/ForwardControlFlowIntegrity.cpp
2014-11-11 21:26:33 +00:00

375 lines
14 KiB
C++

//===-- ForwardControlFlowIntegrity.cpp: Forward-Edge CFI -----------------===//
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
///
/// \file
/// \brief A pass that instruments code with fast checks for indirect calls and
/// hooks for a function to check violations.
///
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "cfi"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/JumpInstrTableInfo.h"
#include "llvm/CodeGen/ForwardControlFlowIntegrity.h"
#include "llvm/CodeGen/JumpInstrTables.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/IR/Attributes.h"
#include "llvm/IR/CallSite.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/GlobalValue.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/InlineAsm.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Operator.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/Verifier.h"
#include "llvm/Pass.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
STATISTIC(NumCFIIndirectCalls,
"Number of indirect call sites rewritten by the CFI pass");
char ForwardControlFlowIntegrity::ID = 0;
INITIALIZE_PASS_BEGIN(ForwardControlFlowIntegrity, "forward-cfi",
"Control-Flow Integrity", true, true)
INITIALIZE_PASS_DEPENDENCY(JumpInstrTableInfo);
INITIALIZE_PASS_DEPENDENCY(JumpInstrTables);
INITIALIZE_PASS_END(ForwardControlFlowIntegrity, "forward-cfi",
"Control-Flow Integrity", true, true)
ModulePass *llvm::createForwardControlFlowIntegrityPass() {
return new ForwardControlFlowIntegrity();
}
ModulePass *llvm::createForwardControlFlowIntegrityPass(
JumpTable::JumpTableType JTT, CFIntegrity CFIType, bool CFIEnforcing,
StringRef CFIFuncName) {
return new ForwardControlFlowIntegrity(JTT, CFIType, CFIEnforcing,
CFIFuncName);
}
// Checks to see if a given CallSite is making an indirect call, including
// cases where the indirect call is made through a bitcast.
static bool isIndirectCall(CallSite &CS) {
if (CS.getCalledFunction())
return false;
// Check the value to see if it is merely a bitcast of a function. In
// this case, it will translate to a direct function call in the resulting
// assembly, so we won't treat it as an indirect call here.
const Value *V = CS.getCalledValue();
if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
return !(CE->isCast() && isa<Function>(CE->getOperand(0)));
}
// Otherwise, since we know it's a call, it must be an indirect call
return true;
}
static const char cfi_failure_func_name[] = "__llvm_cfi_pointer_warning";
ForwardControlFlowIntegrity::ForwardControlFlowIntegrity()
: ModulePass(ID), IndirectCalls(), JTType(JumpTable::Single),
CFIType(CFIntegrity::Sub), CFIEnforcing(false), CFIFuncName("") {
initializeForwardControlFlowIntegrityPass(*PassRegistry::getPassRegistry());
}
ForwardControlFlowIntegrity::ForwardControlFlowIntegrity(
JumpTable::JumpTableType JTT, CFIntegrity CFIType, bool CFIEnforcing,
std::string CFIFuncName)
: ModulePass(ID), IndirectCalls(), JTType(JTT), CFIType(CFIType),
CFIEnforcing(CFIEnforcing), CFIFuncName(CFIFuncName) {
initializeForwardControlFlowIntegrityPass(*PassRegistry::getPassRegistry());
}
ForwardControlFlowIntegrity::~ForwardControlFlowIntegrity() {}
void ForwardControlFlowIntegrity::getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<JumpInstrTableInfo>();
AU.addRequired<JumpInstrTables>();
}
void ForwardControlFlowIntegrity::getIndirectCalls(Module &M) {
// To get the indirect calls, we iterate over all functions and iterate over
// the list of basic blocks in each. We extract a total list of indirect calls
// before modifying any of them, since our modifications will modify the list
// of basic blocks.
for (Function &F : M) {
for (BasicBlock &BB : F) {
for (Instruction &I : BB) {
CallSite CS(&I);
if (!(CS && isIndirectCall(CS)))
continue;
Value *CalledValue = CS.getCalledValue();
// Don't rewrite this instruction if the indirect call is actually just
// inline assembly, since our transformation will generate an invalid
// module in that case.
if (isa<InlineAsm>(CalledValue))
continue;
IndirectCalls.push_back(&I);
}
}
}
}
void ForwardControlFlowIntegrity::updateIndirectCalls(Module &M,
CFITables &CFIT) {
Type *Int64Ty = Type::getInt64Ty(M.getContext());
for (Instruction *I : IndirectCalls) {
CallSite CS(I);
Value *CalledValue = CS.getCalledValue();
// Get the function type for this call and look it up in the tables.
