96 lines · cpp
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-exception6//7//===----------------------------------------------------------------------===//8//9// This checker tests the 3rd argument of mmap's calls to check if10// it is writable and executable in the same time. It's somehow11// 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 25using namespace clang;26using namespace ento;27 28namespace {29class MmapWriteExecChecker30 : 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 41public:42 void checkASTDecl(const TranslationUnitDecl *TU, AnalysisManager &Mgr,43 BugReporter &BR) const;44 void checkPreCall(const CallEvent &Call, CheckerContext &C) const;45};46}47 48void 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 63void 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 89void ento::registerMmapWriteExecChecker(CheckerManager &Mgr) {90 Mgr.registerChecker<MmapWriteExecChecker>();91}92 93bool ento::shouldRegisterMmapWriteExecChecker(const CheckerManager &) {94 return true;95}96