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;
31 CallDescription MprotectFn;
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:
MmapWriteExecChecker()39 MmapWriteExecChecker() : MmapFn({"mmap"}, 6), MprotectFn({"mprotect"}, 3) {}
40 void checkPreCall(const CallEvent &Call, CheckerContext &C) const;
41 int ProtExecOv;
42 int ProtReadOv;
43 };
44 }
45
46 int MmapWriteExecChecker::ProtWrite = 0x02;
47 int MmapWriteExecChecker::ProtExec = 0x04;
48 int MmapWriteExecChecker::ProtRead = 0x01;
49
checkPreCall(const CallEvent & Call,CheckerContext & C) const50 void MmapWriteExecChecker::checkPreCall(const CallEvent &Call,
51 CheckerContext &C) const {
52 if (matchesAny(Call, MmapFn, MprotectFn)) {
53 SVal ProtVal = Call.getArgSVal(2);
54 auto ProtLoc = ProtVal.getAs<nonloc::ConcreteInt>();
55 if (!ProtLoc)
56 return;
57 int64_t Prot = ProtLoc->getValue().getSExtValue();
58 if (ProtExecOv != ProtExec)
59 ProtExec = ProtExecOv;
60 if (ProtReadOv != ProtRead)
61 ProtRead = ProtReadOv;
62
63 // Wrong settings
64 if (ProtRead == ProtExec)
65 return;
66
67 if ((Prot & (ProtWrite | ProtExec)) == (ProtWrite | ProtExec)) {
68 ExplodedNode *N = C.generateNonFatalErrorNode();
69 if (!N)
70 return;
71
72 auto Report = std::make_unique<PathSensitiveBugReport>(
73 BT,
74 "Both PROT_WRITE and PROT_EXEC flags are set. This can "
75 "lead to exploitable memory regions, which could be overwritten "
76 "with malicious code",
77 N);
78 Report->addRange(Call.getArgSourceRange(2));
79 C.emitReport(std::move(Report));
80 }
81 }
82 }
83
registerMmapWriteExecChecker(CheckerManager & mgr)84 void ento::registerMmapWriteExecChecker(CheckerManager &mgr) {
85 MmapWriteExecChecker *Mwec =
86 mgr.registerChecker<MmapWriteExecChecker>();
87 Mwec->ProtExecOv =
88 mgr.getAnalyzerOptions()
89 .getCheckerIntegerOption(Mwec, "MmapProtExec");
90 Mwec->ProtReadOv =
91 mgr.getAnalyzerOptions()
92 .getCheckerIntegerOption(Mwec, "MmapProtRead");
93 }
94
shouldRegisterMmapWriteExecChecker(const CheckerManager & mgr)95 bool ento::shouldRegisterMmapWriteExecChecker(const CheckerManager &mgr) {
96 return true;
97 }
98