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: 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 50 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 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 95 bool ento::shouldRegisterMmapWriteExecChecker(const CheckerManager &mgr) { 96 return true; 97 } 98