linux-kernel - Re: [PATCH bpf 1/2] bpf: fix alignment of netns_dev/netns_ino fields in bpf_{map,prog}

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Date:   Tue, 29 May 2018 10:17:34 -0700
From:   Song Liu <liu.song.a23@...il.com>
To:     Eugene Syromiatnikov <esyr@...hat.com>
Cc:     netdev@...r.kernel.org, open list <linux-kernel@...r.kernel.org>,
        Martin KaFai Lau <kafai@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jiri Olsa <jolsa@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        Lawrence Brakmo <brakmo@...com>, Andrey Ignatov <rdna@...com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        John Fastabend <john.fastabend@...il.com>,
        "Dmitry V. Levin" <ldv@...linux.org>
Subject: Re: [PATCH bpf 1/2] bpf: fix alignment of netns_dev/netns_ino fields
 in bpf_{map,prog}_info

On Sun, May 27, 2018 at 4:28 AM, Eugene Syromiatnikov <esyr@...hat.com> wrote:
> Recent introduction of netns_dev/netns_ino to bpf_map_info/bpf_prog info
> has broken compat, as offsets of these fields are different in 32-bit
> and 64-bit ABIs.  One fix (other than implementing compat support in
> syscall in order to handle this discrepancy) is to use __aligned_u64
> instead of __u64 for these fields.
>
> Reported-by: Dmitry V. Levin <ldv@...linux.org>
> Fixes: 52775b33bb507 ("bpf: offload: report device information about
> offloaded maps")
> Fixes: 675fc275a3a2d ("bpf: offload: report device information for
> offloaded programs")
>
> Signed-off-by: Eugene Syromiatnikov <esyr@...hat.com>
> ---
>  include/uapi/linux/bpf.h       | 8 ++++----
>  tools/include/uapi/linux/bpf.h | 8 ++++----
>  2 files changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index c5ec897..903010a 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -1017,8 +1017,8 @@ struct bpf_prog_info {
>         __aligned_u64 map_ids;
>         char name[BPF_OBJ_NAME_LEN];
>         __u32 ifindex;
> -       __u64 netns_dev;
> -       __u64 netns_ino;
> +       __aligned_u64 netns_dev;
> +       __aligned_u64 netns_ino;
>  } __attribute__((aligned(8)));

Shall we add a __u32 padding variable before netns_dev? We can use it
for in the future.

Thanks,
Song

>
>  struct bpf_map_info {
> @@ -1030,8 +1030,8 @@ struct bpf_map_info {
>         __u32 map_flags;
>         char  name[BPF_OBJ_NAME_LEN];
>         __u32 ifindex;
> -       __u64 netns_dev;
> -       __u64 netns_ino;
> +       __aligned_u64 netns_dev;
> +       __aligned_u64 netns_ino;
>  } __attribute__((aligned(8)));
>
>  /* User bpf_sock_addr struct to access socket fields and sockaddr struct passed
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index c5ec897..903010a 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -1017,8 +1017,8 @@ struct bpf_prog_info {
>         __aligned_u64 map_ids;
>         char name[BPF_OBJ_NAME_LEN];
>         __u32 ifindex;
> -       __u64 netns_dev;
> -       __u64 netns_ino;
> +       __aligned_u64 netns_dev;
> +       __aligned_u64 netns_ino;
>  } __attribute__((aligned(8)));
>
>  struct bpf_map_info {
> @@ -1030,8 +1030,8 @@ struct bpf_map_info {
>         __u32 map_flags;
>         char  name[BPF_OBJ_NAME_LEN];
>         __u32 ifindex;
> -       __u64 netns_dev;
> -       __u64 netns_ino;
> +       __aligned_u64 netns_dev;
> +       __aligned_u64 netns_ino;
>  } __attribute__((aligned(8)));
>
>  /* User bpf_sock_addr struct to access socket fields and sockaddr struct passed
> --
> 2.1.4
>