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Date: Wed, 18 Oct 2017 07:10:36 -0700
From: John Fastabend <john.r.fastabend@...il.com>
To: alexei.starovoitov@...il.com, davem@...emloft.net
Cc: netdev@...r.kernel.org, borkmann@...earbox.net
Subject: [net PATCH 2/5] bpf: avoid preempt enable/disable in sockmap using
tcp_skb_cb region
From: John Fastabend <john.fastabend@...il.com>
SK_SKB BPF programs are run from the socket/tcp context but early in
the stack before much of the TCP metadata is needed in tcp_skb_cb. So
we can use some unused fields to place BPF metadata needed for SK_SKB
programs when implementing the redirect function.
This allows us to drop the preempt disable logic. It does however
require an API change so sk_redirect_map() has been updated to
additionally provide ctx_ptr to skb. Note, we do however continue to
disable/enable preemption around actual BPF program running to account
for map updates.
Signed-off-by: John Fastabend <john.fastabend@...il.com>
Acked-by: Daniel Borkmann <daniel@...earbox.net>
---
include/linux/filter.h | 2 +
include/net/tcp.h | 5 +++
kernel/bpf/sockmap.c | 19 ++++++-------
net/core/filter.c | 29 ++++++++++----------
samples/sockmap/sockmap_kern.c | 2 +
tools/include/uapi/linux/bpf.h | 3 +-
tools/testing/selftests/bpf/bpf_helpers.h | 2 +
tools/testing/selftests/bpf/sockmap_verdict_prog.c | 4 +--
8 files changed, 36 insertions(+), 30 deletions(-)
diff --git a/include/linux/filter.h b/include/linux/filter.h
index d29e58f..818a0b2 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -728,7 +728,7 @@ void xdp_do_flush_map(void);
void bpf_warn_invalid_xdp_action(u32 act);
void bpf_warn_invalid_xdp_redirect(u32 ifindex);
-struct sock *do_sk_redirect_map(void);
+struct sock *do_sk_redirect_map(struct sk_buff *skb);
#ifdef CONFIG_BPF_JIT
extern int bpf_jit_enable;
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 89974c5..b1ef98e 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -840,6 +840,11 @@ struct tcp_skb_cb {
struct inet6_skb_parm h6;
#endif
} header; /* For incoming skbs */
+ struct {
+ __u32 key;
+ __u32 flags;
+ struct bpf_map *map;
+ } bpf;
};
};
diff --git a/kernel/bpf/sockmap.c b/kernel/bpf/sockmap.c
index c68899d..beaabb2 100644
--- a/kernel/bpf/sockmap.c
+++ b/kernel/bpf/sockmap.c
@@ -39,6 +39,7 @@
#include <linux/workqueue.h>
#include <linux/list.h>
#include <net/strparser.h>
+#include <net/tcp.h>
struct bpf_stab {
struct bpf_map map;
@@ -101,9 +102,16 @@ static int smap_verdict_func(struct smap_psock *psock, struct sk_buff *skb)
return SK_DROP;
skb_orphan(skb);
+ /* We need to ensure that BPF metadata for maps is also cleared
+ * when we orphan the skb so that we don't have the possibility
+ * to reference a stale map.
+ */
+ TCP_SKB_CB(skb)->bpf.map = NULL;
skb->sk = psock->sock;
bpf_compute_data_end(skb);
+ preempt_disable();
rc = (*prog->bpf_func)(skb, prog->insnsi);
+ preempt_enable();
skb->sk = NULL;
return rc;
@@ -114,17 +122,10 @@ static void smap_do_verdict(struct smap_psock *psock, struct sk_buff *skb)
struct sock *sk;
int rc;
- /* Because we use per cpu values to feed input from sock redirect
- * in BPF program to do_sk_redirect_map() call we need to ensure we
- * are not preempted. RCU read lock is not sufficient in this case
- * with CONFIG_PREEMPT_RCU enabled so we must be explicit here.
