Package optimization allows bypassing resilience, but that assumes the memory layout of the

decl being accessed is correct. When this assumption fails due to a deserialization error
of its members, the use site accesses the layout with a wrong field offset, resulting in
UB or a crash. The deserialization error is currently not caught at compile time due to
LangOpts.EnableDeserializationRecovery being enabled by default to allow for recovery of some
of the deserialization errors at a later time. In case of member deserialization, however,
it's not necessarily recovered later on.

This PR tracks whether member deserialization had an error by recursively loading members and
checking for deserialization error, and fails and emits a diagnostic. It provides a way to
prevent resilience bypassing when the deserialized decl's layout is incorrect.

Resolves rdar://132411524

Author: elsh

include/swift/AST/DeclContext.h

@@ -815,6 +815,22 @@ class IterableDeclContext {
   /// while skipping the body of this context.
   unsigned HasDerivativeDeclarations : 1;
 
+  /// Members of a decl are deserialized lazily. This is set when
+  /// deserialization of all members is done, regardless of errors.
+  unsigned DeserializedMembers : 1;
+
+  /// Deserialization errors are attempted to be recovered later or
+  /// silently dropped due to `EnableDeserializationRecovery` being
+  /// on by default. The following flag is set when deserializing
+  /// members fails regardless of the `EnableDeserializationRecovery`
+  /// value and is used to prevent decl containing such members from
+  /// being accessed non-resiliently.
+  unsigned HasDeserializeMemberError : 1;
+
+  /// Used to track whether members of this decl and their respective
+  /// members were checked for deserialization errors recursively.
+  unsigned CheckedForDeserializeMemberError : 1;
+
   template<class A, class B, class C>
   friend struct ::llvm::CastInfo;
 
@@ -825,6 +841,9 @@ class IterableDeclContext {
   /// Retrieve the \c ASTContext in which this iterable context occurs.
   ASTContext &getASTContext() const;
 
+  void setCheckedForDeserializeMemberError(bool checked) { CheckedForDeserializeMemberError = checked; }
+  bool checkedForDeserializeMemberError() const { return CheckedForDeserializeMemberError; }
+
 public:
   IterableDeclContext(IterableDeclContextKind kind)
     : LastDeclAndKind(nullptr, kind) {
@@ -833,6 +852,9 @@ class IterableDeclContext {
     HasDerivativeDeclarations = 0;
     HasNestedClassDeclarations = 0;
     InFreestandingMacroArgument = 0;
+    DeserializedMembers = 0;
+    HasDeserializeMemberError = 0;
+    CheckedForDeserializeMemberError = 0;
   }
 
   /// Determine the kind of iterable context we have.
@@ -842,6 +864,18 @@ class IterableDeclContext {
 
   bool hasUnparsedMembers() const;
 
+  void setDeserializedMembers(bool deserialized) { DeserializedMembers = deserialized; }
+  bool didDeserializeMembers() const { return DeserializedMembers; }
+
+  void setHasDeserializeMemberError(bool hasError) { HasDeserializeMemberError = hasError; }
+  bool hasDeserializeMemberError() const { return HasDeserializeMemberError; }
+
+  /// This recursively checks whether members of this decl and their respective
+  /// members were deserialized correctly and emits a diagnostic in case of an error.
+  /// Requires accessing module and this decl's module are in the same package,
+  /// and this decl's module has package optimization enabled.
+  void checkDeserializeMemberErrorInPackage(ModuleDecl *accessingModule);
+
   bool maybeHasOperatorDeclarations() const {
     return HasOperatorDeclarations;
   }

include/swift/AST/DiagnosticsSema.def

@@ -4733,6 +4733,11 @@ NOTE(ambiguous_because_of_trailing_closure,none,
      "avoid using a trailing closure}0 to call %1",
      (bool, const ValueDecl *))
 
+// In-package resilience bypassing
+ERROR(cannot_bypass_resilience_due_to_missing_member,none,
+      "cannot bypass resilience due to member deserialization failure while attempting to access %select{member %0|missing member}1 of %2 in module %3 from module %4",
+      (Identifier, bool, Identifier, Identifier, Identifier))
+
 // Cannot capture inout-ness of a parameter
 // Partial application of foreign functions not supported
 ERROR(partial_application_of_function_invalid,none,

include/swift/Basic/LangOptions.h

@@ -610,6 +610,13 @@ namespace swift {
     /// from source.
     bool AllowNonResilientAccess = false;
 
