On 5/21/26 3:33 PM, Kees Cook wrote: > Make the DEFINE_KERNEL_PARAM_OPS family route their _get argument to > either .get (struct seq_buf *) or .get_str (char *) at compile time > based on the pointer's actual function signature. Two helper macros > do the routing: > > _KERNEL_PARAM_OPS_GET - return the pointer if it has the seq_buf > signature, otherwise NULL of that type > _KERNEL_PARAM_OPS_GET_STR - mirror image for the char * signature > > Both use _Generic; only the two valid function-pointer types are > listed, so any third-party type is a compile error rather than > silently falling through. > > Now a callback whose body has been migrated from char * to struct > seq_buf * needs no change at its kernel_param_ops initialization site, > because the macro picks up the new type automatically and assigns to > the correct field. > > Signed-off-by: Kees Cook <[email protected]> > --- > include/linux/moduleparam.h | 33 ++++++++++++++++++++++++++------- > 1 file changed, 26 insertions(+), 7 deletions(-) > > diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h > index c52120f6ac28..795bc7c654ef 100644 > --- a/include/linux/moduleparam.h > +++ b/include/linux/moduleparam.h > @@ -85,15 +85,32 @@ struct kernel_param_ops { > * > * static DEFINE_KERNEL_PARAM_OPS(my_ops, my_set, my_get); > * > - * Routing the @_set and @_get function pointers through the macro > - * (rather than naming the struct fields at every call site) lets the > - * field layout change in one place when callbacks are migrated to a > - * new signature. > + * @_get may be either of: > + * int (*)(struct seq_buf *, const struct kernel_param *) (seq_buf) > + * int (*)(char *, const struct kernel_param *) (legacy) > + * > + * The macro uses _Generic to route the function pointer to the > + * matching field (.get or .get_str) at compile time, leaving the > + * other field NULL. Each helper matches the wrong prototype signature > + * and returns NULL, falling through to the default branch otherwise; > + * if @_get has neither expected signature the assignment to the > + * fields gets a normal compile-time type-mismatch error. > */ > +#define _KERNEL_PARAM_OPS_GET(_get) \ > + _Generic((_get), \ > + int (*)(char *, const struct kernel_param *): NULL, \ > + default: (_get)) > + > +#define _KERNEL_PARAM_OPS_GET_STR(_get) > \ > + _Generic((_get), \ > + int (*)(struct seq_buf *, const struct kernel_param *): NULL, \ > + default: (_get)) > + > #define DEFINE_KERNEL_PARAM_OPS(_name, _set, _get) \ > const struct kernel_param_ops _name = { \ > .set = (_set), \ > - .get_str = (_get), \ > + .get = _KERNEL_PARAM_OPS_GET(_get), \ > + .get_str = _KERNEL_PARAM_OPS_GET_STR(_get), \ > } > > /* As DEFINE_KERNEL_PARAM_OPS, with KERNEL_PARAM_OPS_FL_NOARG set. */ > @@ -101,14 +118,16 @@ struct kernel_param_ops { > const struct kernel_param_ops _name = { \ > .flags = KERNEL_PARAM_OPS_FL_NOARG, \ > .set = (_set), \ > - .get_str = (_get), \ > + .get = _KERNEL_PARAM_OPS_GET(_get), \ > + .get_str = _KERNEL_PARAM_OPS_GET_STR(_get), \ > } > > /* As DEFINE_KERNEL_PARAM_OPS, with an additional .free callback. */ > #define DEFINE_KERNEL_PARAM_OPS_FREE(_name, _set, _get, _free) > \ > const struct kernel_param_ops _name = { \ > .set = (_set), \ > - .get_str = (_get), \ > + .get = _KERNEL_PARAM_OPS_GET(_get), \ > + .get_str = _KERNEL_PARAM_OPS_GET_STR(_get), \ > .free = (_free), \ > } >
Reviewed-by: Petr Pavlu <[email protected]> -- Petr
