[ovs-dev] [RFC PATCH 1/5] netdev-afxdp: Enable loading XDP program.

Toshiaki Makita toshiaki.makita1 at gmail.com
Tue Mar 10 15:29:07 UTC 2020


From: William Tu <u9012063 at gmail.com>

Now netdev-afxdp always forwards all packets to userspace because
it is using libbpf's default XDP program, see 'xsk_load_xdp_prog'.
There are some cases when users want to keep packets in kernel instead
of sending to userspace, for example, management traffic such as SSH
should be processed in kernel.

The patch enables loading the user-provided XDP program by
  $ovs-vsctl -- set int afxdp-p0 options:xdp-obj=<path/to/xdp/obj>

So users can implement their filtering logic or traffic steering idea
in their XDP program, and rest of the traffic passes to AF_XDP socket
handled by OVS.

Signed-off-by: William Tu <u9012063 at gmail.com>
Co-Authored-by: Toshiaki Makita <toshiaki.makita1 at gmail.com>
Signed-off-by: Toshiaki Makita <toshiaki.makita1 at gmail.com>
---
v7:
  - rebase to master
  - apply Toshiaki's feedbacks and fixes
    - Close BPF objects by using bpf_object__close()
      Note that bpf_object__close() closes all program fds
      and map fds so no need to close them separately.
    - Use bpf_object__open/load() instead of bpf_prog_load()
      So that we can use bpf_map__reuse_fd() before loading the program.
      It is needed by XDP flow api provider in the following commits.

v6:
    - rebase to master
    - mostly remains the same as v5, but make sure there is no
      leak using bpftool and no repeated loop issued reported from Eelco
      here:
        https://patchwork.ozlabs.org/patch/1199734/
      which has been fixed at
        netdev-afxdp: Avoid removing of XDP program if not loaded.
    - travis: https://travis-ci.org/williamtu/ovs-travis/builds/638126505
---
 Documentation/intro/install/afxdp.rst |  59 ++++++++++
 NEWS                                  |   2 +
 lib/netdev-afxdp.c                    | 151 ++++++++++++++++++++++++--
 lib/netdev-linux-private.h            |   3 +
 4 files changed, 208 insertions(+), 7 deletions(-)

diff --git a/Documentation/intro/install/afxdp.rst b/Documentation/intro/install/afxdp.rst
index 99003e4db..4f8f15fcf 100644
--- a/Documentation/intro/install/afxdp.rst
+++ b/Documentation/intro/install/afxdp.rst
@@ -291,6 +291,65 @@ Or, use OVS pmd tool::
   ovs-appctl dpif-netdev/pmd-stats-show
 
 
+Loading Custom XDP Program
+--------------------------
+By defailt, netdev-afxdp always forwards all packets to userspace because
+it is using libbpf's default XDP program. There are some cases when users
+want to keep packets in kernel instead of sending to userspace, for example,
+management traffic such as SSH should be processed in kernel. This can be
+done by loading the user-provided XDP program::
+
+  ovs-vsctl -- set int afxdp-p0 options:xdp-obj=<path/to/xdp/obj>
+
+So users can implement their filtering logic or traffic steering idea
+in their XDP program, and rest of the traffic passes to AF_XDP socket
+handled by OVS. To set it back to default, use::
+
+  ovs-vsctl remove int afxdp-p0 options xdp-obj
+
+Below is a sample C program compiled under kernel's samples/bpf/.
+
+.. code-block:: c
+
+  #include <uapi/linux/bpf.h>
+  #include "bpf_helpers.h"
+
+  #if LINUX_VERSION_CODE < KERNEL_VERSION(5,3,0)
+  /* Kernel version before 5.3 needed an additional map */
+  struct bpf_map_def SEC("maps") qidconf_map = {
+      .type = BPF_MAP_TYPE_ARRAY,
+      .key_size = sizeof(int),
+      .value_size = sizeof(int),
+      .max_entries = 64,
+  };
+  #endif
+
+  /* OVS will associate map 'xsks_map' to xsk socket. */
+  struct bpf_map_def SEC("maps") xsks_map = {
+      .type = BPF_MAP_TYPE_XSKMAP,
+      .key_size = sizeof(int),
+      .value_size = sizeof(int),
+      .max_entries = 32,
+  };
+
+  SEC("xdp_sock")
+  int xdp_sock_prog(struct xdp_md *ctx)
+  {
+      int index = ctx->rx_queue_index;
+
+      /* Customized by user.
+       * For example
+       * 1) filter out all SSH traffic and return XDP_PASS
+       *    for kernel to process.
+       * 2) Drop unwanted packet by returning XDP_DROP.
+       */
+
+      /* Rest of packets goes to AF_XDP. */
+      return bpf_redirect_map(&xsks_map, index, 0);
+  }
+  char _license[] SEC("license") = "GPL";
+
+
 Example Script
 --------------
 
