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28ae9ee2e1
For preparation of bug 1620312, CanRunScriptChecker needs to allow references which are initialized with safe instance(s) to run script. Unfortunately, this does not allow references which are initialized with safe references recursively because it requires more complicated checks but it must be not used in many places. Differential Revision: https://phabricator.services.mozilla.com/D174436
451 lines
20 KiB
C++
451 lines
20 KiB
C++
/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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/**
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* This checker implements the "can run script" analysis. The idea is to detect
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* functions that can run script that are being passed reference-counted
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* arguments (including "this") whose refcount might go to zero as a result of
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* the script running. We want to prevent that.
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*
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* The approach is to attempt to enforce the following invariants on the call
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* graph:
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*
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* 1) Any caller of a MOZ_CAN_RUN_SCRIPT function is itself MOZ_CAN_RUN_SCRIPT.
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* 2) If a virtual MOZ_CAN_RUN_SCRIPT method overrides a base class method,
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* that base class method is also MOZ_CAN_RUN_SCRIPT.
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*
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* Invariant 2 ensures that we don't accidentally call a MOZ_CAN_RUN_SCRIPT
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* function via a base-class virtual call. Invariant 1 ensures that
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* the property of being able to run script propagates up the callstack. There
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* is an opt-out for invariant 1: A function (declaration _or_ implementation)
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* can be decorated with MOZ_CAN_RUN_SCRIPT_BOUNDARY to indicate that we do not
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* require it or any of its callers to be MOZ_CAN_RUN_SCRIPT even if it calls
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* MOZ_CAN_RUN_SCRIPT functions.
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*
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* There are two known holes in invariant 1, apart from the
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* MOZ_CAN_RUN_SCRIPT_BOUNDARY opt-out:
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*
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* - Functions called via function pointers can be MOZ_CAN_RUN_SCRIPT even if
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* their caller is not, because we have no way to determine from the function
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* pointer what function is being called.
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* - MOZ_CAN_RUN_SCRIPT destructors can happen in functions that are not
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* MOZ_CAN_RUN_SCRIPT.
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* https://bugzilla.mozilla.org/show_bug.cgi?id=1535523 tracks this.
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*
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* Given those invariants we then require that when calling a MOZ_CAN_RUN_SCRIPT
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* function all refcounted arguments (including "this") satisfy one of these
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* conditions:
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* a) The argument is held via a strong pointer on the stack.
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* b) The argument is a const strong pointer member of "this". We know "this"
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* is being kept alive, and a const strong pointer member can't drop its ref
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* until "this" dies.
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* c) The argument is an argument of the caller (and hence held by a strong
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* pointer somewhere higher up the callstack).
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* d) The argument is explicitly annotated with MOZ_KnownLive, which indicates
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* that something is guaranteed to keep it alive (e.g. it's rooted via a JS
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* reflector).
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* e) The argument is constexpr and therefore cannot disappear.
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*/
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#include "CanRunScriptChecker.h"
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#include "CustomMatchers.h"
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#include "clang/Lex/Lexer.h"
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void CanRunScriptChecker::registerMatchers(MatchFinder *AstMatcher) {
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auto Refcounted = qualType(hasDeclaration(cxxRecordDecl(isRefCounted())));
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auto StackSmartPtr = ignoreTrivials(declRefExpr(to(varDecl(
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hasAutomaticStorageDuration(), hasType(isSmartPtrToRefCounted())))));
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auto ConstMemberOfThisSmartPtr =
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memberExpr(hasType(isSmartPtrToRefCounted()), hasType(isConstQualified()),
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hasObjectExpression(cxxThisExpr()));
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// A smartptr can be known-live for three reasons:
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// 1) It's declared on the stack.
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// 2) It's a const member of "this". We know "this" is alive (recursively)
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// and const members can't change their value hence can't drop their
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// reference until "this" gets destroyed.
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// 3) It's an immediate temporary being constructed at the point where the
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// call is happening.
