xref: /freebsd/contrib/llvm-project/clang/lib/StaticAnalyzer/Checkers/MIGChecker.cpp (revision ec0ea6efa1ad229d75c394c1a9b9cac33af2b1d3)
1 //== MIGChecker.cpp - MIG calling convention checker ------------*- 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 file defines MIGChecker, a Mach Interface Generator calling convention
10 // checker. Namely, in MIG callback implementation the following rules apply:
11 // - When a server routine returns an error code that represents success, it
12 //   must take ownership of resources passed to it (and eventually release
13 //   them).
14 // - Additionally, when returning success, all out-parameters must be
15 //   initialized.
16 // - When it returns any other error code, it must not take ownership,
17 //   because the message and its out-of-line parameters will be destroyed
18 //   by the client that called the function.
19 // For now we only check the last rule, as its violations lead to dangerous
20 // use-after-free exploits.
21 //
22 //===----------------------------------------------------------------------===//
23 
24 #include "clang/AST/Attr.h"
25 #include "clang/Analysis/AnyCall.h"
26 #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
27 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
28 #include "clang/StaticAnalyzer/Core/Checker.h"
29 #include "clang/StaticAnalyzer/Core/CheckerManager.h"
30 #include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"
31 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
32 
33 using namespace clang;
34 using namespace ento;
35 
36 namespace {
37 class MIGChecker : public Checker<check::PostCall, check::PreStmt<ReturnStmt>,
38                                   check::EndFunction> {
39   BugType BT{this, "Use-after-free (MIG calling convention violation)",
40              categories::MemoryError};
41 
42   // The checker knows that an out-of-line object is deallocated if it is
43   // passed as an argument to one of these functions. If this object is
44   // additionally an argument of a MIG routine, the checker keeps track of that
45   // information and issues a warning when an error is returned from the
46   // respective routine.
47   std::vector<std::pair<CallDescription, unsigned>> Deallocators = {
48 #define CALL(required_args, deallocated_arg, ...)                              \
49   {{{__VA_ARGS__}, required_args}, deallocated_arg}
50       // E.g., if the checker sees a C function 'vm_deallocate' that is
51       // defined on class 'IOUserClient' that has exactly 3 parameters, it knows
52       // that argument #1 (starting from 0, i.e. the second argument) is going
53       // to be consumed in the sense of the MIG consume-on-success convention.
54       CALL(3, 1, "vm_deallocate"),
55       CALL(3, 1, "mach_vm_deallocate"),
56       CALL(2, 0, "mig_deallocate"),
57       CALL(2, 1, "mach_port_deallocate"),
58       CALL(1, 0, "device_deallocate"),
59       CALL(1, 0, "iokit_remove_connect_reference"),
60       CALL(1, 0, "iokit_remove_reference"),
61       CALL(1, 0, "iokit_release_port"),
62       CALL(1, 0, "ipc_port_release"),
63       CALL(1, 0, "ipc_port_release_sonce"),
64       CALL(1, 0, "ipc_voucher_attr_control_release"),
65       CALL(1, 0, "ipc_voucher_release"),
66       CALL(1, 0, "lock_set_dereference"),
67       CALL(1, 0, "memory_object_control_deallocate"),
68       CALL(1, 0, "pset_deallocate"),
69       CALL(1, 0, "semaphore_dereference"),
70       CALL(1, 0, "space_deallocate"),
71       CALL(1, 0, "space_inspect_deallocate"),
72       CALL(1, 0, "task_deallocate"),
73       CALL(1, 0, "task_inspect_deallocate"),
74       CALL(1, 0, "task_name_deallocate"),
75       CALL(1, 0, "thread_deallocate"),
76       CALL(1, 0, "thread_inspect_deallocate"),
77       CALL(1, 0, "upl_deallocate"),
78       CALL(1, 0, "vm_map_deallocate"),
79       // E.g., if the checker sees a method 'releaseAsyncReference64()' that is
80       // defined on class 'IOUserClient' that takes exactly 1 argument, it knows
81       // that the argument is going to be consumed in the sense of the MIG
82       // consume-on-success convention.
