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| -rw-r--r-- | build/clang-plugin/CanRunScriptChecker.cpp | 380 |
1 files changed, 380 insertions, 0 deletions
diff --git a/build/clang-plugin/CanRunScriptChecker.cpp b/build/clang-plugin/CanRunScriptChecker.cpp new file mode 100644 index 0000000000..f75f0380e0 --- /dev/null +++ b/build/clang-plugin/CanRunScriptChecker.cpp @@ -0,0 +1,380 @@ +/* This Source Code Form is subject to the terms of the Mozilla Public + * License, v. 2.0. If a copy of the MPL was not distributed with this + * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ + +/** + * This checker implements the "can run script" analysis. The idea is to detect + * functions that can run script that are being passed reference-counted + * arguments (including "this") whose refcount might go to zero as a result of + * the script running. We want to prevent that. + * + * The approach is to attempt to enforce the following invariants on the call + * graph: + * + * 1) Any caller of a MOZ_CAN_RUN_SCRIPT function is itself MOZ_CAN_RUN_SCRIPT. + * 2) If a virtual MOZ_CAN_RUN_SCRIPT method overrides a base class method, + * that base class method is also MOZ_CAN_RUN_SCRIPT. + * + * Invariant 2 ensures that we don't accidentally call a MOZ_CAN_RUN_SCRIPT + * function via a base-class virtual call. Invariant 1 ensures that + * the property of being able to run script propagates up the callstack. There + * is an opt-out for invariant 1: A function (declaration _or_ implementation) + * can be decorated with MOZ_CAN_RUN_SCRIPT_BOUNDARY to indicate that we do not + * require it or any of its callers to be MOZ_CAN_RUN_SCRIPT even if it calls + * MOZ_CAN_RUN_SCRIPT functions. + * + * There are two known holes in invariant 1, apart from the + * MOZ_CAN_RUN_SCRIPT_BOUNDARY opt-out: + * + * - Functions called via function pointers can be MOZ_CAN_RUN_SCRIPT even if + * their caller is not, because we have no way to determine from the function + * pointer what function is being called. + * - MOZ_CAN_RUN_SCRIPT destructors can happen in functions that are not + * MOZ_CAN_RUN_SCRIPT. + * https://bugzilla.mozilla.org/show_bug.cgi?id=1535523 tracks this. + * + * Given those invariants we then require that when calling a MOZ_CAN_RUN_SCRIPT + * function all refcounted arguments (including "this") satisfy one of these + * conditions: + * a) The argument is held via a strong pointer on the stack. + * b) The argument is a const strong pointer member of "this". We know "this" + * is being kept alive, and a const strong pointer member can't drop its ref + * until "this" dies. + * c) The argument is an argument of the caller (and hence held by a strong + * pointer somewhere higher up the callstack). + * d) The argument is explicitly annotated with MOZ_KnownLive, which indicates + * that something is guaranteed to keep it alive (e.g. it's rooted via a JS + * reflector). + * e) The argument is constexpr and therefore cannot disappear. + */ + +#include "CanRunScriptChecker.h" +#include "CustomMatchers.h" +#include "clang/Lex/Lexer.h" + +void CanRunScriptChecker::registerMatchers(MatchFinder *AstMatcher) { + auto Refcounted = qualType(hasDeclaration(cxxRecordDecl(isRefCounted()))); + auto StackSmartPtr = + ignoreTrivials(declRefExpr(to(varDecl(hasAutomaticStorageDuration(), + hasType(isSmartPtrToRefCounted()))))); + auto ConstMemberOfThisSmartPtr = + memberExpr(hasType(isSmartPtrToRefCounted()), hasType(isConstQualified()), + hasObjectExpression(cxxThisExpr())); + // A smartptr can be known-live for three reasons: + // 1) It's declared on the stack. + // 2) It's a const member of "this". We know "this" is alive (recursively) + // and const members can't change their value hence can't drop their + // reference until "this" gets destroyed. + // 3) It's an immediate temporary being constructed at the point where the + // call is happening. + auto KnownLiveSmartPtr = anyOf( + StackSmartPtr, ConstMemberOfThisSmartPtr, + ignoreTrivials(cxxConstructExpr(hasType(isSmartPtrToRefCounted())))); + + auto MozKnownLiveCall = + ignoreTrivials(callExpr(callee(functionDecl(hasName("MOZ_KnownLive"))))); + + // Params of the calling function are presumed live, because it itself should + // be MOZ_CAN_RUN_SCRIPT. Note that this is subject to + // https://bugzilla.mozilla.org/show_bug.cgi?id=1537656 a the moment. + auto KnownLiveParam = anyOf( + // "this" is OK + cxxThisExpr(), + // A parameter of the calling function is OK. + declRefExpr(to(parmVarDecl()))); + + // A matcher that matches various things that are known to be live directly, + // without making any assumptions about operators. + auto KnownLiveBase = anyOf( + // Things that are known to be a stack or immutable refptr. + KnownLiveSmartPtr, + // MOZ_KnownLive() calls. + MozKnownLiveCall, + // Params of the caller function. + KnownLiveParam, + // Constexpr things. + declRefExpr(to(varDecl(isConstexpr())))); + + // A matcher that matches various known-live things that don't involve + // non-unary operators. + auto KnownLiveSimple = anyOf( + // Things that are just known live. + KnownLiveBase, + // Method calls on a live things that are smart ptrs. Note that we don't + // want to allow general method calls on live things, because those can + // return non-live objects (e.g. consider "live_pointer->foo()" as an + // example). For purposes of this analysis we are assuming the method + // calls on smart ptrs all just return the pointer inside, + cxxMemberCallExpr( + on(allOf(hasType(isSmartPtrToRefCounted()), KnownLiveBase))), + // operator* or operator-> on a thing that is already known to be live. + cxxOperatorCallExpr(anyOf(hasOverloadedOperatorName("*"), + hasOverloadedOperatorName("->")), + hasAnyArgument(KnownLiveBase), argumentCountIs(1)), + // A dereference on a thing that is known to be live. This is _not_ + // caught by the "operator* or operator->" clause above, because + // cxxOperatorCallExpr() only catches cases when a class defines + // operator*. The default (built-in) operator* matches unaryOperator() + // instead.), + unaryOperator( + unaryDereferenceOperator(), + hasUnaryOperand( + // If we're doing *someArg, the argument of the dereference is an + // ImplicitCastExpr LValueToRValue which has the DeclRefExpr as an + // argument. We could try to match that explicitly with a custom + // matcher (none of the built-in matchers seem to match on the + // thing being cast for an implicitCastExpr), but it's simpler to + // just use ignoreTrivials to strip off the cast. + ignoreTrivials(KnownLiveBase))), + // Taking a pointer to a live reference. We explicitly want to exclude + // things that are not of type reference-to-refcounted or type refcounted, + // because if someone takes a pointer to a pointer to refcounted or a + // pointer to a smart ptr and passes those in to a callee that definitely + // does not guarantee liveness; in fact the callee could modify those + // things! In practice they would be the wrong type anyway, though, so + // it's hard to add a test for this. + unaryOperator(hasOperatorName("&"), + hasUnaryOperand(allOf(anyOf(hasType(references(Refcounted)), + hasType(Refcounted)), + ignoreTrivials(KnownLiveBase))))); + + auto KnownLive = anyOf( + // Anything above, of course. + KnownLiveSimple, + // Conditional operators where both arms are live. + conditionalOperator(hasFalseExpression(ignoreTrivials(KnownLiveSimple)), + hasTrueExpression(ignoreTrivials(KnownLiveSimple))) + // We're not handling cases like a dereference of a conditional operator, + // mostly because handling a dereference in general is so ugly. I + // _really_ wish I could just write a recursive matcher here easily. + ); + + auto InvalidArg = ignoreTrivialsConditional( + // We want to consider things if there is anything refcounted involved, + // including in any of the trivials that we otherwise strip off. + anyOf(hasType(Refcounted), hasType(pointsTo(Refcounted)), + hasType(references(Refcounted)), hasType(isSmartPtrToRefCounted())), + // We want to find any expression, + expr( + // which is not known live, + unless(KnownLive), + // and which is not a