Fixes a bug in SILCombiner that caused a use-after-free

lib/SIL/SILVerifier.cpp

@@ -2396,9 +2396,39 @@ public:
             break;
         case SILInstructionKind::DestroyAddrInst:
           return true;
-        case SILInstructionKind::UncheckedAddrCastInst:
+        case SILInstructionKind::UncheckedAddrCastInst: {
-          // Escaping use lets be conservative here.
+          // Don't be too conservative here, we have a new case:
+          // sil-combine producing a new code pattern for devirtualizer
+          // open_existential_addr immutable_access -> witness_method
+          // witness_method gets transformed into unchecked_addr_cast
+          // we are "OK" If one of the new users is an non-consuming apply
+          // we are also "OK" if we have a single non-consuming user
+          auto isCastToNonConsuming = [=](UncheckedAddrCastInst *I) -> bool {
+            for (auto *use : I->getUses()) {
+              auto *inst = use->getUser();
+              switch (inst->getKind()) {
+              case SILInstructionKind::ApplyInst:
+              case SILInstructionKind::TryApplyInst:
+              case SILInstructionKind::PartialApplyInst:
+                if (!isConsumingOrMutatingApplyUse(use))
+                  return true;
+                break;
+              case SILInstructionKind::LoadInst:
+              case SILInstructionKind::DebugValueAddrInst:
+                if (I->hasOneUse())
+                  return true;
+                break;
+              default:
+                break;
+              }
+            }
+            return false;
+          };
+          if (isCastToNonConsuming(dyn_cast<UncheckedAddrCastInst>(inst))) {
+            break;
+          }
           return true;
+        }
         case SILInstructionKind::CheckedCastAddrBranchInst:
           if (cast<CheckedCastAddrBranchInst>(inst)->getConsumptionKind() !=
               CastConsumptionKind::CopyOnSuccess)

lib/SILOptimizer/SILCombiner/SILCombine.cpp

@@ -341,11 +341,12 @@ class SILCombine : public SILFunctionTransform {
   /// The entry point to the transformation.
   void run() override {
     auto *AA = PM->getAnalysis<AliasAnalysis>();
+    auto *DA = PM->getAnalysis<DominanceAnalysis>();
 
     // Create a SILBuilder with a tracking list for newly added
     // instructions, which we will periodically move to our worklist.
     SILBuilder B(*getFunction(), &TrackingList);
-    SILCombiner Combiner(B, AA, getOptions().RemoveRuntimeAsserts);
+    SILCombiner Combiner(B, AA, DA, getOptions().RemoveRuntimeAsserts);
     bool Changed = Combiner.runOnFunction(*getFunction());
     assert(TrackingList.empty() &&
            "TrackingList should be fully processed by SILCombiner");

lib/SILOptimizer/SILCombiner/SILCombiner.h

@@ -114,6 +114,8 @@ class SILCombiner :
 
   AliasAnalysis *AA;
 
+  DominanceAnalysis *DA;
+
   /// Worklist containing all of the instructions primed for simplification.
   SILCombineWorklist Worklist;
 
@@ -133,11 +135,12 @@ class SILCombiner :
   CastOptimizer CastOpt;
 
 public:
-  SILCombiner(SILBuilder &B, AliasAnalysis *AA, bool removeCondFails)
+  SILCombiner(SILBuilder &B, AliasAnalysis *AA, DominanceAnalysis *DA,
-      : AA(AA), Worklist(), MadeChange(false), RemoveCondFails(removeCondFails),
+              bool removeCondFails)
-        Iteration(0), Builder(B),
+      : AA(AA), DA(DA), Worklist(), MadeChange(false),
+        RemoveCondFails(removeCondFails), Iteration(0), Builder(B),
         CastOpt(/* ReplaceInstUsesAction */
-                [&](SingleValueInstruction *I, ValueBase * V) {
+                [&](SingleValueInstruction *I, ValueBase *V) {
                   replaceInstUsesWith(*I, V);
                 },
                 /* EraseAction */

lib/SILOptimizer/SILCombiner/SILCombinerApplyVisitors.cpp

@@ -844,6 +844,23 @@ getConformanceAndConcreteType(ASTContext &Ctx,
                          ConcreteTypeDef, NewSelf);
 }
 
+static bool isUseAfterFree(SILValue val, SILInstruction *Apply,
+                           DominanceInfo *DT) {
+  for (auto Use : val->getUses()) {
+    auto *User = Use->getUser();
+    if (!isa<DeallocStackInst>(User) && !isa<DestroyAddrInst>(User) &&
+        !isa<DeinitExistentialAddrInst>(User)) {
+      continue;
+    }
+    if (!DT->properlyDominates(Apply, User)) {
+      // we have use-after-free - Conservative heuristic
+      // Non conservative solution would require data flow analysis
+      return true;
+    }
+  }
+  return false;
+}
+
 /// Propagate information about a concrete type from init_existential_addr
 /// or init_existential_ref into witness_method conformances and into
 /// apply instructions.
@@ -920,6 +937,16 @@ SILCombiner::propagateConcreteTypeOfInitExistential(FullApplySite AI,
       default:
         break;
     }
+    // check if using the value in the apply would cause use-after-free
+    auto *DT = DA->get(AI.getFunction());
+    auto *apply = AI.getInstruction();
+    auto op = InitExistential->getOperand(0);
+    if (isUseAfterFree(op, apply, DT)) {
+      return nullptr;
+    }
+    if (isUseAfterFree(NewSelf, apply, DT)) {
+      return nullptr;
+    }
   }
   // Create a new apply instruction that uses the concrete type instead
   // of the existential type.