+    /// When Package CMO is enabled, deserialization checks are done to
+    /// ensure that the members of a decl are correctly deserialized to maintain
+    /// proper layout. This ensures that bypassing resilience is safe. Accessing
+    /// an incorrectly laid-out decl directly can lead to runtime crashes. This flag
+    /// should only be used temporarily during migration to enable Package CMO.
+    bool SkipDeserializationChecksForPackageCMO = false;
+
     /// Enables dumping type witness systems from associated type inference.
     bool DumpTypeWitnessSystems = false;
 

include/swift/Option/Options.td

@@ -1079,6 +1079,10 @@ def Oplayground : Flag<["-"], "Oplayground">, Group<O_Group>,
   Flags<[HelpHidden, FrontendOption, ModuleInterfaceOption]>,
   HelpText<"Compile with optimizations appropriate for a playground">;
 
+def ExperimentalSkipDeserializationChecksForPackageCMO : Flag<["-"], "experimental-skip-deserialization-checks-for-package-cmo">,
+  Flags<[FrontendOption]>,
+  HelpText<"Skip deserialization checks for package-cmo; use only for experimental purposes">;
+
 def ExperimentalPackageCMO : Flag<["-"], "experimental-package-cmo">,
   Flags<[FrontendOption]>,
   HelpText<"Deprecated; use -package-cmo instead">;

lib/AST/Decl.cpp

@@ -4723,14 +4723,51 @@ bool ValueDecl::hasOpenAccess(const DeclContext *useDC) const {
 }
 
 bool ValueDecl::bypassResilienceInPackage(ModuleDecl *accessingModule) const {
-  // If the defining module is built with package-cmo, bypass
-  // resilient access from the use site that belongs to a module
-  // in the same package.
+  // To allow bypassing resilience when accessing this decl from another
+  // module, it should be in the same package as this decl's module.
   auto declModule = getModuleContext();
-  return declModule->inSamePackage(accessingModule) &&
-         declModule->isResilient() &&
-         declModule->allowNonResilientAccess() &&
-         declModule->serializePackageEnabled();
+  if (!declModule->inSamePackage(accessingModule))
+    return false;
+  // Package optimization allows bypassing resilience, but it assumes the
+  // memory layout of the decl being accessed is correct. When this assumption
+  // fails due to a deserialization error of its members, the use site incorrectly
+  // accesses the layout of the decl with a wrong field offset, resulting in UB
+  // or a crash.
+  // The deserialization error is currently not caught at compile time due to
+  // LangOpts.EnableDeserializationRecovery being enabled by default (to allow
+  // for recovery of some of the deserialization errors at a later time). In case
+  // of member deserialization, however, it's not necessarily recovered later on
+  // and is silently dropped, causing UB or a crash at runtime.
+  // The following tracks errors in member deserialization by recursively loading
+  // members of a type (if not done already) and checking whether the type's
+  // members, and their respective types (recursively), encountered deserialization
+  // failures.
+  // If any such type is found, it fails and emits a diagnostic at compile time.
+  // Simply disallowing resilience bypassing for this decl here is insufficient
+  // because it would cause a type requirement mismatch later during SIL
+  // deserialiaztion; e.g. generated SIL in the imported module might contain
+  // an instruction that allows a direct access, while the caller in client module
+  // might require a non-direct access due to a deserialization error.
+  if (declModule->isResilient() &&
+      declModule->allowNonResilientAccess() &&
+      declModule->serializePackageEnabled()) {
+    // Fail and diagnose if there is a member deserialization error,
+    // with an option to skip for temporary/migration purposes.
+    if (!getASTContext().LangOpts.SkipDeserializationChecksForPackageResilienceBypass) {
+      // Since we're checking for deserialization errors, make sure the
+      // accessing module is different from this decl's module.
+      if (accessingModule &&
+          accessingModule != declModule) {
+        if (auto IDC = dyn_cast<IterableDeclContext>(this)) {
+          // Recursively check if members and their members have failing
+          // deserialization, and emit a diagnostic.
+          IDC->checkDeserializeMemberErrorInPackage(accessingModule);
+        }
+      }
+    }
+    return true;
+  }
+  return false;
 }
 
 /// Given the formal access level for using \p VD, compute the scope where

lib/AST/DeclContext.cpp

@@ -26,6 +26,7 @@
 #include "swift/AST/SourceFile.h"
 #include "swift/AST/TypeCheckRequests.h"
 #include "swift/AST/Types.h"
+#include "swift/AST/DiagnosticsSema.h"
 #include "swift/Basic/Assertions.h"
 #include "swift/Basic/SourceManager.h"
 #include "swift/Basic/Statistic.h"
@@ -1174,6 +1175,145 @@ void IterableDeclContext::loadAllMembers() const {
     --s->getFrontendCounters().NumUnloadedLazyIterableDeclContexts;
 }
 
