From: Daniel Borkmann <daniel@iogearbox.net>
Date: Tue, 14 May 2019 01:18:55 +0200
Subject: bpf: add map_lookup_elem_sys_only for lookups from syscall side
Patch-mainline: Queued in subsystem maintainer repository
Git-repo: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
Git-commit: c6110222c6f49ea68169f353565eb865488a8619
References: bsc#1083647

Add a callback map_lookup_elem_sys_only() that map implementations
could use over map_lookup_elem() from system call side in case the
map implementation needs to handle the latter differently than from
the BPF data path. If map_lookup_elem_sys_only() is set, this will
be preferred pick for map lookups out of user space. This hook is
used in a follow-up fix for LRU map, but once development window
opens, we can convert other map types from map_lookup_elem() (here,
the one called upon BPF_MAP_LOOKUP_ELEM cmd is meant) over to use
the callback to simplify and clean up the latter.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Gary Lin <glin@suse.com>
---
 include/linux/bpf.h  |    1 +
 kernel/bpf/syscall.c |    5 ++++-
 2 files changed, 5 insertions(+), 1 deletion(-)

--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -34,6 +34,7 @@ struct bpf_map_ops {
 	void (*map_free)(struct bpf_map *map);
 	int (*map_get_next_key)(struct bpf_map *map, void *key, void *next_key);
 	void (*map_release_uref)(struct bpf_map *map);
+	void *(*map_lookup_elem_sys_only)(struct bpf_map *map, void *key);
 
 	/* funcs callable from userspace and from eBPF programs */
 	void *(*map_lookup_elem)(struct bpf_map *map, void *key);
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -675,7 +675,10 @@ static int map_lookup_elem(union bpf_att
 		err = bpf_fd_htab_map_lookup_elem(map, key, value);
 	} else {
 		rcu_read_lock();
-		ptr = map->ops->map_lookup_elem(map, key);
+		if (map->ops->map_lookup_elem_sys_only)
+			ptr = map->ops->map_lookup_elem_sys_only(map, key);
+		else
+			ptr = map->ops->map_lookup_elem(map, key);
 		if (IS_ERR(ptr)) {
 			err = PTR_ERR(ptr);
 		} else if (!ptr) {