bpf: Return target info when a tracing bpf_link is queried

There is currently no way to discover the target of a tracing program
attachment after the fact. Add this information to bpf_link_info and return
it when querying the bpf_link fd.

Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210413091607.58945-1-toke@redhat.com

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 51c2ffa..6023a13 100644 (file)
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -487,6 +487,15 @@ static inline u64 bpf_trampoline_compute_key(const struct bpf_prog *tgt_prog,
                return ((u64)btf_obj_id(btf) << 32) | 0x80000000 | btf_id;
 }
 
+/* unpack the IDs from the key as constructed above */
+static inline void bpf_trampoline_unpack_key(u64 key, u32 *obj_id, u32 *btf_id)
+{
+       if (obj_id)
+               *obj_id = key >> 32;
+       if (btf_id)
+               *btf_id = key & 0x7FFFFFFF;
+}
+
 int bpf_check_attach_target(struct bpf_verifier_log *log,
                            const struct bpf_prog *prog,
                            const struct bpf_prog *tgt_prog,

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 85c924b..df164a4 100644 (file)
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -5416,6 +5416,8 @@ struct bpf_link_info {
                } raw_tracepoint;
                struct {
                        __u32 attach_type;
+                       __u32 target_obj_id; /* prog_id for PROG_EXT, otherwise btf object id */
+                       __u32 target_btf_id; /* BTF type id inside the object */
                } tracing;
                struct {
                        __u64 cgroup_id;

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 6428634..fd49519 100644 (file)
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2551,6 +2551,9 @@ static int bpf_tracing_link_fill_link_info(const struct bpf_link *link,
                container_of(link, struct bpf_tracing_link, link);
 
        info->tracing.attach_type = tr_link->attach_type;
+       bpf_trampoline_unpack_key(tr_link->trampoline->key,
+                                 &info->tracing.target_obj_id,
+                                 &info->tracing.target_btf_id);
 
        return 0;
 }

diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 85c924b..df164a4 100644 (file)
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -5416,6 +5416,8 @@ struct bpf_link_info {
                } raw_tracepoint;
                struct {
                        __u32 attach_type;
+                       __u32 target_obj_id; /* prog_id for PROG_EXT, otherwise btf object id */
+                       __u32 target_btf_id; /* BTF type id inside the object */
                } tracing;
                struct {
                        __u64 cgroup_id;