Type *VTy = CalledValue->getType();
PointerType *PTy = dyn_cast<PointerType>(VTy);
Type *EltTy = PTy->getElementType();
FunctionType *FunTy = dyn_cast<FunctionType>(EltTy);
FunctionType *TransformedTy = JumpInstrTables::transformType(JTType, FunTy);
++NumCFIIndirectCalls;
Constant *JumpTableStart = nullptr;
Constant *JumpTableMask = nullptr;
Constant *JumpTableSize = nullptr;
// Some call sites have function types that don't correspond to any
// address-taken function in the module. This happens when function pointers
// are passed in from external code.
auto it = CFIT.find(TransformedTy);
if (it == CFIT.end()) {
// In this case, make sure that the function pointer will change by
// setting the mask and the start to be 0 so that the transformed
// function is 0.
JumpTableStart = ConstantInt::get(Int64Ty, 0);
JumpTableMask = ConstantInt::get(Int64Ty, 0);
JumpTableSize = ConstantInt::get(Int64Ty, 0);
} else {
JumpTableStart = it->second.StartValue;
JumpTableMask = it->second.MaskValue;
JumpTableSize = it->second.Size;
}
rewriteFunctionPointer(M, I, CalledValue, JumpTableStart, JumpTableMask,
JumpTableSize);
}
return;
}
bool ForwardControlFlowIntegrity::runOnModule(Module &M) {
JumpInstrTableInfo *JITI = &getAnalysis<JumpInstrTableInfo>();
Type *Int64Ty = Type::getInt64Ty(M.getContext());
Type *VoidPtrTy = Type::getInt8PtrTy(M.getContext());
// JumpInstrTableInfo stores information about the alignment of each entry.
// The alignment returned by JumpInstrTableInfo is alignment in bytes, not
// in the exponent.
ByteAlignment = JITI->entryByteAlignment();
LogByteAlignment = llvm::Log2_64(ByteAlignment);
// Set up tables for control-flow integrity based on information about the
// jump-instruction tables.
CFITables CFIT;
for (const auto &KV : JITI->getTables()) {
uint64_t Size = static_cast<uint64_t>(KV.second.size());
uint64_t TableSize = NextPowerOf2(Size);
int64_t MaskValue = ((TableSize << LogByteAlignment) - 1) & -ByteAlignment;
Constant *JumpTableMaskValue = ConstantInt::get(Int64Ty, MaskValue);
Constant *JumpTableSize = ConstantInt::get(Int64Ty, Size);
// The base of the table is defined to be the first jumptable function in
// the table.
Function *First = KV.second.begin()->second;
Constant *JumpTableStartValue = ConstantExpr::getBitCast(First, VoidPtrTy);
CFIT[KV.first].StartValue = JumpTableStartValue;
CFIT[KV.first].MaskValue = JumpTableMaskValue;
CFIT[KV.first].Size = JumpTableSize;
}
if (CFIT.empty())
return false;
getIndirectCalls(M);
if (!CFIEnforcing) {
addWarningFunction(M);
}
// Update the instructions with the check and the indirect jump through our
// table.
updateIndirectCalls(M, CFIT);
return true;
}
void ForwardControlFlowIntegrity::addWarningFunction(Module &M) {
PointerType *CharPtrTy = Type::getInt8PtrTy(M.getContext());
// Get the type of the Warning Function: void (i8*, i8*),
// where the first argument is the name of the function in which the violation
// occurs, and the second is the function pointer that violates CFI.
SmallVector<Type *, 2> WarningFunArgs;
WarningFunArgs.push_back(CharPtrTy);
WarningFunArgs.push_back(CharPtrTy);
FunctionType *WarningFunTy =
FunctionType::get(Type::getVoidTy(M.getContext()), WarningFunArgs, false);
if (!CFIFuncName.empty()) {
Constant *FailureFun = M.getOrInsertFunction(CFIFuncName, WarningFunTy);
if (!FailureFun)
report_fatal_error("Could not get or insert the function specified by"
" -cfi-func-name");
} else {
// The default warning function swallows the warning and lets the call
// continue, since there's no generic way for it to print out this
// information.
Function *WarningFun = M.getFunction(cfi_failure_func_name);
if (!WarningFun) {
WarningFun =
Function::Create(WarningFunTy, GlobalValue::LinkOnceAnyLinkage,
cfi_failure_func_name, &M);
}
BasicBlock *Entry =
BasicBlock::Create(M.getContext(), "entry", WarningFun, 0);
ReturnInst::Create(M.getContext(), Entry);
}
}
void ForwardControlFlowIntegrity::rewriteFunctionPointer(
Module &M, Instruction *I, Value *FunPtr, Constant *JumpTableStart,
Constant *JumpTableMask, Constant *JumpTableSize) {
IRBuilder<> TempBuilder(I);
Type *OrigFunType = FunPtr->getType();
BasicBlock *CurBB = cast<BasicBlock>(I->getParent());
Function *CurF = cast<Function>(CurBB->getParent());
Type *Int64Ty = Type::getInt64Ty(M.getContext());
Value *TI = TempBuilder.CreatePtrToInt(FunPtr, Int64Ty);
Value *TStartInt = TempBuilder.CreatePtrToInt(JumpTableStart, Int64Ty);
Value *NewFunPtr = nullptr;
Value *Check = nullptr;
switch (CFIType) {
case CFIntegrity::Sub: {
// This is the subtract, mask, and add version.
