bpf: Rewrite kfunc argument handling

As we continue to add more features, argument types, kfunc flags, and
different extensions to kfuncs, the code to verify the correctness of
the kfunc prototype wrt the passed in registers has become ad-hoc and
ugly to read. To make life easier, and make a very clear split between
different stages of argument processing, move all the code into
verifier.c and refactor into easier to read helpers and functions.

This also makes sharing code within the verifier easier with kfunc
argument processing. This will be more and more useful in later patches
as we are now moving to implement very core BPF helpers as kfuncs, to
keep them experimental before baking into UAPI.

Remove all kfunc related bits now from btf_check_func_arg_match, as
users have been converted away to refactored kfunc argument handling.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20221118015614.2013203-12-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 528 insertions, 17 deletions

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index c8f3abe9b08e..7d7a91c54709 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -5550,8 +5550,8 @@ int check_mem_reg(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
 	return err;
 }
 
-int check_kfunc_mem_size_reg(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
-			     u32 regno)
+static int check_kfunc_mem_size_reg(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
+				    u32 regno)
 {
 	struct bpf_reg_state *mem_reg = &cur_regs(env)[regno - 1];
 	bool may_be_null = type_may_be_null(mem_reg->type);
@@ -7863,19 +7863,517 @@ static void mark_btf_func_reg_size(struct bpf_verifier_env *env, u32 regno,
 	}
 }
 
