[PATCH v2] bpf: fix uapi bpf_prog_info fields alignment

[PATCH v2] bpf: fix uapi bpf_prog_info fields alignment

[Baruch Siach]

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@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
---
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;
+	};
 	__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..766eae02d7ae 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/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;
+	};
 	__u64 netns_dev;
 	__u64 netns_ino;
 	__u32 nr_jited_ksyms;
-- 
2.20.1

Re: [PATCH v2] bpf: fix uapi bpf_prog_info fields alignment

[Alexei Starovoitov]

On Tue, Jun 25, 2019 at 4:07 AM Baruch Siach <baruch@tkos.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. 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@kernel.org>
> Cc: Daniel Borkmann <daniel@iogearbox.net>
> Cc: Geert Uytterhoeven <geert@linux-m68k.org>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Signed-off-by: Baruch Siach <baruch@tkos.co.il>
> ---
> 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; ?

Re: [PATCH v2] bpf: fix uapi bpf_prog_info fields alignment

[Dmitry V. Levin]

[-- Attachment #1: Type: text/plain, Size: 2189 bytes --]

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@tkos.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. 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@kernel.org>
> > Cc: Daniel Borkmann <daniel@iogearbox.net>
> > Cc: Geert Uytterhoeven <geert@linux-m68k.org>
> > Cc: Linus Torvalds <torvalds@linux-foundation.org>
> > Signed-off-by: Baruch Siach <baruch@tkos.co.il>
> > ---
> > 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.


-- 
ldv

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 801 bytes --]

Re: [PATCH v2] bpf: fix uapi bpf_prog_info fields alignment

[Alexei Starovoitov]

On Tue, Jun 25, 2019 at 8:08 AM Dmitry V. Levin <ldv@altlinux.org> wrote:
>
> 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@tkos.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. 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@kernel.org>
> > > Cc: Daniel Borkmann <daniel@iogearbox.net>
> > > Cc: Geert Uytterhoeven <geert@linux-m68k.org>
> > > Cc: Linus Torvalds <torvalds@linux-foundation.org>
> > > Signed-off-by: Baruch Siach <baruch@tkos.co.il>
> > > ---
> > > 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.

because __aligned_u64 is used for pointers.

Re: [PATCH v2] bpf: fix uapi bpf_prog_info fields alignment

[Dmitry V. Levin]

[-- Attachment #1: Type: text/plain, Size: 2715 bytes --]

On Tue, Jun 25, 2019 at 08:19:35AM -0700, Alexei Starovoitov wrote:
> On Tue, Jun 25, 2019 at 8:08 AM Dmitry V. Levin <ldv@altlinux.org> wrote:
> > 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@tkos.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. 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@kernel.org>
> > > > Cc: Daniel Borkmann <daniel@iogearbox.net>
> > > > Cc: Geert Uytterhoeven <geert@linux-m68k.org>
> > > > Cc: Linus Torvalds <torvalds@linux-foundation.org>
> > > > Signed-off-by: Baruch Siach <baruch@tkos.co.il>
> > > > ---
> > > > 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.
> 
> because __aligned_u64 is used for pointers.

Does the fact that __aligned_u64 is used for pointers mean that
__aligned_u64 should not be used for anything but pointers?


-- 
ldv

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 801 bytes --]