bpf: Add kfunc filter function to 'struct btf_kfunc_id_set'

This commit adds the ability to filter kfuncs to certain BPF program
types. This is required to limit bpf_sock_destroy kfunc implemented in
follow-up commits to programs with attach type 'BPF_TRACE_ITER'.

The commit adds a callback filter to 'struct btf_kfunc_id_set'. The
filter has access to the `bpf_prog` construct including its properties
such as `expected_attached_type`.

Signed-off-by: Aditi Ghag <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Martin KaFai Lau <[e-mail]>

include/linux/btf.h

···
 union bpf_attr;
 struct btf_show;
 struct btf_id_set;
+struct bpf_prog;
+
+typedef int (*btf_kfunc_filter_t)(const struct bpf_prog *prog, u32 kfunc_id);
 
 struct btf_kfunc_id_set {
 	struct module *owner;
 	struct btf_id_set8 *set;
+	btf_kfunc_filter_t filter;
 };
 
 struct btf_id_dtor_kfunc {
···
 	return bsearch(&id, set->pairs, set->cnt, sizeof(set->pairs[0]), btf_id_cmp_func);
 }
 
-struct bpf_prog;
 struct bpf_verifier_log;
 
 #ifdef CONFIG_BPF_SYSCALL
···
 const char *btf_name_by_offset(const struct btf *btf, u32 offset);
 struct btf *btf_parse_vmlinux(void);
 struct btf *bpf_prog_get_target_btf(const struct bpf_prog *prog);
-u32 *btf_kfunc_id_set_contains(const struct btf *btf,
-			       enum bpf_prog_type prog_type,
-			       u32 kfunc_btf_id);
-u32 *btf_kfunc_is_modify_return(const struct btf *btf, u32 kfunc_btf_id);
+u32 *btf_kfunc_id_set_contains(const struct btf *btf, u32 kfunc_btf_id,
+			       const struct bpf_prog *prog);
+u32 *btf_kfunc_is_modify_return(const struct btf *btf, u32 kfunc_btf_id,
+				const struct bpf_prog *prog);
 int register_btf_kfunc_id_set(enum bpf_prog_type prog_type,
 			      const struct btf_kfunc_id_set *s);
 int register_btf_fmodret_id_set(const struct btf_kfunc_id_set *kset);
···
 	return NULL;
 }
 static inline u32 *btf_kfunc_id_set_contains(const struct btf *btf,
-					     enum bpf_prog_type prog_type,
-					     u32 kfunc_btf_id)
+					     u32 kfunc_btf_id,
+					     struct bpf_prog *prog)
+
 {
 	return NULL;
 }

kernel/bpf/btf.c

···
 enum {
 	BTF_KFUNC_SET_MAX_CNT = 256,
 	BTF_DTOR_KFUNC_MAX_CNT = 256,
+	BTF_KFUNC_FILTER_MAX_CNT = 16,
+};
+
+struct btf_kfunc_hook_filter {
+	btf_kfunc_filter_t filters[BTF_KFUNC_FILTER_MAX_CNT];
+	u32 nr_filters;
 };
 
 struct btf_kfunc_set_tab {
 	struct btf_id_set8 *sets[BTF_KFUNC_HOOK_MAX];
+	struct btf_kfunc_hook_filter hook_filters[BTF_KFUNC_HOOK_MAX];
 };
 
 struct btf_id_dtor_kfunc_tab {
···
 /* Kernel Function (kfunc) BTF ID set registration API */
 
 static int btf_populate_kfunc_set(struct btf *btf, enum btf_kfunc_hook hook,
-				  struct btf_id_set8 *add_set)
+				  const struct btf_kfunc_id_set *kset)
 {
+	struct btf_kfunc_hook_filter *hook_filter;
+	struct btf_id_set8 *add_set = kset->set;
 	bool vmlinux_set = !btf_is_module(btf);
+	bool add_filter = !!kset->filter;
 	struct btf_kfunc_set_tab *tab;
 	struct btf_id_set8 *set;
 	u32 set_cnt;
···
 		return 0;
 
 	tab = btf->kfunc_set_tab;
+
+	if (tab && add_filter) {
+		u32 i;
+
+		hook_filter = &tab->hook_filters[hook];
+		for (i = 0; i < hook_filter->nr_filters; i++) {
+			if (hook_filter->filters[i] == kset->filter) {
+				add_filter = false;
+				break;
+			}
+		}
+
+		if (add_filter && hook_filter->nr_filters == BTF_KFUNC_FILTER_MAX_CNT) {
+			ret = -E2BIG;
+			goto end;
+		}
+	}
+
 	if (!tab) {
 		tab = kzalloc(sizeof(*tab), GFP_KERNEL | __GFP_NOWARN);
 		if (!tab)
···
 	 */
 	if (!vmlinux_set) {
 		tab->sets[hook] = add_set;
-		return 0;
+		goto do_add_filter;
 	}
 
