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//===- X86WinFixupBufferSecurityCheck.cpp Fix Buffer Security Check Call -===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
// Buffer Security Check implementation inserts windows specific callback into
// code. On windows, __security_check_cookie call gets call everytime function
// is return without fixup. Since this function is defined in runtime library,
// it incures cost of call in dll which simply does comparison and returns most
// time. With Fixup, We selective move to call in DLL only if comparison fails.
//===----------------------------------------------------------------------===//
#include "X86.h"
#include "X86FrameLowering.h"
#include "X86InstrInfo.h"
#include "X86Subtarget.h"
#include "llvm/CodeGen/LivePhysRegs.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/IR/Module.h"
#include <iterator>
using namespace llvm;
#define DEBUG_TYPE "x86-win-fixup-bscheck"
namespace {
class X86WinFixupBufferSecurityCheckPass : public MachineFunctionPass {
public:
static char ID;
X86WinFixupBufferSecurityCheckPass() : MachineFunctionPass(ID) {}
StringRef getPassName() const override {
return "X86 Windows Fixup Buffer Security Check";
}
bool runOnMachineFunction(MachineFunction &MF) override;
std::pair<MachineBasicBlock *, MachineInstr *>
getSecurityCheckerBasicBlock(MachineFunction &MF);
void getGuardCheckSequence(MachineBasicBlock *CurMBB, MachineInstr *CheckCall,
MachineInstr *SeqMI[5]);
void SplitBasicBlock(MachineBasicBlock *CurMBB, MachineBasicBlock *NewRetMBB,
MachineBasicBlock::iterator SplitIt);
void FinishBlock(MachineBasicBlock *MBB);
void FinishFunction(MachineBasicBlock *FailMBB, MachineBasicBlock *NewRetMBB);
std::pair<MachineInstr *, MachineInstr *>
CreateFailCheckSequence(MachineBasicBlock *CurMBB, MachineBasicBlock *FailMBB,
MachineInstr *SeqMI[5]);
};
} // end anonymous namespace
char X86WinFixupBufferSecurityCheckPass::ID = 0;
INITIALIZE_PASS(X86WinFixupBufferSecurityCheckPass, DEBUG_TYPE, DEBUG_TYPE,
false, false)
FunctionPass *llvm::createX86WinFixupBufferSecurityCheckPass() {
return new X86WinFixupBufferSecurityCheckPass();
}
void X86WinFixupBufferSecurityCheckPass::SplitBasicBlock(
MachineBasicBlock *CurMBB, MachineBasicBlock *NewRetMBB,
MachineBasicBlock::iterator SplitIt) {
NewRetMBB->splice(NewRetMBB->end(), CurMBB, SplitIt, CurMBB->end());
}
std::pair<MachineBasicBlock *, MachineInstr *>
X86WinFixupBufferSecurityCheckPass::getSecurityCheckerBasicBlock(
MachineFunction &MF) {
MachineBasicBlock::reverse_iterator RBegin, REnd;
for (auto &MBB : llvm::reverse(MF)) {
for (RBegin = MBB.rbegin(), REnd = MBB.rend(); RBegin != REnd; ++RBegin) {
auto &MI = *RBegin;
if (MI.getOpcode() == X86::CALL64pcrel32 &&
MI.getNumExplicitOperands() == 1) {
auto MO = MI.getOperand(0);
if (MO.isGlobal()) {
auto Callee = dyn_cast<Function>(MO.getGlobal());
if (Callee && Callee->getName() == "__security_check_cookie") {
return std::make_pair(&MBB, &MI);
break;
}
}
}
}
}
return std::make_pair(nullptr, nullptr);
}
void X86WinFixupBufferSecurityCheckPass::getGuardCheckSequence(
MachineBasicBlock *CurMBB, MachineInstr *CheckCall,
MachineInstr *SeqMI[5]) {
MachineBasicBlock::iterator UIt(CheckCall);
MachineBasicBlock::reverse_iterator DIt(CheckCall);
// Seq From StackUp to Stack Down Is fixed.
