On Fri, Jul 29, 2022 at 05:08:09PM -0700, Stanislav Fomichev wrote:
> Apparently, no existing selftest covers it. Add a new one where
> we load cgroup/bind4 program and attach fentry to it.
> Calling bpf_obj_get_info_by_fd on the fentry program
> should return non-zero btf_id/btf_obj_id instead of crashing the kernel.
>
> Signed-off-by: Stanislav Fomichev <sdf@xxxxxxxxxx>
> ---
> .../selftests/bpf/prog_tests/attach_to_bpf.c | 109 ++++++++++++++++++
> .../selftests/bpf/progs/attach_to_bpf.c | 12 ++
> 2 files changed, 121 insertions(+)
> create mode 100644 tools/testing/selftests/bpf/prog_tests/attach_to_bpf.c
> create mode 100644 tools/testing/selftests/bpf/progs/attach_to_bpf.c
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/attach_to_bpf.c b/tools/testing/selftests/bpf/prog_tests/attach_to_bpf.c
> new file mode 100644
> index 000000000000..fcf726c5ff0f
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/attach_to_bpf.c
> @@ -0,0 +1,109 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#define _GNU_SOURCE
> +#include <stdlib.h>
> +#include <bpf/btf.h>
> +#include <test_progs.h>
> +#include <network_helpers.h>
> +#include "attach_to_bpf.skel.h"
> +
> +char bpf_log_buf[BPF_LOG_BUF_SIZE];
static
> +
> +static int find_prog_btf_id(const char *name, __u32 attach_prog_fd)
> +{
> + struct bpf_prog_info info = {};
> + __u32 info_len = sizeof(info);
> + struct btf *btf;
> + int err;
> +
> + err = bpf_obj_get_info_by_fd(attach_prog_fd, &info, &info_len);
> + if (err)
> + return err;
> +
> + if (!info.btf_id)
> + return -EINVAL;
> +
> + btf = btf__load_from_kernel_by_id(info.btf_id);
> + err = libbpf_get_error(btf);
> + if (err)
> + return err;
> +
> + err = btf__find_by_name_kind(btf, name, BTF_KIND_FUNC);
> + btf__free(btf);
> + if (err <= 0)
> + return err;
> +
> + return err;
> +}
> +
> +int load_fentry(int attach_prog_fd, int attach_btf_id)
static
> +{
> + LIBBPF_OPTS(bpf_prog_load_opts, opts,
> + .expected_attach_type = BPF_TRACE_FENTRY,
> + .attach_prog_fd = attach_prog_fd,
> + .attach_btf_id = attach_btf_id,
> + .log_buf = bpf_log_buf,
> + .log_size = sizeof(bpf_log_buf),
> + );
> + struct bpf_insn insns[] = {
> + BPF_MOV64_IMM(BPF_REG_0, 0),
> + BPF_EXIT_INSN(),
> + };
> + int ret;
> +
> + ret = bpf_prog_load(BPF_PROG_TYPE_TRACING,
> + "bind4_fentry",
> + "GPL",
> + insns,
> + ARRAY_SIZE(insns),
> + &opts);
> + if (ret)
> + printf("verifier log: %s\n", bpf_log_buf);
If this fentry prog is in the attach_to_bpf.c and load by skel, this printf
and the bpf_log_buf can go away. I wonder if it can use the '?' like
SEC("?cgroup/bind4") and SEC("?fentry"). Then opens attach_to_bpf.skel.h
twice and use bpf_program__set_autoload() to load individual program.
Another option could be to reuse the progs/bind4_prog.c and directly
put the fentry program in the attach_to_bpf.c.
btw, this test feels like something that could be a few line
addition to the test_fexit_bpf2bpf_common() in fexit_bpf2bpf.c.
Adding one to test fentry into a cgroup bpf prog is also good.
No strong opinion here also.
> + return ret;
> +}
> +
> +void test_attach_to_bpf(void)
> +{
> + struct attach_to_bpf *skel = NULL;
> + struct bpf_prog_info info = {};
> + __u32 info_len = sizeof(info);
> + int cgroup_fd = -1;
> + int fentry_fd = -1;
> + int btf_id;
> +
> + cgroup_fd = test__join_cgroup("/attach_to_bpf");
> + if (!ASSERT_GE(cgroup_fd, 0, "cgroup_fd"))
> + return;
> +
> + skel = attach_to_bpf__open_and_load();
> + if (!ASSERT_OK_PTR(skel, "skel"))
> + goto cleanup;
> +
> + skel->links.bind4 = bpf_program__attach_cgroup(skel->progs.bind4, cgroup_fd);
> + if (!ASSERT_OK_PTR(skel, "bpf_program__attach_cgroup"))
> + goto cleanup;
> +
> + btf_id = find_prog_btf_id("bind4", bpf_program__fd(skel->progs.bind4));
> + if (!ASSERT_GE(btf_id, 0, "find_prog_btf_id"))
> + goto cleanup;
> +
> + fentry_fd = load_fentry(bpf_program__fd(skel->progs.bind4), btf_id);
> + if (!ASSERT_GE(fentry_fd, 0, "load_fentry"))
> + goto cleanup;
> +
> + /* Make sure bpf_obj_get_info_by_fd works correctly when attaching
> + * to another BPF program.
> + */
> +
> + if (!ASSERT_OK(bpf_obj_get_info_by_fd(fentry_fd, &info, &info_len),
> + "bpf_obj_get_info_by_fd"))
> + goto cleanup;
> +
> + ASSERT_EQ(info.btf_id, 0, "info.btf_id");
> + ASSERT_GT(info.attach_btf_id, 0, "info.attach_btf_id");
> + ASSERT_GT(info.attach_btf_obj_id, 0, "info.attach_btf_obj_id");
> +
> +cleanup:
> + close(cgroup_fd);
> + close(fentry_fd);
> + attach_to_bpf__destroy(skel);
> +}
> diff --git a/tools/testing/selftests/bpf/progs/attach_to_bpf.c b/tools/testing/selftests/bpf/progs/attach_to_bpf.c
> new file mode 100644
> index 000000000000..3f111fe96f8f
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/attach_to_bpf.c
nit. attach_to_bpf.c sounds too broad.
May be fentry_to_cgroup_bpf.c ?
> @@ -0,0 +1,12 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <linux/bpf.h>
> +#include <bpf/bpf_helpers.h>
> +
> +SEC("cgroup/bind4")
> +int bind4(struct bpf_sock_addr *ctx)
> +{
> + return 1;
> +}
> +
> +char _license[] SEC("license") = "GPL";
> --
> 2.37.1.455.g008518b4e5-goog
>
