[PATCH bpf-next v4 0/4] XDP: Support atomic replacement of XDP interface attachments

[PATCH bpf-next v4 0/4] XDP: Support atomic replacement of XDP interface attachments

[Toke Høiland-Jørgensen]

This series adds support for atomically replacing the XDP program loaded on an
interface. This is achieved by means of a new netlink attribute that can specify
the expected previous program to replace on the interface. If set, the kernel
will compare this "expected id" attribute with the program currently loaded on
the interface, and reject the operation if it does not match.

With this primitive, userspace applications can avoid stepping on each other's
toes when simultaneously updating the loaded XDP program.

Changelog:

v4:
- Switch back to passing FD instead of ID (Andrii)
- Rename flag to XDP_FLAGS_REPLACE (for consistency with other similar uses)

v3:
- Pass existing ID instead of FD (Jakub)
- Use opts struct for new libbpf function (Andrii)

v2:
- Fix checkpatch nits and add .strict_start_type to netlink policy (Jakub)

---

Toke Høiland-Jørgensen (4):
      xdp: Support specifying expected existing program when attaching XDP
      tools: Add EXPECTED_FD-related definitions in if_link.h
      libbpf: Add function to set link XDP fd while specifying old program
      selftests/bpf: Add tests for attaching XDP programs


 include/linux/netdevice.h                          |  2 +-
 include/uapi/linux/if_link.h                       |  4 +-
 net/core/dev.c                                     | 26 +++++++--
 net/core/rtnetlink.c                               | 14 +++++
 tools/include/uapi/linux/if_link.h                 |  4 +-
 tools/lib/bpf/libbpf.h                             |  8 +++
 tools/lib/bpf/libbpf.map                           |  1 +
 tools/lib/bpf/netlink.c                            | 34 +++++++++++-
 .../testing/selftests/bpf/prog_tests/xdp_attach.c  | 62 ++++++++++++++++++++++
 9 files changed, 146 insertions(+), 9 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/xdp_attach.c

[PATCH bpf-next v4 1/4] xdp: Support specifying expected existing program when attaching XDP

[Toke Høiland-Jørgensen]

From: Toke Høiland-Jørgensen <toke@redhat.com>

While it is currently possible for userspace to specify that an existing
XDP program should not be replaced when attaching to an interface, there is
no mechanism to safely replace a specific XDP program with another.

This patch adds a new netlink attribute, IFLA_XDP_EXPECTED_FD, which can be
set along with IFLA_XDP_FD. If set, the kernel will check that the program
currently loaded on the interface matches the expected one, and fail the
operation if it does not. This corresponds to a 'cmpxchg' memory operation.
Setting the new attribute with a negative value means that no program is
expected to be attached, which corresponds to setting the UPDATE_IF_NOEXIST
flag.

A new companion flag, XDP_FLAGS_REPLACE, is also added to explicitly
request checking of the EXPECTED_FD attribute. This is needed for userspace
to discover whether the kernel supports the new attribute.

Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
---
 include/linux/netdevice.h    |    2 +-
 include/uapi/linux/if_link.h |    4 +++-
 net/core/dev.c               |   26 +++++++++++++++++++++-----
 net/core/rtnetlink.c         |   14 ++++++++++++++
 4 files changed, 39 insertions(+), 7 deletions(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 654808bfad83..b503d468f0df 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -3768,7 +3768,7 @@ struct sk_buff *dev_hard_start_xmit(struct sk_buff *skb, struct net_device *dev,
 