+// Checks whether members of this decl and their respective members
+// (recursively) were deserialized correctly and emits a diagnostic
+// if deserialization failed. Requires accessing module and this decl's
+// module are in the same package, and this decl's module has package
+// optimization enabled.
+void IterableDeclContext::checkDeserializeMemberErrorInPackage(ModuleDecl *accessingModule) {
+  // Only check if accessing module is in the same package as this
+  // decl's module, which has package optimization enabled.
+  if (!getDecl()->getModuleContext()->inSamePackage(accessingModule) ||
+      !getDecl()->getModuleContext()->isResilient() ||
+      !getDecl()->getModuleContext()->serializePackageEnabled())
+    return;
+  // Bail if already checked for an error.
+  if (checkedForDeserializeMemberError())
+    return;
+  // If members were not deserialized, force load here.
+  if (!didDeserializeMembers()) {
+    // This needs to be set to force load all members if not done already.
+    setHasLazyMembers(true);
+    // Calling getMembers actually loads the members.
+    auto members = getMembers();
+    assert(!hasLazyMembers());
+    assert(didDeserializeMembers());
+  }
+  // Members could have been deserialized from other flows. Check
+  // for an error here. First mark this decl 'checked' to prevent
+  // infinite recursion in case of self-referencing members.
+  setCheckedForDeserializeMemberError(true);
+
+  // If members are already loaded above or by other flows,
+  // calling getMembers here should be inexpensive.
+  auto memberList = getMembers();
+
+  // This decl contains a member deserialization error; emit a diag.
+  if (hasDeserializeMemberError()) {
+    auto containerID = Identifier();
+    if (auto container = dyn_cast<NominalTypeDecl>(getDecl())) {
+      containerID = container->getBaseIdentifier();
+    }
+
+    auto foundMissing = false;
+    for (auto member: memberList) {
+      // Only storage vars can affect memory layout so
+      // look up pattern binding decl or var decl.
+      if (auto *PBD = dyn_cast<PatternBindingDecl>(member)) {
+        // If this pattern binding decl is empty, we have
+        // a missing member.
+        if (PBD->getNumPatternEntries() == 0)
+          foundMissing = true;
+      }
+      // Check if a member can be cast to MissingMemberDecl.
+      if (auto missingMember = dyn_cast<MissingMemberDecl>(member)) {
+        if (!missingMember->getName().getBaseName().isSpecial() &&
+            foundMissing) {
+          foundMissing = false;
+          auto missingMemberID = missingMember->getName().getBaseIdentifier();
+          getASTContext().Diags.diagnose(member->getLoc(),
+                                         diag::cannot_bypass_resilience_due_to_missing_member,
+                                         missingMemberID,
+                                         missingMemberID.empty(),
+                                         containerID,
+                                         getDecl()->getModuleContext()->getBaseIdentifier(),
+                                         accessingModule->getBaseIdentifier());
+          continue;
+        }
+      }
+      // If not handled above, emit a diag here.
+      if (foundMissing) {
+        getASTContext().Diags.diagnose(getDecl()->getLoc(),
+                                       diag::cannot_bypass_resilience_due_to_missing_member,
+                                       Identifier(),
+                                       true,
+                                       containerID,
+                                       getDecl()->getModuleContext()->getBaseIdentifier(),
+                                       accessingModule->getBaseIdentifier());
+      }
+    }
+  } else {
+    // This decl does not contain a member deserialization error.
+    // Check for members of this decl's members recursively to
+    // see if a member deserialization failed.
+    for (auto member: memberList) {
+      // Only storage vars can affect memory layout so
+      // look up pattern binding decl or var decl.
+      if (auto *PBD = dyn_cast<PatternBindingDecl>(member)) {
+        for (auto i : range(PBD->getNumPatternEntries())) {
+          auto pattern = PBD->getPattern(i);
+          pattern->forEachVariable([&](const VarDecl *VD) {
+            // Bail if the var is static or has no storage
+            if (VD->isStatic() ||
+               !VD->hasStorageOrWrapsStorage())
+              return;
+            // Unwrap in case this var is optional.
+            auto varType = VD->getInterfaceType()->getCanonicalType();
+            if (auto unwrapped = varType->getCanonicalType()->getOptionalObjectType()) {
+              varType = unwrapped->getCanonicalType();
+            }
+            // Handle BoundGenericType, e.g. [Foo: Bar], Dictionary<Foo, Bar>.
+            // Check for its arguments types, i.e. Foo, Bar.
+            if (auto boundGeneric = varType->getAs<BoundGenericType>()) {
+                for (auto arg : boundGeneric->getGenericArgs()) {
+                  if (auto argNominal = arg->getNominalOrBoundGenericNominal()) {
+                    if (auto argIDC = dyn_cast<IterableDeclContext>(argNominal)) {
+                      argIDC->checkDeserializeMemberErrorInPackage(getDecl()->getModuleContext());
+                      if (argIDC->hasDeserializeMemberError()) {
+                         setHasDeserializeMemberError(true);
+                        break;
+                      }
+                    }
+                  }
+                }
+            } else if (auto tupleType = varType->getAs<TupleType>()) {
+              // Handle TupleType, e.g. (Foo, Var).
+              for (auto element : tupleType->getElements()) {
+                if (auto elementNominal = element.getType()->getNominalOrBoundGenericNominal()) {
+                    if (auto elementIDC = dyn_cast<IterableDeclContext>(elementNominal)) {
+                      elementIDC->checkDeserializeMemberErrorInPackage(getDecl()->getModuleContext());
+                      if (elementIDC->hasDeserializeMemberError()) {
+                         setHasDeserializeMemberError(true);
+                        break;
+                      }
+                    }
+                  }
+                }
+            } else if (auto varNominal = varType->getNominalOrBoundGenericNominal()) {
+              if (auto varIDC = dyn_cast<IterableDeclContext>(varNominal)) {
+                varIDC->checkDeserializeMemberErrorInPackage(getDecl()->getModuleContext());
+                if (varIDC->hasDeserializeMemberError()) {
+                   setHasDeserializeMemberError(true);
+                }
+              }
+            }
+          });
+        }
+      }
+    }
+  }
+}
+
 bool IterableDeclContext::wasDeserialized() const {
   const DeclContext *DC = getAsGenericContext();
   if (auto F = dyn_cast<FileUnit>(DC->getModuleScopeContext())) {

