Merge branch 'bpf_link-XDP'

Andrii Nakryiko says:

====================
Following cgroup and netns examples, implement bpf_link support for XDP.

The semantics is described in patch #2. Program and link attachments are
mutually exclusive, in the sense that neither link can replace attached
program nor program can replace attached link. Link can't replace attached
link as well, as is the case for any other bpf_link implementation.

Patch #1 refactors existing BPF program-based attachment API and centralizes
high-level query/attach decisions in generic kernel code, while drivers are
kept simple and are instructed with low-level decisions about attaching and
detaching specific bpf_prog. This also makes QUERY command unnecessary, and
patch #8 removes support for it from all kernel drivers. If that's a bad idea,
we can drop that patch altogether.

With refactoring in patch #1, adding bpf_xdp_link is completely transparent to
drivers, they are still functioning at the level of "effective" bpf_prog, that
should be called in XDP data path.

Corresponding libbpf support for BPF XDP link is added in patch #5.

v3->v4:
- fix a compilation warning in one of drivers (Jakub);

v2->v3:
- fix build when CONFIG_BPF_SYSCALL=n (kernel test robot);

v1->v2:
- fix prog refcounting bug (David);
- split dev_change_xdp_fd() changes into 2 patches (David);
- add extack messages to all user-induced errors (David).
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

7 files changed, 170 insertions, 3 deletions

diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 828c2f6438f2..e1ba4ae6a916 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -230,6 +230,7 @@ enum bpf_attach_type {
 	BPF_CGROUP_INET_SOCK_RELEASE,
 	BPF_XDP_CPUMAP,
 	BPF_SK_LOOKUP,
+	BPF_XDP,
 	__MAX_BPF_ATTACH_TYPE
 };
 
@@ -242,6 +243,7 @@ enum bpf_link_type {
 	BPF_LINK_TYPE_CGROUP = 3,
 	BPF_LINK_TYPE_ITER = 4,
 	BPF_LINK_TYPE_NETNS = 5,
+	BPF_LINK_TYPE_XDP = 6,
 
 	MAX_BPF_LINK_TYPE,
 };
@@ -614,7 +616,10 @@ union bpf_attr {
 
 	struct { /* struct used by BPF_LINK_CREATE command */
 		__u32		prog_fd;	/* eBPF program to attach */
-		__u32		target_fd;	/* object to attach to */
+		union {
+			__u32		target_fd;	/* object to attach to */
+			__u32		target_ifindex; /* target ifindex */
+		};
 		__u32		attach_type;	/* attach type */
 		__u32		flags;		/* extra flags */
 	} link_create;
@@ -4064,6 +4069,9 @@ struct bpf_link_info {
 			__u32 netns_ino;
 			__u32 attach_type;
 		} netns;
+		struct {
+			__u32 ifindex;
+		} xdp;
 	};
 } __attribute__((aligned(8)));
 
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index e51479d60285..54830d603fee 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -6915,7 +6915,8 @@ static const struct bpf_sec_def section_defs[] = {
 						BPF_XDP_DEVMAP),
 	BPF_EAPROG_SEC("xdp_cpumap/",		BPF_PROG_TYPE_XDP,
 						BPF_XDP_CPUMAP),
-	BPF_PROG_SEC("xdp",			BPF_PROG_TYPE_XDP),
+	BPF_EAPROG_SEC("xdp",			BPF_PROG_TYPE_XDP,
+						BPF_XDP),
 	BPF_PROG_SEC("perf_event",		BPF_PROG_TYPE_PERF_EVENT),
 	BPF_PROG_SEC("lwt_in",			BPF_PROG_TYPE_LWT_IN),
 	BPF_PROG_SEC("lwt_out",			BPF_PROG_TYPE_LWT_OUT),
@@ -8281,6 +8282,12 @@ bpf_program__attach_netns(struct bpf_program *prog, int netns_fd)
 	return bpf_program__attach_fd(prog, netns_fd, "netns");
 }
 
+struct bpf_link *bpf_program__attach_xdp(struct bpf_program *prog, int ifindex)
+{
+	/* target_fd/target_ifindex use the same field in LINK_CREATE */
+	return bpf_program__attach_fd(prog, ifindex, "xdp");
+}
+
 struct bpf_link *
 bpf_program__attach_iter(struct bpf_program *prog,
 			 const struct bpf_iter_attach_opts *opts)
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index c6813791fa7e..9924385462ab 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -257,6 +257,8 @@ LIBBPF_API struct bpf_link *
 bpf_program__attach_cgroup(struct bpf_program *prog, int cgroup_fd);
 LIBBPF_API struct bpf_link *
 bpf_program__attach_netns(struct bpf_program *prog, int netns_fd);
+LIBBPF_API struct bpf_link *
+bpf_program__attach_xdp(struct bpf_program *prog, int ifindex);
 
 struct bpf_map;
 
