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diff --git a/lib/Target/X86/ShadowCallStack.cpp b/lib/Target/X86/ShadowCallStack.cpp
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+//===------- ShadowCallStack.cpp - Shadow Call Stack pass -----------------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// The ShadowCallStack pass instruments function prologs/epilogs to check that
+// the return address has not been corrupted during the execution of the
+// function. The return address is stored in a 'shadow call stack' addressed
+// using the %gs segment register.
+//
+//===----------------------------------------------------------------------===//
+
+#include "X86.h"
+#include "X86InstrBuilder.h"
+#include "X86InstrInfo.h"
+#include "X86Subtarget.h"
+
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/CodeGen/MachineModuleInfo.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/CodeGen/TargetInstrInfo.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/raw_ostream.h"
+
+using namespace llvm;
+
+namespace llvm {
+void initializeShadowCallStackPass(PassRegistry &);
+}
+
+namespace {
+
+class ShadowCallStack : public MachineFunctionPass {
+public:
+ static char ID;
+
+ ShadowCallStack() : MachineFunctionPass(ID) {
+ initializeShadowCallStackPass(*PassRegistry::getPassRegistry());
+ }
+
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
+ MachineFunctionPass::getAnalysisUsage(AU);
+ }
+
+ bool runOnMachineFunction(MachineFunction &Fn) override;
+
+private:
+ // Do not instrument leaf functions with this many or fewer instructions. The
+ // shadow call stack instrumented prolog/epilog are slightly race-y reading
+ // and checking the saved return address, so it is better to not instrument
+ // functions that have fewer instructions than the instrumented prolog/epilog
+ // race.
+ static const size_t SkipLeafInstructions = 3;
+};
+
+char ShadowCallStack::ID = 0;
+} // end anonymous namespace.
+
+static void addProlog(MachineFunction &Fn, const TargetInstrInfo *TII,
+ MachineBasicBlock &MBB, const DebugLoc &DL);
+static void addPrologLeaf(MachineFunction &Fn, const TargetInstrInfo *TII,
+ MachineBasicBlock &MBB, const DebugLoc &DL,
+ MCPhysReg FreeRegister);
+
+static void addEpilog(const TargetInstrInfo *TII, MachineBasicBlock &MBB,
+ MachineInstr &MI, MachineBasicBlock &TrapBB);
+static void addEpilogLeaf(const TargetInstrInfo *TII, MachineBasicBlock &MBB,
+ MachineInstr &MI, MachineBasicBlock &TrapBB,
+ MCPhysReg FreeRegister);
+// Generate a longer epilog that only uses r10 when a tailcall branches to r11.
+static void addEpilogOnlyR10(const TargetInstrInfo *TII, MachineBasicBlock &MBB,
+ MachineInstr &MI, MachineBasicBlock &TrapBB);
+
+// Helper function to add ModR/M references for [Seg: Reg + Offset] memory
+// accesses
+static inline const MachineInstrBuilder &
+addSegmentedMem(const MachineInstrBuilder &MIB, MCPhysReg Seg, MCPhysReg Reg,
+ int Offset = 0) {
+ return MIB.addReg(Reg).addImm(1).addReg(0).addImm(Offset).addReg(Seg);
+}
+
+static void addProlog(MachineFunction &Fn, const TargetInstrInfo *TII,
+ MachineBasicBlock &MBB, const DebugLoc &DL) {
+ const MCPhysReg ReturnReg = X86::R10;
+ const MCPhysReg OffsetReg = X86::R11;
+
+ auto MBBI = MBB.begin();
+ // mov r10, [rsp]
+ addDirectMem(BuildMI(MBB, MBBI, DL, TII->get(X86::MOV64rm)).addDef(ReturnReg),
+ X86::RSP);
+ // xor r11, r11
+ BuildMI(MBB, MBBI, DL, TII->get(X86::XOR64rr))
+ .addDef(OffsetReg)
+ .addReg(OffsetReg, RegState::Undef)
+ .addReg(OffsetReg, RegState::Undef);
+ // add QWORD [gs:r11], 8
+ addSegmentedMem(BuildMI(MBB, MBBI, DL, TII->get(X86::ADD64mi8)), X86::GS,
+ OffsetReg)
+ .addImm(8);
+ // mov r11, [gs:r11]
+ addSegmentedMem(
+ BuildMI(MBB, MBBI, DL, TII->get(X86::MOV64rm)).addDef(OffsetReg), X86::GS,
+ OffsetReg);
+ // mov [gs:r11], r10
+ addSegmentedMem(BuildMI(MBB, MBBI, DL, TII->get(X86::MOV64mr)), X86::GS,
+ OffsetReg)
+ .addReg(ReturnReg);
+}
+
+static void addPrologLeaf(MachineFunction &Fn, const TargetInstrInfo *TII,
+ MachineBasicBlock &MBB, const DebugLoc &DL,
+ MCPhysReg FreeRegister) {
+ // mov REG, [rsp]
+ addDirectMem(BuildMI(MBB, MBB.begin(), DL, TII->get(X86::MOV64rm))
+ .addDef(FreeRegister),
+ X86::RSP);
+}
+
+static void addEpilog(const TargetInstrInfo *TII, MachineBasicBlock &MBB,
+ MachineInstr &MI, MachineBasicBlock &TrapBB) {
+ const DebugLoc &DL = MI.getDebugLoc();
+
+ // xor r11, r11
+ BuildMI(MBB, MI, DL, TII->get(X86::XOR64rr))
+ .addDef(X86::R11)
+ .addReg(X86::R11, RegState::Undef)
+ .addReg(X86::R11, RegState::Undef);
+ // mov r10, [gs:r11]
+ addSegmentedMem(BuildMI(MBB, MI, DL, TII->get(X86::MOV64rm)).addDef(X86::R10),
+ X86::GS, X86::R11);
+ // mov r10, [gs:r10]
+ addSegmentedMem(BuildMI(MBB, MI, DL, TII->get(X86::MOV64rm)).addDef(X86::R10),
+ X86::GS, X86::R10);
+ // sub QWORD [gs:r11], 8
+ // This instruction should not be moved up to avoid a signal race.