test/SILOptimizer/sr-5068.sil

@@ -0,0 +1,133 @@
+// RUN: %target-sil-opt -assume-parsing-unqualified-ownership-sil %s -sil-combine | %FileCheck %s
+
+sil_stage canonical
+
+import Builtin
+import Swift
+import SwiftShims
+
+class UIViewController {
+}
+
+class ExternalFramework {
+  func objects<T>(_ type: T.Type) -> Results<T> where T : Object
+}
+
+class Object {
+}
+
+final class Results<T: Object> {
+}
+
+public protocol ReadonlyExternalFramework {
+  func objects<T>(_ type: T.Type) -> Results<T> where T : Object
+}
+
+extension ExternalFramework : ReadonlyExternalFramework {
+}
+
+public enum ExternalFrameworkProvider {
+  static func readonly() -> ReadonlyExternalFramework
+}
+
+public enum ModelDataService {
+  public static func getCurrent(from ExternalFramework: ReadonlyExternalFramework) -> Model?
+  public static func count(in ExternalFramework: ReadonlyExternalFramework) -> Int
+}
+
+var events: [String]
+
+var currentModel: Model { get }
+
+public class Model : Object {
+  @sil_stored var id: Int { get set }
+  override init()
+  init(value: Any)
+  deinit
+}
+
+sil @ExternalFrameworkInit : $@convention(method) (@thick ExternalFramework.Type) -> (@owned ExternalFramework, @error Error)
+
+sil @ResultsCountGetter : $@convention(method) <τ_0_0 where τ_0_0 : Object> (@guaranteed Results<τ_0_0>) -> Int
+
+sil @GetRawPointer : $@convention(thin) () -> Builtin.RawPointer
+
+sil @GetOptionalModel : $@convention(method) (@in ReadonlyExternalFramework, @thin ModelDataService.Type) -> @owned Optional<Model>
+
+// CHECK-LABEL: sil hidden @BuggyFunction : $@convention(thin) () -> @owned Model {
+// CHECK: [[ALLOC:%.*]] = alloc_stack $ReadonlyExternalFramework, let, name "ExternalFramework"
+// CHECK-NEXT: [[INITE:%.*]] = init_existential_addr [[ALLOC]] : $*ReadonlyExternalFramework, $ExternalFramework
+// CHECK: [[TALLOC1:%.*]] = alloc_stack $ReadonlyExternalFramework
+// CHECK-NEXT: copy_addr [[ALLOC]] to [initialization] [[TALLOC1]] : $*ReadonlyExternalFramework
+// CHECK-NEXT: apply {{%.*}}([[TALLOC1]], {{%.*}}) : $@convention(method) (@in ReadonlyExternalFramework, @thin ModelDataService.Type) -> @owned Optional<Model>
+// CHECK: [[TALLOC2:%.*]] = alloc_stack $ReadonlyExternalFramework
+// CHECK-NEXT: copy_addr [[ALLOC]] to [initialization] [[TALLOC2]] : $*ReadonlyExternalFramework
+// CHECK-NEXT: destroy_addr [[ALLOC]]
+// CHECK: [[OEADDR:%.*]] = open_existential_addr immutable_access [[TALLOC2]] : $*ReadonlyExternalFramework
+sil hidden @BuggyFunction : $@convention(thin) () -> @owned Model {
+bb0:
+  %0 = alloc_stack $ReadonlyExternalFramework, let, name "ExternalFramework" // users: %1, %166, %72, %163, %71, %168, %10
+  %1 = init_existential_addr %0 : $*ReadonlyExternalFramework, $ExternalFramework // user: %6
+  // function_ref ExternalFramework.__allocating_init()
+  %2 = function_ref @ExternalFrameworkInit : $@convention(method) (@thick ExternalFramework.Type) -> (@owned ExternalFramework, @error Error) // user: %4
+  %3 = metatype $@thick ExternalFramework.Type                // user: %4
+  try_apply %2(%3) : $@convention(method) (@thick ExternalFramework.Type) -> (@owned ExternalFramework, @error Error), normal bb1, error bb2 // id: %4
+
+// %5                                             // user: %6
+bb1(%5 : $ExternalFramework):                                 // Preds: bb0
+  store %5 to %1 : $*ExternalFramework                        // id: %6
+  // function_ref static ModelDataService.getCurrent(from:)
+  %7 = function_ref @GetOptionalModel : $@convention(method) (@in ReadonlyExternalFramework, @thin ModelDataService.Type) -> @owned Optional<Model> // user: %11
+  %8 = metatype $@thin ModelDataService.Type      // user: %11
+  %9 = alloc_stack $ReadonlyExternalFramework                 // users: %12, %11, %10
+  copy_addr %0 to [initialization] %9 : $*ReadonlyExternalFramework // id: %10
+  %11 = apply %7(%9, %8) : $@convention(method) (@in ReadonlyExternalFramework, @thin ModelDataService.Type) -> @owned Optional<Model> // user: %13
