[PATCH RFC bpf-next 4/7] net: sched: add lightweight update path for cls_bpf
From: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Date: 2021-05-28 20:00:56
Also in:
bpf
Subsystem:
bpf [general] (safe dynamic programs and tools), bpf [networking] (tcx & tc bpf, sock_addr), networking [general], tc subsystem, the rest · Maintainers:
Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Jamal Hadi Salim, Jiri Pirko, Linus Torvalds
This is used by BPF_LINK_UPDATE to replace the attach SCHED_CLS bpf prog effectively changing the classifier implementation for a given filter owned by a bpf_link. Note that READ_ONCE suffices in this case as the ordering for loads from the filter are implicitly provided by the data dependency on BPF prog pointer. On the writer side we can just use a relaxed WRITE_ONCE store to make sure one or the other value is visible to a reader in cls_bpf_classify. Lifetime is managed using RCU so bpf_prog_put path should wait until readers are done for old_prog. All other parties accessing the BPF prog are under RTNL protection, so need no changes. Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com> --- net/sched/cls_bpf.c | 55 +++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 53 insertions(+), 2 deletions(-)
diff --git a/net/sched/cls_bpf.c b/net/sched/cls_bpf.c
index 57d6dedb389a..459a139bcfbe 100644
--- a/net/sched/cls_bpf.c
+++ b/net/sched/cls_bpf.c@@ -9,6 +9,7 @@ * (C) 2013 Daniel Borkmann <dborkman@redhat.com> */ +#include <linux/atomic.h> #include <linux/module.h> #include <linux/types.h> #include <linux/skbuff.h>
@@ -104,11 +105,11 @@ static int cls_bpf_classify(struct sk_buff *skb, const struct tcf_proto *tp, /* It is safe to push/pull even if skb_shared() */ __skb_push(skb, skb->mac_len); bpf_compute_data_pointers(skb); - filter_res = BPF_PROG_RUN(prog->filter, skb); + filter_res = BPF_PROG_RUN(READ_ONCE(prog->filter), skb); __skb_pull(skb, skb->mac_len); } else { bpf_compute_data_pointers(skb); - filter_res = BPF_PROG_RUN(prog->filter, skb); + filter_res = BPF_PROG_RUN(READ_ONCE(prog->filter), skb); } if (prog->exts_integrated) {
@@ -775,6 +776,55 @@ static int cls_bpf_link_detach(struct bpf_link *link) return 0; } +static int cls_bpf_link_update(struct bpf_link *link, struct bpf_prog *new_prog, + struct bpf_prog *old_prog) +{ + struct cls_bpf_link *cls_link; + struct cls_bpf_prog cls_prog; + struct cls_bpf_prog *prog; + int ret; + + rtnl_lock(); + + cls_link = container_of(link, struct cls_bpf_link, link); + if (!cls_link->prog) { + ret = -ENOLINK; + goto out; + } + + prog = cls_link->prog; + + /* BPF_F_REPLACEing? */ + if (old_prog && prog->filter != old_prog) { + ret = -EINVAL; + goto out; + } + + old_prog = prog->filter; + + if (new_prog == old_prog) { + ret = 0; + goto out; + } + + cls_prog = *prog; + cls_prog.filter = new_prog; + + ret = cls_bpf_offload(prog->tp, &cls_prog, prog, NULL); + if (ret < 0) + goto out; + + WRITE_ONCE(prog->filter, new_prog); + + bpf_prog_inc(new_prog); + /* release our reference */ + bpf_prog_put(old_prog); + +out: + rtnl_unlock(); + return ret; +} + static void __bpf_fill_link_info(struct cls_bpf_link *link, struct bpf_link_info *info) {
@@ -859,6 +909,7 @@ static const struct bpf_link_ops cls_bpf_link_ops = { .show_fdinfo = cls_bpf_link_show_fdinfo, #endif .fill_link_info = cls_bpf_link_fill_link_info, + .update_prog = cls_bpf_link_update, }; static inline char *cls_bpf_link_name(u32 prog_id, const char *name)
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2.31.1