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/CallDescription.h"
31 #include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"
32 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
33 #include <optional>
34
35 using namespace clang;
36 using namespace ento;
37
38 namespace {
39 class MIGChecker : public Checker<check::PostCall, check::PreStmt<ReturnStmt>,
40 check::EndFunction> {
41 BugType BT{this, "Use-after-free (MIG calling convention violation)",
42 categories::MemoryError};
43
44 // The checker knows that an out-of-line object is deallocated if it is
45 // passed as an argument to one of these functions. If this object is
46 // additionally an argument of a MIG routine, the checker keeps track of that
47 // information and issues a warning when an error is returned from the
48 // respective routine.
49 CallDescriptionMap<unsigned> Deallocators = {
50 #define CALL(required_args, deallocated_arg, ...) \
51 {{CDM::SimpleFunc, {__VA_ARGS__}, required_args}, deallocated_arg}
52 // E.g., if the checker sees a C function 'vm_deallocate' that has
53 // exactly 3 parameters, it knows that argument #1 (starting from 0, i.e.
54 // the second argument) is going to be consumed in the sense of the MIG
55 // consume-on-success convention.
56 CALL(3, 1, "vm_deallocate"),
57 CALL(3, 1, "mach_vm_deallocate"),
58 CALL(2, 0, "mig_deallocate"),
59 CALL(2, 1, "mach_port_deallocate"),
60 CALL(1, 0, "device_deallocate"),
61 CALL(1, 0, "iokit_remove_connect_reference"),
62 CALL(1, 0, "iokit_remove_reference"),
63 CALL(1, 0, "iokit_release_port"),
64 CALL(1, 0, "ipc_port_release"),
65 CALL(1, 0, "ipc_port_release_sonce"),
66 CALL(1, 0, "ipc_voucher_attr_control_release"),
67 CALL(1, 0, "ipc_voucher_release"),
68 CALL(1, 0, "lock_set_dereference"),
69 CALL(1, 0, "memory_object_control_deallocate"),
70 CALL(1, 0, "pset_deallocate"),
71 CALL(1, 0, "semaphore_dereference"),
72 CALL(1, 0, "space_deallocate"),
73 CALL(1, 0, "space_inspect_deallocate"),
74 CALL(1, 0, "task_deallocate"),
75 CALL(1, 0, "task_inspect_deallocate"),
76 CALL(1, 0, "task_name_deallocate"),
77 CALL(1, 0, "thread_deallocate"),
78 CALL(1, 0, "thread_inspect_deallocate"),
79 CALL(1, 0, "upl_deallocate"),
80 CALL(1, 0, "vm_map_deallocate"),
81 #undef CALL
82 #define CALL(required_args, deallocated_arg, ...) \
83 {{CDM::CXXMethod, {__VA_ARGS__}, required_args}, deallocated_arg}
84 // E.g., if the checker sees a method 'releaseAsyncReference64()' that is
85 // defined on class 'IOUserClient' that takes exactly 1 argument, it knows
86 // that the argument is going to be consumed in the sense of the MIG
87 // consume-on-success convention.
88 CALL(1, 0, "IOUserClient", "releaseAsyncReference64"),
89 CALL(1, 0, "IOUserClient", "releaseNotificationPort"),
90 #undef CALL
91 };
92
93 CallDescription OsRefRetain{CDM::SimpleFunc, {"os_ref_retain"}, 1};
94
95 void checkReturnAux(const ReturnStmt *RS, CheckerContext &C) const;
96
97 public:
98 void checkPostCall(const CallEvent &Call, CheckerContext &C) const;
99
100 // HACK: We're making two attempts to find the bug: checkEndFunction
101 // should normally be enough but it fails when the return value is a literal
102 // that never gets put into the Environment and ends of function with multiple
103 // returns get agglutinated across returns, preventing us from obtaining
104 // the return value. The problem is similar to https://reviews.llvm.org/D25326
105 // but now we step into it in the top-level function.
checkPreStmt(const ReturnStmt * RS,CheckerContext & C) const106 void checkPreStmt(const ReturnStmt *RS, CheckerContext &C) const {
107 checkReturnAux(RS, C);
108 }
checkEndFunction(const ReturnStmt * RS,CheckerContext & C) const109 void checkEndFunction(const ReturnStmt *RS, CheckerContext &C) const {
110 checkReturnAux(RS, C);
111 }
112
113 };
114 } // end anonymous namespace
115
116 // A flag that says that the programmer has called a MIG destructor
117 // for at least one parameter.
