[PATCH bpf-next v4 2/2] selftests/bpf: Add testcase for xdp attaching failure tracepoint

Leon Hwang
2023-07-30T11:50:26Z

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>
---
.../selftests/bpf/prog_tests/xdp_attach.c | 65 +++++++++++++++++++
.../bpf/progs/test_xdp_attach_fail.c | 54 +++++++++++++++
2 files changed, 119 insertions(+)
create mode 100644 tools/testing/selftests/bpf/progs/test_xdp_attach_fail.c

diff --git a/tools/testing/selftests/bpf/prog_tests/xdp_attach.c b/tools/testing/selftests/bpf/prog_tests/xdp_attach.c
index fa3cac5488f5d..8c1cde74e9cd6 100644
--- 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 @@ static void test_xdp_attach(const char *file)
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)
+{
+ int err, fd_xdp;
+ struct bpf_object *obj = NULL;
+ struct test_xdp_attach_fail *skel = NULL;
+ struct perf_buffer *pb = NULL;
+ struct xdp_errmsg errmsg = {};
+
+ 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
index 0000000000000..d7149bbd95f75
--- /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)
+{
+ struct xdp_errmsg errmsg;
+ char *msg = (void *)(__u64) ((void *) ctx + (__u16) ctx->msg);
+
+ 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";
--
2.41.0