bpf: treewide: Annotate BPF kfuncs in BTF

This commit marks kfuncs as such inside the .BTF_ids section. The upshot
of these annotations is that we'll be able to automatically generate
kfunc prototypes for downstream users. The process is as follows:

1. In source, use BTF_KFUNCS_START/END macro pair to mark kfuncs
2. During build, pahole injects into BTF a "bpf_kfunc" BTF_DECL_TAG for
   each function inside BTF_KFUNCS sets
3. At runtime, vmlinux or module BTF is made available in sysfs
4. At runtime, bpftool (or similar) can look at provided BTF and
   generate appropriate prototypes for functions with "bpf_kfunc" tag

To ensure future kfunc are similarly tagged, we now also return error
inside kfunc registration for untagged kfuncs. For vmlinux kfuncs,
we also WARN(), as initcall machinery does not handle errors.

Signed-off-by: Daniel Xu <dxu@dxuuu.xyz>
Acked-by: Benjamin Tissoires <bentiss@kernel.org>
Link: https://lore.kernel.org/r/e55150ceecbf0a5d961e608941165c0bee7bc943.1706491398.git.dxu@dxuuu.xyz
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

4 files changed, 16 insertions, 8 deletions

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index c8c6e6cf18e7..ef380e546952 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -8124,6 +8124,14 @@ int register_btf_kfunc_id_set(enum bpf_prog_type prog_type,
 {
 	enum btf_kfunc_hook hook;
 
+	/* All kfuncs need to be tagged as such in BTF.
+	 * WARN() for initcall registrations that do not check errors.
+	 */
+	if (!(kset->set->flags & BTF_SET8_KFUNCS)) {
+		WARN_ON(!kset->owner);
+		return -EINVAL;
+	}
+
 	hook = bpf_prog_type_to_kfunc_hook(prog_type);
 	return __register_btf_kfunc_id_set(hook, kset);
 }
diff --git a/kernel/bpf/cpumask.c b/kernel/bpf/cpumask.c
index 2e73533a3811..dad0fb1c8e87 100644
--- a/kernel/bpf/cpumask.c
+++ b/kernel/bpf/cpumask.c
@@ -424,7 +424,7 @@ __bpf_kfunc u32 bpf_cpumask_weight(const struct cpumask *cpumask)
 
 __bpf_kfunc_end_defs();
 
-BTF_SET8_START(cpumask_kfunc_btf_ids)
+BTF_KFUNCS_START(cpumask_kfunc_btf_ids)
 BTF_ID_FLAGS(func, bpf_cpumask_create, KF_ACQUIRE | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_cpumask_release, KF_RELEASE)
 BTF_ID_FLAGS(func, bpf_cpumask_acquire, KF_ACQUIRE | KF_TRUSTED_ARGS)
@@ -450,7 +450,7 @@ BTF_ID_FLAGS(func, bpf_cpumask_copy, KF_RCU)
 BTF_ID_FLAGS(func, bpf_cpumask_any_distribute, KF_RCU)
 BTF_ID_FLAGS(func, bpf_cpumask_any_and_distribute, KF_RCU)
 BTF_ID_FLAGS(func, bpf_cpumask_weight, KF_RCU)
-BTF_SET8_END(cpumask_kfunc_btf_ids)
+BTF_KFUNCS_END(cpumask_kfunc_btf_ids)
 
 static const struct btf_kfunc_id_set cpumask_kfunc_set = {
 	.owner = THIS_MODULE,
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index bcb951a2ecf4..4db1c658254c 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -2544,7 +2544,7 @@ __bpf_kfunc void bpf_throw(u64 cookie)
 
 __bpf_kfunc_end_defs();
 
-BTF_SET8_START(generic_btf_ids)
+BTF_KFUNCS_START(generic_btf_ids)
 #ifdef CONFIG_KEXEC_CORE
 BTF_ID_FLAGS(func, crash_kexec, KF_DESTRUCTIVE)
 #endif
@@ -2573,7 +2573,7 @@ BTF_ID_FLAGS(func, bpf_task_get_cgroup1, KF_ACQUIRE | KF_RCU | KF_RET_NULL)
 #endif
 BTF_ID_FLAGS(func, bpf_task_from_pid, KF_ACQUIRE | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_throw)
-BTF_SET8_END(generic_btf_ids)
+BTF_KFUNCS_END(generic_btf_ids)
 
 static const struct btf_kfunc_id_set generic_kfunc_set = {
 	.owner = THIS_MODULE,
@@ -2589,7 +2589,7 @@ BTF_ID(struct, cgroup)
 BTF_ID(func, bpf_cgroup_release_dtor)
 #endif
 
-BTF_SET8_START(common_btf_ids)
+BTF_KFUNCS_START(common_btf_ids)
 BTF_ID_FLAGS(func, bpf_cast_to_kern_ctx)
 BTF_ID_FLAGS(func, bpf_rdonly_cast)
 BTF_ID_FLAGS(func, bpf_rcu_read_lock)
@@ -2618,7 +2618,7 @@ BTF_ID_FLAGS(func, bpf_dynptr_is_null)
 BTF_ID_FLAGS(func, bpf_dynptr_is_rdonly)
 BTF_ID_FLAGS(func, bpf_dynptr_size)
 BTF_ID_FLAGS(func, bpf_dynptr_clone)
-BTF_SET8_END(common_btf_ids)
+BTF_KFUNCS_END(common_btf_ids)
 
 static const struct btf_kfunc_id_set common_kfunc_set = {
 	.owner = THIS_MODULE,
diff --git a/kernel/bpf/map_iter.c b/kernel/bpf/map_iter.c
index 6abd7c5df4b3..9575314f40a6 100644
--- a/kernel/bpf/map_iter.c
+++ b/kernel/bpf/map_iter.c
@@ -213,9 +213,9 @@ __bpf_kfunc s64 bpf_map_sum_elem_count(const struct bpf_map *map)
 
 __bpf_kfunc_end_defs();
 
-BTF_SET8_START(bpf_map_iter_kfunc_ids)
+BTF_KFUNCS_START(bpf_map_iter_kfunc_ids)
 BTF_ID_FLAGS(func, bpf_map_sum_elem_count, KF_TRUSTED_ARGS)
-BTF_SET8_END(bpf_map_iter_kfunc_ids)
+BTF_KFUNCS_END(bpf_map_iter_kfunc_ids)
 
 static const struct btf_kfunc_id_set bpf_map_iter_kfunc_set = {
 	.owner = THIS_MODULE,