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auto KnownLiveSmartPtr = anyOf(
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StackSmartPtr, ConstMemberOfThisSmartPtr,
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ignoreTrivials(cxxConstructExpr(hasType(isSmartPtrToRefCounted()))));
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auto MozKnownLiveCall =
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ignoreTrivials(callExpr(callee(functionDecl(hasName("MOZ_KnownLive")))));
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// Params of the calling function are presumed live, because it itself should
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// be MOZ_CAN_RUN_SCRIPT. Note that this is subject to
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// https://bugzilla.mozilla.org/show_bug.cgi?id=1537656 at the moment.
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auto KnownLiveParam = anyOf(
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// "this" is OK
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cxxThisExpr(),
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// A parameter of the calling function is OK.
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declRefExpr(to(parmVarDecl())));
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auto KnownLiveMemberOfParam =
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memberExpr(hasKnownLiveAnnotation(),
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hasObjectExpression(anyOf(
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ignoreTrivials(KnownLiveParam),
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declRefExpr(to(varDecl(hasAutomaticStorageDuration()))))));
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// A matcher that matches various things that are known to be live directly,
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// without making any assumptions about operators.
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auto KnownLiveBaseExceptRef = anyOf(
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// Things that are known to be a stack or immutable refptr.
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KnownLiveSmartPtr,
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// MOZ_KnownLive() calls.
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MozKnownLiveCall,
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// Params of the caller function.
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KnownLiveParam,
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// Members of the params that are marked as MOZ_KNOWN_LIVE
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KnownLiveMemberOfParam,
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// Constexpr things.
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declRefExpr(to(varDecl(isConstexpr()))));
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// A reference of smart ptr which is initialized with known live thing is OK.
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// FIXME: This does not allow nested references.
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auto RefToKnownLivePtr = ignoreTrivials(declRefExpr(to(varDecl(
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hasAutomaticStorageDuration(), hasType(referenceType()),
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hasInitializer(anyOf(
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KnownLiveSmartPtr, KnownLiveParam, KnownLiveMemberOfParam,
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conditionalOperator(
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hasFalseExpression(ignoreTrivials(anyOf(
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KnownLiveSmartPtr, KnownLiveParam, KnownLiveMemberOfParam,
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declRefExpr(to(varDecl(isConstexpr()))),
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// E.g., for RefPtr<T>::operator*()
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cxxOperatorCallExpr(
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hasOverloadedOperatorName("*"),
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hasAnyArgument(
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anyOf(KnownLiveBaseExceptRef,
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ignoreTrivials(KnownLiveMemberOfParam))),
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argumentCountIs(1)),
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// E.g., for *T
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unaryOperator(unaryDereferenceOperator(),
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hasUnaryOperand(
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ignoreTrivials(KnownLiveBaseExceptRef)))))),
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hasTrueExpression(ignoreTrivials(anyOf(
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KnownLiveSmartPtr, KnownLiveParam, KnownLiveMemberOfParam,
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declRefExpr(to(varDecl(isConstexpr()))),
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// E.g., for RefPtr<T>::operator*()
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cxxOperatorCallExpr(
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hasOverloadedOperatorName("*"),
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hasAnyArgument(
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anyOf(KnownLiveBaseExceptRef,
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ignoreTrivials(KnownLiveMemberOfParam))),
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argumentCountIs(1)),
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// E.g., for *T
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unaryOperator(unaryDereferenceOperator(),
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hasUnaryOperand(ignoreTrivials(
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KnownLiveBaseExceptRef)))))))))))));
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// A matcher that matches various things that are known to be live directly,
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// without making any assumptions about operators.
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auto KnownLiveBase =
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anyOf(KnownLiveBaseExceptRef,
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// Smart pointer refs initialized with known live smart ptrs.
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RefToKnownLivePtr);
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// A matcher that matches various known-live things that don't involve
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// non-unary operators.
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auto KnownLiveSimple = anyOf(
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// Things that are just known live.
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KnownLiveBase,
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// Method calls on a live things that are smart ptrs. Note that we don't
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// want to allow general method calls on live things, because those can
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// return non-live objects (e.g. consider "live_pointer->foo()" as an
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// example). For purposes of this analysis we are assuming the method
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// calls on smart ptrs all just return the pointer inside,
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cxxMemberCallExpr(
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on(anyOf(allOf(hasType(isSmartPtrToRefCounted()), KnownLiveBase),
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// Allow it if calling a member method which is marked as
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// MOZ_KNOWN_LIVE
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KnownLiveMemberOfParam))),
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// operator* or operator-> on a thing that is already known to be live.
