1 //=== ErrnoModeling.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 // This defines a checker `ErrnoModeling`, which is used to make the system
10 // value 'errno' available to other checkers.
11 // The 'errno' value is stored at a special memory region that is accessible
12 // through the `errno_modeling` namespace. The memory region is either the
13 // region of `errno` itself if it is a variable, otherwise an artifically
14 // created region (in the system memory space). If `errno` is defined by using
15 // a function which returns the address of it (this is always the case if it is
16 // not a variable) this function is recognized and evaluated. In this way
17 // `errno` becomes visible to the analysis and checkers can change its value.
18 //
19 //===----------------------------------------------------------------------===//
20
21 #include "ErrnoModeling.h"
22 #include "clang/AST/ParentMapContext.h"
23 #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
24 #include "clang/StaticAnalyzer/Core/Checker.h"
25 #include "clang/StaticAnalyzer/Core/CheckerManager.h"
26 #include "clang/StaticAnalyzer/Core/PathSensitive/CallDescription.h"
27 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
28 #include "clang/StaticAnalyzer/Core/PathSensitive/ProgramState.h"
29 #include "clang/StaticAnalyzer/Core/PathSensitive/SVals.h"
30 #include "llvm/ADT/STLExtras.h"
31 #include "llvm/Support/FormatVariadic.h"
32 #include <optional>
33
34 using namespace clang;
35 using namespace ento;
36
37 namespace {
38
39 // Name of the "errno" variable.
40 // FIXME: Is there a system where it is not called "errno" but is a variable?
41 const char *ErrnoVarName = "errno";
42 // Names of functions that return a location of the "errno" value.
43 // FIXME: Are there other similar function names?
44 const char *ErrnoLocationFuncNames[] = {"__errno_location", "___errno",
45 "__errno", "_errno", "__error"};
46
47 class ErrnoModeling
48 : public Checker<check::ASTDecl<TranslationUnitDecl>, check::BeginFunction,
49 check::LiveSymbols, eval::Call> {
50 public:
51 void checkASTDecl(const TranslationUnitDecl *D, AnalysisManager &Mgr,
52 BugReporter &BR) const;
53 void checkBeginFunction(CheckerContext &C) const;
54 void checkLiveSymbols(ProgramStateRef State, SymbolReaper &SR) const;
55 bool evalCall(const CallEvent &Call, CheckerContext &C) const;
56
57 // The declaration of an "errno" variable or "errno location" function.
58 mutable const Decl *ErrnoDecl = nullptr;
59
60 private:
61 // FIXME: Names from `ErrnoLocationFuncNames` are used to build this set.
62 CallDescriptionSet ErrnoLocationCalls{{{"__errno_location"}, 0, 0},
63 {{"___errno"}, 0, 0},
64 {{"__errno"}, 0, 0},
65 {{"_errno"}, 0, 0},
66 {{"__error"}, 0, 0}};
67 };
68
69 } // namespace
70
71 /// Store a MemRegion that contains the 'errno' integer value.
72 /// The value is null if the 'errno' value was not recognized in the AST.
REGISTER_TRAIT_WITH_PROGRAMSTATE(ErrnoRegion,const MemRegion *)73 REGISTER_TRAIT_WITH_PROGRAMSTATE(ErrnoRegion, const MemRegion *)
74
75 REGISTER_TRAIT_WITH_PROGRAMSTATE(ErrnoState, errno_modeling::ErrnoCheckState)
76
77 /// Search for a variable called "errno" in the AST.
78 /// Return nullptr if not found.
79 static const VarDecl *getErrnoVar(ASTContext &ACtx) {
80 IdentifierInfo &II = ACtx.Idents.get(ErrnoVarName);
81 auto LookupRes = ACtx.getTranslationUnitDecl()->lookup(&II);
82 auto Found = llvm::find_if(LookupRes, [&ACtx](const Decl *D) {
83 if (auto *VD = dyn_cast<VarDecl>(D))
84 return ACtx.getSourceManager().isInSystemHeader(VD->getLocation()) &&
85 VD->hasExternalStorage() &&
86 VD->getType().getCanonicalType() == ACtx.IntTy;
87 return false;
88 });
89 if (Found == LookupRes.end())
90 return nullptr;
91
92 return cast<VarDecl>(*Found);
93 }
94
95 /// Search for a function with a specific name that is used to return a pointer
96 /// to "errno".
