[PATCH bpf-next v1 06/19] bpf: support bpf tracing/iter programs for BPF_LINK_UPDATE

Yonghong Song
2020-04-27T20:12:49Z

Added BPF_LINK_UPDATE support for tracing/iter programs.
This way, a file based bpf iterator, which holds a reference
to the link, can have its bpf program updated without
creating new files.

Signed-off-by: Yonghong Song <yhs@fb.com>
---
include/linux/bpf.h | 2 ++
kernel/bpf/bpf_iter.c | 29 +++++++++++++++++++++++++++++
kernel/bpf/syscall.c | 5 +++++
3 files changed, 36 insertions(+)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 60ecb73d8f6d..4fc39d9b5cd0 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1131,6 +1131,8 @@ struct bpf_prog *bpf_iter_get_prog(struct seq_file *seq, u32 priv_data_size,
u64 *session_id, u64 *seq_num, bool is_last);
int bpf_iter_run_prog(struct bpf_prog *prog, void *ctx);
int bpf_iter_link_attach(const union bpf_attr *attr, struct bpf_prog *prog);
+int bpf_iter_link_replace(struct bpf_link *link, struct bpf_prog *old_prog,
+ struct bpf_prog *new_prog);

int bpf_percpu_hash_copy(struct bpf_map *map, void *key, void *value);
int bpf_percpu_array_copy(struct bpf_map *map, void *key, void *value);
diff --git a/kernel/bpf/bpf_iter.c b/kernel/bpf/bpf_iter.c
index 9532e7bcb8e1..fc1ce5ee5c3f 100644
--- a/kernel/bpf/bpf_iter.c
+++ b/kernel/bpf/bpf_iter.c
@@ -23,6 +23,9 @@ static struct list_head targets;
static struct mutex targets_mutex;
static bool bpf_iter_inited = false;

+/* protect bpf_iter_link.link->prog upddate */
+static struct mutex bpf_iter_mutex;
+
int bpf_iter_reg_target(struct bpf_iter_reg *reg_info)
{
struct bpf_iter_target_info *tinfo;
@@ -33,6 +36,7 @@ int bpf_iter_reg_target(struct bpf_iter_reg *reg_info)
if (!bpf_iter_inited) {
INIT_LIST_HEAD(&targets);
mutex_init(&targets_mutex);
+ mutex_init(&bpf_iter_mutex);
bpf_iter_inited = true;
}

@@ -121,3 +125,28 @@ int bpf_iter_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
kfree(link);
return err;
}
+
+int bpf_iter_link_replace(struct bpf_link *link, struct bpf_prog *old_prog,
+ struct bpf_prog *new_prog)
+{
+ int ret = 0;
+
+ mutex_lock(&bpf_iter_mutex);
+ if (old_prog && link->prog != old_prog) {
+ ret = -EPERM;
+ goto out_unlock;
+ }
+
+ if (link->prog->type != new_prog->type ||
+ link->prog->expected_attach_type != new_prog->expected_attach_type ||
+ strcmp(link->prog->aux->attach_func_name, new_prog->aux->attach_func_name)) {
+ ret = -EINVAL;
+ goto out_unlock;
+ }
+
+ link->prog = new_prog;
+
+out_unlock:
+ mutex_unlock(&bpf_iter_mutex);
+ return ret;
+}
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 8741b5e11c85..b7af4f006f2e 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -3679,6 +3679,11 @@ static int link_update(union bpf_attr *attr)
goto out_put_progs;
}
#endif
+
+ if (link->ops == &bpf_iter_link_lops) {
+ ret = bpf_iter_link_replace(link, old_prog, new_prog);
+ goto out_put_progs;
+ }
ret = -EINVAL;

out_put_progs:
--
2.24.1