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cxxOperatorCallExpr(
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hasAnyOverloadedOperatorName("*", "->"),
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hasAnyArgument(
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anyOf(KnownLiveBase, ignoreTrivials(KnownLiveMemberOfParam))),
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argumentCountIs(1)),
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// A dereference on a thing that is known to be live. This is _not_
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// caught by the "operator* or operator->" clause above, because
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// cxxOperatorCallExpr() only catches cases when a class defines
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// operator*. The default (built-in) operator* matches unaryOperator()
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// instead.),
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unaryOperator(
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unaryDereferenceOperator(),
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hasUnaryOperand(
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// If we're doing *someArg, the argument of the dereference is an
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// ImplicitCastExpr LValueToRValue which has the DeclRefExpr as an
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// argument. We could try to match that explicitly with a custom
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// matcher (none of the built-in matchers seem to match on the
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// thing being cast for an implicitCastExpr), but it's simpler to
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// just use ignoreTrivials to strip off the cast.
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ignoreTrivials(KnownLiveBase))),
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// Taking a pointer to a live reference. We explicitly want to exclude
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// things that are not of type reference-to-refcounted or type refcounted,
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// because if someone takes a pointer to a pointer to refcounted or a
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// pointer to a smart ptr and passes those in to a callee that definitely
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// does not guarantee liveness; in fact the callee could modify those
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// things! In practice they would be the wrong type anyway, though, so
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// it's hard to add a test for this.
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unaryOperator(hasOperatorName("&"),
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hasUnaryOperand(allOf(anyOf(hasType(references(Refcounted)),
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hasType(Refcounted)),
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ignoreTrivials(KnownLiveBase)))));
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auto KnownLive = anyOf(
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// Anything above, of course.
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KnownLiveSimple,
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// Conditional operators where both arms are live.
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conditionalOperator(hasFalseExpression(ignoreTrivials(KnownLiveSimple)),
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hasTrueExpression(ignoreTrivials(KnownLiveSimple)))
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// We're not handling cases like a dereference of a conditional operator,
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// mostly because handling a dereference in general is so ugly. I
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// _really_ wish I could just write a recursive matcher here easily.
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);
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auto InvalidArg = ignoreTrivialsConditional(
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// We want to consider things if there is anything refcounted involved,
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// including in any of the trivials that we otherwise strip off.
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anyOf(hasType(Refcounted), hasType(pointsTo(Refcounted)),
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hasType(references(Refcounted)), hasType(isSmartPtrToRefCounted())),
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// We want to find any expression,
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expr(
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// which is not known live,
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unless(KnownLive),
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// and which is not a default arg with value nullptr, since those are
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// always safe,
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unless(cxxDefaultArgExpr(isNullDefaultArg())),
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// and which is not a literal nullptr,
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unless(cxxNullPtrLiteralExpr()), expr().bind("invalidArg")));
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// A matcher which will mark the first invalid argument it finds invalid, but
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// will always match, even if it finds no invalid arguments, so it doesn't
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// preclude other matchers from running and maybe finding invalid args.
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auto OptionalInvalidExplicitArg = anyOf(
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// We want to find any argument which is invalid.
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hasAnyArgument(InvalidArg),
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// This makes this matcher optional.
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anything());
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// Please note that the hasCanRunScriptAnnotation() matchers are not present
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// directly in the cxxMemberCallExpr, callExpr and constructExpr matchers
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// because we check that the corresponding functions can run script later in
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// the checker code.
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AstMatcher->addMatcher(
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expr(
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anyOf(
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// We want to match a method call expression,
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cxxMemberCallExpr(
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// which optionally has an invalid arg,
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OptionalInvalidExplicitArg,
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// or which optionally has an invalid this argument,
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anyOf(on(InvalidArg), anything()), expr().bind("callExpr")),
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// or a regular call expression,
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callExpr(
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// which optionally has an invalid arg.
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OptionalInvalidExplicitArg, expr().bind("callExpr")),
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// or a construct expression,
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cxxConstructExpr(
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// which optionally has an invalid arg.
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OptionalInvalidExplicitArg, expr().bind("constructExpr"))),
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anyOf(
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// We want to match the parent function.
