1 | //===-- CFGuardLongjmp.cpp - Longjmp symbols for CFGuard --------*- C++ -*-===// |
2 | // |
3 | // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
4 | // See https://llvm.org/LICENSE.txt for license information. |
5 | // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
6 | // |
7 | //===----------------------------------------------------------------------===// |
8 | /// |
9 | /// \file |
10 | /// This file contains a machine function pass to insert a symbol after each |
11 | /// call to _setjmp and store this in the MachineFunction's LongjmpTargets |
12 | /// vector. This will be used to emit the table of valid longjmp targets used |
13 | /// by Control Flow Guard. |
14 | /// |
15 | //===----------------------------------------------------------------------===// |
16 | |
17 | #include "llvm/ADT/Statistic.h" |
18 | #include "llvm/CodeGen/MachineBasicBlock.h" |
19 | #include "llvm/CodeGen/MachineFunctionPass.h" |
20 | #include "llvm/CodeGen/MachineInstr.h" |
21 | #include "llvm/CodeGen/MachineModuleInfo.h" |
22 | #include "llvm/CodeGen/MachineOperand.h" |
23 | #include "llvm/CodeGen/Passes.h" |
24 | #include "llvm/InitializePasses.h" |
25 | |
26 | using namespace llvm; |
27 | |
28 | #define DEBUG_TYPE "cfguard-longjmp" |
29 | |
30 | STATISTIC(CFGuardLongjmpTargets, |
31 | "Number of Control Flow Guard longjmp targets" ); |
32 | |
33 | namespace { |
34 | |
35 | /// MachineFunction pass to insert a symbol after each call to _setjmp and store |
36 | /// this in the MachineFunction's LongjmpTargets vector. |
37 | class CFGuardLongjmp : public MachineFunctionPass { |
38 | public: |
39 | static char ID; |
40 | |
41 | CFGuardLongjmp() : MachineFunctionPass(ID) { |
42 | initializeCFGuardLongjmpPass(*PassRegistry::getPassRegistry()); |
43 | } |
44 | |
45 | StringRef getPassName() const override { |
46 | return "Control Flow Guard longjmp targets" ; |
47 | } |
48 | |
49 | bool runOnMachineFunction(MachineFunction &MF) override; |
50 | }; |
51 | |
52 | } // end anonymous namespace |
53 | |
54 | char CFGuardLongjmp::ID = 0; |
55 | |
56 | INITIALIZE_PASS(CFGuardLongjmp, "CFGuardLongjmp" , |
57 | "Insert symbols at valid longjmp targets for /guard:cf" , false, |
58 | false) |
59 | FunctionPass *llvm::createCFGuardLongjmpPass() { return new CFGuardLongjmp(); } |
60 | |
61 | bool CFGuardLongjmp::runOnMachineFunction(MachineFunction &MF) { |
62 | |
63 | // Skip modules for which the cfguard flag is not set. |
64 | if (!MF.getMMI().getModule()->getModuleFlag(Key: "cfguard" )) |
65 | return false; |
66 | |
67 | // Skip functions that do not have calls to _setjmp. |
68 | if (!MF.getFunction().callsFunctionThatReturnsTwice()) |
69 | return false; |
70 | |
71 | SmallVector<MachineInstr *, 8> SetjmpCalls; |
72 | |
73 | // Iterate over all instructions in the function and add calls to functions |
74 | // that return twice to the list of targets. |
75 | for (MachineBasicBlock &MBB : MF) { |
76 | for (MachineInstr &MI : MBB) { |
77 | |
78 | // Skip instructions that are not calls. |
79 | if (!MI.isCall() || MI.getNumOperands() < 1) |
80 | continue; |
81 | |
82 | // Iterate over operands to find calls to global functions. |
83 | for (MachineOperand &MO : MI.operands()) { |
84 | if (!MO.isGlobal()) |
85 | continue; |
86 | |
87 | auto *F = dyn_cast<Function>(Val: MO.getGlobal()); |
88 | if (!F) |
89 | continue; |
90 | |
91 | // If the instruction calls a function that returns twice, add |
92 | // it to the list of targets. |
93 | if (F->hasFnAttribute(Attribute::ReturnsTwice)) { |
94 | SetjmpCalls.push_back(Elt: &MI); |
95 | break; |
96 | } |
97 | } |
98 | } |
99 | } |
100 | |
101 | if (SetjmpCalls.empty()) |
102 | return false; |
103 | |
104 | unsigned SetjmpNum = 0; |
105 | |
106 | // For each possible target, create a new symbol and insert it immediately |
107 | // after the call to setjmp. Add this symbol to the MachineFunction's list |
108 | // of longjmp targets. |
109 | for (MachineInstr *Setjmp : SetjmpCalls) { |
110 | SmallString<128> SymbolName; |
111 | raw_svector_ostream(SymbolName) << "$cfgsj_" << MF.getName() << SetjmpNum++; |
112 | MCSymbol *SjSymbol = MF.getContext().getOrCreateSymbol(Name: SymbolName); |
113 | |
114 | Setjmp->setPostInstrSymbol(MF, Symbol: SjSymbol); |
115 | MF.addLongjmpTarget(Target: SjSymbol); |
116 | CFGuardLongjmpTargets++; |
117 | } |
118 | |
119 | return true; |
120 | } |
121 | |