83       CALL(1, 0, "IOUserClient", "releaseAsyncReference64"),
84       CALL(1, 0, "IOUserClient", "releaseNotificationPort"),
85 #undef CALL
86   };
87 
88   CallDescription OsRefRetain{"os_ref_retain", 1};
89 
90   void checkReturnAux(const ReturnStmt *RS, CheckerContext &C) const;
91 
92 public:
93   void checkPostCall(const CallEvent &Call, CheckerContext &C) const;
94 
95   // HACK: We're making two attempts to find the bug: checkEndFunction
96   // should normally be enough but it fails when the return value is a literal
97   // that never gets put into the Environment and ends of function with multiple
98   // returns get agglutinated across returns, preventing us from obtaining
99   // the return value. The problem is similar to https://reviews.llvm.org/D25326
100   // but now we step into it in the top-level function.
101   void checkPreStmt(const ReturnStmt *RS, CheckerContext &C) const {
102     checkReturnAux(RS, C);
103   }
104   void checkEndFunction(const ReturnStmt *RS, CheckerContext &C) const {
105     checkReturnAux(RS, C);
106   }
107 
108 };
109 } // end anonymous namespace
110 
111 // A flag that says that the programmer has called a MIG destructor
112 // for at least one parameter.
113 REGISTER_TRAIT_WITH_PROGRAMSTATE(ReleasedParameter, bool)
114 // A set of parameters for which the check is suppressed because
115 // reference counting is being performed.
116 REGISTER_SET_WITH_PROGRAMSTATE(RefCountedParameters, const ParmVarDecl *)
117 
118 static const ParmVarDecl *getOriginParam(SVal V, CheckerContext &C,
119                                          bool IncludeBaseRegions = false) {
120   // TODO: We should most likely always include base regions here.
121   SymbolRef Sym = V.getAsSymbol(IncludeBaseRegions);
122   if (!Sym)
123     return nullptr;
124 
125   // If we optimistically assume that the MIG routine never re-uses the storage
126   // that was passed to it as arguments when it invalidates it (but at most when
127   // it assigns to parameter variables directly), this procedure correctly
128   // determines if the value was loaded from the transitive closure of MIG
129   // routine arguments in the heap.
130   while (const MemRegion *MR = Sym->getOriginRegion()) {
131     const auto *VR = dyn_cast<VarRegion>(MR);
132     if (VR && VR->hasStackParametersStorage() &&
133            VR->getStackFrame()->inTopFrame())
134       return cast<ParmVarDecl>(VR->getDecl());
135 
136     const SymbolicRegion *SR = MR->getSymbolicBase();
137     if (!SR)
138       return nullptr;
139 
140     Sym = SR->getSymbol();
141   }
142 
143   return nullptr;
144 }
145 
146 static bool isInMIGCall(CheckerContext &C) {
147   const LocationContext *LC = C.getLocationContext();
148   assert(LC && "Unknown location context");
149 
150   const StackFrameContext *SFC;
151   // Find the top frame.
152   while (LC) {
153     SFC = LC->getStackFrame();
154     LC = SFC->getParent();
155   }
156 
157   const Decl *D = SFC->getDecl();
158 
159   if (Optional<AnyCall> AC = AnyCall::forDecl(D)) {
160     // Even though there's a Sema warning when the return type of an annotated
161     // function is not a kern_return_t, this warning isn't an error, so we need
162     // an extra sanity check here.
163     // FIXME: AnyCall doesn't support blocks yet, so they remain unchecked
164     // for now.
165     if (!AC->getReturnType(C.getASTContext())
166              .getCanonicalType()->isSignedIntegerType())
167       return false;
168   }
169 
170   if (D->hasAttr<MIGServerRoutineAttr>())
171     return true;
172 
173   // See if there's an annotated method in the superclass.
174   if (const auto *MD = dyn_cast<CXXMethodDecl>(D))
175     for (const auto *OMD: MD->overridden_methods())
176       if (OMD->hasAttr<MIGServerRoutineAttr>())
177         return true;
178 
179   return false;
180 }
181 
182 void MIGChecker::checkPostCall(const CallEvent &Call, CheckerContext &C) const {
183   if (Call.isCalled(OsRefRetain)) {
184     // If the code is doing reference counting over the parameter,
185     // it opens up an opportunity for safely calling a destructor function.
186     // TODO: We should still check for over-releases.