lib/AST/TypeSubstitution.cpp

@@ -997,8 +997,7 @@ ReplaceOpaqueTypesWithUnderlyingTypes::shouldPerformSubstitution(
   // resilient expansion if the context's and the opaque type's module are in
   // the same package.
   if (contextExpansion == ResilienceExpansion::Maximal &&
-      module->isResilient() && module->serializePackageEnabled() &&
-      module->inSamePackage(contextModule))
+      namingDecl->bypassResilienceInPackage(contextModule))
     return OpaqueSubstitutionKind::SubstituteSamePackageMaximalResilience;
 
   // Allow general replacement from non resilient modules. Otherwise, disallow.

lib/ClangImporter/ImportDecl.cpp

@@ -9835,17 +9835,22 @@ ClangImporter::Implementation::loadAllMembers(Decl *D, uint64_t extra) {
   // Check whether we're importing an Objective-C container of some sort.
   auto objcContainer =
     dyn_cast_or_null<clang::ObjCContainerDecl>(D->getClangDecl());
+  auto *IDC = dyn_cast<IterableDeclContext>(D);
 
   // If not, we're importing globals-as-members into an extension.
   if (objcContainer) {
     loadAllMembersOfSuperclassIfNeeded(dyn_cast<ClassDecl>(D));
     loadAllMembersOfObjcContainer(D, objcContainer);
+    if (IDC) // Set member deserialization status
+      IDC->setDeserializedMembers(true);
     return;
   }
 
   if (isa_and_nonnull<clang::RecordDecl>(D->getClangDecl())) {
     loadAllMembersOfRecordDecl(cast<NominalTypeDecl>(D),
                                cast<clang::RecordDecl>(D->getClangDecl()));
+    if (IDC) // Set member deserialization status
+      IDC->setDeserializedMembers(true);
     return;
   }
 
@@ -9856,6 +9861,8 @@ ClangImporter::Implementation::loadAllMembers(Decl *D, uint64_t extra) {
   }
 
   loadAllMembersIntoExtension(D, extra);
+  if (IDC) // Set member deserialization status
+    IDC->setDeserializedMembers(true);
 }
 
 void ClangImporter::Implementation::loadAllMembersIntoExtension(

lib/Frontend/CompilerInvocation.cpp

@@ -1354,6 +1354,7 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
     }
   }
 
+  Opts.SkipDeserializationChecksForPackageResilienceBypass = Args.hasArg(OPT_ExperimentalSkipDeserializationChecksForPackageResilienceBypass);
   Opts.AllowNonResilientAccess =
       Args.hasArg(OPT_experimental_allow_non_resilient_access) ||
       Args.hasArg(OPT_allow_non_resilient_access) ||

lib/SIL/IR/TypeLowering.cpp

@@ -2449,13 +2449,8 @@ namespace {
         // The same should happen if the type was resilient and serialized in
         // another module in the same package with package-cmo enabled, which
         // treats those modules to be in the same resilience domain.
-        auto declModule = D->getModuleContext();
-        bool sameModule = (declModule == &TC.M);
-        bool serializedPackage = declModule != &TC.M &&
-                                 declModule->inSamePackage(&TC.M) &&
-                                 declModule->isResilient() &&
-                                 declModule->serializePackageEnabled();
-        auto inSameResilienceDomain = sameModule || serializedPackage;
+        auto inSameResilienceDomain = D->getModuleContext() == &TC.M ||
+                                      D->bypassResilienceInPackage(&TC.M);
         if (inSameResilienceDomain)
           properties.addSubobject(RecursiveProperties::forResilient());