// ADJCALLSTACKUP64
++UIt;
SeqMI[4] = &*UIt;
// CALL __security_check_cookie
SeqMI[3] = CheckCall;
// COPY function slot cookie
++DIt;
SeqMI[2] = &*DIt;
// ADJCALLSTACKDOWN64
++DIt;
SeqMI[1] = &*DIt;
MachineBasicBlock::reverse_iterator XIt(SeqMI[1]);
for (; XIt != CurMBB->rbegin(); ++XIt) {
auto &CI = *XIt;
if ((CI.getOpcode() == X86::XOR64_FP) || (CI.getOpcode() == X86::XOR32_FP))
break;
}
SeqMI[0] = &*XIt;
}
std::pair<MachineInstr *, MachineInstr *>
X86WinFixupBufferSecurityCheckPass::CreateFailCheckSequence(
MachineBasicBlock *CurMBB, MachineBasicBlock *FailMBB,
MachineInstr *SeqMI[5]) {
auto MF = CurMBB->getParent();
Module &M = *MF->getFunction().getParent();
GlobalVariable *GV = M.getGlobalVariable("__security_cookie");
assert(GV && " Security Cookie was not installed!");
const TargetInstrInfo *TII = MF->getSubtarget().getInstrInfo();
MachineInstr *GuardXor = SeqMI[0];
MachineBasicBlock::iterator InsertPt(GuardXor);
++InsertPt;
// Compare security_Cookie with XOR_Val, if not same, we have violation
auto CMI = BuildMI(*CurMBB, InsertPt, DebugLoc(), TII->get(X86::CMP64rm))
.addReg(GuardXor->getOperand(0).getReg())
.addReg(X86::RIP)
.addImm(1)
.addReg(X86::NoRegister)
.addGlobalAddress(GV)
.addReg(X86::NoRegister);
BuildMI(*CurMBB, InsertPt, DebugLoc(), TII->get(X86::JCC_1))
.addMBB(FailMBB)
.addImm(X86::COND_NE);
auto JMI = BuildMI(*CurMBB, InsertPt, DebugLoc(), TII->get(X86::JMP_1));
return std::make_pair(CMI.getInstr(), JMI.getInstr());
}
void X86WinFixupBufferSecurityCheckPass::FinishBlock(MachineBasicBlock *MBB) {
LivePhysRegs LiveRegs;
computeAndAddLiveIns(LiveRegs, *MBB);
}
void X86WinFixupBufferSecurityCheckPass::FinishFunction(
MachineBasicBlock *FailMBB, MachineBasicBlock *NewRetMBB) {
FailMBB->getParent()->RenumberBlocks();
// FailMBB includes call to MSCV RT where is __security_check_cookie
// function is called. This function uses regcall and it expects cookie
// value from stack slot.( even if this is modified)
// Before going further we compute back livein for this block to make sure
// it is live and provided.
FinishBlock(FailMBB);
FinishBlock(NewRetMBB);
}
bool X86WinFixupBufferSecurityCheckPass::runOnMachineFunction(
MachineFunction &MF) {
bool Changed = false;
const X86Subtarget &STI = MF.getSubtarget<X86Subtarget>();
if (!(STI.isTargetWindowsItanium() || STI.isTargetWindowsMSVC()))
return Changed;
// Check if security cookie was installed or not
Module &M = *MF.getFunction().getParent();
GlobalVariable *GV = M.getGlobalVariable("__security_cookie");
if (!GV)
return Changed;
const TargetInstrInfo *TII = MF.getSubtarget().getInstrInfo();
// Check if security check cookie was installed or not
auto [CurMBB, CheckCall] = getSecurityCheckerBasicBlock(MF);
if (!CheckCall)
return Changed;
MachineBasicBlock *FailMBB = MF.CreateMachineBasicBlock();
MachineBasicBlock *NewRetMBB = MF.CreateMachineBasicBlock();
MF.insert(MF.end(), NewRetMBB);
MF.insert(MF.end(), FailMBB);
MachineInstr *SeqMI[5];
getGuardCheckSequence(CurMBB, CheckCall, SeqMI);
// MachineInstr * GuardXor = SeqMI[0];
auto FailSeqRange = CreateFailCheckSequence(CurMBB, FailMBB, SeqMI);
MachineInstrBuilder JMI(MF, FailSeqRange.second);
// After Inserting JMP_1, we can not have two terminators
// in same block, split CurrentMBB after JMP_1
MachineBasicBlock::iterator SplitIt(SeqMI[4]);
++SplitIt;
SplitBasicBlock(CurMBB, NewRetMBB, SplitIt);
// Fill up Failure Routine, move Fail Check Squence from CurMBB to FailMBB
MachineBasicBlock::iterator U1It(SeqMI[1]);
MachineBasicBlock::iterator U2It(SeqMI[4]);
++U2It;
FailMBB->splice(FailMBB->end(), CurMBB, U1It, U2It);
BuildMI(*FailMBB, FailMBB->end(), DebugLoc(), TII->get(X86::INT3));
// Move left over instruction after StackUp
// from Current Basic BLocks into New Return Block
JMI.addMBB(NewRetMBB);
MachineBasicBlock::iterator SplicePt(JMI.getInstr());
++SplicePt;
if (SplicePt != CurMBB->end())
NewRetMBB->splice(NewRetMBB->end(), CurMBB, SplicePt);
// Restructure Basic Blocks
CurMBB->addSuccessor(NewRetMBB);
CurMBB->addSuccessor(FailMBB);
FinishFunction(FailMBB, NewRetMBB);
return !Changed;
}
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