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 6f0856abe299..ca49a6a7e5b2 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -286,6 +286,7 @@ LIBBPF_0.1.0 {
 		bpf_map__set_value_size;
 		bpf_map__type;
 		bpf_map__value_size;
+		bpf_program__attach_xdp;
 		bpf_program__autoload;
 		bpf_program__is_sk_lookup;
 		bpf_program__set_autoload;
diff --git a/tools/testing/selftests/bpf/prog_tests/section_names.c b/tools/testing/selftests/bpf/prog_tests/section_names.c
index 713167449c98..8b571890c57e 100644
--- a/tools/testing/selftests/bpf/prog_tests/section_names.c
+++ b/tools/testing/selftests/bpf/prog_tests/section_names.c
@@ -35,7 +35,7 @@ static struct sec_name_test tests[] = {
 		{-EINVAL, 0},
 	},
 	{"raw_tp/", {0, BPF_PROG_TYPE_RAW_TRACEPOINT, 0}, {-EINVAL, 0} },
-	{"xdp", {0, BPF_PROG_TYPE_XDP, 0}, {-EINVAL, 0} },
+	{"xdp", {0, BPF_PROG_TYPE_XDP, BPF_XDP}, {0, BPF_XDP} },
 	{"perf_event", {0, BPF_PROG_TYPE_PERF_EVENT, 0}, {-EINVAL, 0} },
 	{"lwt_in", {0, BPF_PROG_TYPE_LWT_IN, 0}, {-EINVAL, 0} },
 	{"lwt_out", {0, BPF_PROG_TYPE_LWT_OUT, 0}, {-EINVAL, 0} },
diff --git a/tools/testing/selftests/bpf/prog_tests/xdp_link.c b/tools/testing/selftests/bpf/prog_tests/xdp_link.c
new file mode 100644
index 000000000000..52cba6795d40
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/xdp_link.c
@@ -0,0 +1,137 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020 Facebook */
+#include <uapi/linux/if_link.h>
+#include <test_progs.h>
+#include "test_xdp_link.skel.h"
+
+#define IFINDEX_LO 1
+
+void test_xdp_link(void)
+{
+	__u32 duration = 0, id1, id2, id0 = 0, prog_fd1, prog_fd2, err;
+	DECLARE_LIBBPF_OPTS(bpf_xdp_set_link_opts, opts, .old_fd = -1);
+	struct test_xdp_link *skel1 = NULL, *skel2 = NULL;
+	struct bpf_link_info link_info;
+	struct bpf_prog_info prog_info;
+	struct bpf_link *link;
+	__u32 link_info_len = sizeof(link_info);
+	__u32 prog_info_len = sizeof(prog_info);
+
+	skel1 = test_xdp_link__open_and_load();
+	if (CHECK(!skel1, "skel_load", "skeleton open and load failed\n"))
+		goto cleanup;
+	prog_fd1 = bpf_program__fd(skel1->progs.xdp_handler);
+
+	skel2 = test_xdp_link__open_and_load();
+	if (CHECK(!skel2, "skel_load", "skeleton open and load failed\n"))
+		goto cleanup;
+	prog_fd2 = bpf_program__fd(skel2->progs.xdp_handler);
+
+	memset(&prog_info, 0, sizeof(prog_info));
+	err = bpf_obj_get_info_by_fd(prog_fd1, &prog_info, &prog_info_len);
+	if (CHECK(err, "fd_info1", "failed %d\n", -errno))
+		goto cleanup;
+	id1 = prog_info.id;
+
+	memset(&prog_info, 0, sizeof(prog_info));
+	err = bpf_obj_get_info_by_fd(prog_fd2, &prog_info, &prog_info_len);
+	if (CHECK(err, "fd_info2", "failed %d\n", -errno))
+		goto cleanup;
+	id2 = prog_info.id;
+
+	/* set initial prog attachment */
+	err = bpf_set_link_xdp_fd_opts(IFINDEX_LO, prog_fd1, XDP_FLAGS_REPLACE, &opts);
+	if (CHECK(err, "fd_attach", "initial prog attach failed: %d\n", err))
+		goto cleanup;
+
+	/* validate prog ID */
+	err = bpf_get_link_xdp_id(IFINDEX_LO, &id0, 0);
+	CHECK(err || id0 != id1, "id1_check",
+	      "loaded prog id %u != id1 %u, err %d", id0, id1, err);
+
+	/* BPF link is not allowed to replace prog attachment */
+	link = bpf_program__attach_xdp(skel1->progs.xdp_handler, IFINDEX_LO);
+	if (CHECK(!IS_ERR(link), "link_attach_fail", "unexpected success\n")) {
+		bpf_link__destroy(link);
+		/* best-effort detach prog */
+		opts.old_fd = prog_fd1;