// Subtract from the base.
Value *Sub = TempBuilder.CreateSub(TI, TStartInt);
// Mask the difference to force this to be a table offset.
Value *And = TempBuilder.CreateAnd(Sub, JumpTableMask);
// Add it back to the base.
Value *Result = TempBuilder.CreateAdd(And, TStartInt);
// Convert it back into a function pointer that we can call.
NewFunPtr = TempBuilder.CreateIntToPtr(Result, OrigFunType);
break;
}
case CFIntegrity::Ror: {
// This is the subtract and rotate version.
// Rotate right by the alignment value. The optimizer should recognize
// this sequence as a rotation.
// This cast is safe, since unsigned is always a subset of uint64_t.
uint64_t LogByteAlignment64 = static_cast<uint64_t>(LogByteAlignment);
Constant *RightShift = ConstantInt::get(Int64Ty, LogByteAlignment64);
Constant *LeftShift = ConstantInt::get(Int64Ty, 64 - LogByteAlignment64);
// Subtract from the base.
Value *Sub = TempBuilder.CreateSub(TI, TStartInt);
// Create the equivalent of a rotate-right instruction.
Value *Shr = TempBuilder.CreateLShr(Sub, RightShift);
Value *Shl = TempBuilder.CreateShl(Sub, LeftShift);
Value *Or = TempBuilder.CreateOr(Shr, Shl);
// Perform unsigned comparison to check for inclusion in the table.
Check = TempBuilder.CreateICmpULT(Or, JumpTableSize);
NewFunPtr = FunPtr;
break;
}
case CFIntegrity::Add: {
// This is the mask and add version.
// Mask the function pointer to turn it into an offset into the table.
Value *And = TempBuilder.CreateAnd(TI, JumpTableMask);
// Then or this offset to the base and get the pointer value.
Value *Result = TempBuilder.CreateAdd(And, TStartInt);
// Convert it back into a function pointer that we can call.
NewFunPtr = TempBuilder.CreateIntToPtr(Result, OrigFunType);
break;
}
}
if (!CFIEnforcing) {
// If a check hasn't been added (in the rotation version), then check to see
// if it's the same as the original function. This check determines whether
// or not we call the CFI failure function.
if (!Check)
Check = TempBuilder.CreateICmpEQ(NewFunPtr, FunPtr);
BasicBlock *InvalidPtrBlock =
BasicBlock::Create(M.getContext(), "invalid.ptr", CurF, 0);
BasicBlock *ContinuationBB = CurBB->splitBasicBlock(I);
// Remove the unconditional branch that connects the two blocks.
TerminatorInst *TermInst = CurBB->getTerminator();
TermInst->eraseFromParent();
// Add a conditional branch that depends on the Check above.
BranchInst::Create(ContinuationBB, InvalidPtrBlock, Check, CurBB);
// Call the warning function for this pointer, then continue.
Instruction *BI = BranchInst::Create(ContinuationBB, InvalidPtrBlock);
insertWarning(M, InvalidPtrBlock, BI, FunPtr);
} else {
// Modify the instruction to call this value.
CallSite CS(I);
CS.setCalledFunction(NewFunPtr);
}
}
void ForwardControlFlowIntegrity::insertWarning(Module &M, BasicBlock *Block,
Instruction *I, Value *FunPtr) {
Function *ParentFun = cast<Function>(Block->getParent());
// Get the function to call right before the instruction.
Function *WarningFun = nullptr;
if (CFIFuncName.empty()) {
WarningFun = M.getFunction(cfi_failure_func_name);
} else {
WarningFun = M.getFunction(CFIFuncName);
}
assert(WarningFun && "Could not find the CFI failure function");
Type *VoidPtrTy = Type::getInt8PtrTy(M.getContext());
IRBuilder<> WarningInserter(I);
// Create a mergeable GlobalVariable containing the name of the function.
Value *ParentNameGV =
WarningInserter.CreateGlobalString(ParentFun->getName());
Value *ParentNamePtr = WarningInserter.CreateBitCast(ParentNameGV, VoidPtrTy);
Value *FunVoidPtr = WarningInserter.CreateBitCast(FunPtr, VoidPtrTy);
WarningInserter.CreateCall2(WarningFun, ParentNamePtr, FunVoidPtr);
}