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/CallDescription.h" 21 #include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h" 22 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h" 23 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerHelpers.h" 24 25 using namespace clang; 26 using namespace ento; 27 28 namespace { 29 class MmapWriteExecChecker 30 : public Checker<check::ASTDecl<TranslationUnitDecl>, check::PreCall> { 31 CallDescription MmapFn{CDM::CLibrary, {"mmap"}, 6}; 32 CallDescription MprotectFn{CDM::CLibrary, {"mprotect"}, 3}; 33 const BugType BT{this, "W^X check fails, Write Exec prot flags set", 34 "Security"}; 35 36 // Default values are used if definition of the flags is not found. 37 mutable int ProtRead = 0x01; 38 mutable int ProtWrite = 0x02; 39 mutable int ProtExec = 0x04; 40 41 public: 42 void checkASTDecl(const TranslationUnitDecl *TU, AnalysisManager &Mgr, 43 BugReporter &BR) const; 44 void checkPreCall(const CallEvent &Call, CheckerContext &C) const; 45 }; 46 } 47 48 void MmapWriteExecChecker::checkASTDecl(const TranslationUnitDecl *TU, 49 AnalysisManager &Mgr, 50 BugReporter &BR) const { 51 Preprocessor &PP = Mgr.getPreprocessor(); 52 const std::optional<int> FoundProtRead = tryExpandAsInteger("PROT_READ", PP); 53 const std::optional<int> FoundProtWrite = 54 tryExpandAsInteger("PROT_WRITE", PP); 55 const std::optional<int> FoundProtExec = tryExpandAsInteger("PROT_EXEC", PP); 56 if (FoundProtRead && FoundProtWrite && FoundProtExec) { 57 ProtRead = *FoundProtRead; 58 ProtWrite = *FoundProtWrite; 59 ProtExec = *FoundProtExec; 60 } 61 } 62 63 void MmapWriteExecChecker::checkPreCall(const CallEvent &Call, 64 CheckerContext &C) const { 65 if (matchesAny(Call, MmapFn, MprotectFn)) { 66 SVal ProtVal = Call.getArgSVal(2); 67 auto ProtLoc = ProtVal.getAs<nonloc::ConcreteInt>(); 68 if (!ProtLoc) 69 return; 70 int64_t Prot = ProtLoc->getValue()->getSExtValue(); 71 72 if ((Prot & ProtWrite) && (Prot & ProtExec)) { 73 ExplodedNode *N = C.generateNonFatalErrorNode(); 74 if (!N) 75 return; 76 77 auto Report = std::make_unique<PathSensitiveBugReport>( 78 BT, 79 "Both PROT_WRITE and PROT_EXEC flags are set. This can " 80 "lead to exploitable memory regions, which could be overwritten " 81 "with malicious code", 82 N); 83 Report->addRange(Call.getArgSourceRange(2)); 84 C.emitReport(std::move(Report)); 85 } 86 } 87 } 88 89 void ento::registerMmapWriteExecChecker(CheckerManager &Mgr) { 90 Mgr.registerChecker<MmapWriteExecChecker>(); 91 } 92 93 bool ento::shouldRegisterMmapWriteExecChecker(const CheckerManager &) { 94 return true; 95 } 96