+struct bpf_kfunc_call_arg_meta {
+	/* In parameters */
+	struct btf *btf;
+	u32 func_id;
+	u32 kfunc_flags;
+	const struct btf_type *func_proto;
+	const char *func_name;
+	/* Out parameters */
+	u32 ref_obj_id;
+	u8 release_regno;
+	bool r0_rdonly;
+	u64 r0_size;
+};
+
+static bool is_kfunc_acquire(struct bpf_kfunc_call_arg_meta *meta)
+{
+	return meta->kfunc_flags & KF_ACQUIRE;
+}
+
+static bool is_kfunc_ret_null(struct bpf_kfunc_call_arg_meta *meta)
+{
+	return meta->kfunc_flags & KF_RET_NULL;
+}
+
+static bool is_kfunc_release(struct bpf_kfunc_call_arg_meta *meta)
+{
+	return meta->kfunc_flags & KF_RELEASE;
+}
+
+static bool is_kfunc_trusted_args(struct bpf_kfunc_call_arg_meta *meta)
+{
+	return meta->kfunc_flags & KF_TRUSTED_ARGS;
+}
+
+static bool is_kfunc_sleepable(struct bpf_kfunc_call_arg_meta *meta)
+{
+	return meta->kfunc_flags & KF_SLEEPABLE;
+}
+
+static bool is_kfunc_destructive(struct bpf_kfunc_call_arg_meta *meta)
+{
+	return meta->kfunc_flags & KF_DESTRUCTIVE;
+}
+
+static bool is_kfunc_arg_kptr_get(struct bpf_kfunc_call_arg_meta *meta, int arg)
+{
+	return arg == 0 && (meta->kfunc_flags & KF_KPTR_GET);
+}
+
+static bool is_kfunc_arg_mem_size(const struct btf *btf,
+				  const struct btf_param *arg,
+				  const struct bpf_reg_state *reg)
+{
+	int len, sfx_len = sizeof("__sz") - 1;
+	const struct btf_type *t;
+	const char *param_name;
+
+	t = btf_type_skip_modifiers(btf, arg->type, NULL);
+	if (!btf_type_is_scalar(t) || reg->type != SCALAR_VALUE)
+		return false;
+
+	/* In the future, this can be ported to use BTF tagging */
+	param_name = btf_name_by_offset(btf, arg->name_off);
+	if (str_is_empty(param_name))
+		return false;
+	len = strlen(param_name);
+	if (len < sfx_len)
+		return false;
+	param_name += len - sfx_len;
+	if (strncmp(param_name, "__sz", sfx_len))
+		return false;
+
+	return true;
+}
+
+static bool is_kfunc_arg_scalar_with_name(const struct btf *btf,
+					  const struct btf_param *arg,
+					  const char *name)
+{
+	int len, target_len = strlen(name);
+	const char *param_name;
+
+	param_name = btf_name_by_offset(btf, arg->name_off);
+	if (str_is_empty(param_name))
+		return false;
+	len = strlen(param_name);
+	if (len != target_len)
+		return false;
+	if (strcmp(param_name, name))
+		return false;
+
+	return true;
+}
+
+enum {
+	KF_ARG_DYNPTR_ID,
+};
+
+BTF_ID_LIST(kf_arg_btf_ids)
+BTF_ID(struct, bpf_dynptr_kern)
+
+static bool is_kfunc_arg_dynptr(const struct btf *btf,
+				const struct btf_param *arg)
+{
+	const struct btf_type *t;
+	u32 res_id;
+
+	t = btf_type_skip_modifiers(btf, arg->type, NULL);
+	if (!t)
+		return false;
+	if (!btf_type_is_ptr(t))
+		return false;
+	t = btf_type_skip_modifiers(btf, t->type, &res_id);
+	if (!t)
+		return false;
+	return btf_types_are_same(btf, res_id, btf_vmlinux, kf_arg_btf_ids[KF_ARG_DYNPTR_ID]);
+}
+
+/* Returns true if struct is composed of scalars, 4 levels of nesting allowed */
+static bool __btf_type_is_scalar_struct(struct bpf_verifier_env *env,
+					const struct btf *btf,
+					const struct btf_type *t, int rec)
+{
+	const struct btf_type *member_type;
+	const struct btf_member *member;
+	u32 i;
+
+	if (!btf_type_is_struct(t))
+		return false;
+
+	for_each_member(i, t, member) {
+		const struct btf_array *array;
+
+		member_type = btf_type_skip_modifiers(btf, member->type, NULL);
+		if (btf_type_is_struct(member_type)) {
+			if (rec >= 3) {
+				verbose(env, "max struct nesting depth exceeded\n");
+				return false;
+			}
+			if (!__btf_type_is_scalar_struct(env, btf, member_type, rec + 1))
+				return false;
+			continue;
+		}
+		if (btf_type_is_array(member_type)) {
+			array = btf_array(member_type);
+			if (!array->nelems)
+				return false;
+			member_type = btf_type_skip_modifiers(btf, array->type, NULL);
+			if (!btf_type_is_scalar(member_type))
+				return false;
+			continue;
+		}
+		if (!btf_type_is_scalar(member_type))
+			return false;
+	}
+	return true;
+}
+
+
+static u32 *reg2btf_ids[__BPF_REG_TYPE_MAX] = {
+#ifdef CONFIG_NET
+	[PTR_TO_SOCKET] = &btf_sock_ids[BTF_SOCK_TYPE_SOCK],
+	[PTR_TO_SOCK_COMMON] = &btf_sock_ids[BTF_SOCK_TYPE_SOCK_COMMON],
+	[PTR_TO_TCP_SOCK] = &btf_sock_ids[BTF_SOCK_TYPE_TCP],
+#endif
+};
+
+enum kfunc_ptr_arg_type {
+	KF_ARG_PTR_TO_CTX,
+	KF_ARG_PTR_TO_KPTR,	     /* PTR_TO_KPTR but type specific */
+	KF_ARG_PTR_TO_DYNPTR,
+	KF_ARG_PTR_TO_BTF_ID,	     /* Also covers reg2btf_ids conversions */
+	KF_ARG_PTR_TO_MEM,
+	KF_ARG_PTR_TO_MEM_SIZE,	     /* Size derived from next argument, skip it */
+};
+
+static enum kfunc_ptr_arg_type
+get_kfunc_ptr_arg_type(struct bpf_verifier_env *env,
+		       struct bpf_kfunc_call_arg_meta *meta,
+		       const struct btf_type *t, const struct btf_type *ref_t,
+		       const char *ref_tname, const struct btf_param *args,
+		       int argno, int nargs)
+{
+	u32 regno = argno + 1;
+	struct bpf_reg_state *regs = cur_regs(env);
+	struct bpf_reg_state *reg = &regs[regno];
+	bool arg_mem_size = false;
+
+	/* In this function, we verify the kfunc's BTF as per the argument type,
+	 * leaving the rest of the verification with respect to the register
+	 * type to our caller. When a set of conditions hold in the BTF type of
+	 * arguments, we resolve it to a known kfunc_ptr_arg_type.
