[PATCH bpf-next 1/2] bpf: include sub program tags in bpf_prog_info

[Song Liu]

This patch adds nr_prog_tags and prog_tags to bpf_prog_info. This is a
reliable way for user space to get tags of all sub programs. Before this
patch, user space need to find sub program tags via kallsyms.

This feature will be used in BPF introspection, where user space queries
information about BPF programs via sys_bpf.

Signed-off-by: Song Liu <songliubrav...@fb.com>
---
 include/uapi/linux/bpf.h |  2 ++
 kernel/bpf/syscall.c     | 27 +++++++++++++++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 1bee1135866a..368d185aa32f 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -2703,6 +2703,8 @@ struct bpf_prog_info {
        __u32 jited_line_info_cnt;
        __u32 line_info_rec_size;
        __u32 jited_line_info_rec_size;
+       __u32 nr_prog_tags;
+       __aligned_u64 prog_tags;
 } __attribute__((aligned(8)));
 
 struct bpf_map_info {
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 19c88cff7880..df7b1822d585 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2322,6 +2322,33 @@ static int bpf_prog_get_info_by_fd(struct bpf_prog *prog,
                }
        }
 
+       ulen = info.nr_prog_tags;
+       info.nr_prog_tags = prog->aux->func_cnt ? : 1;
+       if (ulen) {
+               if (bpf_dump_raw_ok()) {
+                       __u8 __user (*user_prog_tags)[BPF_TAG_SIZE];
+                       u32 i;
+
+                       user_prog_tags = u64_to_user_ptr(info.prog_tags);
+                       ulen = min_t(u32, info.nr_prog_tags, ulen);
+                       if (prog->aux->func_cnt) {
+                               for (i = 0; i < ulen; i++) {
+                                       if (copy_to_user(
+                                                   user_prog_tags[i],
+                                                   prog->aux->func[i]->tag,
+                                                   BPF_TAG_SIZE))
+                                               return -EFAULT;
+                               }
+                       } else {
+                               if (copy_to_user(user_prog_tags[0],
+                                                prog->tag, BPF_TAG_SIZE))
+                                       return -EFAULT;
+                       }
+               } else {
+                       info.nr_prog_tags = 0;
+               }
+       }
+
 done:
        if (copy_to_user(uinfo, &info, info_len) ||
            put_user(info_len, &uattr->info.info_len))
-- 
2.17.1