REGISTER_TRAIT_WITH_PROGRAMSTATE(ReleasedParameter,bool)118 REGISTER_TRAIT_WITH_PROGRAMSTATE(ReleasedParameter, bool)
119 // A set of parameters for which the check is suppressed because
120 // reference counting is being performed.
121 REGISTER_SET_WITH_PROGRAMSTATE(RefCountedParameters, const ParmVarDecl *)
122
123 static const ParmVarDecl *getOriginParam(SVal V, CheckerContext &C,
124 bool IncludeBaseRegions = false) {
125 // TODO: We should most likely always include base regions here.
126 SymbolRef Sym = V.getAsSymbol(IncludeBaseRegions);
127 if (!Sym)
128 return nullptr;
129
130 // If we optimistically assume that the MIG routine never re-uses the storage
131 // that was passed to it as arguments when it invalidates it (but at most when
132 // it assigns to parameter variables directly), this procedure correctly
133 // determines if the value was loaded from the transitive closure of MIG
134 // routine arguments in the heap.
135 while (const MemRegion *MR = Sym->getOriginRegion()) {
136 const auto *VR = dyn_cast<VarRegion>(MR);
137 if (VR && VR->hasStackParametersStorage() &&
138 VR->getStackFrame()->inTopFrame())
139 return cast<ParmVarDecl>(VR->getDecl());
140
141 const SymbolicRegion *SR = MR->getSymbolicBase();
142 if (!SR)
143 return nullptr;
144
145 Sym = SR->getSymbol();
146 }
147
148 return nullptr;
149 }
150
isInMIGCall(CheckerContext & C)151 static bool isInMIGCall(CheckerContext &C) {
152 const LocationContext *LC = C.getLocationContext();
153 assert(LC && "Unknown location context");
154
155 const StackFrameContext *SFC;
156 // Find the top frame.
157 while (LC) {
158 SFC = LC->getStackFrame();
159 LC = SFC->getParent();
160 }
161
162 const Decl *D = SFC->getDecl();
163
164 if (std::optional<AnyCall> AC = AnyCall::forDecl(D)) {
165 // Even though there's a Sema warning when the return type of an annotated
166 // function is not a kern_return_t, this warning isn't an error, so we need
167 // an extra check here.
168 // FIXME: AnyCall doesn't support blocks yet, so they remain unchecked
169 // for now.
170 if (!AC->getReturnType(C.getASTContext())
171 .getCanonicalType()->isSignedIntegerType())
172 return false;
173 }
174
175 if (D->hasAttr<MIGServerRoutineAttr>())
176 return true;
177
178 // See if there's an annotated method in the superclass.
179 if (const auto *MD = dyn_cast<CXXMethodDecl>(D))
180 for (const auto *OMD: MD->overridden_methods())
181 if (OMD->hasAttr<MIGServerRoutineAttr>())
182 return true;
183
184 return false;
185 }
186
checkPostCall(const CallEvent & Call,CheckerContext & C) const187 void MIGChecker::checkPostCall(const CallEvent &Call, CheckerContext &C) const {
188 if (OsRefRetain.matches(Call)) {
189 // If the code is doing reference counting over the parameter,
190 // it opens up an opportunity for safely calling a destructor function.
191 // TODO: We should still check for over-releases.
192 if (const ParmVarDecl *PVD =
193 getOriginParam(Call.getArgSVal(0), C, /*IncludeBaseRegions=*/true)) {
194 // We never need to clean up the program state because these are
195 // top-level parameters anyway, so they're always live.
