fix_nvoc_dtor.cocci: fix NVOC_DYNAMIC_DTOR CFI violations

Signed-off-by: Mathias Krause <minipli@grsecurity.net>

Author: minipli-oss

src/nvidia/fix_nvoc_dtor.cocci

@@ -0,0 +1,49 @@
+// Coccinelle script to fix 'dtor' function pointer casts to use proper
+// types to prevent runtime CFI violations, e.g. under RAP.
+//
+// We need to create a thunk in any case as there may be calls to the strongly
+// typed function from other TUs, causing CFI violations if we'd just change
+// the function's signature to match the dtor function pointer prototype.
+//
+// typedef void (*NVOC_DYNAMIC_DTOR)(Dynamic*);
+//
+// (c) 2025,2026 Open Source Security, Inc. All Rights Reserved.
+
+// replace function casts to (NVOC_DYNAMIC_DTOR) with its thunk
+@dtor_cast@
+identifier fn;
+fresh identifier fnthunk = "THUNK_" ## fn;
+@@
+- (NVOC_DYNAMIC_DTOR) &fn
++ &fnthunk
+
+// add decl for the thunk, if needed, i.e. if the original func had one
+@thunk_decl@
+identifier dtor_cast.fn, dtor_cast.fnthunk, arg;
+typedef Dynamic;
+type T, R;
+@@
+// XXX: matching function decls is only poorly supported, so we need this hack
+(
+-R fn(T)
++R fn(T);
++static void fnthunk(Dynamic *)
+;
+|
+-R fn(T arg)
++R fn(T arg);
++static void fnthunk(Dynamic *arg)
+;
+)
+
+// add thunk function
+@thunk_def@
+identifier dtor_cast.fn, dtor_cast.fnthunk, arg;
+typedef Dynamic;
+type T, R;
+@@
+R fn(T arg) { ... }
++
++static void fnthunk(Dynamic *arg) {
++  fn((T)arg);
++}