- */
- preempt_disable();
rc = smap_verdict_func(psock, skb);
switch (rc) {
case SK_REDIRECT:
- sk = do_sk_redirect_map();
- preempt_enable();
+ sk = do_sk_redirect_map(skb);
if (likely(sk)) {
struct smap_psock *peer = smap_psock_sk(sk);
@@ -141,8 +142,6 @@ static void smap_do_verdict(struct smap_psock *psock, struct sk_buff *skb)
/* Fall through and free skb otherwise */
case SK_DROP:
default:
- if (rc != SK_REDIRECT)
- preempt_enable();
kfree_skb(skb);
}
}
diff --git a/net/core/filter.c b/net/core/filter.c
index 74b8c91..ca1ba0b 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -1839,31 +1839,31 @@ static const struct bpf_func_proto bpf_redirect_proto = {
.arg2_type = ARG_ANYTHING,
};
-BPF_CALL_3(bpf_sk_redirect_map, struct bpf_map *, map, u32, key, u64, flags)
+BPF_CALL_4(bpf_sk_redirect_map, struct sk_buff *, skb,
+ struct bpf_map *, map, u32, key, u64, flags)
{
- struct redirect_info *ri = this_cpu_ptr(&redirect_info);
+ struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);
if (unlikely(flags))
return SK_ABORTED;
- ri->ifindex = key;
- ri->flags = flags;
- ri->map = map;
+ tcb->bpf.key = key;
+ tcb->bpf.flags = flags;
+ tcb->bpf.map = map;
return SK_REDIRECT;
}
-struct sock *do_sk_redirect_map(void)
+struct sock *do_sk_redirect_map(struct sk_buff *skb)
{
- struct redirect_info *ri = this_cpu_ptr(&redirect_info);
+ struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);
struct sock *sk = NULL;
- if (ri->map) {
- sk = __sock_map_lookup_elem(ri->map, ri->ifindex);
+ if (tcb->bpf.map) {
+ sk = __sock_map_lookup_elem(tcb->bpf.map, tcb->bpf.key);
- ri->ifindex = 0;
- ri->map = NULL;
- /* we do not clear flags for future lookup */
+ tcb->bpf.key = 0;
+ tcb->bpf.map = NULL;
}
return sk;
@@ -1873,9 +1873,10 @@ static const struct bpf_func_proto bpf_sk_redirect_map_proto = {
.func = bpf_sk_redirect_map,
.gpl_only = false,
.ret_type = RET_INTEGER,
- .arg1_type = ARG_CONST_MAP_PTR,
- .arg2_type = ARG_ANYTHING,
+ .arg1_type = ARG_PTR_TO_CTX,
+ .arg2_type = ARG_CONST_MAP_PTR,
.arg3_type = ARG_ANYTHING,
+ .arg4_type = ARG_ANYTHING,
};
BPF_CALL_1(bpf_get_cgroup_classid, const struct sk_buff *, skb)
diff --git a/samples/sockmap/sockmap_kern.c b/samples/sockmap/sockmap_kern.c
index f9b38ef..52b0053 100644
--- a/samples/sockmap/sockmap_kern.c
+++ b/samples/sockmap/sockmap_kern.c
@@ -62,7 +62,7 @@ int bpf_prog2(struct __sk_buff *skb)
ret = 1;
bpf_printk("sockmap: %d -> %d @ %d\n", lport, bpf_ntohl(rport), ret);
- return bpf_sk_redirect_map(&sock_map, ret, 0);
+ return bpf_sk_redirect_map(skb, &sock_map, ret, 0);
}
SEC("sockops")
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 43ab5c4..be9a631 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -569,9 +569,10 @@ union bpf_attr {
* @flags: reserved for future use
* Return: 0 on success or negative error code
*
- * int bpf_sk_redirect_map(map, key, flags)
+ * int bpf_sk_redirect_map(skb, map, key, flags)
* Redirect skb to a sock in map using key as a lookup key for the
* sock in map.
+ * @skb: pointer to skb
* @map: pointer to sockmap
* @key: key to lookup sock in map
* @flags: reserved for future use
diff --git a/tools/testing/selftests/bpf/bpf_helpers.h b/tools/testing/selftests/bpf/bpf_helpers.h
index 36fb916..b2e02bd 100644
--- a/tools/testing/selftests/bpf/bpf_helpers.h
+++ b/tools/testing/selftests/bpf/bpf_helpers.h
@@ -65,7 +65,7 @@ static int (*bpf_xdp_adjust_head)(void *ctx, int offset) =
static int (*bpf_setsockopt)(void *ctx, int level, int optname, void *optval,
int optlen) =
(void *) BPF_FUNC_setsockopt;
-static int (*bpf_sk_redirect_map)(void *map, int key, int flags) =
+static int (*bpf_sk_redirect_map)(void *ctx, void *map, int key, int flags) =
(void *) BPF_FUNC_sk_redirect_map;
static int (*bpf_sock_map_update)(void *map, void *key, void *value,
unsigned long long flags) =
diff --git a/tools/testing/selftests/bpf/sockmap_verdict_prog.c b/tools/testing/selftests/bpf/sockmap_verdict_prog.c
index 9b99bd1..2cd2d55 100644
--- a/tools/testing/selftests/bpf/sockmap_verdict_prog.c
+++ b/tools/testing/selftests/bpf/sockmap_verdict_prog.c
@@ -61,8 +61,8 @@ int bpf_prog2(struct __sk_buff *skb)
bpf_printk("verdict: data[0] = redir(%u:%u)\n", map, sk);
if (!map)
- return bpf_sk_redirect_map(&sock_map_rx, sk, 0);
- return bpf_sk_redirect_map(&sock_map_tx, sk, 0);
+ return bpf_sk_redirect_map(skb, &sock_map_rx, sk, 0);
+ return bpf_sk_redirect_map(skb, &sock_map_tx, sk, 0);
}
char _license[] SEC("license") = "GPL";
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