bpf: Add verifier support for bpf_timer argument in kfuncs

Extend the verifier to recognize struct bpf_timer as a valid kfunc
argument type. Previously, bpf_timer was only supported in BPF helpers.

This prepares for adding timer-related kfuncs in subsequent patches.

Signed-off-by: Mykyta Yatsenko <yatsenko@meta.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20260201025403.66625-3-alexei.starovoitov@gmail.com

Author: mykyta5

kernel/bpf/verifier.c

@@ -8675,13 +8675,25 @@ static int check_map_field_pointer(struct bpf_verifier_env *env, u32 regno,
 }
 
 static int process_timer_func(struct bpf_verifier_env *env, int regno,
-			      struct bpf_call_arg_meta *meta)
+			      struct bpf_map_desc *map)
 {
 	if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
 		verbose(env, "bpf_timer cannot be used for PREEMPT_RT.\n");
 		return -EOPNOTSUPP;
 	}
-	return check_map_field_pointer(env, regno, BPF_TIMER, &meta->map);
+	return check_map_field_pointer(env, regno, BPF_TIMER, map);
+}
+
+static int process_timer_helper(struct bpf_verifier_env *env, int regno,
+				struct bpf_call_arg_meta *meta)
+{
+	return process_timer_func(env, regno, &meta->map);
+}
+
+static int process_timer_kfunc(struct bpf_verifier_env *env, int regno,
+			       struct bpf_kfunc_call_arg_meta *meta)
+{
+	return process_timer_func(env, regno, &meta->map);
 }
 
 static int process_kptr_func(struct bpf_verifier_env *env, int regno,
@@ -9973,7 +9985,7 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
 		}
 		break;
 	case ARG_PTR_TO_TIMER:
-		err = process_timer_func(env, regno, meta);
+		err = process_timer_helper(env, regno, meta);
 		if (err)
 			return err;
 		break;
@@ -12238,7 +12250,8 @@ enum {
 	KF_ARG_WORKQUEUE_ID,
 	KF_ARG_RES_SPIN_LOCK_ID,
 	KF_ARG_TASK_WORK_ID,
-	KF_ARG_PROG_AUX_ID
+	KF_ARG_PROG_AUX_ID,
+	KF_ARG_TIMER_ID
 };
 
 BTF_ID_LIST(kf_arg_btf_ids)
@@ -12251,6 +12264,7 @@ BTF_ID(struct, bpf_wq)
 BTF_ID(struct, bpf_res_spin_lock)
 BTF_ID(struct, bpf_task_work)
 BTF_ID(struct, bpf_prog_aux)
+BTF_ID(struct, bpf_timer)
 
 static bool __is_kfunc_ptr_arg_type(const struct btf *btf,
 				    const struct btf_param *arg, int type)
@@ -12294,6 +12308,11 @@ static bool is_kfunc_arg_rbtree_node(const struct btf *btf, const struct btf_par
 	return __is_kfunc_ptr_arg_type(btf, arg, KF_ARG_RB_NODE_ID);
 }
 
+static bool is_kfunc_arg_timer(const struct btf *btf, const struct btf_param *arg)
+{
+	return __is_kfunc_ptr_arg_type(btf, arg, KF_ARG_TIMER_ID);
+}
+
 static bool is_kfunc_arg_wq(const struct btf *btf, const struct btf_param *arg)
 {
 	return __is_kfunc_ptr_arg_type(btf, arg, KF_ARG_WORKQUEUE_ID);
@@ -12393,6 +12412,7 @@ enum kfunc_ptr_arg_type {
 	KF_ARG_PTR_TO_NULL,
 	KF_ARG_PTR_TO_CONST_STR,
 	KF_ARG_PTR_TO_MAP,
+	KF_ARG_PTR_TO_TIMER,
 	KF_ARG_PTR_TO_WORKQUEUE,
 	KF_ARG_PTR_TO_IRQ_FLAG,
 	KF_ARG_PTR_TO_RES_SPIN_LOCK,
@@ -12646,6 +12666,9 @@ get_kfunc_ptr_arg_type(struct bpf_verifier_env *env,
 	if (is_kfunc_arg_wq(meta->btf, &args[argno]))
 		return KF_ARG_PTR_TO_WORKQUEUE;
 
+	if (is_kfunc_arg_timer(meta->btf, &args[argno]))
+		return KF_ARG_PTR_TO_TIMER;
+
 	if (is_kfunc_arg_task_work(meta->btf, &args[argno]))
 		return KF_ARG_PTR_TO_TASK_WORK;
 
@@ -13439,6 +13462,7 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
 		case KF_ARG_PTR_TO_REFCOUNTED_KPTR:
 		case KF_ARG_PTR_TO_CONST_STR:
 		case KF_ARG_PTR_TO_WORKQUEUE:
+		case KF_ARG_PTR_TO_TIMER:
 		case KF_ARG_PTR_TO_TASK_WORK:
 		case KF_ARG_PTR_TO_IRQ_FLAG:
 		case KF_ARG_PTR_TO_RES_SPIN_LOCK:
@@ -13738,6 +13762,15 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
 			if (ret < 0)
 				return ret;
 			break;
+		case KF_ARG_PTR_TO_TIMER:
+			if (reg->type != PTR_TO_MAP_VALUE) {
+				verbose(env, "arg#%d doesn't point to a map value\n", i);
+				return -EINVAL;
+			}
+			ret = process_timer_kfunc(env, regno, meta);
+			if (ret < 0)
+				return ret;
+			break;
 		case KF_ARG_PTR_TO_TASK_WORK:
 			if (reg->type != PTR_TO_MAP_VALUE) {
 				verbose(env, "arg#%d doesn't point to a map value\n", i);
@@ -21429,20 +21462,6 @@ static int check_map_prog_compatibility(struct bpf_verifier_env *env,
 		}
 	}
 
-	if (btf_record_has_field(map->record, BPF_TIMER)) {
-		if (is_tracing_prog_type(prog_type)) {
-			verbose(env, "tracing progs cannot use bpf_timer yet\n");
-			return -EINVAL;
-		}
-	}
-
-	if (btf_record_has_field(map->record, BPF_WORKQUEUE)) {
-		if (is_tracing_prog_type(prog_type)) {
-			verbose(env, "tracing progs cannot use bpf_wq yet\n");
-			return -EINVAL;
-		}
-	}
-
 	if ((bpf_prog_is_offloaded(prog->aux) || bpf_map_is_offloaded(map)) &&
 	    !bpf_offload_prog_map_match(prog, map)) {
 		verbose(env, "offload device mismatch between prog and map\n");