On Sun, Mar 20, 2022 at 8:55 AM Kumar Kartikeya Dwivedi
<memxor@xxxxxxxxx> wrote:
>
> + /* Find and stash the function pointer for the destruction function that
> + * needs to be eventually invoked from the map free path.
> + */
> + if (info_arr[i].flags & BPF_MAP_VALUE_OFF_F_REF) {
> + const struct btf_type *dtor_func, *dtor_func_proto;
> + const struct btf_param *args;
> + const char *dtor_func_name;
> + unsigned long addr;
> + s32 dtor_btf_id;
> + u32 nr_args;
> +
> + /* This call also serves as a whitelist of allowed objects that
> + * can be used as a referenced pointer and be stored in a map at
> + * the same time.
> + */
> + dtor_btf_id = btf_find_dtor_kfunc(off_btf, id);
> + if (dtor_btf_id < 0) {
> + ret = dtor_btf_id;
> + btf_put(off_btf);
> + goto end;
> + }
> +
> + dtor_func = btf_type_by_id(off_btf, dtor_btf_id);
> + if (!dtor_func || !btf_type_is_func(dtor_func)) {
> + ret = -EINVAL;
> + btf_put(off_btf);
> + goto end;
> + }
> +
> + dtor_func_proto = btf_type_by_id(off_btf, dtor_func->type);
> + if (!dtor_func_proto || !btf_type_is_func_proto(dtor_func_proto)) {
> + ret = -EINVAL;
> + btf_put(off_btf);
> + goto end;
> + }
> +
> + /* Make sure the prototype of the destructor kfunc is 'void func(type *)' */
> + t = btf_type_by_id(off_btf, dtor_func_proto->type);
> + if (!t || !btf_type_is_void(t)) {
> + ret = -EINVAL;
> + btf_put(off_btf);
> + goto end;
> + }
> +
> + nr_args = btf_type_vlen(dtor_func_proto);
> + args = btf_params(dtor_func_proto);
> +
> + t = NULL;
> + if (nr_args)
> + t = btf_type_by_id(off_btf, args[0].type);
> + /* Allow any pointer type, as width on targets Linux supports
> + * will be same for all pointer types (i.e. sizeof(void *))
> + */
> + if (nr_args != 1 || !t || !btf_type_is_ptr(t)) {
> + ret = -EINVAL;
> + btf_put(off_btf);
> + goto end;
> + }
> +
> + if (btf_is_module(btf)) {
> + mod = btf_try_get_module(off_btf);
> + if (!mod) {
> + ret = -ENXIO;
> + btf_put(off_btf);
> + goto end;
> + }
> + }
> +
> + dtor_func_name = __btf_name_by_offset(off_btf, dtor_func->name_off);
> + addr = kallsyms_lookup_name(dtor_func_name);
> + if (!addr) {
> + ret = -EINVAL;
> + module_put(mod);
> + btf_put(off_btf);
> + goto end;
> + }
> + tab->off[i].dtor = (void *)addr;
Most of the above should probably be in register_btf_id_dtor_kfuncs().
It's best to fail early.
Here we'll just remember dtor function pointer to speed up release.
