netdev - Re: [PATCH v3] bpf: fix uapi bpf_prog

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Message-ID: <CAPhsuW4woTdoK1gMrFG=BZAXGD=ovYgm1YJ5G88DcWBrhSOYww@mail.gmail.com>
Date:   Fri, 28 Jun 2019 13:19:03 -0700
From:   Song Liu <liu.song.a23@...il.com>
To:     Baruch Siach <baruch@...s.co.il>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        "Dmitry V . Levin" <ldv@...linux.org>,
        Arnd Bergmann <arnd@...db.de>, linux-arch@...r.kernel.org,
        Jiri Olsa <jolsa@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v3] bpf: fix uapi bpf_prog_info fields alignment

On Thu, Jun 27, 2019 at 9:11 PM Baruch Siach <baruch@...s.co.il> wrote:
>
> Merge commit 1c8c5a9d38f60 ("Merge
> git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next") undid the
> fix from commit 36f9814a494 ("bpf: fix uapi hole for 32 bit compat
> applications") by taking the gpl_compatible 1-bit field definition from
> commit b85fab0e67b162 ("bpf: Add gpl_compatible flag to struct
> bpf_prog_info") as is. That breaks architectures with 16-bit alignment
> like m68k. Add 31-bit pad after gpl_compatible to restore alignment of
> following fields.
>
> Thanks to Dmitry V. Levin his analysis of this bug history.
>
> Cc: Jiri Olsa <jolsa@...nel.org>
> Cc: Daniel Borkmann <daniel@...earbox.net>
> Cc: Geert Uytterhoeven <geert@...ux-m68k.org>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Signed-off-by: Baruch Siach <baruch@...s.co.il>
Acked-by: Song Liu <songliubraving@...com>

> ---
> v3:
> Use alignment pad as Alexei Starovoitov suggested
>
> v2:
> Use anonymous union with pad to make it less likely to break again in
> the future.
> ---
>  include/uapi/linux/bpf.h       | 1 +
>  tools/include/uapi/linux/bpf.h | 1 +
>  2 files changed, 2 insertions(+)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index a8b823c30b43..29a5bc3d5c66 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -3143,6 +3143,7 @@ struct bpf_prog_info {
>         char name[BPF_OBJ_NAME_LEN];
>         __u32 ifindex;
>         __u32 gpl_compatible:1;
> +       __u32 :31; /* alignment pad */
>         __u64 netns_dev;
>         __u64 netns_ino;
>         __u32 nr_jited_ksyms;
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index a8b823c30b43..29a5bc3d5c66 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -3143,6 +3143,7 @@ struct bpf_prog_info {
>         char name[BPF_OBJ_NAME_LEN];
>         __u32 ifindex;
>         __u32 gpl_compatible:1;
> +       __u32 :31; /* alignment pad */
>         __u64 netns_dev;
>         __u64 netns_ino;
>         __u32 nr_jited_ksyms;
> --
> 2.20.1
>