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//===-- CrossDSOCFI.cpp - Externalize this module's CFI checks ------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass exports all llvm.bitset's found in the module in the form of a
// __cfi_check function, which can be used to verify cross-DSO call targets.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/IPO.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/EquivalenceClasses.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/IR/Constant.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/GlobalObject.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/MDBuilder.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Operator.h"
#include "llvm/Pass.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
using namespace llvm;
#define DEBUG_TYPE "cross-dso-cfi"
STATISTIC(TypeIds, "Number of unique type identifiers");
namespace {
struct CrossDSOCFI : public ModulePass {
static char ID;
CrossDSOCFI() : ModulePass(ID) {
initializeCrossDSOCFIPass(*PassRegistry::getPassRegistry());
}
Module *M;
MDNode *VeryLikelyWeights;
ConstantInt *extractBitSetTypeId(MDNode *MD);
void buildCFICheck();
bool doInitialization(Module &M) override;
bool runOnModule(Module &M) override;
};
} // anonymous namespace
INITIALIZE_PASS_BEGIN(CrossDSOCFI, "cross-dso-cfi", "Cross-DSO CFI", false,
false)
INITIALIZE_PASS_END(CrossDSOCFI, "cross-dso-cfi", "Cross-DSO CFI", false, false)
char CrossDSOCFI::ID = 0;
ModulePass *llvm::createCrossDSOCFIPass() { return new CrossDSOCFI; }
bool CrossDSOCFI::doInitialization(Module &Mod) {
M = &Mod;
VeryLikelyWeights =
MDBuilder(M->getContext()).createBranchWeights((1U << 20) - 1, 1);
return false;
}
/// extractBitSetTypeId - Extracts TypeId from a hash-based bitset MDNode.
ConstantInt *CrossDSOCFI::extractBitSetTypeId(MDNode *MD) {
// This check excludes vtables for classes inside anonymous namespaces.
auto TM = dyn_cast<ValueAsMetadata>(MD->getOperand(0));
if (!TM)
return nullptr;
auto C = dyn_cast_or_null<ConstantInt>(TM->getValue());
if (!C) return nullptr;
// We are looking for i64 constants.
if (C->getBitWidth() != 64) return nullptr;
// Sanity check.
auto FM = dyn_cast_or_null<ValueAsMetadata>(MD->getOperand(1));
// Can be null if a function was removed by an optimization.
if (FM) {
auto F = dyn_cast<Function>(FM->getValue());
// But can never be a function declaration.
assert(!F || !F->isDeclaration());
(void)F; // Suppress unused variable warning in the no-asserts build.
}
return C;
}
/// buildCFICheck - emits __cfi_check for the current module.
void CrossDSOCFI::buildCFICheck() {
// FIXME: verify that __cfi_check ends up near the end of the code section,
// but before the jump slots created in LowerBitSets.
llvm::DenseSet<uint64_t> BitSetIds;
NamedMDNode *BitSetNM = M->getNamedMetadata("llvm.bitsets");
if (BitSetNM)
for (unsigned I = 0, E = BitSetNM->getNumOperands(); I != E; ++I)
if (ConstantInt *TypeId = extractBitSetTypeId(BitSetNM->getOperand(I)))
BitSetIds.insert(TypeId->getZExtValue());
LLVMContext &Ctx = M->getContext();
Constant *C = M->getOrInsertFunction(
"__cfi_check",
FunctionType::get(
Type::getVoidTy(Ctx),
{Type::getInt64Ty(Ctx), PointerType::getUnqual(Type::getInt8Ty(Ctx))},
false));
Function *F = dyn_cast<Function>(C);
F->setAlignment(4096);
auto args = F->arg_begin();
Argument &CallSiteTypeId = *(args++);
CallSiteTypeId.setName("CallSiteTypeId");
Argument &Addr = *(args++);
Addr.setName("Addr");
assert(args == F->arg_end());
BasicBlock *BB = BasicBlock::Create(Ctx, "entry", F);
BasicBlock *TrapBB = BasicBlock::Create(Ctx, "trap", F);
IRBuilder<> IRBTrap(TrapBB);
Function *TrapFn = Intrinsic::getDeclaration(M, Intrinsic::trap);
llvm::CallInst *TrapCall = IRBTrap.CreateCall(TrapFn);
TrapCall->setDoesNotReturn();
TrapCall->setDoesNotThrow();
IRBTrap.CreateUnreachable();
BasicBlock *ExitBB = BasicBlock::Create(Ctx, "exit", F);
IRBuilder<> IRBExit(ExitBB);
IRBExit.CreateRetVoid();
IRBuilder<> IRB(BB);
SwitchInst *SI = IRB.CreateSwitch(&CallSiteTypeId, TrapBB, BitSetIds.size());
for (uint64_t TypeId : BitSetIds) {
ConstantInt *CaseTypeId = ConstantInt::get(Type::getInt64Ty(Ctx), TypeId);
BasicBlock *TestBB = BasicBlock::Create(Ctx, "test", F);
IRBuilder<> IRBTest(TestBB);
Function *BitsetTestFn =
Intrinsic::getDeclaration(M, Intrinsic::bitset_test);
Value *Test = IRBTest.CreateCall(
BitsetTestFn, {&Addr, MetadataAsValue::get(
Ctx, ConstantAsMetadata::get(CaseTypeId))});
BranchInst *BI = IRBTest.CreateCondBr(Test, ExitBB, TrapBB);
BI->setMetadata(LLVMContext::MD_prof, VeryLikelyWeights);
SI->addCase(CaseTypeId, TestBB);
++TypeIds;
}
}
bool CrossDSOCFI::runOnModule(Module &M) {
if (M.getModuleFlag("Cross-DSO CFI") == nullptr)
return false;
buildCFICheck();
return true;
}
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