bpf: Add poke dependency tracking for prog array maps

This work adds program tracking to prog array maps. This is needed such
that upon prog array updates/deletions we can fix up all programs which
make use of this tail call map. We add ops->map_poke_{un,}track()
helpers to maps to maintain the list of programs and ops->map_poke_run()
for triggering the actual update.

bpf_array_aux is extended to contain the list head and poke_mutex in
order to serialize program patching during updates/deletions.
bpf_free_used_maps() will untrack the program shortly before dropping
the reference to the map. For clearing out the prog array once all urefs
are dropped we need to use schedule_work() to have a sleepable context.

The prog_array_map_poke_run() is triggered during updates/deletions and
walks the maintained prog list. It checks in their poke_tabs whether the
map and key is matching and runs the actual bpf_arch_text_poke() for
patching in the nop or new jmp location. Depending on the type of update,
we use one of BPF_MOD_{NOP_TO_JUMP,JUMP_TO_NOP,JUMP_TO_JUMP}.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/1fb364bb3c565b3e415d5ea348f036ff379e779d.1574452833.git.daniel@iogearbox.net

1 files changed, 7 insertions, 2 deletions

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 608b7085e0c9..49e32acad7d8 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -2050,11 +2050,16 @@ static void bpf_free_cgroup_storage(struct bpf_prog_aux *aux)
 
 static void bpf_free_used_maps(struct bpf_prog_aux *aux)
 {
+	struct bpf_map *map;
 	int i;
 
 	bpf_free_cgroup_storage(aux);
-	for (i = 0; i < aux->used_map_cnt; i++)
-		bpf_map_put(aux->used_maps[i]);
+	for (i = 0; i < aux->used_map_cnt; i++) {
+		map = aux->used_maps[i];
+		if (map->ops->map_poke_untrack)
+			map->ops->map_poke_untrack(map, aux);
+		bpf_map_put(map);
+	}
 	kfree(aux->used_maps);
 }