1 // MacOSXAPIChecker.h - Checks proper use of various MacOS X APIs --*- C++ -*-//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This defines MacOSXAPIChecker, which is an assortment of checks on calls
11 // to various, widely used Apple APIs.
12 //
13 // FIXME: What's currently in BasicObjCFoundationChecks.cpp should be migrated
14 // to here, using the new Checker interface.
15 //
16 //===----------------------------------------------------------------------===//
17 
18 #include "ClangSACheckers.h"
19 #include "clang/Basic/TargetInfo.h"
20 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
21 #include "clang/StaticAnalyzer/Core/Checker.h"
22 #include "clang/StaticAnalyzer/Core/CheckerManager.h"
23 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
24 #include "clang/StaticAnalyzer/Core/PathSensitive/ProgramStateTrait.h"
25 #include "llvm/ADT/SmallString.h"
26 #include "llvm/ADT/StringSwitch.h"
27 #include "llvm/Support/raw_ostream.h"
28 
29 using namespace clang;
30 using namespace ento;
31 
32 namespace {
33 class MacOSXAPIChecker : public Checker< check::PreStmt<CallExpr> > {
34   mutable std::unique_ptr<BugType> BT_dispatchOnce;
35 
36   static const ObjCIvarRegion *getParentIvarRegion(const MemRegion *R);
37 
38 public:
39   void checkPreStmt(const CallExpr *CE, CheckerContext &C) const;
40 
41   void CheckDispatchOnce(CheckerContext &C, const CallExpr *CE,
42                          StringRef FName) const;
43 
44   typedef void (MacOSXAPIChecker::*SubChecker)(CheckerContext &,
45                                                const CallExpr *,
46                                                StringRef FName) const;
47 };
48 } //end anonymous namespace
49 
50 //===----------------------------------------------------------------------===//
51 // dispatch_once and dispatch_once_f
52 //===----------------------------------------------------------------------===//
53 
54 const ObjCIvarRegion *
55 MacOSXAPIChecker::getParentIvarRegion(const MemRegion *R) {
56   const SubRegion *SR = dyn_cast<SubRegion>(R);
57   while (SR) {
58     if (const ObjCIvarRegion *IR = dyn_cast<ObjCIvarRegion>(SR))
59       return IR;
60     SR = dyn_cast<SubRegion>(SR->getSuperRegion());
61   }
62   return nullptr;
63 }
64 
65 void MacOSXAPIChecker::CheckDispatchOnce(CheckerContext &C, const CallExpr *CE,
66                                          StringRef FName) const {
67   if (CE->getNumArgs() < 1)
68     return;
69 
70   // Check if the first argument is improperly allocated.  If so, issue a
71   // warning because that's likely to be bad news.
72   const MemRegion *R = C.getSVal(CE->getArg(0)).getAsRegion();
73   if (!R)
74     return;
75 
76   // Global variables are fine.
77   const MemRegion *RB = R->getBaseRegion();
78   const MemSpaceRegion *RS = RB->getMemorySpace();
79   if (isa<GlobalsSpaceRegion>(RS))
80     return;
81 
82   // Handle _dispatch_once.  In some versions of the OS X SDK we have the case
83   // that dispatch_once is a macro that wraps a call to _dispatch_once.
84   // _dispatch_once is then a function which then calls the real dispatch_once.
85   // Users do not care; they just want the warning at the top-level call.
86   if (CE->getLocStart().isMacroID()) {
87     StringRef TrimmedFName = FName.ltrim('_');
88     if (TrimmedFName != FName)
89       FName = TrimmedFName;
90   }
91 
92   SmallString<256> S;
93   llvm::raw_svector_ostream os(S);
94   bool SuggestStatic = false;
95   os << "Call to '" << FName << "' uses";
96   if (const VarRegion *VR = dyn_cast<VarRegion>(RB)) {
97     // We filtered out globals earlier, so it must be a local variable
98     // or a block variable which is under UnknownSpaceRegion.
99     if (VR != R)
100       os << " memory within";
101     if (VR->getDecl()->hasAttr<BlocksAttr>())
102       os << " the block variable '";
103     else
104       os << " the local variable '";
105     os << VR->getDecl()->getName() << '\'';
106     SuggestStatic = true;
107   } else if (const ObjCIvarRegion *IVR = getParentIvarRegion(R)) {
108     if (IVR != R)
109       os << " memory within";
110     os << " the instance variable '" << IVR->getDecl()->getName() << '\'';
111   } else if (isa<HeapSpaceRegion>(RS)) {
112     os << " heap-allocated memory";
113   } else if (isa<UnknownSpaceRegion>(RS)) {
114     // Presence of an IVar superregion has priority over this branch, because
115     // ObjC objects are on the heap even if the core doesn't realize this.
116     // Presence of a block variable base region has priority over this branch,
117     // because block variables are known to be either on stack or on heap
118     // (might actually move between the two, hence UnknownSpace).
119     return;
120   } else {
121     os << " stack allocated memory";
122   }
123   os << " for the predicate value.  Using such transient memory for "
124         "the predicate is potentially dangerous.";
125   if (SuggestStatic)
126     os << "  Perhaps you intended to declare the variable as 'static'?";
127 
128   ExplodedNode *N = C.generateErrorNode();
129   if (!N)
130     return;
131 
132   if (!BT_dispatchOnce)
133     BT_dispatchOnce.reset(new BugType(this, "Improper use of 'dispatch_once'",
134                                       "API Misuse (Apple)"));
135 
136   auto report = llvm::make_unique<BugReport>(*BT_dispatchOnce, os.str(), N);
137   report->addRange(CE->getArg(0)->getSourceRange());
138   C.emitReport(std::move(report));
139 }
140 
141 //===----------------------------------------------------------------------===//
142 // Central dispatch function.
143 //===----------------------------------------------------------------------===//
144 
145 void MacOSXAPIChecker::checkPreStmt(const CallExpr *CE,
146                                     CheckerContext &C) const {
147   StringRef Name = C.getCalleeName(CE);
148   if (Name.empty())
149     return;
150 
151   SubChecker SC =
152     llvm::StringSwitch<SubChecker>(Name)
153       .Cases("dispatch_once",
154              "_dispatch_once",
155              "dispatch_once_f",
156              &MacOSXAPIChecker::CheckDispatchOnce)
157       .Default(nullptr);
158 
159   if (SC)
160     (this->*SC)(C, CE, Name);
161 }
162 
163 //===----------------------------------------------------------------------===//
164 // Registration.
165 //===----------------------------------------------------------------------===//
166 
167 void ento::registerMacOSXAPIChecker(CheckerManager &mgr) {
168   mgr.registerChecker<MacOSXAPIChecker>();
169 }
170