1 //== MIGChecker.cpp - MIG calling convention checker ------------*- C++ -*--==//
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
7 //===----------------------------------------------------------------------===//
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
14 // - Additionally, when returning success, all out-parameters must be
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.
22 //===----------------------------------------------------------------------===//
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"
33 using namespace clang;
37 class MIGChecker : public Checker<check::PostCall, check::PreStmt<ReturnStmt>,
39 BugType BT{this, "Use-after-free (MIG calling convention violation)",
40 categories::MemoryError};
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"),
88 CallDescription OsRefRetain{"os_ref_retain", 1};
90 void checkReturnAux(const ReturnStmt *RS, CheckerContext &C) const;
93 void checkPostCall(const CallEvent &Call, CheckerContext &C) const;
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);
104 void checkEndFunction(const ReturnStmt *RS, CheckerContext &C) const {
105 checkReturnAux(RS, C);
109 } // end anonymous namespace
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 *)
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);
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());
136 const SymbolicRegion *SR = MR->getSymbolicBase();
140 Sym = SR->getSymbol();
146 static bool isInMIGCall(CheckerContext &C) {
147 const LocationContext *LC = C.getLocationContext();
148 assert(LC && "Unknown location context");
150 const StackFrameContext *SFC;
151 // Find the top frame.
153 SFC = LC->getStackFrame();
154 LC = SFC->getParent();
157 const Decl *D = SFC->getDecl();
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
165 if (!AC->getReturnType(C.getASTContext())
166 .getCanonicalType()->isSignedIntegerType())
170 if (D->hasAttr<MIGServerRoutineAttr>())
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>())
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));
199 auto I = llvm::find_if(Deallocators,
200 [&](const std::pair<CallDescription, unsigned> &Item) {
201 return Call.isCalled(Item.first);
203 if (I == Deallocators.end())
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))
213 const NoteTag *T = C.getNoteTag([this, PVD](BugReport &BR) -> std::string {
214 if (&BR.getBugType() != &BT)
217 llvm::raw_svector_ostream OS(Str);
218 OS << "Value passed through parameter '" << PVD->getName()
219 << "\' is deallocated";
222 C.addTransition(State->set<ReleasedParameter>(true), T);
225 // Returns true if V can potentially represent a "successful" kern_return_t.
226 static bool mayBeSuccess(SVal V, CheckerContext &C) {
227 ProgramStateRef State = C.getState();
229 // Can V represent KERN_SUCCESS?
230 if (!State->isNull(V).isConstrainedFalse())
233 SValBuilder &SVB = C.getSValBuilder();
234 ASTContext &ACtx = C.getASTContext();
236 // Can V represent MIG_NO_REPLY?
237 static const int MigNoReply = -305;
238 V = SVB.evalEQ(C.getState(), V, SVB.makeIntVal(MigNoReply, ACtx.IntTy));
239 if (!State->isNull(V).isConstrainedTrue())
242 // If none of the above, it's definitely an error.
246 void MIGChecker::checkReturnAux(const ReturnStmt *RS, CheckerContext &C) const {
247 // It is very unlikely that a MIG callback will be called from anywhere
248 // within the project under analysis and the caller isn't itself a routine
249 // that follows the MIG calling convention. Therefore we're safe to believe
250 // that it's always the top frame that is of interest. There's a slight chance
251 // that the user would want to enforce the MIG calling convention upon
252 // a random routine in the middle of nowhere, but given that the convention is
253 // fairly weird and hard to follow in the first place, there's relatively
254 // little motivation to spread it this way.
261 // We know that the function is non-void, but what if the return statement
262 // is not there in the code? It's not a compile error, we should not crash.
266 ProgramStateRef State = C.getState();
267 if (!State->get<ReleasedParameter>())
270 SVal V = C.getSVal(RS);
271 if (mayBeSuccess(V, C))
274 ExplodedNode *N = C.generateErrorNode();
278 auto R = std::make_unique<PathSensitiveBugReport>(
280 "MIG callback fails with error after deallocating argument value. "
281 "This is a use-after-free vulnerability because the caller will try to "
282 "deallocate it again",
285 R->addRange(RS->getSourceRange());
286 bugreporter::trackExpressionValue(N, RS->getRetValue(), *R,
287 bugreporter::TrackingKind::Thorough, false);
288 C.emitReport(std::move(R));
291 void ento::registerMIGChecker(CheckerManager &Mgr) {
292 Mgr.registerChecker<MIGChecker>();
295 bool ento::shouldRegisterMIGChecker(const LangOptions &LO) {