Re: [PATCH bpf-next v4 3/3] selftests/bpf: Add test for xdp_md context in BPF_PROG_TEST_RUN

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On 6/4/21 3:02 PM, Zvi Effron wrote:
Add a test for using xdp_md as a context to BPF_PROG_TEST_RUN for XDP
programs.

The test uses a BPF program that takes in a return value from XDP
metadata, then reduces the size of the XDP metadata by 4 bytes.

Test cases validate the possible failure cases for passing in invalid
xdp_md contexts, that the return value is successfully passed
in, and that the adjusted metadata is successfully copied out.

Co-developed-by: Cody Haas <chaas@xxxxxxxxxxxxx>
Signed-off-by: Cody Haas <chaas@xxxxxxxxxxxxx>
Co-developed-by: Lisa Watanabe <lwatanabe@xxxxxxxxxxxxx>
Signed-off-by: Lisa Watanabe <lwatanabe@xxxxxxxxxxxxx>
Signed-off-by: Zvi Effron <zeffron@xxxxxxxxxxxxx>
---
  .../bpf/prog_tests/xdp_context_test_run.c     | 114 ++++++++++++++++++
  .../bpf/progs/test_xdp_context_test_run.c     |  20 +++
  2 files changed, 134 insertions(+)
  create mode 100644 tools/testing/selftests/bpf/prog_tests/xdp_context_test_run.c
  create mode 100644 tools/testing/selftests/bpf/progs/test_xdp_context_test_run.c

diff --git a/tools/testing/selftests/bpf/prog_tests/xdp_context_test_run.c b/tools/testing/selftests/bpf/prog_tests/xdp_context_test_run.c
new file mode 100644
index 000000000000..0dbdebbc66ce
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/xdp_context_test_run.c
@@ -0,0 +1,114 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <test_progs.h>
+#include <network_helpers.h>
+#include "test_xdp_context_test_run.skel.h"
+
+void test_xdp_context_test_run(void)
+{
+	struct test_xdp_context_test_run *skel = NULL;
+	char data[sizeof(pkt_v4) + sizeof(__u32)];
+	char buf[128];
+	char bad_ctx[sizeof(struct xdp_md)];
+	struct xdp_md ctx_in, ctx_out;
+	DECLARE_LIBBPF_OPTS(bpf_test_run_opts, opts,
+			    .data_in = &data,
+			    .data_out = buf,
+				.data_size_in = sizeof(data),
+			    .data_size_out = sizeof(buf),
+			    .ctx_out = &ctx_out,
+			    .ctx_size_out = sizeof(ctx_out),
+			    .repeat = 1,
+		);
+	int err, prog_fd;
+
+	skel = test_xdp_context_test_run__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "skel"))
+		return;
+	prog_fd = bpf_program__fd(skel->progs._xdp_context);
+
+	*(__u32 *)data = XDP_PASS;
+	*(struct ipv4_packet *)(data + sizeof(__u32)) = pkt_v4;
+
+	memset(&ctx_in, 0, sizeof(ctx_in));
+	opts.ctx_in = &ctx_in;
+	opts.ctx_size_in = sizeof(ctx_in);
+
+	opts.ctx_in = &ctx_in;
+	opts.ctx_size_in = sizeof(ctx_in);

The above two assignments are redundant.

+	ctx_in.data_meta = 0;
+	ctx_in.data = sizeof(__u32);
+	ctx_in.data_end = ctx_in.data + sizeof(pkt_v4);
+	err = bpf_prog_test_run_opts(prog_fd, &opts);
+	ASSERT_OK(err, "bpf_prog_test_run(test1)");
+	ASSERT_EQ(opts.retval, XDP_PASS, "test1-retval");
+	ASSERT_EQ(opts.data_size_out, sizeof(pkt_v4), "test1-datasize");
+	ASSERT_EQ(opts.ctx_size_out, opts.ctx_size_in, "test1-ctxsize");
+	ASSERT_EQ(ctx_out.data_meta, 0, "test1-datameta");
+	ASSERT_EQ(ctx_out.data, ctx_out.data_meta, "test1-data");

I suggest just to test ctx_out.data == 0. It just happens
the input data - meta = 4 and bpf program adjuested by 4.
If they are not the same, the result won't be equal to data_meta.

+	ASSERT_EQ(ctx_out.data_end, sizeof(pkt_v4), "test1-dataend");
+
+	/* Data past the end of the kernel's struct xdp_md must be 0 */
+	bad_ctx[sizeof(bad_ctx) - 1] = 1;
+	opts.ctx_in = bad_ctx;
+	opts.ctx_size_in = sizeof(bad_ctx);
+	err = bpf_prog_test_run_opts(prog_fd, &opts);
+	ASSERT_EQ(errno, 22, "test2-errno");
+	ASSERT_ERR(err, "bpf_prog_test_run(test2)");

I suggest to drop this test. Basically you did here
is to have non-zero egress_ifindex which is not allowed.
You have a test below.

