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

[Yonghong Song <yhs@fb.com>]

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@riotgames.com>
> Signed-off-by: Cody Haas <chaas@riotgames.com>
> Co-developed-by: Lisa Watanabe <lwatanabe@riotgames.com>
> Signed-off-by: Lisa Watanabe <lwatanabe@riotgames.com>
> Signed-off-by: Zvi Effron <zeffron@riotgames.com>
> ---
>   .../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";
>