default arg with value nullptr, since those are + // always safe, + unless(cxxDefaultArgExpr(isNullDefaultArg())), + // and which is not a literal nullptr, + unless(cxxNullPtrLiteralExpr()), expr().bind("invalidArg"))); + + // A matcher which will mark the first invalid argument it finds invalid, but + // will always match, even if it finds no invalid arguments, so it doesn't + // preclude other matchers from running and maybe finding invalid args. + auto OptionalInvalidExplicitArg = anyOf( + // We want to find any argument which is invalid. + hasAnyArgument(InvalidArg), + + // This makes this matcher optional. + anything()); + + // Please note that the hasCanRunScriptAnnotation() matchers are not present + // directly in the cxxMemberCallExpr, callExpr and constructExpr matchers + // because we check that the corresponding functions can run script later in + // the checker code. + AstMatcher->addMatcher( + expr( + anyOf( + // We want to match a method call expression, + cxxMemberCallExpr( + // which optionally has an invalid arg, + OptionalInvalidExplicitArg, + // or which optionally has an invalid this argument, + anyOf(on(InvalidArg), anything()), expr().bind("callExpr")), + // or a regular call expression, + callExpr( + // which optionally has an invalid arg. + OptionalInvalidExplicitArg, expr().bind("callExpr")), + // or a construct expression, + cxxConstructExpr( + // which optionally has an invalid arg. + OptionalInvalidExplicitArg, expr().bind("constructExpr"))), + + anyOf( + // We want to match the parent function. + forFunction(functionDecl().bind("nonCanRunScriptParentFunction")), + + // ... optionally. + anything())), + this); +} + +void CanRunScriptChecker::onStartOfTranslationUnit() { + IsFuncSetBuilt = false; + CanRunScriptFuncs.clear(); +} + +namespace { +/// This class is a callback used internally to match function declarations with +/// the MOZ_CAN_RUN_SCRIPT annotation, adding these functions to the +/// can-run-script function set and making sure the functions they override (if +/// any) also have the annotation. +class FuncSetCallback : public MatchFinder::MatchCallback { +public: + FuncSetCallback(CanRunScriptChecker &Checker, + std::unordered_set<const FunctionDecl *> &FuncSet) + : CanRunScriptFuncs(FuncSet), Checker(Checker) {} + + void run(const MatchFinder::MatchResult &Result) override; + +private: + /// This method checks the methods overriden by the given parameter. + void checkOverriddenMethods(const CXXMethodDecl *Method); + + std::unordered_set<const FunctionDecl *> &CanRunScriptFuncs; + CanRunScriptChecker &Checker; +}; + +void FuncSetCallback::run(const MatchFinder::MatchResult &Result) { + const FunctionDecl *Func; + if (auto *Lambda = Result.Nodes.getNodeAs<LambdaExpr>("lambda")) { + Func = Lambda->getCallOperator(); + if (!Func || !hasCustomAttribute<moz_can_run_script>(Func)) + return; + } else { + Func = Result.Nodes.getNodeAs<FunctionDecl>("canRunScriptFunction"); + } + + CanRunScriptFuncs.insert(Func); + + // If this is a method, we check the methods it overrides. + if (auto *Method = dyn_cast<CXXMethodDecl>(Func)) { + checkOverriddenMethods(Method); + } +} + +void FuncSetCallback::checkOverriddenMethods(const CXXMethodDecl *Method) { + for (auto OverriddenMethod : Method->overridden_methods()) { + if (!hasCustomAttribute<moz_can_run_script>(OverriddenMethod)) { + const char *ErrorNonCanRunScriptOverridden = + "functions marked as MOZ_CAN_RUN_SCRIPT cannot override functions " + "that are not marked MOZ_CAN_RUN_SCRIPT"; + const char *NoteNonCanRunScriptOverridden = + "overridden function declared here"; + + Checker.diag(Method->getLocation(), ErrorNonCanRunScriptOverridden, + DiagnosticIDs::Error); + Checker.diag(OverriddenMethod->getLocation(), + NoteNonCanRunScriptOverridden, DiagnosticIDs::Note); + } + } +} +} // namespace + +void CanRunScriptChecker::buildFuncSet(ASTContext *Context) { + // We create a match finder. + MatchFinder Finder; + // We create the callback which will be called when we find a function with + // a MOZ_CAN_RUN_SCRIPT