+
+	/* The egress cannot be specified */
+	ctx_in.egress_ifindex = 1;
+	err = bpf_prog_test_run_opts(prog_fd, &opts);
+	ASSERT_EQ(errno, 22, "test3-errno");

Use EINVAL explicitly? The same for below a few other cases.

+	ASSERT_ERR(err, "bpf_prog_test_run(test3)");
+
+	/* data_meta must reference the start of data */
+	ctx_in.data_meta = sizeof(__u32);
+	ctx_in.data = ctx_in.data_meta;
+	ctx_in.data_end = ctx_in.data + sizeof(pkt_v4);
+	ctx_in.egress_ifindex = 0;
+	err = bpf_prog_test_run_opts(prog_fd, &opts);
+	ASSERT_EQ(errno, 22, "test4-errno");
+	ASSERT_ERR(err, "bpf_prog_test_run(test4)");
+
+	/* Metadata must be 32 bytes or smaller */
+	ctx_in.data_meta = 0;
+	ctx_in.data = sizeof(__u32)*9;
+	ctx_in.data_end = ctx_in.data + sizeof(pkt_v4);
+	err = bpf_prog_test_run_opts(prog_fd, &opts);
+	ASSERT_EQ(errno, 22, "test5-errno");
+	ASSERT_ERR(err, "bpf_prog_test_run(test5)");

This test is not necessary if ctx size should be
<= sizeof(struct xdp_md). So far, I think we can
require it must be sizeof(struct xdp_md). If
in the future, kernel struct xdp_md is extended,
it may be changed to accept both old and new
xdp_md's similar to other uapi data strcture
like struct bpf_prog_info if there is a desire.
In my opinion, the kernel should just stick
to sizeof(struct xdp_md) size since the functionality
is implemented as a *testing* mechanism.

+
+	/* Metadata's size must be a multiple of 4 */
+	ctx_in.data = 3;
+	err = bpf_prog_test_run_opts(prog_fd, &opts);
+	ASSERT_EQ(errno, 22, "test6-errno");
+	ASSERT_ERR(err, "bpf_prog_test_run(test6)");
+
+	/* Total size of data must match data_end - data_meta */
+	ctx_in.data = 0;
+	ctx_in.data_end = sizeof(pkt_v4) - 4;
+	err = bpf_prog_test_run_opts(prog_fd, &opts);
+	ASSERT_EQ(errno, 22, "test7-errno");
+	ASSERT_ERR(err, "bpf_prog_test_run(test7)");
+
+	ctx_in.data_end = sizeof(pkt_v4) + 4;
+	err = bpf_prog_test_run_opts(prog_fd, &opts);
+	ASSERT_EQ(errno, 22, "test8-errno");
+	ASSERT_ERR(err, "bpf_prog_test_run(test8)");
+
+	/* RX queue cannot be specified without specifying an ingress */
+	ctx_in.data_end = sizeof(pkt_v4);
+	ctx_in.ingress_ifindex = 0;
+	ctx_in.rx_queue_index = 1;
+	err = bpf_prog_test_run_opts(prog_fd, &opts);
+	ASSERT_EQ(errno, 22, "test9-errno");
+	ASSERT_ERR(err, "bpf_prog_test_run(test9)");
+
+	ctx_in.ingress_ifindex = 1;
+	ctx_in.rx_queue_index = 1;
+	err = bpf_prog_test_run_opts(prog_fd, &opts);
+	ASSERT_EQ(errno, 22, "test10-errno");
+	ASSERT_ERR(err, "bpf_prog_test_run(test10)");

Why this failure? I guess it is due to device search failure, right?
So this test MAY succeed if the underlying host happens with
a proper configuration with ingress_ifindex = 1 and rx_queue_index = 1,
right?

+
+	test_xdp_context_test_run__destroy(skel);
+}
diff --git a/tools/testing/selftests/bpf/progs/test_xdp_context_test_run.c b/tools/testing/selftests/bpf/progs/test_xdp_context_test_run.c
new file mode 100644
index 000000000000..56fd0995b67c
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_xdp_context_test_run.c
@@ -0,0 +1,20 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+
+SEC("xdp")
+int _xdp_context(struct xdp_md *xdp)

Maybe drop prefix "_" from the function name?

+{
+	void *data = (void *)(unsigned long)xdp->data;
+	__u32 *metadata = (void *)(unsigned long)xdp->data_meta;

The above code is okay as verifier will rewrite correctly with actual address. But I still suggest to use "long" instead of "unsigned long"
to be consistent with other bpf programs.

+	__u32 ret;
+
+	if (metadata + 1 > data)
+		return XDP_ABORTED;
+	ret = *metadata;
+	if (bpf_xdp_adjust_meta(xdp, 4))
+		return XDP_ABORTED;
+	return ret;
+}
+
+char _license[] SEC("license") = "GPL";




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