 	/* In case of vmlinux sets, there may be more than one set being
···
 
 	sort(set->pairs, set->cnt, sizeof(set->pairs[0]), btf_id_cmp_func, NULL);
 
+do_add_filter:
+	if (add_filter) {
+		hook_filter = &tab->hook_filters[hook];
+		hook_filter->filters[hook_filter->nr_filters++] = kset->filter;
+	}
 	return 0;
 end:
 	btf_free_kfunc_set_tab(btf);
···
 
 static u32 *__btf_kfunc_id_set_contains(const struct btf *btf,
 					enum btf_kfunc_hook hook,
-					u32 kfunc_btf_id)
+					u32 kfunc_btf_id,
+					const struct bpf_prog *prog)
 {
+	struct btf_kfunc_hook_filter *hook_filter;
 	struct btf_id_set8 *set;
-	u32 *id;
+	u32 *id, i;
 
 	if (hook >= BTF_KFUNC_HOOK_MAX)
 		return NULL;
 	if (!btf->kfunc_set_tab)
 		return NULL;
+	hook_filter = &btf->kfunc_set_tab->hook_filters[hook];
+	for (i = 0; i < hook_filter->nr_filters; i++) {
+		if (hook_filter->filters[i](prog, kfunc_btf_id))
+			return NULL;
+	}
 	set = btf->kfunc_set_tab->sets[hook];
 	if (!set)
 		return NULL;
···
  * protection for looking up a well-formed btf->kfunc_set_tab.
  */
 u32 *btf_kfunc_id_set_contains(const struct btf *btf,
-			       enum bpf_prog_type prog_type,
-			       u32 kfunc_btf_id)
+			       u32 kfunc_btf_id,
+			       const struct bpf_prog *prog)
 {
+	enum bpf_prog_type prog_type = resolve_prog_type(prog);
 	enum btf_kfunc_hook hook;
 	u32 *kfunc_flags;
 
-	kfunc_flags = __btf_kfunc_id_set_contains(btf, BTF_KFUNC_HOOK_COMMON, kfunc_btf_id);
+	kfunc_flags = __btf_kfunc_id_set_contains(btf, BTF_KFUNC_HOOK_COMMON, kfunc_btf_id, prog);
 	if (kfunc_flags)
 		return kfunc_flags;
 
 	hook = bpf_prog_type_to_kfunc_hook(prog_type);
-	return __btf_kfunc_id_set_contains(btf, hook, kfunc_btf_id);
+	return __btf_kfunc_id_set_contains(btf, hook, kfunc_btf_id, prog);
 }
 
-u32 *btf_kfunc_is_modify_return(const struct btf *btf, u32 kfunc_btf_id)
+u32 *btf_kfunc_is_modify_return(const struct btf *btf, u32 kfunc_btf_id,
+				const struct bpf_prog *prog)
 {
-	return __btf_kfunc_id_set_contains(btf, BTF_KFUNC_HOOK_FMODRET, kfunc_btf_id);
+	return __btf_kfunc_id_set_contains(btf, BTF_KFUNC_HOOK_FMODRET, kfunc_btf_id, prog);
 }
 
 static int __register_btf_kfunc_id_set(enum btf_kfunc_hook hook,
···
 			goto err_out;
 	}
 
-	ret = btf_populate_kfunc_set(btf, hook, kset->set);
+	ret = btf_populate_kfunc_set(btf, hook, kset);
+
 err_out:
 	btf_put(btf);
 	return ret;

kernel/bpf/verifier.c

···
 		*kfunc_name = func_name;
 	func_proto = btf_type_by_id(desc_btf, func->type);
 
-	kfunc_flags = btf_kfunc_id_set_contains(desc_btf, resolve_prog_type(env->prog), func_id);
+	kfunc_flags = btf_kfunc_id_set_contains(desc_btf, func_id, env->prog);
 	if (!kfunc_flags) {
 		return -EACCES;
 	}
···
 				 * in the fmodret id set with the KF_SLEEPABLE flag.
 				 */
 				else {
-					u32 *flags = btf_kfunc_is_modify_return(btf, btf_id);
+					u32 *flags = btf_kfunc_is_modify_return(btf, btf_id,
+										prog);
 
 					if (flags && (*flags & KF_SLEEPABLE))
 						ret = 0;
···
 				return -EINVAL;
 			}
 			ret = -EINVAL;
-			if (btf_kfunc_is_modify_return(btf, btf_id) ||
+			if (btf_kfunc_is_modify_return(btf, btf_id, prog) ||
 			    !check_attach_modify_return(addr, tname))
 				ret = 0;
 			if (ret) {