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 49 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 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 94 bool ento::shouldRegisterMmapWriteExecChecker(const CheckerManager &mgr) { 95 return true; 96 } 97