[PATCHv2 bpf-next 1/5] bpf: Allow trampoline re-attach for tracing and lsm programs

[Jiri Olsa]

Currently we don't allow re-attaching of trampolines. Once
it's detached, it can't be re-attach even when the program
is still loaded.

Adding the possibility to re-attach the loaded tracing and
lsm programs.

Signed-off-by: Jiri Olsa <jo...@kernel.org>
---
 kernel/bpf/syscall.c    | 23 +++++++++++++++++------
 kernel/bpf/trampoline.c |  2 +-
 2 files changed, 18 insertions(+), 7 deletions(-)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 6428634da57e..f416735b20b3 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2645,14 +2645,25 @@ static int bpf_tracing_prog_attach(struct bpf_prog 
*prog,
         *   target_btf_id using the link_create API.
         *
         * - if tgt_prog == NULL when this function was called using the old
-         *   raw_tracepoint_open API, and we need a target from prog->aux
-         *
-         * The combination of no saved target in prog->aux, and no target
-         * specified on load is illegal, and we reject that here.
+        *   raw_tracepoint_open API, and we need a target from prog->aux
+        *
+        * - if prog->aux->dst_trampoline and tgt_prog is NULL, the program
+        *   was detached and is going for re-attachment.
         */
        if (!prog->aux->dst_trampoline && !tgt_prog) {
-               err = -ENOENT;
-               goto out_unlock;
+               /*
+                * Allow re-attach for TRACING and LSM programs. If it's
+                * currently linked, bpf_trampoline_link_prog will fail.
+                * EXT programs need to specify tgt_prog_fd, so they
+                * re-attach in separate code path.
+                */
+               if (prog->type != BPF_PROG_TYPE_TRACING &&
+                   prog->type != BPF_PROG_TYPE_LSM) {
+                       err = -EINVAL;
+                       goto out_put_prog;
+               }
+               btf_id = prog->aux->attach_btf_id;
+               key = bpf_trampoline_compute_key(NULL, prog->aux->attach_btf, 
btf_id);
        }
 
        if (!prog->aux->dst_trampoline ||
diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index 4aa8b52adf25..0d937c63fc22 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -467,7 +467,7 @@ int bpf_trampoline_unlink_prog(struct bpf_prog *prog, 
struct bpf_trampoline *tr)
                tr->extension_prog = NULL;
                goto out;
        }
-       hlist_del(&prog->aux->tramp_hlist);
+       hlist_del_init(&prog->aux->tramp_hlist);
        tr->progs_cnt[kind]--;
        err = bpf_trampoline_update(tr);
 out:
-- 
2.30.2