Reject function protos that have different cfi_salt values.

Author: bwendling

clang/lib/AST/ASTContext.cpp

@@ -11441,6 +11441,11 @@ QualType ASTContext::mergeFunctionTypes(QualType lhs, QualType rhs,
     if (lproto->getMethodQuals() != rproto->getMethodQuals())
       return {};
 
+    // Function protos with different 'cfi_salt' values aren't compatible.
+    if (lproto->getExtraAttributeInfo().CFISalt !=
+        rproto->getExtraAttributeInfo().CFISalt)
+      return {};
+
     // Function effects are handled similarly to noreturn, see above.
     FunctionEffectsRef LHSFX = lproto->getFunctionEffects();
     FunctionEffectsRef RHSFX = rproto->getFunctionEffects();

clang/lib/Sema/SemaType.cpp

@@ -7947,6 +7947,10 @@ static bool handleFunctionTypeAttr(TypeProcessingState &state, ParsedAttr &attr,
     if (!S.checkStringLiteralArgumentAttr(attr, 0, Argument))
       return false;
 
+    // Delay if this is not a function type.
+    if (!unwrapped.isFunctionType())
+      return false;
+
     const auto *FnTy = unwrapped.get()->getAs<FunctionProtoType>();
     FunctionProtoType::ExtProtoInfo EPI = FnTy->getExtProtoInfo();
     EPI.ExtraAttributeInfo.CFISalt = Argument;

clang/test/Sema/attr-cfi-salt.c

@@ -0,0 +1,38 @@
+// RUN: %clang_cc1 -fsyntax-only -fsanitize=kcfi -verify %s
+
+#define __cfi_salt(S) __attribute__((cfi_salt(S)))
+
+int foo(int a, int b) __cfi_salt("pepper"); // ok
+int foo(int a, int b) __cfi_salt("pepper"); // ok
+
+typedef int (*bar_t)(void) __cfi_salt("pepper"); // ok
+typedef int (*bar_t)(void) __cfi_salt("pepper"); // ok
+
+#if 0
+// FIXME: These should fail.
+int b(void) __cfi_salt("salt 'n") __cfi_salt("pepper");
+bar_t bar_fn __cfi_salt("salt 'n");
+#endif
+
+int baz __cfi_salt("salt");
+    // expected-warning@-1{{'cfi_salt' only applies to function types}}
+
+int baz_fn(int a, int b) __cfi_salt("salt 'n");
+    // expected-note@-1{{previous declaration is here}}
+int baz_fn(int a, int b) __cfi_salt("pepper");
+    // expected-error@-1{{conflicting types for 'baz_fn'}}
+
+int mux_fn(int a, int b) __cfi_salt("salt 'n");
+    // expected-note@-1{{previous declaration is here}}
+int mux_fn(int a, int b) __cfi_salt("pepper") {
+    // expected-error@-1{{conflicting types for 'mux_fn'}}
+  return a * b;
+}
+
+typedef int qux_t __cfi_salt("salt");
+    // expected-warning@-1{{'cfi_salt' only applies to function types}}
+
+typedef int (*quux_t)(void) __cfi_salt("salt 'n");
+    // expected-note@-1{{previous definition is here}}
+typedef int (*quux_t)(void) __cfi_salt("pepper");
+    // expected-error@-1{{typedef redefinition with different type}}