netdev - Re: [PATCH bpf-next 5/5] bpf, testing: Add selftest to read/write sockaddr from user space

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Date:   Fri, 25 Oct 2019 15:14:49 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     Alexei Starovoitov <ast@...nel.org>, bpf <bpf@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        Ilya Leoshkevich <iii@...ux.ibm.com>
Subject: Re: [PATCH bpf-next 5/5] bpf, testing: Add selftest to read/write
 sockaddr from user space

On Fri, Oct 25, 2019 at 1:44 PM Daniel Borkmann <daniel@...earbox.net> wrote:
>
> Tested on x86-64 and Ilya was also kind enough to give it a spin on
> s390x, both passing with probe_user:OK there. The test is using the
> newly added bpf_probe_read_user() to dump sockaddr from connect call
> into BPF map and overrides the user buffer via bpf_probe_write_user():
>
>   # ./test_progs
>   [...]
>   #17 pkt_md_access:OK
>   #18 probe_user:OK
>   #19 prog_run_xattr:OK
>   [...]
>
> Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
> Tested-by: Ilya Leoshkevich <iii@...ux.ibm.com>
> ---
>  .../selftests/bpf/prog_tests/probe_user.c     | 80 +++++++++++++++++++
>  .../selftests/bpf/progs/test_probe_user.c     | 33 ++++++++
>  2 files changed, 113 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/probe_user.c
>  create mode 100644 tools/testing/selftests/bpf/progs/test_probe_user.c
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/probe_user.c b/tools/testing/selftests/bpf/prog_tests/probe_user.c
> new file mode 100644
> index 000000000000..e37761bda8a4
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/probe_user.c
> @@ -0,0 +1,80 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <test_progs.h>
> +
> +void test_probe_user(void)
> +{
> +#define kprobe_name "__sys_connect"
> +       const char *prog_name = "kprobe/" kprobe_name;
> +       const char *obj_file = "./test_probe_user.o";
> +       DECLARE_LIBBPF_OPTS(bpf_object_open_opts, opts,
> +               .relaxed_maps = true,

do we need relaxed_maps in this case?

> +       );
> +       int err, results_map_fd, sock_fd, duration;
> +       struct sockaddr curr, orig, tmp;
> +       struct sockaddr_in *in = (struct sockaddr_in *)&curr;
> +       struct bpf_link *kprobe_link = NULL;
> +       struct bpf_program *kprobe_prog;
> +       struct bpf_object *obj;
> +       static const int zero = 0;
> +

[...]

> +
> +struct {
> +       __uint(type, BPF_MAP_TYPE_ARRAY);
> +       __uint(max_entries, 1);
> +       __type(key, int);
> +       __type(value, struct sockaddr_in);
> +} results_map SEC(".maps");
> +
> +SEC("kprobe/__sys_connect")
> +int handle_sys_connect(struct pt_regs *ctx)
> +{
> +       void *ptr = (void *)PT_REGS_PARM2(ctx);
> +       struct sockaddr_in old, new;
> +       const int zero = 0;
> +
> +       bpf_probe_read_user(&old, sizeof(old), ptr);
> +       bpf_map_update_elem(&results_map, &zero, &old, 0);

could have used global data and read directly into it :)

> +       __builtin_memset(&new, 0xab, sizeof(new));
> +       bpf_probe_write_user(ptr, &new, sizeof(new));
> +
> +       return 0;
> +}
> +
> +char _license[] SEC("license") = "GPL";
> --
> 2.21.0
>