 typedef int (*bpf_op_t)(struct net_device *dev, struct netdev_bpf *bpf);
 int dev_change_xdp_fd(struct net_device *dev, struct netlink_ext_ack *extack,
-		      int fd, u32 flags);
+		      int fd, int expected_fd, u32 flags);
 u32 __dev_xdp_query(struct net_device *dev, bpf_op_t xdp_op,
 		    enum bpf_netdev_command cmd);
 int xdp_umem_query(struct net_device *dev, u16 queue_id);
diff --git a/include/uapi/linux/if_link.h b/include/uapi/linux/if_link.h
index 61e0801c82df..c2f768c8d65b 100644
--- a/include/uapi/linux/if_link.h
+++ b/include/uapi/linux/if_link.h
@@ -972,11 +972,12 @@ enum {
 #define XDP_FLAGS_SKB_MODE		(1U << 1)
 #define XDP_FLAGS_DRV_MODE		(1U << 2)
 #define XDP_FLAGS_HW_MODE		(1U << 3)
+#define XDP_FLAGS_REPLACE		(1U << 4)
 #define XDP_FLAGS_MODES			(XDP_FLAGS_SKB_MODE | \
 					 XDP_FLAGS_DRV_MODE | \
 					 XDP_FLAGS_HW_MODE)
 #define XDP_FLAGS_MASK			(XDP_FLAGS_UPDATE_IF_NOEXIST | \
-					 XDP_FLAGS_MODES)
+					 XDP_FLAGS_MODES | XDP_FLAGS_REPLACE)
 
 /* These are stored into IFLA_XDP_ATTACHED on dump. */
 enum {
@@ -996,6 +997,7 @@ enum {
 	IFLA_XDP_DRV_PROG_ID,
 	IFLA_XDP_SKB_PROG_ID,
 	IFLA_XDP_HW_PROG_ID,
+	IFLA_XDP_EXPECTED_FD,
 	__IFLA_XDP_MAX,
 };
 
diff --git a/net/core/dev.c b/net/core/dev.c
index d84541c24446..651a3c28d33a 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -8655,15 +8655,17 @@ static void dev_xdp_uninstall(struct net_device *dev)
  *	@dev: device
  *	@extack: netlink extended ack
  *	@fd: new program fd or negative value to clear
+ *	@expected_fd: old program fd that userspace expects to replace or clear
  *	@flags: xdp-related flags
  *
  *	Set or clear a bpf program for a device
  */
 int dev_change_xdp_fd(struct net_device *dev, struct netlink_ext_ack *extack,
-		      int fd, u32 flags)
+		      int fd, int expected_fd, u32 flags)
 {
 	const struct net_device_ops *ops = dev->netdev_ops;
 	enum bpf_netdev_command query;
+	u32 prog_id, expected_id = 0;
 	struct bpf_prog *prog = NULL;
 	bpf_op_t bpf_op, bpf_chk;
 	bool offload;
@@ -8684,15 +8686,29 @@ int dev_change_xdp_fd(struct net_device *dev, struct netlink_ext_ack *extack,
 	if (bpf_op == bpf_chk)
 		bpf_chk = generic_xdp_install;
 
-	if (fd >= 0) {
-		u32 prog_id;
+	prog_id = __dev_xdp_query(dev, bpf_op, query);
+	if (flags & XDP_FLAGS_REPLACE) {
+		if (expected_fd >= 0) {
+			prog = bpf_prog_get_type_dev(expected_fd,
+						     BPF_PROG_TYPE_XDP,
+						     bpf_op == ops->ndo_bpf);
+			if (IS_ERR(prog))
+				return PTR_ERR(prog);
+			expected_id = prog->aux->id;
+			bpf_prog_put(prog);
+		}
 
+		if (prog_id != expected_id) {
+			NL_SET_ERR_MSG(extack, "Active program does not match expected");
+			return -EEXIST;
+		}
+	}
+	if (fd >= 0) {
 		if (!offload && __dev_xdp_query(dev, bpf_chk, XDP_QUERY_PROG)) {
 			NL_SET_ERR_MSG(extack, "native and generic XDP can't be active at the same time");
 			return -EEXIST;
 		}
 
-		prog_id = __dev_xdp_query(dev, bpf_op, query);
 		if ((flags & XDP_FLAGS_UPDATE_IF_NOEXIST) && prog_id) {
 			NL_SET_ERR_MSG(extack, "XDP program already attached");
 			return -EBUSY;
@@ -8715,7 +8731,7 @@ int dev_change_xdp_fd(struct net_device *dev, struct netlink_ext_ack *extack,
 			return 0;
 		}
 	} else {
-		if (!__dev_xdp_query(dev, bpf_op, query))
+		if (!prog_id)
 			return 0;
 	}
 