+ addSegmentedMem(BuildMI(MBB, MI, DL, TII->get(X86::SUB64mi8)),
+ X86::GS, X86::R11)
+ .addImm(8);
+ // cmp [rsp], r10
+ addDirectMem(BuildMI(MBB, MI, DL, TII->get(X86::CMP64mr)), X86::RSP)
+ .addReg(X86::R10);
+ // jne trap
+ BuildMI(MBB, MI, DL, TII->get(X86::JNE_1)).addMBB(&TrapBB);
+ MBB.addSuccessor(&TrapBB);
+}
+
+static void addEpilogLeaf(const TargetInstrInfo *TII, MachineBasicBlock &MBB,
+ MachineInstr &MI, MachineBasicBlock &TrapBB,
+ MCPhysReg FreeRegister) {
+ const DebugLoc &DL = MI.getDebugLoc();
+
+ // cmp [rsp], REG
+ addDirectMem(BuildMI(MBB, MI, DL, TII->get(X86::CMP64mr)), X86::RSP)
+ .addReg(FreeRegister);
+ // jne trap
+ BuildMI(MBB, MI, DL, TII->get(X86::JNE_1)).addMBB(&TrapBB);
+ MBB.addSuccessor(&TrapBB);
+}
+
+static void addEpilogOnlyR10(const TargetInstrInfo *TII, MachineBasicBlock &MBB,
+ MachineInstr &MI, MachineBasicBlock &TrapBB) {
+ const DebugLoc &DL = MI.getDebugLoc();
+
+ // xor r10, r10
+ BuildMI(MBB, MI, DL, TII->get(X86::XOR64rr))
+ .addDef(X86::R10)
+ .addReg(X86::R10, RegState::Undef)
+ .addReg(X86::R10, RegState::Undef);
+ // mov r10, [gs:r10]
+ addSegmentedMem(BuildMI(MBB, MI, DL, TII->get(X86::MOV64rm)).addDef(X86::R10),
+ X86::GS, X86::R10);
+ // mov r10, [gs:r10]
+ addSegmentedMem(BuildMI(MBB, MI, DL, TII->get(X86::MOV64rm)).addDef(X86::R10),
+ X86::GS, X86::R10);
+ // sub QWORD [gs:0], 8
+ // This instruction should not be moved up to avoid a signal race.
+ addSegmentedMem(BuildMI(MBB, MI, DL, TII->get(X86::SUB64mi8)), X86::GS, 0)
+ .addImm(8);
+ // cmp [rsp], r10
+ addDirectMem(BuildMI(MBB, MI, DL, TII->get(X86::CMP64mr)), X86::RSP)
+ .addReg(X86::R10);
+ // jne trap
+ BuildMI(MBB, MI, DL, TII->get(X86::JNE_1)).addMBB(&TrapBB);
+ MBB.addSuccessor(&TrapBB);
+}
+
+bool ShadowCallStack::runOnMachineFunction(MachineFunction &Fn) {
+ if (!Fn.getFunction().hasFnAttribute(Attribute::ShadowCallStack) ||
+ Fn.getFunction().hasFnAttribute(Attribute::Naked))
+ return false;
+
+ if (Fn.empty() || !Fn.getRegInfo().tracksLiveness())
+ return false;
+
+ // FIXME: Skip functions that have r10 or r11 live on entry (r10 can be live
+ // on entry for parameters with the nest attribute.)
+ if (Fn.front().isLiveIn(X86::R10) || Fn.front().isLiveIn(X86::R11))
+ return false;
+
+ // FIXME: Skip functions with conditional and r10 tail calls for now.
