1 // MmapWriteExecChecker.cpp - Check for the prot argument -----------------===//
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 // This checker tests the 3rd argument of mmap's calls to check if
10 // it is writable and executable in the same time. It's somehow
11 // an optional checker since for example in JIT libraries it is pretty common.
12 //
13 //===----------------------------------------------------------------------===//
14
15 #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
16
17 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
18 #include "clang/StaticAnalyzer/Core/Checker.h"
19 #include "clang/StaticAnalyzer/Core/CheckerManager.h"
20 #include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"
21 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
22
23 using namespace clang;
24 using namespace ento;
25 using llvm::APSInt;
26
27 namespace {
28 class MmapWriteExecChecker : public Checker<check::PreCall> {
29 CallDescription MmapFn;
30 CallDescription MprotectFn;
31 static int ProtWrite;
32 static int ProtExec;
33 static int ProtRead;
34 mutable std::unique_ptr<BugType> BT;
35 public:
MmapWriteExecChecker()36 MmapWriteExecChecker() : MmapFn("mmap", 6), MprotectFn("mprotect", 3) {}
37 void checkPreCall(const CallEvent &Call, CheckerContext &C) const;
38 int ProtExecOv;
39 int ProtReadOv;
40 };
41 }
42
43 int MmapWriteExecChecker::ProtWrite = 0x02;
44 int MmapWriteExecChecker::ProtExec = 0x04;
45 int MmapWriteExecChecker::ProtRead = 0x01;
46
checkPreCall(const CallEvent & Call,CheckerContext & C) const47 void MmapWriteExecChecker::checkPreCall(const CallEvent &Call,
48 CheckerContext &C) const {
49 if (Call.isCalled(MmapFn) || Call.isCalled(MprotectFn)) {
50 SVal ProtVal = Call.getArgSVal(2);
51 Optional<nonloc::ConcreteInt> ProtLoc = ProtVal.getAs<nonloc::ConcreteInt>();
52 int64_t Prot = ProtLoc->getValue().getSExtValue();
53 if (ProtExecOv != ProtExec)
54 ProtExec = ProtExecOv;
55 if (ProtReadOv != ProtRead)
56 ProtRead = ProtReadOv;
57
58 // Wrong settings
59 if (ProtRead == ProtExec)
60 return;
61
62 if ((Prot & (ProtWrite | ProtExec)) == (ProtWrite | ProtExec)) {
63 if (!BT)
64 BT.reset(new BugType(this, "W^X check fails, Write Exec prot flags set", "Security"));
65
66 ExplodedNode *N = C.generateNonFatalErrorNode();
67 if (!N)
68 return;
69
70 auto Report = std::make_unique<PathSensitiveBugReport>(
71 *BT, "Both PROT_WRITE and PROT_EXEC flags are set. This can "
72 "lead to exploitable memory regions, which could be overwritten "
73 "with malicious code", N);
74 Report->addRange(Call.getArgSourceRange(2));
75 C.emitReport(std::move(Report));
76 }
77 }
78 }
79
registerMmapWriteExecChecker(CheckerManager & mgr)80 void ento::registerMmapWriteExecChecker(CheckerManager &mgr) {
81 MmapWriteExecChecker *Mwec =
82 mgr.registerChecker<MmapWriteExecChecker>();
83 Mwec->ProtExecOv =
84 mgr.getAnalyzerOptions()
85 .getCheckerIntegerOption(Mwec, "MmapProtExec");
86 Mwec->ProtReadOv =
87 mgr.getAnalyzerOptions()
88 .getCheckerIntegerOption(Mwec, "MmapProtRead");
89 }
90
shouldRegisterMmapWriteExecChecker(const CheckerManager & mgr)91 bool ento::shouldRegisterMmapWriteExecChecker(const CheckerManager &mgr) {
92 return true;
93 }
94