+	 */
+	if (btf_get_prog_ctx_type(&env->log, meta->btf, t, resolve_prog_type(env->prog), argno))
+		return KF_ARG_PTR_TO_CTX;
+
+	if (is_kfunc_arg_kptr_get(meta, argno)) {
+		if (!btf_type_is_ptr(ref_t)) {
+			verbose(env, "arg#0 BTF type must be a double pointer for kptr_get kfunc\n");
+			return -EINVAL;
+		}
+		ref_t = btf_type_by_id(meta->btf, ref_t->type);
+		ref_tname = btf_name_by_offset(meta->btf, ref_t->name_off);
+		if (!btf_type_is_struct(ref_t)) {
+			verbose(env, "kernel function %s args#0 pointer type %s %s is not supported\n",
+				meta->func_name, btf_type_str(ref_t), ref_tname);
+			return -EINVAL;
+		}
+		return KF_ARG_PTR_TO_KPTR;
+	}
+
+	if (is_kfunc_arg_dynptr(meta->btf, &args[argno]))
+		return KF_ARG_PTR_TO_DYNPTR;
+
+	if ((base_type(reg->type) == PTR_TO_BTF_ID || reg2btf_ids[base_type(reg->type)])) {
+		if (!btf_type_is_struct(ref_t)) {
+			verbose(env, "kernel function %s args#%d pointer type %s %s is not supported\n",
+				meta->func_name, argno, btf_type_str(ref_t), ref_tname);
+			return -EINVAL;
+		}
+		return KF_ARG_PTR_TO_BTF_ID;
+	}
+
+	if (argno + 1 < nargs && is_kfunc_arg_mem_size(meta->btf, &args[argno + 1], &regs[regno + 1]))
+		arg_mem_size = true;
+
+	/* This is the catch all argument type of register types supported by
+	 * check_helper_mem_access. However, we only allow when argument type is
+	 * pointer to scalar, or struct composed (recursively) of scalars. When
+	 * arg_mem_size is true, the pointer can be void *.
+	 */
+	if (!btf_type_is_scalar(ref_t) && !__btf_type_is_scalar_struct(env, meta->btf, ref_t, 0) &&
+	    (arg_mem_size ? !btf_type_is_void(ref_t) : 1)) {
+		verbose(env, "arg#%d pointer type %s %s must point to %sscalar, or struct with scalar\n",
+			argno, btf_type_str(ref_t), ref_tname, arg_mem_size ? "void, " : "");
+		return -EINVAL;
+	}
+	return arg_mem_size ? KF_ARG_PTR_TO_MEM_SIZE : KF_ARG_PTR_TO_MEM;
+}
+
+static int process_kf_arg_ptr_to_btf_id(struct bpf_verifier_env *env,
+					struct bpf_reg_state *reg,
+					const struct btf_type *ref_t,
+					const char *ref_tname, u32 ref_id,
+					struct bpf_kfunc_call_arg_meta *meta,
+					int argno)
+{
+	const struct btf_type *reg_ref_t;
+	bool strict_type_match = false;
+	const struct btf *reg_btf;
+	const char *reg_ref_tname;
+	u32 reg_ref_id;
+
+	if (reg->type == PTR_TO_BTF_ID) {
+		reg_btf = reg->btf;
+		reg_ref_id = reg->btf_id;
+	} else {
+		reg_btf = btf_vmlinux;
+		reg_ref_id = *reg2btf_ids[base_type(reg->type)];
+	}
+
+	if (is_kfunc_trusted_args(meta) || (is_kfunc_release(meta) && reg->ref_obj_id))
+		strict_type_match = true;
+
+	reg_ref_t = btf_type_skip_modifiers(reg_btf, reg_ref_id, &reg_ref_id);
+	reg_ref_tname = btf_name_by_offset(reg_btf, reg_ref_t->name_off);
+	if (!btf_struct_ids_match(&env->log, reg_btf, reg_ref_id, reg->off, meta->btf, ref_id, strict_type_match)) {
+		verbose(env, "kernel function %s args#%d expected pointer to %s %s but R%d has a pointer to %s %s\n",
+			meta->func_name, argno, btf_type_str(ref_t), ref_tname, argno + 1,
+			btf_type_str(reg_ref_t), reg_ref_tname);
+		return -EINVAL;
+	}
+	return 0;
+}
+
+static int process_kf_arg_ptr_to_kptr(struct bpf_verifier_env *env,
+				      struct bpf_reg_state *reg,
+				      const struct btf_type *ref_t,
+				      const char *ref_tname,
+				      struct bpf_kfunc_call_arg_meta *meta,
+				      int argno)
+{
+	struct btf_field *kptr_field;
+
+	/* check_func_arg_reg_off allows var_off for
+	 * PTR_TO_MAP_VALUE, but we need fixed offset to find
+	 * off_desc.
+	 */
+	if (!tnum_is_const(reg->var_off)) {
+		verbose(env, "arg#0 must have constant offset\n");
+		return -EINVAL;
+	}
+
+	kptr_field = btf_record_find(reg->map_ptr->record, reg->off + reg->var_off.value, BPF_KPTR);
+	if (!kptr_field || kptr_field->type != BPF_KPTR_REF) {
+		verbose(env, "arg#0 no referenced kptr at map value offset=%llu\n",
+			reg->off + reg->var_off.value);
+		return -EINVAL;
+	}
+
+	if (!btf_struct_ids_match(&env->log, meta->btf, ref_t->type, 0, kptr_field->kptr.btf,
+				  kptr_field->kptr.btf_id, true)) {
+		verbose(env, "kernel function %s args#%d expected pointer to %s %s\n",
+			meta->func_name, argno, btf_type_str(ref_t), ref_tname);
+		return -EINVAL;
+	}
+	return 0;
+}
+
+static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_arg_meta *meta)
+{
+	const char *func_name = meta->func_name, *ref_tname;
+	const struct btf *btf = meta->btf;
+	const struct btf_param *args;
+	u32 i, nargs;
+	int ret;
+
+	args = (const struct btf_param *)(meta->func_proto + 1);
+	nargs = btf_type_vlen(meta->func_proto);
+	if (nargs > MAX_BPF_FUNC_REG_ARGS) {
+		verbose(env, "Function %s has %d > %d args\n", func_name, nargs,
+			MAX_BPF_FUNC_REG_ARGS);
+		return -EINVAL;
+	}
+
+	/* Check that BTF function arguments match actual types that the
+	 * verifier sees.
+	 */
+	for (i = 0; i < nargs; i++) {
+		struct bpf_reg_state *regs = cur_regs(env), *reg = &regs[i + 1];
+		const struct btf_type *t, *ref_t, *resolve_ret;
+		enum bpf_arg_type arg_type = ARG_DONTCARE;
+		u32 regno = i + 1, ref_id, type_size;
+		bool is_ret_buf_sz = false;
+		int kf_arg_type;
+
+		t = btf_type_skip_modifiers(btf, args[i].type, NULL);
+		if (btf_type_is_scalar(t)) {
