selftests/bpf: Add testcase for xdp attaching failure tracepoint

Add a test case for the tracepoint of xdp attaching failure by bpf
tracepoint when attach XDP to a device with invalid flags option.

The bpf tracepoint retrieves error message from the tracepoint, and
then put the error message to a perf buffer. The testing code receives
error message from perf buffer, and then ASSERT "Invalid XDP flags for
BPF link attachment".

Signed-off-by: Leon Hwang <hffilwlqm@gmail.com>
Link: https://lore.kernel.org/r/20230801142621.7925-3-hffilwlqm@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/tools/testing/selftests/bpf/prog_tests/xdp_attach.c b/tools/testing/selftests/bpf/prog_tests/xdp_attach.c
index fa3cac5..e6bcb60 100644 (file)
--- a/tools/testing/selftests/bpf/prog_tests/xdp_attach.c
+++ b/tools/testing/selftests/bpf/prog_tests/xdp_attach.c
@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <test_progs.h>
+#include "test_xdp_attach_fail.skel.h"
 
 #define IFINDEX_LO 1
 #define XDP_FLAGS_REPLACE              (1U << 4)
@@ -85,10 +86,74 @@ out_1:
        bpf_object__close(obj1);
 }
 
+#define ERRMSG_LEN 64
+
+struct xdp_errmsg {
+       char msg[ERRMSG_LEN];
+};
+
+static void on_xdp_errmsg(void *ctx, int cpu, void *data, __u32 size)
+{
+       struct xdp_errmsg *ctx_errmg = ctx, *tp_errmsg = data;
+
+       memcpy(&ctx_errmg->msg, &tp_errmsg->msg, ERRMSG_LEN);
+}
+
+static const char tgt_errmsg[] = "Invalid XDP flags for BPF link attachment";
+
+static void test_xdp_attach_fail(const char *file)
+{
+       struct test_xdp_attach_fail *skel = NULL;
+       struct xdp_errmsg errmsg = {};
+       struct perf_buffer *pb = NULL;
+       struct bpf_object *obj = NULL;
+       int err, fd_xdp;
+
+       LIBBPF_OPTS(bpf_link_create_opts, opts);
+
+       skel = test_xdp_attach_fail__open_and_load();
+       if (!ASSERT_OK_PTR(skel, "test_xdp_attach_fail__open_and_load"))
+               goto out_close;
+
+       err = test_xdp_attach_fail__attach(skel);
+       if (!ASSERT_EQ(err, 0, "test_xdp_attach_fail__attach"))
+               goto out_close;
+
+       /* set up perf buffer */
+       pb = perf_buffer__new(bpf_map__fd(skel->maps.xdp_errmsg_pb), 1,
+                             on_xdp_errmsg, NULL, &errmsg, NULL);
+       if (!ASSERT_OK_PTR(pb, "perf_buffer__new"))
+               goto out_close;
+
+       err = bpf_prog_test_load(file, BPF_PROG_TYPE_XDP, &obj, &fd_xdp);
+       if (!ASSERT_EQ(err, 0, "bpf_prog_test_load"))
+               goto out_close;
+
+       opts.flags = 0xFF; // invalid flags to fail to attach XDP prog
+       err = bpf_link_create(fd_xdp, IFINDEX_LO, BPF_XDP, &opts);
+       if (!ASSERT_EQ(err, -EINVAL, "bpf_link_create"))
+               goto out_close;
+
+       /* read perf buffer */
+       err = perf_buffer__poll(pb, 100);
+       if (!ASSERT_GT(err, -1, "perf_buffer__poll"))
+               goto out_close;
+
+       ASSERT_STRNEQ((const char *) errmsg.msg, tgt_errmsg,
+                     42 /* strlen(tgt_errmsg) */, "check error message");
+
+out_close:
+       perf_buffer__free(pb);
+       bpf_object__close(obj);
+       test_xdp_attach_fail__destroy(skel);
+}
+
 void serial_test_xdp_attach(void)
 {
        if (test__start_subtest("xdp_attach"))
                test_xdp_attach("./test_xdp.bpf.o");
        if (test__start_subtest("xdp_attach_dynptr"))
                test_xdp_attach("./test_xdp_dynptr.bpf.o");
+       if (test__start_subtest("xdp_attach_failed"))
+               test_xdp_attach_fail("./xdp_dummy.bpf.o");
 }

diff --git a/tools/testing/selftests/bpf/progs/test_xdp_attach_fail.c b/tools/testing/selftests/bpf/progs/test_xdp_attach_fail.c
new file mode 100644 (file)
index 0000000..2ff1b59
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_xdp_attach_fail.c
@@ -0,0 +1,54 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright Leon Hwang */
+
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+
+#define ERRMSG_LEN 64
+
+struct xdp_errmsg {
+       char msg[ERRMSG_LEN];
+};
+
+struct {
+       __uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY);
+       __type(key, int);
+       __type(value, int);
+} xdp_errmsg_pb SEC(".maps");
+
+struct xdp_attach_error_ctx {
+       unsigned long unused;
+
+       /*
+        * bpf does not support tracepoint __data_loc directly.
+        *
+        * Actually, this field is a 32 bit integer whose value encodes
+        * information on where to find the actual data. The first 2 bytes is
+        * the size of the data. The last 2 bytes is the offset from the start
+        * of the tracepoint struct where the data begins.
+        * -- https://github.com/iovisor/bpftrace/pull/1542
+        */
+       __u32 msg; // __data_loc char[] msg;
+};
+
+/*
+ * Catch the error message at the tracepoint.
+ */
+
+SEC("tp/xdp/bpf_xdp_link_attach_failed")
+int tp__xdp__bpf_xdp_link_attach_failed(struct xdp_attach_error_ctx *ctx)
+{
+       char *msg = (void *)(__u64) ((void *) ctx + (__u16) ctx->msg);
+       struct xdp_errmsg errmsg = {};
+
+       bpf_probe_read_kernel_str(&errmsg.msg, ERRMSG_LEN, msg);
+       bpf_perf_event_output(ctx, &xdp_errmsg_pb, BPF_F_CURRENT_CPU, &errmsg,
+                             ERRMSG_LEN);
+       return 0;
+}
+
+/*
+ * Reuse the XDP program in xdp_dummy.c.
+ */
+
+char LICENSE[] SEC("license") = "GPL";