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forFunction(functionDecl().bind("nonCanRunScriptParentFunction")),
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// ... optionally.
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anything())),
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this);
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}
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void CanRunScriptChecker::onStartOfTranslationUnit() {
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IsFuncSetBuilt = false;
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CanRunScriptFuncs.clear();
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}
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namespace {
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/// This class is a callback used internally to match function declarations with
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/// the MOZ_CAN_RUN_SCRIPT annotation, adding these functions to the
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/// can-run-script function set and making sure the functions they override (if
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/// any) also have the annotation.
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class FuncSetCallback : public MatchFinder::MatchCallback {
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public:
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FuncSetCallback(CanRunScriptChecker &Checker,
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std::unordered_set<const FunctionDecl *> &FuncSet)
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: CanRunScriptFuncs(FuncSet), Checker(Checker) {}
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void run(const MatchFinder::MatchResult &Result) override;
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private:
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/// This method checks the methods overriden by the given parameter.
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void checkOverriddenMethods(const CXXMethodDecl *Method);
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std::unordered_set<const FunctionDecl *> &CanRunScriptFuncs;
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CanRunScriptChecker &Checker;
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};
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void FuncSetCallback::run(const MatchFinder::MatchResult &Result) {
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const FunctionDecl *Func;
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if (auto *Lambda = Result.Nodes.getNodeAs<LambdaExpr>("lambda")) {
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Func = Lambda->getCallOperator();
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if (!Func || !hasCustomAttribute<moz_can_run_script>(Func))
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return;
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} else {
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Func = Result.Nodes.getNodeAs<FunctionDecl>("canRunScriptFunction");
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const char *ErrorAttrInDefinition =
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"MOZ_CAN_RUN_SCRIPT must be put in front "
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"of the declaration, not the definition";
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const char *NoteAttrInDefinition = "The first declaration exists here";
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if (!Func->isFirstDecl() &&
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!hasCustomAttribute<moz_can_run_script_for_definition>(Func)) {
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const FunctionDecl *FirstDecl = Func->getFirstDecl();
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if (!hasCustomAttribute<moz_can_run_script>(FirstDecl)) {
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Checker.diag(Func->getLocation(), ErrorAttrInDefinition,
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DiagnosticIDs::Error);
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Checker.diag(FirstDecl->getLocation(), NoteAttrInDefinition,
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DiagnosticIDs::Note);
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}
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}
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}
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CanRunScriptFuncs.insert(Func);
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// If this is a method, we check the methods it overrides.
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if (auto *Method = dyn_cast<CXXMethodDecl>(Func)) {
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checkOverriddenMethods(Method);
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}
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}
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void FuncSetCallback::checkOverriddenMethods(const CXXMethodDecl *Method) {
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for (auto OverriddenMethod : Method->overridden_methods()) {
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if (!hasCustomAttribute<moz_can_run_script>(OverriddenMethod)) {
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const char *ErrorNonCanRunScriptOverridden =
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"functions marked as MOZ_CAN_RUN_SCRIPT cannot override functions "
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"that are not marked MOZ_CAN_RUN_SCRIPT";
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const char *NoteNonCanRunScriptOverridden =
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"overridden function declared here";
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Checker.diag(Method->getLocation(), ErrorNonCanRunScriptOverridden,
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DiagnosticIDs::Error);
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Checker.diag(OverriddenMethod->getLocation(),
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NoteNonCanRunScriptOverridden, DiagnosticIDs::Note);
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}
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}
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}
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} // namespace
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void CanRunScriptChecker::buildFuncSet(ASTContext *Context) {
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// We create a match finder.
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MatchFinder Finder;
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// We create the callback which will be called when we find a function with
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// a MOZ_CAN_RUN_SCRIPT annotation.
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FuncSetCallback Callback(*this, CanRunScriptFuncs);
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// We add the matcher to the finder, linking it to our callback.
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Finder.addMatcher(
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functionDecl(hasCanRunScriptAnnotation()).bind("canRunScriptFunction"),
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&Callback);
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Finder.addMatcher(lambdaExpr().bind("lambda"), &Callback);
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// We start the analysis, given the ASTContext our main checker is in.