97 /// Return nullptr if no such function was found.
getErrnoFunc(ASTContext & ACtx)98 static const FunctionDecl *getErrnoFunc(ASTContext &ACtx) {
99 SmallVector<const Decl *> LookupRes;
100 for (StringRef ErrnoName : ErrnoLocationFuncNames) {
101 IdentifierInfo &II = ACtx.Idents.get(ErrnoName);
102 llvm::append_range(LookupRes, ACtx.getTranslationUnitDecl()->lookup(&II));
103 }
104
105 auto Found = llvm::find_if(LookupRes, [&ACtx](const Decl *D) {
106 if (auto *FD = dyn_cast<FunctionDecl>(D))
107 return ACtx.getSourceManager().isInSystemHeader(FD->getLocation()) &&
108 FD->isExternC() && FD->getNumParams() == 0 &&
109 FD->getReturnType().getCanonicalType() ==
110 ACtx.getPointerType(ACtx.IntTy);
111 return false;
112 });
113 if (Found == LookupRes.end())
114 return nullptr;
115
116 return cast<FunctionDecl>(*Found);
117 }
118
checkASTDecl(const TranslationUnitDecl * D,AnalysisManager & Mgr,BugReporter & BR) const119 void ErrnoModeling::checkASTDecl(const TranslationUnitDecl *D,
120 AnalysisManager &Mgr, BugReporter &BR) const {
121 // Try to find an usable `errno` value.
122 // It can be an external variable called "errno" or a function that returns a
123 // pointer to the "errno" value. This function can have different names.
124 // The actual case is dependent on the C library implementation, we
125 // can only search for a match in one of these variations.
126 // We assume that exactly one of these cases might be true.
127 ErrnoDecl = getErrnoVar(Mgr.getASTContext());
128 if (!ErrnoDecl)
129 ErrnoDecl = getErrnoFunc(Mgr.getASTContext());
130 }
131
checkBeginFunction(CheckerContext & C) const132 void ErrnoModeling::checkBeginFunction(CheckerContext &C) const {
133 if (!C.inTopFrame())
134 return;
135
136 ASTContext &ACtx = C.getASTContext();
137 ProgramStateRef State = C.getState();
138
139 if (const auto *ErrnoVar = dyn_cast_or_null<VarDecl>(ErrnoDecl)) {
140 // There is an external 'errno' variable.
141 // Use its memory region.
142 // The memory region for an 'errno'-like variable is allocated in system
143 // space by MemRegionManager.
144 const MemRegion *ErrnoR =
145 State->getRegion(ErrnoVar, C.getLocationContext());
146 assert(ErrnoR && "Memory region should exist for the 'errno' variable.");
147 State = State->set<ErrnoRegion>(ErrnoR);
148 State =
149 errno_modeling::setErrnoValue(State, C, 0, errno_modeling::Irrelevant);
150 C.addTransition(State);
151 } else if (ErrnoDecl) {
152 assert(isa<FunctionDecl>(ErrnoDecl) && "Invalid errno location function.");
153 // There is a function that returns the location of 'errno'.
154 // We must create a memory region for it in system space.
155 // Currently a symbolic region is used with an artifical symbol.
156 // FIXME: It is better to have a custom (new) kind of MemRegion for such
157 // cases.
158 SValBuilder &SVB = C.getSValBuilder();
159 MemRegionManager &RMgr = C.getStateManager().getRegionManager();
160
161 const MemSpaceRegion *GlobalSystemSpace =
162 RMgr.getGlobalsRegion(MemRegion::GlobalSystemSpaceRegionKind);
163
164 // Create an artifical symbol for the region.
165 // It is not possible to associate a statement or expression in this case.
