Merge branch 'extend-struct_ops-support-for-operators'

Amery Hung says:

====================
This patchset supports struct_ops operators that acquire kptrs through
arguments and operators that return a kptr. A coming new struct_ops use
case, bpf qdisc [0], has two operators that are not yet supported by
current struct_ops infrastructure. Qdisc_ops::enqueue requires getting
referenced skb kptr from the argument; Qdisc_ops::dequeue needs to return
a referenced skb kptr. This patchset will allow bpf qdisc and other
potential struct_ops implementers to do so.

For struct_ops implementers:

- To get a kptr from an argument, a struct_ops implementer needs to
  annotate the argument name in the stub function with "__ref" suffix.

- The kptr return will automatically work as we now allow operators that
  return a struct pointer.

- The verifier allows returning a null pointer. More control can be
  added later if there is a future struct_ops implementer only expecting
  valid pointers.

For struct_ops users:

- The referenced kptr acquired through the argument needs to be released
  or xchged into maps just like ones acquired via kfuncs.

- To return a referenced kptr in struct_ops,
  1) The type of the pointer must matches the return type
  2) The pointer must comes from the kernel (not locally allocated), and
  3) The pointer must be in its unmodified form

[0] https://lore.kernel.org/bpf/20250210174336.2024258-1-ameryhung@gmail.com/
---
v2
- Replace kcalloc+memcpy with kmemdup_array in
  bpf_prog_ctx_arg_info_init()
- Remove unnecessary checks when kfree-ing ctx_arg_info
- Remove conditional assignment of ref_obj_id in btf_ctx_access()

v1
- Link: https://lore.kernel.org/bpf/20250214164520.1001211-1-ameryhung@gmail.com/
- Fix missing kfree for ctx_arg_info
====================

Link: https://patch.msgid.link/20250217190640.1748177-1-ameryhung@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

include/linux/bpf.h

@@ -968,6 +968,7 @@ struct bpf_insn_access_aux {
 		struct {
 			struct btf *btf;
 			u32 btf_id;
+			u32 ref_obj_id;
 		};
 	};
 	struct bpf_verifier_log *log; /* for verbose logs */
@@ -1481,6 +1482,8 @@ struct bpf_ctx_arg_aux {
 	enum bpf_reg_type reg_type;
 	struct btf *btf;
 	u32 btf_id;
+	u32 ref_obj_id;
+	bool refcounted;
 };
 
 struct btf_mod_pair {
@@ -1507,7 +1510,7 @@ struct bpf_prog_aux {
 	u32 max_rdonly_access;
 	u32 max_rdwr_access;
 	struct btf *attach_btf;
-	const struct bpf_ctx_arg_aux *ctx_arg_info;
+	struct bpf_ctx_arg_aux *ctx_arg_info;
 	void __percpu *priv_stack_ptr;
 	struct mutex dst_mutex; /* protects dst_* pointers below, *after* prog becomes visible */
 	struct bpf_prog *dst_prog;
@@ -1945,6 +1948,9 @@ static inline void bpf_struct_ops_desc_release(struct bpf_struct_ops_desc *st_op
 
 #endif
 
+int bpf_prog_ctx_arg_info_init(struct bpf_prog *prog,
+			       const struct bpf_ctx_arg_aux *info, u32 cnt);
+
 #if defined(CONFIG_CGROUP_BPF) && defined(CONFIG_BPF_LSM)
 int bpf_trampoline_link_cgroup_shim(struct bpf_prog *prog,
 				    int cgroup_atype);
@@ -2546,7 +2552,7 @@ struct bpf_iter__bpf_map_elem {
 
 int bpf_iter_reg_target(const struct bpf_iter_reg *reg_info);
 void bpf_iter_unreg_target(const struct bpf_iter_reg *reg_info);
-bool bpf_iter_prog_supported(struct bpf_prog *prog);
+int bpf_iter_prog_supported(struct bpf_prog *prog);
 const struct bpf_func_proto *
 bpf_iter_get_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog);
 int bpf_iter_link_attach(const union bpf_attr *attr, bpfptr_t uattr, struct bpf_prog *prog);

kernel/bpf/bpf_iter.c

@@ -335,7 +335,7 @@ static void cache_btf_id(struct bpf_iter_target_info *tinfo,
 	tinfo->btf_id = prog->aux->attach_btf_id;
 }
 
-bool bpf_iter_prog_supported(struct bpf_prog *prog)
+int bpf_iter_prog_supported(struct bpf_prog *prog)
 {
 	const char *attach_fname = prog->aux->attach_func_name;
 	struct bpf_iter_target_info *tinfo = NULL, *iter;
@@ -344,7 +344,7 @@ bool bpf_iter_prog_supported(struct bpf_prog *prog)
 	int prefix_len = strlen(prefix);
 
 	if (strncmp(attach_fname, prefix, prefix_len))
-		return false;
+		return -EINVAL;
 
 	mutex_lock(&targets_mutex);
 	list_for_each_entry(iter, &targets, list) {
@@ -360,12 +360,11 @@ bool bpf_iter_prog_supported(struct bpf_prog *prog)
 	}
 	mutex_unlock(&targets_mutex);
 
-	if (tinfo) {
-		prog->aux->ctx_arg_info_size = tinfo->reg_info->ctx_arg_info_size;
-		prog->aux->ctx_arg_info = tinfo->reg_info->ctx_arg_info;
-	}
+	if (!tinfo)
+		return -EINVAL;
 
