[clang][ptrauth] Warn about the use of a weak signing schema

clang/include/clang/AST/ASTContext.h

@@ -659,6 +659,11 @@ class ASTContext : public RefCountedBase<ASTContext> {
     return findPointerAuthContent(T) != PointerAuthContent::None;
   }
 
+  // A simple helper function to short circuit pointer auth checks.
+  bool isPointerAuthenticationAvailable() const {
+    return LangOpts.PointerAuthCalls || LangOpts.PointerAuthIntrinsics;
+  }
+
 private:
   llvm::DenseMap<const CXXRecordDecl *, CXXRecordDeclRelocationInfo>
       RelocatableClasses;
@@ -670,10 +675,6 @@ class ASTContext : public RefCountedBase<ASTContext> {
     AddressDiscriminatedData
   };
 
-  // A simple helper function to short circuit pointer auth checks.
-  bool isPointerAuthenticationAvailable() const {
-    return LangOpts.PointerAuthCalls || LangOpts.PointerAuthIntrinsics;
-  }
   PointerAuthContent findPointerAuthContent(QualType T) const;
   mutable llvm::DenseMap<const RecordDecl *, PointerAuthContent>
       RecordContainsAddressDiscriminatedPointerAuth;

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -1046,6 +1046,11 @@ def err_ptrauth_address_discrimination_invalid : Error<
 def err_ptrauth_extra_discriminator_invalid : Error<
   "invalid extra discriminator flag '%0'; '__ptrauth' requires a value between "
   "'0' and '%1'">;
+def warn_ptrauth_weak_schema
+    : Warning<"%0 has internal linkage with a %select{|default }1"
+              "pointer authentication schema that should be overridden by "
+              "%select{a|an explicit}1 schema with unique diversifiers">,
+      InGroup<DiagGroup<"ptrauth-weak-schema">>;
 
 /// main()
 // static main() is not an error in C, just in C++.

clang/lib/Sema/SemaDecl.cpp

@@ -8357,6 +8357,16 @@ NamedDecl *Sema::ActOnVariableDeclarator(
                                    D.isFunctionDefinition());
   }
 
+  // Warn about the use of a weak pointer authentication schema on a variable
+  // with internal linkage.
+  if (Context.isPointerAuthenticationAvailable() &&
+      NewVD->isFunctionPointerType() && !NewVD->isExternallyVisible()) {
+    PointerAuthQualifier Q = NewVD->getType().getQualifiers().getPointerAuth();
+    if (!Q || (!Q.isAddressDiscriminated() && Q.getExtraDiscriminator() == 0)) {
+      Diag(NewVD->getLocation(), diag::warn_ptrauth_weak_schema) << NewVD << !Q;
+    }
+  }
+
   if (NewTemplate) {
     if (NewVD->isInvalidDecl())
       NewTemplate->setInvalidDecl();

clang/test/Sema/ptrauth-weak-schema.c

@@ -0,0 +1,60 @@
+// RUN: %clang_cc1 -triple arm64e-apple-ios -fptrauth-calls -fptrauth-intrinsics -fsyntax-only -Wno-unused-variable -verify %s
+// RUN: %clang_cc1 -triple arm64e-apple-ios -DNO_PTRAUTH -fsyntax-only -Wno-unused-variable -verify=noptrauth %s
+
+// noptrauth-no-diagnostics
+
+#include <ptrauth.h>
+
+#if defined(__PTRAUTH__) == defined(NO_PTRAUTH)
+#error expected pointer authentication state does not match actual
+#endif
+
+#if defined(NO_PTRAUTH)
+#define FN_PTR_AUTH(address_diversity, constant_discriminator)
+#else
+#define FN_PTR_AUTH(address_diversity, constant_discriminator) \
+  __ptrauth(ptrauth_key_function_pointer, address_diversity, constant_discriminator)
+#endif
+
+// Global variables with external linkage and weak pointer authentication should
+// not raise any warning.
+extern void(* g1_external_weak)(void);
+void(* FN_PTR_AUTH(0, 0) g2_external_weak)(void);
+
+// Global variables with internal linkage and strong pointer authentication
+// should not raise any warning.
+static void(* FN_PTR_AUTH(1, 65535) g1_internal_strong)(void);
+static void(* FN_PTR_AUTH(0, 65535) g2_internal_strong)(void);
+static void(* FN_PTR_AUTH(1, 0) g3_internal_strong)(void);
+
+#if !defined(NO_PTRAUTH)
+// Global variables with internal linkage and weak pointer authentication should
+// raise a warning.
+static void(* g1_internal_weak)(void);
+// expected-warning@-1 {{'g1_internal_weak' has internal linkage with a default pointer authentication schema that should be overridden by an explicit schema with unique diversifiers}}
+static void(* FN_PTR_AUTH(0, 0) g2_internal_weak)(void);
+// expected-warning@-1 {{'g2_internal_weak' has internal linkage with a pointer authentication schema that should be overridden by a schema with unique diversifiers}}
+
+// Assert that -Wptrauth-weak-schema silences warnings.
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wptrauth-weak-schema"
+static void(* g3_internal_weak)(void);
+#pragma clang diagnostic pop
+#endif
+
+void test_local_variables(void) {
+    #if !defined(NO_PTRAUTH)
+    // Local variables (internal linkage) with weak pointer authentication
+    // should raise a warning.
+    static void(* l1_internal_weak)(void);
+    // expected-warning@-1 {{'l1_internal_weak' has internal linkage with a default pointer authentication schema that should be overridden by an explicit schema with unique diversifiers}}
+    static void(* FN_PTR_AUTH(0, 0) l2_internal_weak)(void);
+    // expected-warning@-1 {{'l2_internal_weak' has internal linkage with a pointer authentication schema that should be overridden by a schema with unique diversifiers}}
+    #endif
+
+    // Local variables (internal linkage) with strong pointer authentication
+    // should not raise any warning.
+    void(* FN_PTR_AUTH(1, 65535) l1_internal_strong)(void);
+    void(* FN_PTR_AUTH(0, 65535) l2_internal_strong)(void);
+    void(* FN_PTR_AUTH(1, 0) l3_internal_strong)(void);
+}