+			if (reg->type != SCALAR_VALUE) {
+				verbose(env, "R%d is not a scalar\n", regno);
+				return -EINVAL;
+			}
+			if (is_kfunc_arg_scalar_with_name(btf, &args[i], "rdonly_buf_size")) {
+				meta->r0_rdonly = true;
+				is_ret_buf_sz = true;
+			} else if (is_kfunc_arg_scalar_with_name(btf, &args[i], "rdwr_buf_size")) {
+				is_ret_buf_sz = true;
+			}
+
+			if (is_ret_buf_sz) {
+				if (meta->r0_size) {
+					verbose(env, "2 or more rdonly/rdwr_buf_size parameters for kfunc");
+					return -EINVAL;
+				}
+
+				if (!tnum_is_const(reg->var_off)) {
+					verbose(env, "R%d is not a const\n", regno);
+					return -EINVAL;
+				}
+
+				meta->r0_size = reg->var_off.value;
+				ret = mark_chain_precision(env, regno);
+				if (ret)
+					return ret;
+			}
+			continue;
+		}
+
+		if (!btf_type_is_ptr(t)) {
+			verbose(env, "Unrecognized arg#%d type %s\n", i, btf_type_str(t));
+			return -EINVAL;
+		}
+
+		if (reg->ref_obj_id) {
+			if (is_kfunc_release(meta) && meta->ref_obj_id) {
+				verbose(env, "verifier internal error: more than one arg with ref_obj_id R%d %u %u\n",
+					regno, reg->ref_obj_id,
+					meta->ref_obj_id);
+				return -EFAULT;
+			}
+			meta->ref_obj_id = reg->ref_obj_id;
+			if (is_kfunc_release(meta))
+				meta->release_regno = regno;
+		}
+
+		ref_t = btf_type_skip_modifiers(btf, t->type, &ref_id);
+		ref_tname = btf_name_by_offset(btf, ref_t->name_off);
+
+		kf_arg_type = get_kfunc_ptr_arg_type(env, meta, t, ref_t, ref_tname, args, i, nargs);
+		if (kf_arg_type < 0)
+			return kf_arg_type;
+
+		switch (kf_arg_type) {
+		case KF_ARG_PTR_TO_BTF_ID:
+			if (!is_kfunc_trusted_args(meta))
+				break;
+			if (!reg->ref_obj_id) {
+				verbose(env, "R%d must be referenced\n", regno);
+				return -EINVAL;
+			}
+			fallthrough;
+		case KF_ARG_PTR_TO_CTX:
+			/* Trusted arguments have the same offset checks as release arguments */
+			arg_type |= OBJ_RELEASE;
+			break;
+		case KF_ARG_PTR_TO_KPTR:
+		case KF_ARG_PTR_TO_DYNPTR:
+		case KF_ARG_PTR_TO_MEM:
+		case KF_ARG_PTR_TO_MEM_SIZE:
+			/* Trusted by default */
+			break;
+		default:
+			WARN_ON_ONCE(1);
+			return -EFAULT;
+		}
+
+		if (is_kfunc_release(meta) && reg->ref_obj_id)
+			arg_type |= OBJ_RELEASE;
+		ret = check_func_arg_reg_off(env, reg, regno, arg_type);
+		if (ret < 0)
+			return ret;
+
+		switch (kf_arg_type) {
+		case KF_ARG_PTR_TO_CTX:
+			if (reg->type != PTR_TO_CTX) {
+				verbose(env, "arg#%d expected pointer to ctx, but got %s\n", i, btf_type_str(t));
+				return -EINVAL;
+			}
+			break;
+		case KF_ARG_PTR_TO_KPTR:
+			if (reg->type != PTR_TO_MAP_VALUE) {
+				verbose(env, "arg#0 expected pointer to map value\n");
+				return -EINVAL;
+			}
+			ret = process_kf_arg_ptr_to_kptr(env, reg, ref_t, ref_tname, meta, i);
+			if (ret < 0)
+				return ret;
+			break;
+		case KF_ARG_PTR_TO_DYNPTR:
+			if (reg->type != PTR_TO_STACK) {
+				verbose(env, "arg#%d expected pointer to stack\n", i);
+				return -EINVAL;
+			}
+
+			if (!is_dynptr_reg_valid_init(env, reg)) {
+				verbose(env, "arg#%d pointer type %s %s must be valid and initialized\n",
+					i, btf_type_str(ref_t), ref_tname);
+				return -EINVAL;
+			}
+
+			if (!is_dynptr_type_expected(env, reg, ARG_PTR_TO_DYNPTR | DYNPTR_TYPE_LOCAL)) {
+				verbose(env, "arg#%d pointer type %s %s points to unsupported dynamic pointer type\n",
+					i, btf_type_str(ref_t), ref_tname);
+				return -EINVAL;
+			}
+			break;
+		case KF_ARG_PTR_TO_BTF_ID:
+			/* Only base_type is checked, further checks are done here */
+			if (reg->type != PTR_TO_BTF_ID &&
+			    (!reg2btf_ids[base_type(reg->type)] || type_flag(reg->type))) {
+				verbose(env, "arg#%d expected pointer to btf or socket\n", i);
+				return -EINVAL;
+			}
+			ret = process_kf_arg_ptr_to_btf_id(env, reg, ref_t, ref_tname, ref_id, meta, i);
+			if (ret < 0)
+				return ret;
+			break;
+		case KF_ARG_PTR_TO_MEM:
+			resolve_ret = btf_resolve_size(btf, ref_t, &type_size);
+			if (IS_ERR(resolve_ret)) {
+				verbose(env, "arg#%d reference type('%s %s') size cannot be determined: %ld\n",
+					i, btf_type_str(ref_t), ref_tname, PTR_ERR(resolve_ret));
+				return -EINVAL;
+			}
+			ret = check_mem_reg(env, reg, regno, type_size);
+			if (ret < 0)
+				return ret;
+			break;
+		case KF_ARG_PTR_TO_MEM_SIZE:
+			ret = check_kfunc_mem_size_reg(env, &regs[regno + 1], regno + 1);
+			if (ret < 0) {
+				verbose(env, "arg#%d arg#%d memory, len pair leads to invalid memory access\n", i, i + 1);
+				return ret;
+			}
+			/* Skip next '__sz' argument */
+			i++;
+			break;
+		}
+	}
+
+	if (is_kfunc_release(meta) && !meta->release_regno) {
+		verbose(env, "release kernel function %s expects refcounted PTR_TO_BTF_ID\n",
+			func_name);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
 static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
 			    int *insn_idx_p)
 {
 	const struct btf_type *t, *func, *func_proto, *ptr_type;
 	struct bpf_reg_state *regs = cur_regs(env);
-	struct bpf_kfunc_arg_meta meta = { 0 };
 	const char *func_name, *ptr_type_name;
+	struct bpf_kfunc_call_arg_meta meta;
 	u32 i, nargs, func_id, ptr_type_id;
 	int err, insn_idx = *insn_idx_p;
 	const struct btf_param *args;
 	struct btf *desc_btf;
 	u32 *kfunc_flags;
-	bool acq;
 