diff --git a/NEWS b/NEWS
index 32ca2e0c6..f8c4dcbcc 100644
--- a/NEWS
+++ b/NEWS
@@ -35,6 +35,8 @@ v2.13.0 - 14 Feb 2020
          generic               - former SKB
          best-effort [default] - new one, chooses the best available from
                                  3 above modes
+     * New option 'xdp-obj' for loading custom XDP program.  Default uses
+       the libbpf builtin XDP program.
    - DPDK:
      * DPDK pdump packet capture support disabled by default. New configure
        option '--enable-dpdk-pdump' to enable it.
diff --git a/lib/netdev-afxdp.c b/lib/netdev-afxdp.c
index 482400d8d..a526c8339 100644
--- a/lib/netdev-afxdp.c
+++ b/lib/netdev-afxdp.c
@@ -21,6 +21,7 @@
 #include "netdev-afxdp.h"
 #include "netdev-afxdp-pool.h"
 
+#include <bpf/bpf.h>
 #include <errno.h>
 #include <inttypes.h>
 #include <linux/rtnetlink.h>
@@ -32,6 +33,7 @@
 #include <stdlib.h>
 #include <sys/resource.h>
 #include <sys/socket.h>
+#include <sys/stat.h>
 #include <sys/types.h>
 #include <unistd.h>
 
@@ -96,7 +98,8 @@ static struct xsk_socket_info *xsk_configure(int ifindex, int xdp_queue_id,
                                              enum afxdp_mode mode,
                                              bool use_need_wakeup,
                                              bool report_socket_failures);
-static void xsk_remove_xdp_program(uint32_t ifindex, enum afxdp_mode);
+static void xsk_remove_xdp_program(uint32_t ifindex, enum afxdp_mode,
+                                   struct bpf_object *obj);
 static void xsk_destroy(struct xsk_socket_info *xsk);
 static int xsk_configure_all(struct netdev *netdev);
 static void xsk_destroy_all(struct netdev *netdev);
@@ -258,6 +261,49 @@ netdev_afxdp_sweep_unused_pools(void *aux OVS_UNUSED)
     ovs_mutex_unlock(&unused_pools_mutex);
 }
 
+static int
+xsk_load_prog(struct netdev *netdev, const char *path, struct bpf_object **pobj,
+              int *prog_fd)
+{
+    struct bpf_object_open_attr attr = {
+        .prog_type = BPF_PROG_TYPE_XDP,
+        .file = path,
+    };
+    struct bpf_program *prog;
+    struct bpf_object *obj;
+
+    obj = bpf_object__open_xattr(&attr);
+    if (libbpf_get_error(obj)) {
+        VLOG_ERR("%s: Can't open XDP program at '%s'",
+                 netdev_get_name(netdev), path);
+        return EINVAL;
+    }
+
+    prog = bpf_program__next(NULL, obj);
+    if (!prog) {
+        VLOG_ERR("%s: '%s' does not contain bpf program",
+                 netdev_get_name(netdev), path);
+        return EINVAL;
+    }
+
+    if (bpf_program__get_type(prog) != BPF_PROG_TYPE_XDP) {
+        VLOG_ERR("%s: First program in '%s' is not XDP type",
+                 netdev_get_name(netdev), path);
+        return EINVAL;
+    }
+
+    if (bpf_object__load(obj)) {
+        VLOG_ERR("%s: Can't load XDP program at '%s'",
+                 netdev_get_name(netdev), path);
+        return EINVAL;
+    }
+
+    *pobj = obj;
+    *prog_fd = bpf_program__fd(prog);
+
+    return 0;
+}
+
 static struct xsk_umem_info *
 xsk_configure_umem(void *buffer, uint64_t size)
 {
@@ -474,6 +520,47 @@ xsk_configure_queue(struct netdev_linux *dev, int ifindex, int queue_id,
     return 0;
 }
 
