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 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerHelpers.h" 25 26 using namespace clang; 27 using namespace ento; 28 29 namespace { 30 class MmapWriteExecChecker 31 : public Checker<check::ASTDecl<TranslationUnitDecl>, check::PreCall> { 32 CallDescription MmapFn{CDM::CLibrary, {"mmap"}, 6}; 33 CallDescription MprotectFn{CDM::CLibrary, {"mprotect"}, 3}; 34 const BugType BT{this, "W^X check fails, Write Exec prot flags set", 35 "Security"}; 36 37 // Default values are used if definition of the flags is not found. 38 mutable int ProtRead = 0x01; 39 mutable int ProtWrite = 0x02; 40 mutable int ProtExec = 0x04; 41 42 public: 43 void checkASTDecl(const TranslationUnitDecl *TU, AnalysisManager &Mgr, 44 BugReporter &BR) const; 45 void checkPreCall(const CallEvent &Call, CheckerContext &C) const; 46 }; 47 } 48 49 void MmapWriteExecChecker::checkASTDecl(const TranslationUnitDecl *TU, 50 AnalysisManager &Mgr, 51 BugReporter &BR) const { 52 Preprocessor &PP = Mgr.getPreprocessor(); 53 const std::optional<int> FoundProtRead = tryExpandAsInteger("PROT_READ", PP); 54 const std::optional<int> FoundProtWrite = 55 tryExpandAsInteger("PROT_WRITE", PP); 56 const std::optional<int> FoundProtExec = tryExpandAsInteger("PROT_EXEC", PP); 57 if (FoundProtRead && FoundProtWrite && FoundProtExec) { 58 ProtRead = *FoundProtRead; 59 ProtWrite = *FoundProtWrite; 60 ProtExec = *FoundProtExec; 61 } 62 } 63 64 void MmapWriteExecChecker::checkPreCall(const CallEvent &Call, 65 CheckerContext &C) const { 66 if (matchesAny(Call, MmapFn, MprotectFn)) { 67 SVal ProtVal = Call.getArgSVal(2); 68 auto ProtLoc = ProtVal.getAs<nonloc::ConcreteInt>(); 69 if (!ProtLoc) 70 return; 71 int64_t Prot = ProtLoc->getValue()->getSExtValue(); 72 73 if ((Prot & ProtWrite) && (Prot & ProtExec)) { 74 ExplodedNode *N = C.generateNonFatalErrorNode(); 75 if (!N) 76 return; 77 78 auto Report = std::make_unique<PathSensitiveBugReport>( 79 BT, 80 "Both PROT_WRITE and PROT_EXEC flags are set. This can " 81 "lead to exploitable memory regions, which could be overwritten " 82 "with malicious code", 83 N); 84 Report->addRange(Call.getArgSourceRange(2)); 85 C.emitReport(std::move(Report)); 86 } 87 } 88 } 89 90 void ento::registerMmapWriteExecChecker(CheckerManager &Mgr) { 91 Mgr.registerChecker<MmapWriteExecChecker>(); 92 } 93 94 bool ento::shouldRegisterMmapWriteExecChecker(const CheckerManager &) { 95 return true; 96 } 97