On Tue, Jun 25, 2019 at 07:16:55AM -0700, Alexei Starovoitov wrote:
> On Tue, Jun 25, 2019 at 4:07 AM Baruch Siach <baruch@xxxxxxxxxx> 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. Embed gpl_compatible into an anonymous union with 32-bit pad
> > member to restore alignment of following fields.
> >
> > Thanks to Dmitry V. Levin his analysis of this bug history.
> >
> > Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
> > Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
> > Cc: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
> > Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Baruch Siach <baruch@xxxxxxxxxx>
> > ---
> > v2:
> > Use anonymous union with pad to make it less likely to break again in
> > the future.
> > ---
> > include/uapi/linux/bpf.h | 5 ++++-
> > tools/include/uapi/linux/bpf.h | 5 ++++-
> > 2 files changed, 8 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> > index a8b823c30b43..766eae02d7ae 100644
> > --- a/include/uapi/linux/bpf.h
> > +++ b/include/uapi/linux/bpf.h
> > @@ -3142,7 +3142,10 @@ struct bpf_prog_info {
> > __aligned_u64 map_ids;
> > char name[BPF_OBJ_NAME_LEN];
> > __u32 ifindex;
> > - __u32 gpl_compatible:1;
> > + union {
> > + __u32 gpl_compatible:1;
> > + __u32 pad;
> > + };
>
> Nack for the reasons explained in the previous thread
> on the same subject.
> Why cannot you go with earlier suggestion of _u32 :31; ?
By the way, why not use aligned types as suggested by Geert?
They are already used for other members of struct bpf_prog_info anyway.
FWIW, we use aligned types for bpf in strace and that approach
proved to be more robust than manual padding.
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