Re: [PATCH bpf-next v2 3/3] selftests/bpf: Add test for xdp_md context in BPF_PROG_TEST_RUN

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Thu, May 27, 2021 at 1:14 PM Zvi Effron <zeffron@riotgames.com> 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     | 116 ++++++++++++++++++
>  .../bpf/progs/test_xdp_context_test_run.c     |  20 +++
>  2 files changed, 136 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..f6d312005b7c
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/xdp_context_test_run.c
> @@ -0,0 +1,116 @@
> +// 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;
> +       struct bpf_test_run_opts tattr = {

see LIBBPF_DECLARE_OPTS, please use it

and please call it opts, it's not attribute

> +               .sz = sizeof(struct bpf_test_run_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;
> +
> +

extra empty line

> +       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));
> +       tattr.ctx_in = &ctx_in;
> +       tattr.ctx_size_in = sizeof(ctx_in);
> +
> +       tattr.ctx_in = &ctx_in;
> +       tattr.ctx_size_in = sizeof(ctx_in);
> +       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, &tattr);
> +       ASSERT_OK(err, "bpf_prog_test_run(test1)");
> +       ASSERT_EQ(tattr.retval, XDP_PASS, "test1-retval");
> +       ASSERT_EQ(tattr.data_size_out, sizeof(pkt_v4), "test1-datasize");
> +       ASSERT_EQ(tattr.ctx_size_out, tattr.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");
> +       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;
> +       tattr.ctx_in = bad_ctx;
> +       tattr.ctx_size_in = sizeof(bad_ctx);
> +       err = bpf_prog_test_run_opts(prog_fd, &tattr);
> +       ASSERT_ERR(err, "bpf_prog_test_run(test2)");
> +       ASSERT_EQ(errno, 22, "test2-errno");

by the time you are checking errno it might get overwritten. If you
want to check errno, you have to remember it right after the function
returns

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

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