+  dealloc_stack %9 : $*ReadonlyExternalFramework              // id: %12
+  switch_enum %11 : $Optional<Model>, case #Optional.some!enumelt.1: bb4, case #Optional.none!enumelt: bb3 // id: %13
+
+// %14                                            // user: %15
+bb2(%14 : $Error):                                // Preds: bb0
+  %15 = builtin "unexpectedError"(%14 : $Error) : $()
+  unreachable                                     // id: %16
+
+bb3:                                              // Preds: bb1
+  // function_ref events.unsafeMutableAddressor
+  %17 = function_ref @GetRawPointer : $@convention(thin) () -> Builtin.RawPointer // user: %18
+  %18 = apply %17() : $@convention(thin) () -> Builtin.RawPointer // user: %19
+  %19 = pointer_to_address %18 : $Builtin.RawPointer to [strict] $*Array<String> // users: %158, %156, %152, %151
+  %70 = alloc_stack $ReadonlyExternalFramework                // users: %106, %99, %73, %107, %71
+  copy_addr %0 to [initialization] %70 : $*ReadonlyExternalFramework // id: %71
+  destroy_addr %0 : $*ReadonlyExternalFramework               // id: %72
+  debug_value_addr %70 : $*ReadonlyExternalFramework, let, name "ExternalFramework", argno 1 // id: %73
+  %75 = integer_literal $Builtin.Word, 1          // user: %78
+  %76 = integer_literal $Builtin.Int64, 1         // user: %77
+  %77 = struct $Int (%76 : $Builtin.Int64)        // user: %81
+  %78 = alloc_ref [tail_elems $Any * %75 : $Builtin.Word] $_ContiguousArrayStorage<Any> // user: %81
+  %79 = metatype $@thin Array<Any>.Type           // user: %81
+  %99 = open_existential_addr immutable_access %70 : $*ReadonlyExternalFramework to $*@opened("ED59E038-AA25-11E7-9DEA-685B3593C496") ReadonlyExternalFramework // users: %102, %102, %100
+  %100 = witness_method $@opened("ED59E038-AA25-11E7-9DEA-685B3593C496") ReadonlyExternalFramework, #ReadonlyExternalFramework.objects!1 : <Self where Self : ReadonlyExternalFramework><T where T : Object> (Self) -> (T.Type) -> Results<T>, %99 : $*@opened("ED59E038-AA25-11E7-9DEA-685B3593C496") ReadonlyExternalFramework : $@convention(witness_method) <τ_0_0 where τ_0_0 : ReadonlyExternalFramework><τ_1_0 where τ_1_0 : Object> (@thick τ_1_0.Type, @in_guaranteed τ_0_0) -> @owned Results<τ_1_0> // type-defs: %99; user: %102
+  %101 = metatype $@thick Model.Type              // user: %102
+  %102 = apply %100<@opened("ED59E038-AA25-11E7-9DEA-685B3593C496") ReadonlyExternalFramework, Model>(%101, %99) : $@convention(witness_method) <τ_0_0 where τ_0_0 : ReadonlyExternalFramework><τ_1_0 where τ_1_0 : Object> (@thick τ_1_0.Type, @in_guaranteed τ_0_0) -> @owned Results<τ_1_0> // type-defs: %99; users: %105, %104
+  // function_ref Results.count.getter
+  %103 = function_ref @ResultsCountGetter : $@convention(method) <τ_0_0 where τ_0_0 : Object> (@guaranteed Results<τ_0_0>) -> Int // user: %104
+  %104 = apply %103<Model>(%102) : $@convention(method) <τ_0_0 where τ_0_0 : Object> (@guaranteed Results<τ_0_0>) -> Int // user: %108
+  strong_release %102 : $Results<Model>           // id: %105
+  destroy_addr %70 : $*ReadonlyExternalFramework              // id: %106
+  dealloc_stack %70 : $*ReadonlyExternalFramework             // id: %107
+  %159 = tuple ()
+  %160 = alloc_ref [objc] $Model                  // users: %162, %161
+  dealloc_stack %0 : $*ReadonlyExternalFramework              // id: %163
+  br bb5(%160 : $Model)                           // id: %164
+
+// %165                                           // users: %169, %167
+bb4(%165 : $Model):                               // Preds: bb1
+  destroy_addr %0 : $*ReadonlyExternalFramework               // id: %166
+  debug_value %165 : $Model, let, name "user"     // id: %167
+  dealloc_stack %0 : $*ReadonlyExternalFramework              // id: %168
+  br bb5(%165 : $Model)                           // id: %169
+
+// %170                                           // user: %171
+bb5(%170 : $Model):                               // Preds: bb3 bb4
+  return %170 : $Model                            // id: %171
+} // end sil function 'BuggyFunction'
+