166 const SymbolConjured *Sym = SVB.conjureSymbol(
167 nullptr, C.getLocationContext(),
168 ACtx.getLValueReferenceType(ACtx.IntTy), C.blockCount(), &ErrnoDecl);
169
170 // The symbolic region is untyped, create a typed sub-region in it.
171 // The ElementRegion is used to make the errno region a typed region.
172 const MemRegion *ErrnoR = RMgr.getElementRegion(
173 ACtx.IntTy, SVB.makeZeroArrayIndex(),
174 RMgr.getSymbolicRegion(Sym, GlobalSystemSpace), C.getASTContext());
175 State = State->set<ErrnoRegion>(ErrnoR);
176 State =
177 errno_modeling::setErrnoValue(State, C, 0, errno_modeling::Irrelevant);
178 C.addTransition(State);
179 }
180 }
181
evalCall(const CallEvent & Call,CheckerContext & C) const182 bool ErrnoModeling::evalCall(const CallEvent &Call, CheckerContext &C) const {
183 // Return location of "errno" at a call to an "errno address returning"
184 // function.
185 if (ErrnoLocationCalls.contains(Call)) {
186 ProgramStateRef State = C.getState();
187
188 const MemRegion *ErrnoR = State->get<ErrnoRegion>();
189 if (!ErrnoR)
190 return false;
191
192 State = State->BindExpr(Call.getOriginExpr(), C.getLocationContext(),
193 loc::MemRegionVal{ErrnoR});
194 C.addTransition(State);
195 return true;
196 }
197
198 return false;
199 }
200
checkLiveSymbols(ProgramStateRef State,SymbolReaper & SR) const201 void ErrnoModeling::checkLiveSymbols(ProgramStateRef State,
202 SymbolReaper &SR) const {
203 // The special errno region should never garbage collected.
204 if (const auto *ErrnoR = State->get<ErrnoRegion>())
205 SR.markLive(ErrnoR);
206 }
207
208 namespace clang {
209 namespace ento {
210 namespace errno_modeling {
211
getErrnoValue(ProgramStateRef State)212 std::optional<SVal> getErrnoValue(ProgramStateRef State) {
213 const MemRegion *ErrnoR = State->get<ErrnoRegion>();
214 if (!ErrnoR)
215 return {};
216 QualType IntTy = State->getAnalysisManager().getASTContext().IntTy;
217 return State->getSVal(ErrnoR, IntTy);
218 }
219
setErrnoValue(ProgramStateRef State,const LocationContext * LCtx,SVal Value,ErrnoCheckState EState)220 ProgramStateRef setErrnoValue(ProgramStateRef State,
221 const LocationContext *LCtx, SVal Value,
222 ErrnoCheckState EState) {
223 const MemRegion *ErrnoR = State->get<ErrnoRegion>();
224 if (!ErrnoR)
225 return State;
226 // First set the errno value, the old state is still available at 'checkBind'
227 // or 'checkLocation' for errno value.