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 14e6ea21c378..709ebbf8ab5b 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -1872,7 +1872,9 @@ static const struct nla_policy ifla_port_policy[IFLA_PORT_MAX+1] = {
 };
 
 static const struct nla_policy ifla_xdp_policy[IFLA_XDP_MAX + 1] = {
+	[IFLA_XDP_UNSPEC]	= { .strict_start_type = IFLA_XDP_EXPECTED_FD },
 	[IFLA_XDP_FD]		= { .type = NLA_S32 },
+	[IFLA_XDP_EXPECTED_FD]	= { .type = NLA_S32 },
 	[IFLA_XDP_ATTACHED]	= { .type = NLA_U8 },
 	[IFLA_XDP_FLAGS]	= { .type = NLA_U32 },
 	[IFLA_XDP_PROG_ID]	= { .type = NLA_U32 },
@@ -2799,8 +2801,20 @@ static int do_setlink(const struct sk_buff *skb,
 		}
 
 		if (xdp[IFLA_XDP_FD]) {
+			int expected_fd = -1;
+
+			if (xdp_flags & XDP_FLAGS_REPLACE) {
+				if (!xdp[IFLA_XDP_EXPECTED_FD]) {
+					err = -EINVAL;
+					goto errout;
+				}
+				expected_fd =
+					nla_get_s32(xdp[IFLA_XDP_EXPECTED_FD]);
+			}
+
 			err = dev_change_xdp_fd(dev, extack,
 						nla_get_s32(xdp[IFLA_XDP_FD]),
+						expected_fd,
 						xdp_flags);
 			if (err)
 				goto errout;

[PATCH bpf-next v4 2/4] tools: Add EXPECTED_FD-related definitions in if_link.h

[Toke Høiland-Jørgensen]

From: Toke Høiland-Jørgensen <toke@redhat.com>

This adds the IFLA_XDP_EXPECTED_FD netlink attribute definition and the
XDP_FLAGS_REPLACE flag to if_link.h in tools/include.

Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
---
 tools/include/uapi/linux/if_link.h |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tools/include/uapi/linux/if_link.h b/tools/include/uapi/linux/if_link.h
index 024af2d1d0af..b1ec7c949e6a 100644
--- a/tools/include/uapi/linux/if_link.h
+++ b/tools/include/uapi/linux/if_link.h
@@ -960,11 +960,12 @@ enum {
 #define XDP_FLAGS_SKB_MODE		(1U << 1)
 #define XDP_FLAGS_DRV_MODE		(1U << 2)
 #define XDP_FLAGS_HW_MODE		(1U << 3)
+#define XDP_FLAGS_REPLACE		(1U << 4)
 #define XDP_FLAGS_MODES			(XDP_FLAGS_SKB_MODE | \
 					 XDP_FLAGS_DRV_MODE | \
 					 XDP_FLAGS_HW_MODE)
 #define XDP_FLAGS_MASK			(XDP_FLAGS_UPDATE_IF_NOEXIST | \
-					 XDP_FLAGS_MODES)
+					 XDP_FLAGS_MODES | XDP_FLAGS_REPLACE)
 
 /* These are stored into IFLA_XDP_ATTACHED on dump. */
 enum {
@@ -984,6 +985,7 @@ enum {
 	IFLA_XDP_DRV_PROG_ID,
 	IFLA_XDP_SKB_PROG_ID,
 	IFLA_XDP_HW_PROG_ID,
+	IFLA_XDP_EXPECTED_FD,
 	__IFLA_XDP_MAX,
 };
 

[PATCH bpf-next v4 3/4] libbpf: Add function to set link XDP fd while specifying old program

[Toke Høiland-Jørgensen]

From: Toke Høiland-Jørgensen <toke@redhat.com>

This adds a new function to set the XDP fd while specifying the FD of the
program to replace, using the newly added IFLA_XDP_EXPECTED_FD netlink
parameter. The new function uses the opts struct mechanism to be extendable
in the future.

Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
---
 tools/lib/bpf/libbpf.h   |    8 ++++++++
 tools/lib/bpf/libbpf.map |    1 +
 tools/lib/bpf/netlink.c  |   34 +++++++++++++++++++++++++++++++++-
 3 files changed, 42 insertions(+), 1 deletion(-)

diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index d38d7a629417..bf7a35a9556d 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -444,7 +444,15 @@ struct xdp_link_info {
 	__u8 attach_mode;
 };
 
+struct bpf_xdp_set_link_opts {
+	size_t sz;
+	__u32 old_fd;
+};
+#define bpf_xdp_set_link_opts__last_field old_fd
+
 LIBBPF_API int bpf_set_link_xdp_fd(int ifindex, int fd, __u32 flags);
+LIBBPF_API int bpf_set_link_xdp_fd_opts(int ifindex, int fd, __u32 flags,
+					const struct bpf_xdp_set_link_opts *opts);
 LIBBPF_API int bpf_get_link_xdp_id(int ifindex, __u32 *prog_id, __u32 flags);
 LIBBPF_API int bpf_get_link_xdp_info(int ifindex, struct xdp_link_info *info,
 				     size_t info_size, __u32 flags);
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 5129283c0284..dcc87db3ca8a 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -244,4 +244,5 @@ LIBBPF_0.0.8 {
 		bpf_link__pin_path;
 		bpf_link__unpin;
 		bpf_program__set_attach_target;
+		bpf_set_link_xdp_fd_opts;
 } LIBBPF_0.0.7;
diff --git a/tools/lib/bpf/netlink.c b/tools/lib/bpf/netlink.c
index 431bd25c6cdb..18b5319025e1 100644
--- a/tools/lib/bpf/netlink.c
+++ b/tools/lib/bpf/netlink.c
@@ -132,7 +132,8 @@ static int bpf_netlink_recv(int sock, __u32 nl_pid, int seq,
 	return ret;
 }
 
-int bpf_set_link_xdp_fd(int ifindex, int fd, __u32 flags)
+static int __bpf_set_link_xdp_fd_replace(int ifindex, int fd, int old_fd,
+					 __u32 flags)
 {
 	int sock, seq = 0, ret;
 	struct nlattr *nla, *nla_xdp;
@@ -178,6 +179,14 @@ int bpf_set_link_xdp_fd(int ifindex, int fd, __u32 flags)
 		nla->nla_len += nla_xdp->nla_len;
 	}
 
+	if (flags & XDP_FLAGS_REPLACE) {
+		nla_xdp = (struct nlattr *)((char *)nla + nla->nla_len);
+		nla_xdp->nla_type = IFLA_XDP_EXPECTED_FD;
+		nla_xdp->nla_len = NLA_HDRLEN + sizeof(old_fd);
+		memcpy((char *)nla_xdp + NLA_HDRLEN, &old_fd, sizeof(old_fd));
+		nla->nla_len += nla_xdp->nla_len;
+	}
+
 	req.nh.nlmsg_len += NLA_ALIGN(nla->nla_len);
 
 	if (send(sock, &req, req.nh.nlmsg_len, 0) < 0) {
@@ -191,6 +200,29 @@ int bpf_set_link_xdp_fd(int ifindex, int fd, __u32 flags)
 	return ret;
 }
 
+int bpf_set_link_xdp_fd_opts(int ifindex, int fd, __u32 flags,
+			     const struct bpf_xdp_set_link_opts *opts)
+{
+	int old_fd = -1;
+
+	if (!OPTS_VALID(opts, bpf_xdp_set_link_opts))
+		return -EINVAL;
+
+	if (OPTS_HAS(opts, old_fd)) {
+		old_fd = OPTS_GET(opts, old_fd, -1);
+		flags |= XDP_FLAGS_REPLACE;
+	}
+
+	return __bpf_set_link_xdp_fd_replace(ifindex, fd,
+					     old_fd,
+					     flags);
+}
+
+int bpf_set_link_xdp_fd(int ifindex, int fd, __u32 flags)
+{
+	return __bpf_set_link_xdp_fd_replace(ifindex, fd, 0, flags);
+}
+
 static int __dump_link_nlmsg(struct nlmsghdr *nlh,
 			     libbpf_dump_nlmsg_t dump_link_nlmsg, void *cookie)
 {

[PATCH bpf-next v4 4/4] selftests/bpf: Add tests for attaching XDP programs

[Toke Høiland-Jørgensen]

From: Toke Høiland-Jørgensen <toke@redhat.com>

This adds tests for the various replacement operations using
IFLA_XDP_EXPECTED_FD.

Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
---
 .../testing/selftests/bpf/prog_tests/xdp_attach.c  |   62 ++++++++++++++++++++
 1 file changed, 62 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/xdp_attach.c

diff --git a/tools/testing/selftests/bpf/prog_tests/xdp_attach.c b/tools/testing/selftests/bpf/prog_tests/xdp_attach.c
new file mode 100644
index 000000000000..05b294d6b923
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/xdp_attach.c
@@ -0,0 +1,62 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <test_progs.h>
+
+#define IFINDEX_LO 1
+#define XDP_FLAGS_REPLACE		(1U << 4)
+
+void test_xdp_attach(void)
+{
+	struct bpf_object *obj1, *obj2, *obj3;
+	const char *file = "./test_xdp.o";
+	int err, fd1, fd2, fd3;
+	__u32 duration = 0;
+	DECLARE_LIBBPF_OPTS(bpf_xdp_set_link_opts, opts,
+			    .old_fd = -1);
+
+	err = bpf_prog_load(file, BPF_PROG_TYPE_XDP, &obj1, &fd1);
+	if (CHECK_FAIL(err))
+		return;
+	err = bpf_prog_load(file, BPF_PROG_TYPE_XDP, &obj2, &fd2);
+	if (CHECK_FAIL(err))
+		goto out_1;
+	err = bpf_prog_load(file, BPF_PROG_TYPE_XDP, &obj3, &fd3);
+	if (CHECK_FAIL(err))
+		goto out_2;
+
+	err = bpf_set_link_xdp_fd_opts(IFINDEX_LO, fd1, XDP_FLAGS_REPLACE,
+				       &opts);
+	if (CHECK(err, "load_ok", "initial load failed"))
+		goto out_close;
+
+	err = bpf_set_link_xdp_fd_opts(IFINDEX_LO, fd2, XDP_FLAGS_REPLACE,
+				       &opts);
+	if (CHECK(!err, "load_fail", "load with expected id didn't fail"))
+		goto out;
+
+	opts.old_fd = fd1;
+	err = bpf_set_link_xdp_fd_opts(IFINDEX_LO, fd2, 0, &opts);
+	if (CHECK(err, "replace_ok", "replace valid old_fd failed"))
+		goto out;
+
+	err = bpf_set_link_xdp_fd_opts(IFINDEX_LO, fd3, 0, &opts);
+	if (CHECK(!err, "replace_fail", "replace invalid old_fd didn't fail"))
+		goto out;
+
+	err = bpf_set_link_xdp_fd_opts(IFINDEX_LO, -1, 0, &opts);
+	if (CHECK(!err, "remove_fail", "remove invalid old_fd didn't fail"))
+		goto out;
+
+	opts.old_fd = fd2;
+	err = bpf_set_link_xdp_fd_opts(IFINDEX_LO, -1, 0, &opts);
+	if (CHECK(err, "remove_ok", "remove valid old_fd failed"))
+		goto out;
+
+out:
+	bpf_set_link_xdp_fd(IFINDEX_LO, -1, 0);
+out_close:
+	bpf_object__close(obj3);
+out_2:
+	bpf_object__close(obj2);
+out_1:
+	bpf_object__close(obj1);
+}

Re: [PATCH bpf-next v4 0/4] XDP: Support atomic replacement of XDP interface attachments

[Alexei Starovoitov]

On Wed, Mar 25, 2020 at 06:23:25PM +0100, Toke Høiland-Jørgensen wrote:
> This series adds support for atomically replacing the XDP program loaded on an
> interface. This is achieved by means of a new netlink attribute that can specify
> the expected previous program to replace on the interface. If set, the kernel
> will compare this "expected id" attribute with the program currently loaded on
> the interface, and reject the operation if it does not match.
> 
> With this primitive, userspace applications can avoid stepping on each other's
> toes when simultaneously updating the loaded XDP program.
> 
> Changelog:
> 
> v4:
> - Switch back to passing FD instead of ID (Andrii)
> - Rename flag to XDP_FLAGS_REPLACE (for consistency with other similar uses)

please stop resending the set without concluding the previous three! discussion threads.
It's already hard enough for people to follow.