Be more careful in parsing Module::ModFlagBehavior value

to make sure we don't do invalid load of an enum. Share the
conversion code between llvm::Module implementation and the
verifier.

This bug was reported by UBSan.

llvm-svn: 217395

llvm/include/llvm/IR/Module.h

@@ -182,9 +182,17 @@ public:
     /// Appends the two values, which are required to be metadata
     /// nodes. However, duplicate entries in the second list are dropped
     /// during the append operation.
-    AppendUnique = 6
+    AppendUnique = 6,
+
+    // Markers:
+    ModFlagBehaviorFirstVal = Error,
+    ModFlagBehaviorLastVal = AppendUnique
   };
 
+  /// Checks if Value represents a valid ModFlagBehavior, and stores the
+  /// converted result in MFB.
+  static bool isValidModFlagBehavior(Value *V, ModFlagBehavior &MFB);
+
   struct ModuleFlagEntry {
     ModFlagBehavior Behavior;
     MDString *Key;

llvm/lib/IR/Module.cpp

@@ -259,6 +259,17 @@ void Module::eraseNamedMetadata(NamedMDNode *NMD) {
   NamedMDList.erase(NMD);
 }
 
+bool Module::isValidModFlagBehavior(Value *V, ModFlagBehavior &MFB) {
+  if (ConstantInt *Behavior = dyn_cast<ConstantInt>(V)) {
+    uint64_t Val = Behavior->getLimitedValue();
+    if (Val >= ModFlagBehaviorFirstVal && Val <= ModFlagBehaviorLastVal) {
+      MFB = static_cast<ModFlagBehavior>(Val);
+      return true;
+    }
+  }
+  return false;
+}
+
 /// getModuleFlagsMetadata - Returns the module flags in the provided vector.
 void Module::
 getModuleFlagsMetadata(SmallVectorImpl<ModuleFlagEntry> &Flags) const {
@@ -266,15 +277,15 @@ getModuleFlagsMetadata(SmallVectorImpl<ModuleFlagEntry> &Flags) const {
   if (!ModFlags) return;
 
   for (const MDNode *Flag : ModFlags->operands()) {
-    if (Flag->getNumOperands() >= 3 && isa<ConstantInt>(Flag->getOperand(0)) &&
+    ModFlagBehavior MFB;
+    if (Flag->getNumOperands() >= 3 &&
+        isValidModFlagBehavior(Flag->getOperand(0), MFB) &&
         isa<MDString>(Flag->getOperand(1))) {
       // Check the operands of the MDNode before accessing the operands.
       // The verifier will actually catch these failures.
-      ConstantInt *Behavior = cast<ConstantInt>(Flag->getOperand(0));
       MDString *Key = cast<MDString>(Flag->getOperand(1));
       Value *Val = Flag->getOperand(2);
-      Flags.push_back(ModuleFlagEntry(ModFlagBehavior(Behavior->getZExtValue()),
-                                      Key, Val));
+      Flags.push_back(ModuleFlagEntry(MFB, Key, Val));
     }
   }
 }

llvm/lib/IR/Verifier.cpp

@@ -673,24 +673,23 @@ Verifier::visitModuleFlag(const MDNode *Op,
   // constant int), the flag ID (an MDString), and the value.
   Assert1(Op->getNumOperands() == 3,
           "incorrect number of operands in module flag", Op);
-  ConstantInt *Behavior = dyn_cast<ConstantInt>(Op->getOperand(0));
+  Module::ModFlagBehavior MFB;
+  if (!Module::isValidModFlagBehavior(Op->getOperand(0), MFB)) {
+    Assert1(
+        dyn_cast<ConstantInt>(Op->getOperand(0)),
+        "invalid behavior operand in module flag (expected constant integer)",
+        Op->getOperand(0));
+    Assert1(false,
+            "invalid behavior operand in module flag (unexpected constant)",
+            Op->getOperand(0));
+  }
   MDString *ID = dyn_cast<MDString>(Op->getOperand(1));
-  Assert1(Behavior,
-          "invalid behavior operand in module flag (expected constant integer)",
-          Op->getOperand(0));
-  unsigned BehaviorValue = Behavior->getZExtValue();
   Assert1(ID,
           "invalid ID operand in module flag (expected metadata string)",
           Op->getOperand(1));
 
   // Sanity check the values for behaviors with additional requirements.
-  switch (BehaviorValue) {
-  default:
-    Assert1(false,
-            "invalid behavior operand in module flag (unexpected constant)",
-            Op->getOperand(0));
-    break;
-
+  switch (MFB) {
   case Module::Error:
   case Module::Warning:
   case Module::Override:
@@ -726,7 +725,7 @@ Verifier::visitModuleFlag(const MDNode *Op,
   }
 
   // Unless this is a "requires" flag, check the ID is unique.
-  if (BehaviorValue != Module::Require) {
+  if (MFB != Module::Require) {
     bool Inserted = SeenIDs.insert(std::make_pair(ID, Op)).second;
     Assert1(Inserted,
             "module flag identifiers must be unique (or of 'require' type)",