+		bpf_set_link_xdp_fd_opts(IFINDEX_LO, -1, XDP_FLAGS_REPLACE, &opts);
+		goto cleanup;
+	}
+
+	/* detach BPF program */
+	opts.old_fd = prog_fd1;
+	err = bpf_set_link_xdp_fd_opts(IFINDEX_LO, -1, XDP_FLAGS_REPLACE, &opts);
+	if (CHECK(err, "prog_detach", "failed %d\n", err))
+		goto cleanup;
+
+	/* now BPF link should attach successfully */
+	link = bpf_program__attach_xdp(skel1->progs.xdp_handler, IFINDEX_LO);
+	if (CHECK(IS_ERR(link), "link_attach", "failed: %ld\n", PTR_ERR(link)))
+		goto cleanup;
+	skel1->links.xdp_handler = link;
+
+	/* validate prog ID */
+	err = bpf_get_link_xdp_id(IFINDEX_LO, &id0, 0);
+	if (CHECK(err || id0 != id1, "id1_check",
+		  "loaded prog id %u != id1 %u, err %d", id0, id1, err))
+		goto cleanup;
+
+	/* BPF prog attach is not allowed to replace BPF link */
+	opts.old_fd = prog_fd1;
+	err = bpf_set_link_xdp_fd_opts(IFINDEX_LO, prog_fd2, XDP_FLAGS_REPLACE, &opts);
+	if (CHECK(!err, "prog_attach_fail", "unexpected success\n"))
+		goto cleanup;
+
+	/* Can't force-update when BPF link is active */
+	err = bpf_set_link_xdp_fd(IFINDEX_LO, prog_fd2, 0);
+	if (CHECK(!err, "prog_update_fail", "unexpected success\n"))
+		goto cleanup;
+
+	/* Can't force-detach when BPF link is active */
+	err = bpf_set_link_xdp_fd(IFINDEX_LO, -1, 0);
+	if (CHECK(!err, "prog_detach_fail", "unexpected success\n"))
+		goto cleanup;
+
+	/* BPF link is not allowed to replace another BPF link */
+	link = bpf_program__attach_xdp(skel2->progs.xdp_handler, IFINDEX_LO);
+	if (CHECK(!IS_ERR(link), "link_attach_fail", "unexpected success\n")) {
+		bpf_link__destroy(link);
+		goto cleanup;
+	}
+
+	bpf_link__destroy(skel1->links.xdp_handler);
+	skel1->links.xdp_handler = NULL;
+
+	/* new link attach should succeed */
+	link = bpf_program__attach_xdp(skel2->progs.xdp_handler, IFINDEX_LO);
+	if (CHECK(IS_ERR(link), "link_attach", "failed: %ld\n", PTR_ERR(link)))
+		goto cleanup;
+	skel2->links.xdp_handler = link;
+
+	err = bpf_get_link_xdp_id(IFINDEX_LO, &id0, 0);
+	if (CHECK(err || id0 != id2, "id2_check",
+		  "loaded prog id %u != id2 %u, err %d", id0, id1, err))
+		goto cleanup;
+
+	/* updating program under active BPF link works as expected */
+	err = bpf_link__update_program(link, skel1->progs.xdp_handler);
+	if (CHECK(err, "link_upd", "failed: %d\n", err))
+		goto cleanup;
+
+	memset(&link_info, 0, sizeof(link_info));
+	err = bpf_obj_get_info_by_fd(bpf_link__fd(link), &link_info, &link_info_len);
+	if (CHECK(err, "link_info", "failed: %d\n", err))
+		goto cleanup;
+
+	CHECK(link_info.type != BPF_LINK_TYPE_XDP, "link_type",
+	      "got %u != exp %u\n", link_info.type, BPF_LINK_TYPE_XDP);
+	CHECK(link_info.prog_id != id1, "link_prog_id",
+	      "got %u != exp %u\n", link_info.prog_id, id1);
+	CHECK(link_info.xdp.ifindex != IFINDEX_LO, "link_ifindex",
+	      "got %u != exp %u\n", link_info.xdp.ifindex, IFINDEX_LO);
+
+cleanup:
+	test_xdp_link__destroy(skel1);
+	test_xdp_link__destroy(skel2);
+}
diff --git a/tools/testing/selftests/bpf/progs/test_xdp_link.c b/tools/testing/selftests/bpf/progs/test_xdp_link.c
new file mode 100644
index 000000000000..eb93ea95d1d8
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_xdp_link.c
@@ -0,0 +1,12 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020 Facebook */
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+
+char LICENSE[] SEC("license") = "GPL";
+
+SEC("xdp/handler")
+int xdp_handler(struct xdp_md *xdp)
+{
+	return 0;
+}