+static int
+xsk_configure_prog(struct netdev *netdev, int ifindex)
+{
+    struct netdev_linux *dev = netdev_linux_cast(netdev);
+    struct bpf_object *obj;
+    uint32_t prog_id = 0;
+    uint32_t flags;
+    int prog_fd = 0;
+    int mode;
+    int ret;
+
+    mode = dev->xdp_mode_in_use;
+    flags = xdp_modes[mode].xdp_flags | XDP_FLAGS_UPDATE_IF_NOEXIST;
+
+    ret = xsk_load_prog(netdev, dev->xdp_obj_path, &obj, &prog_fd);
+    if (ret) {
+        goto err;
+    }
+    dev->xdp_obj = obj;
+
+    bpf_set_link_xdp_fd(ifindex, prog_fd, flags);
+    ret = bpf_get_link_xdp_id(ifindex, &prog_id, flags);
+    if (ret < 0) {
+        VLOG_ERR("%s: Cannot get XDP prog id.",
+                 netdev_get_name(netdev));
+        goto err;
+    }
+
+    if (!bpf_object__find_map_by_name(obj, "xsks_map")) {
+        VLOG_ERR("%s: Cannot find \"xsks_map\".",
+                 netdev_get_name(netdev));
+        goto err;
+    }
+
+    VLOG_INFO("%s: Loaded custom XDP program at %s prog_id %d.",
+              netdev_get_name(netdev), dev->xdp_obj_path, prog_id);
+    return 0;
+
+err:
+    return ret;
+}
 
 static int
 xsk_configure_all(struct netdev *netdev)
@@ -510,6 +597,13 @@ xsk_configure_all(struct netdev *netdev)
         qid++;
     } else {
         dev->xdp_mode_in_use = dev->xdp_mode;
+        if (dev->xdp_obj_path) {
+            /* XDP program is per-netdev, so all queues share
+             * the same XDP program. */
+            if (xsk_configure_prog(netdev, ifindex)) {
+                goto err;
+            }
+        }
     }
 
     /* Configure remaining queues. */
@@ -584,7 +678,10 @@ xsk_destroy_all(struct netdev *netdev)
 
     VLOG_INFO("%s: Removing xdp program.", netdev_get_name(netdev));
     ifindex = linux_get_ifindex(netdev_get_name(netdev));
-    xsk_remove_xdp_program(ifindex, dev->xdp_mode_in_use);
+    xsk_remove_xdp_program(ifindex, dev->xdp_mode_in_use, dev->xdp_obj);
+    dev->xdp_obj = NULL;
+    free(CONST_CAST(char *, dev->xdp_obj_path));
+    dev->xdp_obj_path = NULL;
 
     if (dev->tx_locks) {
         for (i = 0; i < netdev_n_txq(netdev); i++) {
@@ -601,9 +698,11 @@ netdev_afxdp_set_config(struct netdev *netdev, const struct smap *args,
 {
     struct netdev_linux *dev = netdev_linux_cast(netdev);
     const char *str_xdp_mode;
+    const char *str_xdp_obj;
     enum afxdp_mode xdp_mode;
     bool need_wakeup;
     int new_n_rxq;
+    struct stat s;
 
     ovs_mutex_lock(&dev->mutex);
     new_n_rxq = MAX(smap_get_int(args, "n_rxq", NR_QUEUE), 1);
@@ -637,12 +736,34 @@ netdev_afxdp_set_config(struct netdev *netdev, const struct smap *args,
     }
 #endif
 
+    str_xdp_obj = smap_get_def(args, "xdp-obj", NULL);
+    if (str_xdp_obj) {
+        if (stat(str_xdp_obj, &s)) {
+            ovs_mutex_unlock(&dev->mutex);
+            VLOG_ERR("Invalid xdp-obj '%s': %s.", str_xdp_obj,
+                     ovs_strerror(errno));
+            return EINVAL;
+        } else if (!S_ISREG(s.st_mode)) {
+            ovs_mutex_unlock(&dev->mutex);
+            VLOG_ERR("xdp-obj '%s' is not a regular file.", str_xdp_obj);
+            return EINVAL;
+        }
+    }
+
+    if (str_xdp_obj && xdp_mode == OVS_AF_XDP_MODE_BEST_EFFORT) {
+        ovs_mutex_unlock(&dev->mutex);
+        VLOG_ERR("best-effort mode and xdp-obj can't be set together");
+        return EINVAL;
+    }
+
     if (dev->requested_n_rxq != new_n_rxq
         || dev->requested_xdp_mode != xdp_mode
-        || dev->requested_need_wakeup != need_wakeup) {
+        || dev->requested_need_wakeup != need_wakeup
+        || !nullable_string_is_equal(dev->requested_xdp_obj, str_xdp_obj)) {
         dev->requested_n_rxq = new_n_rxq;
         dev->requested_xdp_mode = xdp_mode;
         dev->requested_need_wakeup = need_wakeup;
+        dev->requested_xdp_obj = nullable_xstrdup(str_xdp_obj);
         netdev_request_reconfigure(netdev);
     }
     ovs_mutex_unlock(&dev->mutex);
@@ -661,6 +782,8 @@ netdev_afxdp_get_config(const struct netdev *netdev, struct smap *args)
                     xdp_modes[dev->xdp_mode_in_use].name);
     smap_add_format(args, "use-need-wakeup", "%s",
                     dev->use_need_wakeup ? "true" : "false");
+    smap_add_format(args, "xdp-obj", "%s",
+                    dev->xdp_obj_path ? dev->xdp_obj_path : "builtin");
     ovs_mutex_unlock(&dev->mutex);
     return 0;
 }
@@ -696,7 +819,8 @@ netdev_afxdp_reconfigure(struct netdev *netdev)
     if (netdev->n_rxq == dev->requested_n_rxq
         && dev->xdp_mode == dev->requested_xdp_mode
         && dev->use_need_wakeup == dev->requested_need_wakeup
-        && dev->xsks) {
+        && dev->xsks
+        && nullable_string_is_equal(dev->xdp_obj_path, dev->requested_xdp_obj)) {
         goto out;
     }
 