 	/* skip for now, but return error when we find this in fixup_kfunc_call */
 	if (!insn->imm)
@@ -7896,24 +8394,34 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
 			func_name);
 		return -EACCES;
 	}
-	if (*kfunc_flags & KF_DESTRUCTIVE && !capable(CAP_SYS_BOOT)) {
-		verbose(env, "destructive kfunc calls require CAP_SYS_BOOT capabilities\n");
+
+	/* Prepare kfunc call metadata */
+	memset(&meta, 0, sizeof(meta));
+	meta.btf = desc_btf;
+	meta.func_id = func_id;
+	meta.kfunc_flags = *kfunc_flags;
+	meta.func_proto = func_proto;
+	meta.func_name = func_name;
+
+	if (is_kfunc_destructive(&meta) && !capable(CAP_SYS_BOOT)) {
+		verbose(env, "destructive kfunc calls require CAP_SYS_BOOT capability\n");
 		return -EACCES;
 	}
 
-	acq = *kfunc_flags & KF_ACQUIRE;
-
-	meta.flags = *kfunc_flags;
+	if (is_kfunc_sleepable(&meta) && !env->prog->aux->sleepable) {
+		verbose(env, "program must be sleepable to call sleepable kfunc %s\n", func_name);
+		return -EACCES;
+	}
 