annotation. + FuncSetCallback Callback(*this, CanRunScriptFuncs); + // We add the matcher to the finder, linking it to our callback. + Finder.addMatcher( + functionDecl(hasCanRunScriptAnnotation()).bind("canRunScriptFunction"), + &Callback); + Finder.addMatcher(lambdaExpr().bind("lambda"), &Callback); + // We start the analysis, given the ASTContext our main checker is in. + Finder.matchAST(*Context); +} + +void CanRunScriptChecker::check(const MatchFinder::MatchResult &Result) { + + // If the set of functions which can run script is not yet built, then build + // it. + if (!IsFuncSetBuilt) { + buildFuncSet(Result.Context); + IsFuncSetBuilt = true; + } + + const char *ErrorInvalidArg = + "arguments must all be strong refs or caller's parameters when calling a " + "function marked as MOZ_CAN_RUN_SCRIPT (including the implicit object " + "argument). '%0' is neither."; + + const char *ErrorNonCanRunScriptParent = + "functions marked as MOZ_CAN_RUN_SCRIPT can only be called from " + "functions also marked as MOZ_CAN_RUN_SCRIPT"; + const char *NoteNonCanRunScriptParent = "caller function declared here"; + + const Expr *InvalidArg; + if (const CXXDefaultArgExpr *defaultArg = + Result.Nodes.getNodeAs<CXXDefaultArgExpr>("invalidArg")) { + InvalidArg = defaultArg->getExpr(); + } else { + InvalidArg = Result.Nodes.getNodeAs<Expr>("invalidArg"); + } + + const CallExpr *Call = Result.Nodes.getNodeAs<CallExpr>("callExpr"); + // If we don't find the FunctionDecl linked to this call or if it's not marked + // as can-run-script, consider that we didn't find a match. + if (Call && (!Call->getDirectCallee() || + !CanRunScriptFuncs.count(Call->getDirectCallee()))) { + Call = nullptr; + } + + const CXXConstructExpr *Construct = + Result.Nodes.getNodeAs<CXXConstructExpr>("constructExpr"); + + // If we don't find the CXXConstructorDecl linked to this construct expression + // or if it's not marked as can-run-script, consider that we didn't find a + // match. + if (Construct && (!Construct->getConstructor() || + !CanRunScriptFuncs.count(Construct->getConstructor()))) { + Construct = nullptr; + } + + const FunctionDecl *ParentFunction = + Result.Nodes.getNodeAs<FunctionDecl>("nonCanRunScriptParentFunction"); + // If the parent function can run script, consider that we didn't find a match + // because we only care about parent functions which can't run script. + // + // In addition, If the parent function is annotated as a + // CAN_RUN_SCRIPT_BOUNDARY, we don't want to complain about it calling a + // CAN_RUN_SCRIPT function. This is a mechanism to opt out of the infectious + // nature of CAN_RUN_SCRIPT which is necessary in some tricky code like + // Bindings. + if (ParentFunction && + (CanRunScriptFuncs.count(ParentFunction) || + hasCustomAttribute<moz_can_run_script_boundary>(ParentFunction))) { + ParentFunction = nullptr; + } + + // Get the call range from either the CallExpr or the ConstructExpr. + SourceRange CallRange; + if (Call) { + CallRange = Call->getSourceRange(); + } else if (Construct) { + CallRange = Construct->getSourceRange(); + } else { + // If we have neither a Call nor a Construct, we have nothing do to here. + return; + } + + // If we have an invalid argument in the call, we emit the diagnostic to + // signal it. + if (InvalidArg) { + const StringRef invalidArgText = Lexer::getSourceText( + CharSourceRange::getTokenRange(InvalidArg->getSourceRange()), + Result.Context->getSourceManager(), Result.Context->getLangOpts()); + diag(InvalidArg->getExprLoc(), ErrorInvalidArg, DiagnosticIDs::Error) + << InvalidArg->getSourceRange() << invalidArgText; + } + + // If the parent function is not marked as MOZ_CAN_RUN_SCRIPT, we emit an + // error and a not indicating it. + if (ParentFunction) { + assert(!hasCustomAttribute<moz_can_run_script>(ParentFunction) && + "Matcher missed something"); + + diag(CallRange.getBegin(), ErrorNonCanRunScriptParent, DiagnosticIDs::Error) + << CallRange; + + diag(ParentFunction->getCanonicalDecl()->getLocation(), + NoteNonCanRunScriptParent, DiagnosticIDs::Note); + } +} |