1 //===-- BlockInCriticalSectionChecker.cpp -----------------------*- C++ -*-===//
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 // Defines a checker for blocks in critical sections. This checker should find
10 // the calls to blocking functions (for example: sleep, getc, fgets, read,
11 // recv etc.) inside a critical section. When sleep(x) is called while a mutex
12 // is held, other threades cannot lock the same mutex. This might take some
13 // time, leading to bad performance or even deadlock.
14 //
15 //===----------------------------------------------------------------------===//
16 
17 #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
18 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
19 #include "clang/StaticAnalyzer/Core/Checker.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 
24 using namespace clang;
25 using namespace ento;
26 
27 namespace {
28 
29 class BlockInCriticalSectionChecker : public Checker<check::PostCall> {
30 
31   mutable IdentifierInfo *IILockGuard, *IIUniqueLock;
32 
33   CallDescription LockFn, UnlockFn, SleepFn, GetcFn, FgetsFn, ReadFn, RecvFn,
34                   PthreadLockFn, PthreadTryLockFn, PthreadUnlockFn,
35                   MtxLock, MtxTimedLock, MtxTryLock, MtxUnlock;
36 
37   StringRef ClassLockGuard, ClassUniqueLock;
38 
39   mutable bool IdentifierInfoInitialized;
40 
41   std::unique_ptr<BugType> BlockInCritSectionBugType;
42 
43   void initIdentifierInfo(ASTContext &Ctx) const;
44 
45   void reportBlockInCritSection(SymbolRef FileDescSym,
46                                 const CallEvent &call,
47                                 CheckerContext &C) const;
48 
49 public:
50   BlockInCriticalSectionChecker();
51 
52   bool isBlockingFunction(const CallEvent &Call) const;
53   bool isLockFunction(const CallEvent &Call) const;
54   bool isUnlockFunction(const CallEvent &Call) const;
55 
56   /// Process unlock.
57   /// Process lock.
58   /// Process blocking functions (sleep, getc, fgets, read, recv)
59   void checkPostCall(const CallEvent &Call, CheckerContext &C) const;
60 };
61 
62 } // end anonymous namespace
63 
64 REGISTER_TRAIT_WITH_PROGRAMSTATE(MutexCounter, unsigned)
65 
66 BlockInCriticalSectionChecker::BlockInCriticalSectionChecker()
67     : IILockGuard(nullptr), IIUniqueLock(nullptr),
68       LockFn("lock"), UnlockFn("unlock"), SleepFn("sleep"), GetcFn("getc"),
69       FgetsFn("fgets"), ReadFn("read"), RecvFn("recv"),
70       PthreadLockFn("pthread_mutex_lock"),
71       PthreadTryLockFn("pthread_mutex_trylock"),
72       PthreadUnlockFn("pthread_mutex_unlock"),
73       MtxLock("mtx_lock"),
74       MtxTimedLock("mtx_timedlock"),
75       MtxTryLock("mtx_trylock"),
76       MtxUnlock("mtx_unlock"),
77       ClassLockGuard("lock_guard"),
78       ClassUniqueLock("unique_lock"),
79       IdentifierInfoInitialized(false) {
80   // Initialize the bug type.
81   BlockInCritSectionBugType.reset(
82       new BugType(this, "Call to blocking function in critical section",
83                         "Blocking Error"));
84 }
85 
86 void BlockInCriticalSectionChecker::initIdentifierInfo(ASTContext &Ctx) const {
87   if (!IdentifierInfoInitialized) {
88     /* In case of checking C code, or when the corresponding headers are not
89      * included, we might end up query the identifier table every time when this
90      * function is called instead of early returning it. To avoid this, a bool
91      * variable (IdentifierInfoInitialized) is used and the function will be run
92      * only once. */
93     IILockGuard  = &Ctx.Idents.get(ClassLockGuard);
94     IIUniqueLock = &Ctx.Idents.get(ClassUniqueLock);
95     IdentifierInfoInitialized = true;
96   }
97 }
98 
99 bool BlockInCriticalSectionChecker::isBlockingFunction(const CallEvent &Call) const {
100   return matchesAny(Call, SleepFn, GetcFn, FgetsFn, ReadFn, RecvFn);
101 }
102 
103 bool BlockInCriticalSectionChecker::isLockFunction(const CallEvent &Call) const {
104   if (const auto *Ctor = dyn_cast<CXXConstructorCall>(&Call)) {
105     auto IdentifierInfo = Ctor->getDecl()->getParent()->getIdentifier();
106     if (IdentifierInfo == IILockGuard || IdentifierInfo == IIUniqueLock)
107       return true;
108   }
109 
110   return matchesAny(Call, LockFn, PthreadLockFn, PthreadTryLockFn, MtxLock,
111                     MtxTimedLock, MtxTryLock);
112 }
113 
114 bool BlockInCriticalSectionChecker::isUnlockFunction(const CallEvent &Call) const {
115   if (const auto *Dtor = dyn_cast<CXXDestructorCall>(&Call)) {
116     const auto *DRecordDecl = cast<CXXRecordDecl>(Dtor->getDecl()->getParent());
117     auto IdentifierInfo = DRecordDecl->getIdentifier();
118     if (IdentifierInfo == IILockGuard || IdentifierInfo == IIUniqueLock)
119       return true;
120   }
121 
122   return matchesAny(Call, UnlockFn, PthreadUnlockFn, MtxUnlock);
123 }
124 
125 void BlockInCriticalSectionChecker::checkPostCall(const CallEvent &Call,
126                                                   CheckerContext &C) const {
127   initIdentifierInfo(C.getASTContext());
128 
129   if (!isBlockingFunction(Call)
130       && !isLockFunction(Call)
131       && !isUnlockFunction(Call))
132     return;
133 
134   ProgramStateRef State = C.getState();
135   unsigned mutexCount = State->get<MutexCounter>();
136   if (isUnlockFunction(Call) && mutexCount > 0) {
137     State = State->set<MutexCounter>(--mutexCount);
138     C.addTransition(State);
139   } else if (isLockFunction(Call)) {
140     State = State->set<MutexCounter>(++mutexCount);
141     C.addTransition(State);
142   } else if (mutexCount > 0) {
143     SymbolRef BlockDesc = Call.getReturnValue().getAsSymbol();
144     reportBlockInCritSection(BlockDesc, Call, C);
145   }
146 }
147 
148 void BlockInCriticalSectionChecker::reportBlockInCritSection(
149     SymbolRef BlockDescSym, const CallEvent &Call, CheckerContext &C) const {
150   ExplodedNode *ErrNode = C.generateNonFatalErrorNode();
151   if (!ErrNode)
152     return;
153 
154   std::string msg;
155   llvm::raw_string_ostream os(msg);
156   os << "Call to blocking function '" << Call.getCalleeIdentifier()->getName()
157      << "' inside of critical section";
158   auto R = std::make_unique<PathSensitiveBugReport>(*BlockInCritSectionBugType,
159                                                     os.str(), ErrNode);
160   R->addRange(Call.getSourceRange());
161   R->markInteresting(BlockDescSym);
162   C.emitReport(std::move(R));
163 }
164 
165 void ento::registerBlockInCriticalSectionChecker(CheckerManager &mgr) {
166   mgr.registerChecker<BlockInCriticalSectionChecker>();
167 }
168 
169 bool ento::shouldRegisterBlockInCriticalSectionChecker(const CheckerManager &mgr) {
170   return true;
171 }
172