 	/* Check the arguments */
-	err = btf_check_kfunc_arg_match(env, desc_btf, func_id, regs, &meta);
+	err = check_kfunc_args(env, &meta);
 	if (err < 0)
 		return err;
 	/* In case of release function, we get register number of refcounted
-	 * PTR_TO_BTF_ID back from btf_check_kfunc_arg_match, do the release now
+	 * PTR_TO_BTF_ID in bpf_kfunc_arg_meta, do the release now.
 	 */
-	if (err) {
-		err = release_reference(env, regs[err].ref_obj_id);
+	if (meta.release_regno) {
+		err = release_reference(env, regs[meta.release_regno].ref_obj_id);
 		if (err) {
 			verbose(env, "kfunc %s#%d reference has not been acquired before\n",
 				func_name, func_id);
@@ -7927,7 +8435,7 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
 	/* Check return type */
 	t = btf_type_skip_modifiers(desc_btf, func_proto->type, NULL);
 
-	if (acq && !btf_type_is_struct_ptr(desc_btf, t)) {
+	if (is_kfunc_acquire(&meta) && !btf_type_is_struct_ptr(meta.btf, t)) {
 		verbose(env, "acquire kernel function does not return PTR_TO_BTF_ID\n");
 		return -EINVAL;
 	}
@@ -7966,20 +8474,23 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
 			regs[BPF_REG_0].type = PTR_TO_BTF_ID;
 			regs[BPF_REG_0].btf_id = ptr_type_id;
 		}
-		if (*kfunc_flags & KF_RET_NULL) {
+		if (is_kfunc_ret_null(&meta)) {
 			regs[BPF_REG_0].type |= PTR_MAYBE_NULL;
 			/* For mark_ptr_or_null_reg, see 93c230e3f5bd6 */
 			regs[BPF_REG_0].id = ++env->id_gen;
 		}
 		mark_btf_func_reg_size(env, BPF_REG_0, sizeof(void *));
-		if (acq) {
+		if (is_kfunc_acquire(&meta)) {
 			int id = acquire_reference_state(env, insn_idx);
 
 			if (id < 0)
 				return id;
-			regs[BPF_REG_0].id = id;
+			if (is_kfunc_ret_null(&meta))
+				regs[BPF_REG_0].id = id;
 			regs[BPF_REG_0].ref_obj_id = id;
 		}
+		if (reg_may_point_to_spin_lock(&regs[BPF_REG_0]) && !regs[BPF_REG_0].id)
+			regs[BPF_REG_0].id = ++env->id_gen;
 	} /* else { add_kfunc_call() ensures it is btf_type_is_void(t) } */
 
 	nargs = btf_type_vlen(func_proto);