@@ -714,6 +838,8 @@ netdev_afxdp_reconfigure(struct netdev *netdev)
     }
     dev->use_need_wakeup = dev->requested_need_wakeup;
 
+    dev->xdp_obj_path = dev->requested_xdp_obj;
+
     err = xsk_configure_all(netdev);
     if (err) {
         VLOG_ERR("%s: AF_XDP device reconfiguration failed.",
@@ -736,7 +862,8 @@ out:
 }
 
 static void
-xsk_remove_xdp_program(uint32_t ifindex, enum afxdp_mode mode)
+xsk_remove_xdp_program(uint32_t ifindex, enum afxdp_mode mode,
+                       struct bpf_object *obj)
 {
     uint32_t flags = xdp_modes[mode].xdp_flags | XDP_FLAGS_UPDATE_IF_NOEXIST;
     uint32_t ret, prog_id = 0;
@@ -753,7 +880,15 @@ xsk_remove_xdp_program(uint32_t ifindex, enum afxdp_mode mode)
         return;
     }
 
-    bpf_set_link_xdp_fd(ifindex, -1, flags);
+    ret = bpf_set_link_xdp_fd(ifindex, -1, flags);
+    if (ret) {
+        VLOG_ERR("Failed to unload prog ID: %d", prog_id);
+    }
+
+    /* Note: bpf_object__close() can handle NULL obj */
+    bpf_object__close(obj);
+
+    VLOG_INFO("Removed XDP program ID: %d", prog_id);
 }
 
 void
@@ -765,7 +900,7 @@ signal_remove_xdp(struct netdev *netdev)
     ifindex = linux_get_ifindex(netdev_get_name(netdev));
 
     VLOG_WARN("Force removing xdp program.");
-    xsk_remove_xdp_program(ifindex, dev->xdp_mode_in_use);
+    xsk_remove_xdp_program(ifindex, dev->xdp_mode_in_use, dev->xdp_obj);
 }
 
 static struct dp_packet_afxdp *
@@ -1179,10 +1314,12 @@ netdev_afxdp_construct(struct netdev *netdev)
     netdev->n_txq = 0;
     dev->xdp_mode = OVS_AF_XDP_MODE_UNSPEC;
     dev->xdp_mode_in_use = OVS_AF_XDP_MODE_UNSPEC;
+    dev->xdp_obj_path = NULL;
 
     dev->requested_n_rxq = NR_QUEUE;
     dev->requested_xdp_mode = OVS_AF_XDP_MODE_BEST_EFFORT;
     dev->requested_need_wakeup = NEED_WAKEUP_DEFAULT;
+    dev->requested_xdp_obj = NULL;
 
     dev->xsks = NULL;
     dev->tx_locks = NULL;
diff --git a/lib/netdev-linux-private.h b/lib/netdev-linux-private.h
index c7c515f70..0f8823c45 100644
--- a/lib/netdev-linux-private.h
+++ b/lib/netdev-linux-private.h
@@ -118,6 +118,9 @@ struct netdev_linux {
     bool requested_need_wakeup;
 
     struct netdev_afxdp_tx_lock *tx_locks;  /* Array of locks for TX queues. */
+    const char *xdp_obj_path;         /* XDP object file path. */
+    const char *requested_xdp_obj;
+    struct bpf_object *xdp_obj;
 #endif
 };
 
-- 
2.24.1



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