187     if (const ParmVarDecl *PVD =
188             getOriginParam(Call.getArgSVal(0), C, /*IncludeBaseRegions=*/true)) {
189       // We never need to clean up the program state because these are
190       // top-level parameters anyway, so they're always live.
191       C.addTransition(C.getState()->add<RefCountedParameters>(PVD));
192     }
193     return;
194   }
195 
196   if (!isInMIGCall(C))
197     return;
198 
199   auto I = llvm::find_if(Deallocators,
200                          [&](const std::pair<CallDescription, unsigned> &Item) {
201                            return Call.isCalled(Item.first);
202                          });
203   if (I == Deallocators.end())
204     return;
205 
206   ProgramStateRef State = C.getState();
207   unsigned ArgIdx = I->second;
208   SVal Arg = Call.getArgSVal(ArgIdx);
209   const ParmVarDecl *PVD = getOriginParam(Arg, C);
210   if (!PVD || State->contains<RefCountedParameters>(PVD))
211     return;
212 
213   const NoteTag *T =
214     C.getNoteTag([this, PVD](PathSensitiveBugReport &BR) -> std::string {
215         if (&BR.getBugType() != &BT)
216           return "";
217         SmallString<64> Str;
218         llvm::raw_svector_ostream OS(Str);
219         OS << "Value passed through parameter '" << PVD->getName()
220            << "\' is deallocated";
221         return std::string(OS.str());
222       });
223   C.addTransition(State->set<ReleasedParameter>(true), T);
224 }
225 
226 // Returns true if V can potentially represent a "successful" kern_return_t.
227 static bool mayBeSuccess(SVal V, CheckerContext &C) {
228   ProgramStateRef State = C.getState();
229 
230   // Can V represent KERN_SUCCESS?
231   if (!State->isNull(V).isConstrainedFalse())
232     return true;
233 
234   SValBuilder &SVB = C.getSValBuilder();
235   ASTContext &ACtx = C.getASTContext();
236 
237   // Can V represent MIG_NO_REPLY?
238   static const int MigNoReply = -305;
239   V = SVB.evalEQ(C.getState(), V, SVB.makeIntVal(MigNoReply, ACtx.IntTy));
240   if (!State->isNull(V).isConstrainedTrue())
241     return true;
242 
243   // If none of the above, it's definitely an error.
244   return false;
245 }
246 
247 void MIGChecker::checkReturnAux(const ReturnStmt *RS, CheckerContext &C) const {
248   // It is very unlikely that a MIG callback will be called from anywhere
249   // within the project under analysis and the caller isn't itself a routine
250   // that follows the MIG calling convention. Therefore we're safe to believe
251   // that it's always the top frame that is of interest. There's a slight chance
252   // that the user would want to enforce the MIG calling convention upon
253   // a random routine in the middle of nowhere, but given that the convention is
254   // fairly weird and hard to follow in the first place, there's relatively
255   // little motivation to spread it this way.
256   if (!C.inTopFrame())
257     return;
258 
259   if (!isInMIGCall(C))
260     return;
261 
262   // We know that the function is non-void, but what if the return statement
263   // is not there in the code? It's not a compile error, we should not crash.
264   if (!RS)
265     return;
266 
267   ProgramStateRef State = C.getState();
268   if (!State->get<ReleasedParameter>())
269     return;
270 
271   SVal V = C.getSVal(RS);
272   if (mayBeSuccess(V, C))
273     return;
274 
275   ExplodedNode *N = C.generateErrorNode();
276   if (!N)
277     return;
278 
279   auto R = std::make_unique<PathSensitiveBugReport>(
280       BT,
281       "MIG callback fails with error after deallocating argument value. "
282       "This is a use-after-free vulnerability because the caller will try to "
283       "deallocate it again",
284       N);
285 
286   R->addRange(RS->getSourceRange());
287   bugreporter::trackExpressionValue(
288       N, RS->getRetValue(), *R,
289       {bugreporter::TrackingKind::Thorough, /*EnableNullFPSuppression=*/false});
290   C.emitReport(std::move(R));
291 }
292 
293 void ento::registerMIGChecker(CheckerManager &Mgr) {
294   Mgr.registerChecker<MIGChecker>();
295 }
296 
297 bool ento::shouldRegisterMIGChecker(const CheckerManager &mgr) {
298   return true;
299 }
300