Date:   Wed, 14 Dec 2022 11:35:13 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Mykola Lysenko <mykolal@...com>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Shuah Khan <shuah@...nel.org>, bpf@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH bpf v4 2/2] selftests/bpf: Add a test for using a cpumap
 from an freplace-to-XDP program

On Tue, Dec 13, 2022 at 5:05 PM Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>
> This adds a simple test for inserting an XDP program into a cpumap that is
> "owned" by an XDP program that was loaded as PROG_TYPE_EXT (as libxdp
> does). Prior to the kernel fix this would fail because the map type
> ownership would be set to PROG_TYPE_EXT instead of being resolved to
> PROG_TYPE_XDP.
>
> v4:
> - Use skeletons for selftest
> v3:
> - Update comment to better explain the cause
> - Add Yonghong's ACK
>
> Acked-by: Yonghong Song <yhs@...com>
> Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
> ---
>  .../selftests/bpf/prog_tests/fexit_bpf2bpf.c  | 54 +++++++++++++++++++
>  .../selftests/bpf/progs/freplace_progmap.c    | 24 +++++++++
>  2 files changed, 78 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/progs/freplace_progmap.c
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/fexit_bpf2bpf.c b/tools/testing/selftests/bpf/prog_tests/fexit_bpf2bpf.c
> index d1e32e792536..efa1fc65840d 100644
> --- a/tools/testing/selftests/bpf/prog_tests/fexit_bpf2bpf.c
> +++ b/tools/testing/selftests/bpf/prog_tests/fexit_bpf2bpf.c
> @@ -4,6 +4,8 @@
>  #include <network_helpers.h>
>  #include <bpf/btf.h>
>  #include "bind4_prog.skel.h"
> +#include "freplace_progmap.skel.h"
> +#include "xdp_dummy.skel.h"
>
>  typedef int (*test_cb)(struct bpf_object *obj);
>
> @@ -500,6 +502,56 @@ static void test_fentry_to_cgroup_bpf(void)
>         bind4_prog__destroy(skel);
>  }
>
> +static void test_func_replace_progmap(void)
> +{
> +       struct bpf_cpumap_val value = { .qsize = 1 };
> +       struct freplace_progmap *skel = NULL;
> +       struct xdp_dummy *tgt_skel = NULL;
> +       int err, tgt_fd;
> +       __u32 key = 0;
> +
> +       skel = freplace_progmap__open();
> +       if (!ASSERT_OK_PTR(skel, "prog_open"))
> +               return;
> +
> +       tgt_skel = xdp_dummy__open_and_load();
> +       if (!ASSERT_OK_PTR(tgt_skel, "tgt_prog_load"))
> +               goto out;
> +
> +       tgt_fd = bpf_program__fd(tgt_skel->progs.xdp_dummy_prog);
> +
> +       /* Change the 'redirect' program type to be a PROG_TYPE_EXT
> +        * with an XDP target
> +        */
> +       bpf_program__set_type(skel->progs.xdp_cpumap_prog, BPF_PROG_TYPE_EXT);
> +       bpf_program__set_expected_attach_type(skel->progs.xdp_cpumap_prog, 0);

you shouldn't need this manual override if you mark xdp_cpumap_prog as
SEC("freplace"), or am I missing something?

but other than this minor thing looks good to me, thanks

Acked-by: Andrii Nakryiko <andrii@...nel.org>



> +       err = bpf_program__set_attach_target(skel->progs.xdp_cpumap_prog,
> +                                            tgt_fd, "xdp_dummy_prog");
> +       if (!ASSERT_OK(err, "set_attach_target"))
> +               goto out;
> +
> +       err = freplace_progmap__load(skel);
> +       if (!ASSERT_OK(err, "obj_load"))
> +               goto out;
> +
> +       /* Prior to fixing the kernel, loading the PROG_TYPE_EXT 'redirect'
> +        * program above will cause the map owner type of 'cpumap' to be set to
> +        * PROG_TYPE_EXT. This in turn will cause the bpf_map_update_elem()
> +        * below to fail, because the program we are inserting into the map is
> +        * of PROG_TYPE_XDP. After fixing the kernel, the initial ownership will
> +        * be correctly resolved to the *target* of the PROG_TYPE_EXT program
> +        * (i.e., PROG_TYPE_XDP) and the map update will succeed.
> +        */
> +       value.bpf_prog.fd = bpf_program__fd(skel->progs.xdp_drop_prog);
> +       err = bpf_map_update_elem(bpf_map__fd(skel->maps.cpu_map),
> +                                 &key, &value, 0);
> +       ASSERT_OK(err, "map_update");
> +
> +out:
> +       xdp_dummy__destroy(tgt_skel);
> +       freplace_progmap__destroy(skel);
> +}
> +
>  /* NOTE: affect other tests, must run in serial mode */
>  void serial_test_fexit_bpf2bpf(void)
>  {
> @@ -525,4 +577,6 @@ void serial_test_fexit_bpf2bpf(void)
>                 test_func_replace_global_func();
>         if (test__start_subtest("fentry_to_cgroup_bpf"))
>                 test_fentry_to_cgroup_bpf();
> +       if (test__start_subtest("func_replace_progmap"))
> +               test_func_replace_progmap();
>  }
> diff --git a/tools/testing/selftests/bpf/progs/freplace_progmap.c b/tools/testing/selftests/bpf/progs/freplace_progmap.c
> new file mode 100644
> index 000000000000..68174c3d7b37
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/freplace_progmap.c
> @@ -0,0 +1,24 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <linux/bpf.h>
> +#include <bpf/bpf_helpers.h>
> +
> +struct {
> +       __uint(type, BPF_MAP_TYPE_CPUMAP);
> +       __uint(key_size, sizeof(__u32));
> +       __uint(value_size, sizeof(struct bpf_cpumap_val));

ok, another minor nit which you ignored, libbpf should be smart enough to accept

__type(key, __u32);
__type(value, struct bpf_cpumap_val);

And if it's not it would be good to know that it's not (and trivially fix it).

> +       __uint(max_entries, 1);
> +} cpu_map SEC(".maps");
> +
> +SEC("xdp/cpumap")
> +int xdp_drop_prog(struct xdp_md *ctx)
> +{
> +       return XDP_DROP;
> +}
> +
> +SEC("xdp")
> +int xdp_cpumap_prog(struct xdp_md *ctx)
> +{
> +       return bpf_redirect_map(&cpu_map, 0, XDP_PASS);
> +}
> +
> +char _license[] SEC("license") = "GPL";
> --
> 2.38.1
>

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