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/BugReporter/CommonBugCategories.h"
19 #include "clang/StaticAnalyzer/Core/Checker.h"
20 #include "clang/StaticAnalyzer/Core/CheckerManager.h"
21 #include "clang/StaticAnalyzer/Core/PathSensitive/CallDescription.h"
22 #include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"
23 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
24
25 using namespace clang;
26 using namespace ento;
27
28 namespace {
29 class MmapWriteExecChecker : public Checker<check::PreCall> {
30 CallDescription MmapFn{CDM::CLibrary, {"mmap"}, 6};
31 CallDescription MprotectFn{CDM::CLibrary, {"mprotect"}, 3};
32 static int ProtWrite;
33 static int ProtExec;
34 static int ProtRead;
35 const BugType BT{this, "W^X check fails, Write Exec prot flags set",
36 "Security"};
37
38 public:
39 void checkPreCall(const CallEvent &Call, CheckerContext &C) const;
40 int ProtExecOv;
41 int ProtReadOv;
42 };
43 }
44
45 int MmapWriteExecChecker::ProtWrite = 0x02;
46 int MmapWriteExecChecker::ProtExec = 0x04;
47 int MmapWriteExecChecker::ProtRead = 0x01;
48
checkPreCall(const CallEvent & Call,CheckerContext & C) const49 void MmapWriteExecChecker::checkPreCall(const CallEvent &Call,
50 CheckerContext &C) const {
51 if (matchesAny(Call, MmapFn, MprotectFn)) {
52 SVal ProtVal = Call.getArgSVal(2);
53 auto ProtLoc = ProtVal.getAs<nonloc::ConcreteInt>();
54 if (!ProtLoc)
55 return;
56 int64_t Prot = ProtLoc->getValue().getSExtValue();
57 if (ProtExecOv != ProtExec)
58 ProtExec = ProtExecOv;
59 if (ProtReadOv != ProtRead)
60 ProtRead = ProtReadOv;
61
62 // Wrong settings
63 if (ProtRead == ProtExec)
64 return;
65
66 if ((Prot & (ProtWrite | ProtExec)) == (ProtWrite | ProtExec)) {
67 ExplodedNode *N = C.generateNonFatalErrorNode();
68 if (!N)
69 return;
70
71 auto Report = std::make_unique<PathSensitiveBugReport>(
72 BT,
73 "Both PROT_WRITE and PROT_EXEC flags are set. This can "
74 "lead to exploitable memory regions, which could be overwritten "
75 "with malicious code",
76 N);
77 Report->addRange(Call.getArgSourceRange(2));
78 C.emitReport(std::move(Report));
79 }
80 }
81 }
82
registerMmapWriteExecChecker(CheckerManager & mgr)83 void ento::registerMmapWriteExecChecker(CheckerManager &mgr) {
84 MmapWriteExecChecker *Mwec =
85 mgr.registerChecker<MmapWriteExecChecker>();
86 Mwec->ProtExecOv =
87 mgr.getAnalyzerOptions()
88 .getCheckerIntegerOption(Mwec, "MmapProtExec");
89 Mwec->ProtReadOv =
90 mgr.getAnalyzerOptions()
91 .getCheckerIntegerOption(Mwec, "MmapProtRead");
92 }
93
shouldRegisterMmapWriteExecChecker(const CheckerManager & mgr)94 bool ento::shouldRegisterMmapWriteExecChecker(const CheckerManager &mgr) {
95 return true;
96 }
97