-	return tinfo != NULL;
+	return bpf_prog_ctx_arg_info_init(prog, tinfo->reg_info->ctx_arg_info,
+					  tinfo->reg_info->ctx_arg_info_size);
 }
 
 const struct bpf_func_proto *

kernel/bpf/bpf_struct_ops.c

@@ -146,6 +146,7 @@ void bpf_struct_ops_image_free(void *image)
 }
 
 #define MAYBE_NULL_SUFFIX "__nullable"
+#define REFCOUNTED_SUFFIX "__ref"
 
 /* Prepare argument info for every nullable argument of a member of a
  * struct_ops type.
@@ -174,11 +175,13 @@ static int prepare_arg_info(struct btf *btf,
 			    struct bpf_struct_ops_arg_info *arg_info)
 {
 	const struct btf_type *stub_func_proto, *pointed_type;
+	bool is_nullable = false, is_refcounted = false;
 	const struct btf_param *stub_args, *args;
 	struct bpf_ctx_arg_aux *info, *info_buf;
 	u32 nargs, arg_no, info_cnt = 0;
 	char ksym[KSYM_SYMBOL_LEN];
 	const char *stub_fname;
+	const char *suffix;
 	s32 stub_func_id;
 	u32 arg_btf_id;
 	int offset;
@@ -223,10 +226,18 @@ static int prepare_arg_info(struct btf *btf,
 	info = info_buf;
 	for (arg_no = 0; arg_no < nargs; arg_no++) {
 		/* Skip arguments that is not suffixed with
-		 * "__nullable".
+		 * "__nullable or __ref".
 		 */
-		if (!btf_param_match_suffix(btf, &stub_args[arg_no],
-					    MAYBE_NULL_SUFFIX))
+		is_nullable = btf_param_match_suffix(btf, &stub_args[arg_no],
+						     MAYBE_NULL_SUFFIX);
+		is_refcounted = btf_param_match_suffix(btf, &stub_args[arg_no],
+						       REFCOUNTED_SUFFIX);
+
+		if (is_nullable)
+			suffix = MAYBE_NULL_SUFFIX;
+		else if (is_refcounted)
+			suffix = REFCOUNTED_SUFFIX;
+		else
 			continue;
 
 		/* Should be a pointer to struct */
@@ -236,7 +247,7 @@ static int prepare_arg_info(struct btf *btf,
 		if (!pointed_type ||
 		    !btf_type_is_struct(pointed_type)) {
 			pr_warn("stub function %s has %s tagging to an unsupported type\n",
-				stub_fname, MAYBE_NULL_SUFFIX);
+				stub_fname, suffix);
 			goto err_out;
 		}
 
@@ -254,11 +265,15 @@ static int prepare_arg_info(struct btf *btf,
 		}
 
 		/* Fill the information of the new argument */
-		info->reg_type =
-			PTR_TRUSTED | PTR_TO_BTF_ID | PTR_MAYBE_NULL;
 		info->btf_id = arg_btf_id;
 		info->btf = btf;
 		info->offset = offset;
+		if (is_nullable) {
+			info->reg_type = PTR_TRUSTED | PTR_TO_BTF_ID | PTR_MAYBE_NULL;
+		} else if (is_refcounted) {
+			info->reg_type = PTR_TRUSTED | PTR_TO_BTF_ID;
+			info->refcounted = true;
+		}
 
 		info++;
 		info_cnt++;
@@ -375,7 +390,7 @@ int bpf_struct_ops_desc_init(struct bpf_struct_ops_desc *st_ops_desc,
 	st_ops_desc->value_type = btf_type_by_id(btf, value_id);
 
 	for_each_member(i, t, member) {
-		const struct btf_type *func_proto;
+		const struct btf_type *func_proto, *ret_type;
 		void **stub_func_addr;
 		u32 moff;
 
@@ -412,6 +427,16 @@ int bpf_struct_ops_desc_init(struct bpf_struct_ops_desc *st_ops_desc,
 		if (!func_proto || bpf_struct_ops_supported(st_ops, moff))
 			continue;
 
+		if (func_proto->type) {
+			ret_type = btf_type_resolve_ptr(btf, func_proto->type, NULL);
+			if (ret_type && !__btf_type_is_struct(ret_type)) {
+				pr_warn("func ptr %s in struct %s returns non-struct pointer, which is not supported\n",
+					mname, st_ops->name);
+				err = -EOPNOTSUPP;
+				goto errout;
+			}
+		}
+
 		if (btf_distill_func_proto(log, btf,
 					   func_proto, mname,
 					   &st_ops->func_models[i])) {

kernel/bpf/btf.c

@@ -6774,6 +6774,7 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
 			info->reg_type = ctx_arg_info->reg_type;
 			info->btf = ctx_arg_info->btf ? : btf_vmlinux;
 			info->btf_id = ctx_arg_info->btf_id;
+			info->ref_obj_id = ctx_arg_info->ref_obj_id;
 			return true;
 		}
 	}

kernel/bpf/syscall.c

@@ -2313,6 +2313,7 @@ static void __bpf_prog_put_noref(struct bpf_prog *prog, bool deferred)
 	kvfree(prog->aux->jited_linfo);
 	kvfree(prog->aux->linfo);
 	kfree(prog->aux->kfunc_tab);
+	kfree(prog->aux->ctx_arg_info);
 	if (prog->aux->attach_btf)
 		btf_put(prog->aux->attach_btf);