228 State = State->bindLoc(loc::MemRegionVal{ErrnoR}, Value, LCtx);
229 return State->set<ErrnoState>(EState);
230 }
231
setErrnoValue(ProgramStateRef State,CheckerContext & C,uint64_t Value,ErrnoCheckState EState)232 ProgramStateRef setErrnoValue(ProgramStateRef State, CheckerContext &C,
233 uint64_t Value, ErrnoCheckState EState) {
234 const MemRegion *ErrnoR = State->get<ErrnoRegion>();
235 if (!ErrnoR)
236 return State;
237 State = State->bindLoc(
238 loc::MemRegionVal{ErrnoR},
239 C.getSValBuilder().makeIntVal(Value, C.getASTContext().IntTy),
240 C.getLocationContext());
241 return State->set<ErrnoState>(EState);
242 }
243
getErrnoLoc(ProgramStateRef State)244 std::optional<Loc> getErrnoLoc(ProgramStateRef State) {
245 const MemRegion *ErrnoR = State->get<ErrnoRegion>();
246 if (!ErrnoR)
247 return {};
248 return loc::MemRegionVal{ErrnoR};
249 }
250
getErrnoState(ProgramStateRef State)251 ErrnoCheckState getErrnoState(ProgramStateRef State) {
252 return State->get<ErrnoState>();
253 }
254
setErrnoState(ProgramStateRef State,ErrnoCheckState EState)255 ProgramStateRef setErrnoState(ProgramStateRef State, ErrnoCheckState EState) {
256 return State->set<ErrnoState>(EState);
257 }
258
clearErrnoState(ProgramStateRef State)259 ProgramStateRef clearErrnoState(ProgramStateRef State) {
260 return setErrnoState(State, Irrelevant);
261 }
262
isErrno(const Decl * D)263 bool isErrno(const Decl *D) {
264 if (const auto *VD = dyn_cast_or_null<VarDecl>(D))
265 if (const IdentifierInfo *II = VD->getIdentifier())
266 return II->getName() == ErrnoVarName;
267 if (const auto *FD = dyn_cast_or_null<FunctionDecl>(D))
268 if (const IdentifierInfo *II = FD->getIdentifier())
269 return llvm::is_contained(ErrnoLocationFuncNames, II->getName());
270 return false;
271 }
272
getErrnoNoteTag(CheckerContext & C,const std::string & Message)273 const NoteTag *getErrnoNoteTag(CheckerContext &C, const std::string &Message) {
274 return C.getNoteTag([Message](PathSensitiveBugReport &BR) -> std::string {
275 const MemRegion *ErrnoR = BR.getErrorNode()->getState()->get<ErrnoRegion>();
276 if (ErrnoR && BR.isInteresting(ErrnoR)) {
277 BR.markNotInteresting(ErrnoR);
278 return Message;
279 }
280 return "";
281 });
282 }
283
setErrnoForStdSuccess(ProgramStateRef State,CheckerContext & C)284 ProgramStateRef setErrnoForStdSuccess(ProgramStateRef State,
285 CheckerContext &C) {
286 return setErrnoState(State, MustNotBeChecked);
287 }
288
setErrnoForStdFailure(ProgramStateRef State,CheckerContext & C,NonLoc ErrnoSym)289 ProgramStateRef setErrnoForStdFailure(ProgramStateRef State, CheckerContext &C,
290 NonLoc ErrnoSym) {
291 SValBuilder &SVB = C.getSValBuilder();
292 NonLoc ZeroVal = SVB.makeZeroVal(C.getASTContext().IntTy).castAs<NonLoc>();
293 DefinedOrUnknownSVal Cond =
294 SVB.evalBinOp(State, BO_NE, ErrnoSym, ZeroVal, SVB.getConditionType())
295 .castAs<DefinedOrUnknownSVal>();
296 State = State->assume(Cond, true);
297 if (!State)
298 return nullptr;
299 return setErrnoValue(State, C.getLocationContext(), ErrnoSym, Irrelevant);
300 }
301
setErrnoStdMustBeChecked(ProgramStateRef State,CheckerContext & C,const Expr * InvalE)302 ProgramStateRef setErrnoStdMustBeChecked(ProgramStateRef State,
303 CheckerContext &C,
304 const Expr *InvalE) {
305 const MemRegion *ErrnoR = State->get<ErrnoRegion>();
306 if (!ErrnoR)
307 return State;
308 State = State->invalidateRegions(ErrnoR, InvalE, C.blockCount(),
309 C.getLocationContext(), false);
310 if (!State)
311 return nullptr;
312 return setErrnoState(State, MustBeChecked);
313 }
314
315 } // namespace errno_modeling
316 } // namespace ento
317 } // namespace clang
318
registerErrnoModeling(CheckerManager & mgr)319 void ento::registerErrnoModeling(CheckerManager &mgr) {
320 mgr.registerChecker<ErrnoModeling>();
321 }
322
shouldRegisterErrnoModeling(const CheckerManager & mgr)323 bool ento::shouldRegisterErrnoModeling(const CheckerManager &mgr) {
324 return true;
325 }
326