196 C.addTransition(C.getState()->add<RefCountedParameters>(PVD));
197 }
198 return;
199 }
200
201 if (!isInMIGCall(C))
202 return;
203
204 const unsigned *ArgIdxPtr = Deallocators.lookup(Call);
205 if (!ArgIdxPtr)
206 return;
207
208 ProgramStateRef State = C.getState();
209 unsigned ArgIdx = *ArgIdxPtr;
210 SVal Arg = Call.getArgSVal(ArgIdx);
211 const ParmVarDecl *PVD = getOriginParam(Arg, C);
212 if (!PVD || State->contains<RefCountedParameters>(PVD))
213 return;
214
215 const NoteTag *T =
216 C.getNoteTag([this, PVD](PathSensitiveBugReport &BR) -> std::string {
217 if (&BR.getBugType() != &BT)
218 return "";
219 SmallString<64> Str;
220 llvm::raw_svector_ostream OS(Str);
221 OS << "Value passed through parameter '" << PVD->getName()
222 << "\' is deallocated";
223 return std::string(OS.str());
224 });
225 C.addTransition(State->set<ReleasedParameter>(true), T);
226 }
227
228 // Returns true if V can potentially represent a "successful" kern_return_t.
mayBeSuccess(SVal V,CheckerContext & C)229 static bool mayBeSuccess(SVal V, CheckerContext &C) {
230 ProgramStateRef State = C.getState();
231
232 // Can V represent KERN_SUCCESS?
233 if (!State->isNull(V).isConstrainedFalse())
234 return true;
235
236 SValBuilder &SVB = C.getSValBuilder();
237 ASTContext &ACtx = C.getASTContext();
238
239 // Can V represent MIG_NO_REPLY?
240 static const int MigNoReply = -305;
241 V = SVB.evalEQ(C.getState(), V, SVB.makeIntVal(MigNoReply, ACtx.IntTy));
242 if (!State->isNull(V).isConstrainedTrue())
243 return true;
244
245 // If none of the above, it's definitely an error.
246 return false;
247 }
248
checkReturnAux(const ReturnStmt * RS,CheckerContext & C) const249 void MIGChecker::checkReturnAux(const ReturnStmt *RS, CheckerContext &C) const {
250 // It is very unlikely that a MIG callback will be called from anywhere
251 // within the project under analysis and the caller isn't itself a routine
252 // that follows the MIG calling convention. Therefore we're safe to believe
253 // that it's always the top frame that is of interest. There's a slight chance
254 // that the user would want to enforce the MIG calling convention upon
255 // a random routine in the middle of nowhere, but given that the convention is
256 // fairly weird and hard to follow in the first place, there's relatively
257 // little motivation to spread it this way.
258 if (!C.inTopFrame())
259 return;
260
261 if (!isInMIGCall(C))
262 return;
263
264 // We know that the function is non-void, but what if the return statement
265 // is not there in the code? It's not a compile error, we should not crash.
266 if (!RS)
267 return;
268
269 ProgramStateRef State = C.getState();
270 if (!State->get<ReleasedParameter>())
271 return;
272
273 SVal V = C.getSVal(RS);
274 if (mayBeSuccess(V, C))
275 return;
276
277 ExplodedNode *N = C.generateErrorNode();
278 if (!N)
279 return;
280
281 auto R = std::make_unique<PathSensitiveBugReport>(
282 BT,
283 "MIG callback fails with error after deallocating argument value. "
284 "This is a use-after-free vulnerability because the caller will try to "
285 "deallocate it again",
286 N);
287
288 R->addRange(RS->getSourceRange());
289 bugreporter::trackExpressionValue(
290 N, RS->getRetValue(), *R,
291 {bugreporter::TrackingKind::Thorough, /*EnableNullFPSuppression=*/false});
292 C.emitReport(std::move(R));
293 }
294
registerMIGChecker(CheckerManager & Mgr)295 void ento::registerMIGChecker(CheckerManager &Mgr) {
296 Mgr.registerChecker<MIGChecker>();
297 }
298
shouldRegisterMIGChecker(const CheckerManager & mgr)299 bool ento::shouldRegisterMIGChecker(const CheckerManager &mgr) {
300 return true;
301 }
302