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Finder.matchAST(*Context);
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}
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void CanRunScriptChecker::check(const MatchFinder::MatchResult &Result) {
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// If the set of functions which can run script is not yet built, then build
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// it.
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if (!IsFuncSetBuilt) {
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buildFuncSet(Result.Context);
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IsFuncSetBuilt = true;
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}
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const char *ErrorInvalidArg =
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"arguments must all be strong refs or caller's parameters when calling a "
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"function marked as MOZ_CAN_RUN_SCRIPT (including the implicit object "
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"argument). '%0' is neither.";
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const char *ErrorNonCanRunScriptParent =
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"functions marked as MOZ_CAN_RUN_SCRIPT can only be called from "
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"functions also marked as MOZ_CAN_RUN_SCRIPT";
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const char *NoteNonCanRunScriptParent = "caller function declared here";
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const Expr *InvalidArg;
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if (const CXXDefaultArgExpr *defaultArg =
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Result.Nodes.getNodeAs<CXXDefaultArgExpr>("invalidArg")) {
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InvalidArg = defaultArg->getExpr();
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} else {
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InvalidArg = Result.Nodes.getNodeAs<Expr>("invalidArg");
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}
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const CallExpr *Call = Result.Nodes.getNodeAs<CallExpr>("callExpr");
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// If we don't find the FunctionDecl linked to this call or if it's not marked
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// as can-run-script, consider that we didn't find a match.
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if (Call && (!Call->getDirectCallee() ||
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!CanRunScriptFuncs.count(Call->getDirectCallee()))) {
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Call = nullptr;
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}
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const CXXConstructExpr *Construct =
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Result.Nodes.getNodeAs<CXXConstructExpr>("constructExpr");
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// If we don't find the CXXConstructorDecl linked to this construct expression
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// or if it's not marked as can-run-script, consider that we didn't find a
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// match.
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if (Construct && (!Construct->getConstructor() ||
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!CanRunScriptFuncs.count(Construct->getConstructor()))) {
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Construct = nullptr;
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}
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const FunctionDecl *ParentFunction =
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Result.Nodes.getNodeAs<FunctionDecl>("nonCanRunScriptParentFunction");
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// If the parent function can run script, consider that we didn't find a match
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// because we only care about parent functions which can't run script.
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//
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// In addition, If the parent function is annotated as a
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// CAN_RUN_SCRIPT_BOUNDARY, we don't want to complain about it calling a
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// CAN_RUN_SCRIPT function. This is a mechanism to opt out of the infectious
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// nature of CAN_RUN_SCRIPT which is necessary in some tricky code like
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// Bindings.
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if (ParentFunction &&
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(CanRunScriptFuncs.count(ParentFunction) ||
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hasCustomAttribute<moz_can_run_script_boundary>(ParentFunction))) {
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ParentFunction = nullptr;
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}
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// Get the call range from either the CallExpr or the ConstructExpr.
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SourceRange CallRange;
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if (Call) {
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CallRange = Call->getSourceRange();
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} else if (Construct) {
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CallRange = Construct->getSourceRange();
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} else {
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// If we have neither a Call nor a Construct, we have nothing do to here.
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return;
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}
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// If we have an invalid argument in the call, we emit the diagnostic to
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// signal it.
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if (InvalidArg) {
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const StringRef invalidArgText = Lexer::getSourceText(
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CharSourceRange::getTokenRange(InvalidArg->getSourceRange()),
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Result.Context->getSourceManager(), Result.Context->getLangOpts());
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diag(InvalidArg->getExprLoc(), ErrorInvalidArg, DiagnosticIDs::Error)
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<< InvalidArg->getSourceRange() << invalidArgText;
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}
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// If the parent function is not marked as MOZ_CAN_RUN_SCRIPT, we emit an
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// error and a not indicating it.
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if (ParentFunction) {
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assert(!hasCustomAttribute<moz_can_run_script>(ParentFunction) &&
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"Matcher missed something");
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diag(CallRange.getBegin(), ErrorNonCanRunScriptParent, DiagnosticIDs::Error)
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<< CallRange;
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diag(ParentFunction->getCanonicalDecl()->getLocation(),
|
|
NoteNonCanRunScriptParent, DiagnosticIDs::Note);
|
|
}
|
|
}
|