+ bool HasReturn = false;
+ for (auto &MBB : Fn) {
+ if (MBB.empty())
+ continue;
+
+ const MachineInstr &MI = MBB.instr_back();
+ if (MI.isReturn())
+ HasReturn = true;
+
+ if (MI.isReturn() && MI.isCall()) {
+ if (MI.findRegisterUseOperand(X86::EFLAGS))
+ return false;
+ // This should only be possible on Windows 64 (see GR64_TC versus
+ // GR64_TCW64.)
+ if (MI.findRegisterUseOperand(X86::R10) ||
+ MI.hasRegisterImplicitUseOperand(X86::R10))
+ return false;
+ }
+ }
+
+ if (!HasReturn)
+ return false;
+
+ // For leaf functions:
+ // 1. Do not instrument very short functions where it would not improve that
+ // function's security.
+ // 2. Detect if there is an unused caller-saved register we can reserve to
+ // hold the return address instead of writing/reading it from the shadow
+ // call stack.
+ MCPhysReg LeafFuncRegister = X86::NoRegister;
+ if (!Fn.getFrameInfo().adjustsStack()) {
+ size_t InstructionCount = 0;
+ std::bitset<X86::NUM_TARGET_REGS> UsedRegs;
+ for (auto &MBB : Fn) {
+ for (auto &LiveIn : MBB.liveins())
+ UsedRegs.set(LiveIn.PhysReg);
+ for (auto &MI : MBB) {
+ if (!MI.isDebugValue() && !MI.isCFIInstruction() && !MI.isLabel())
+ InstructionCount++;
+ for (auto &Op : MI.operands())
+ if (Op.isReg() && Op.isDef())
+ UsedRegs.set(Op.getReg());
+ }
+ }
+
+ if (InstructionCount <= SkipLeafInstructions)
+ return false;
+
+ std::bitset<X86::NUM_TARGET_REGS> CalleeSavedRegs;
+ const MCPhysReg *CSRegs = Fn.getRegInfo().getCalleeSavedRegs();
+ for (size_t i = 0; CSRegs[i]; i++)
+ CalleeSavedRegs.set(CSRegs[i]);
+
+ const TargetRegisterInfo *TRI = Fn.getSubtarget().getRegisterInfo();
+ for (auto &Reg : X86::GR64_NOSPRegClass.getRegisters()) {
+ // FIXME: Optimization opportunity: spill/restore a callee-saved register
+ // if a caller-saved register is unavailable.
+ if (CalleeSavedRegs.test(Reg))
+ continue;
+
+ bool Used = false;
+ for (MCSubRegIterator SR(Reg, TRI, true); SR.isValid(); ++SR)
+ if ((Used = UsedRegs.test(*SR)))
+ break;
+
+ if (!Used) {
+ LeafFuncRegister = Reg;
+ break;
+ }
+ }
+ }
+
+ const bool LeafFuncOptimization = LeafFuncRegister != X86::NoRegister;
+ if (LeafFuncOptimization)
+ // Mark the leaf function register live-in for all MBBs except the entry MBB
+ for (auto I = ++Fn.begin(), E = Fn.end(); I != E; ++I)
+ I->addLiveIn(LeafFuncRegister);
+
+ MachineBasicBlock &MBB = Fn.front();
+ const MachineBasicBlock *NonEmpty = MBB.empty() ? MBB.getFallThrough() : &MBB;
+ const DebugLoc &DL = NonEmpty->front().getDebugLoc();
+
+ const TargetInstrInfo *TII = Fn.getSubtarget().getInstrInfo();
+ if (LeafFuncOptimization)
+ addPrologLeaf(Fn, TII, MBB, DL, LeafFuncRegister);
+ else
+ addProlog(Fn, TII, MBB, DL);
+
+ MachineBasicBlock *Trap = nullptr;
+ for (auto &MBB : Fn) {
+ if (MBB.empty())
+ continue;
+
+ MachineInstr &MI = MBB.instr_back();
+ if (MI.isReturn()) {
+ if (!Trap) {
+ Trap = Fn.CreateMachineBasicBlock();
+ BuildMI(Trap, MI.getDebugLoc(), TII->get(X86::TRAP));
+ Fn.push_back(Trap);
+ }
+
+ if (LeafFuncOptimization)
+ addEpilogLeaf(TII, MBB, MI, *Trap, LeafFuncRegister);
+ else if (MI.findRegisterUseOperand(X86::R11))
+ addEpilogOnlyR10(TII, MBB, MI, *Trap);
+ else
+ addEpilog(TII, MBB, MI, *Trap);
+ }
+ }
+
+ return true;
+}
+
+INITIALIZE_PASS(ShadowCallStack, "shadow-call-stack", "Shadow Call Stack",
+ false, false)
+
+FunctionPass *llvm::createShadowCallStackPass() {
+ return new ShadowCallStack();
+}
generated by cgit v1.2.3 (git 2.25.1) at 2025-11-04 14:48:51 +0000