Re: [PATCH] kbuild: modversions: Fix relative CRC byte order interpretion

Masahiro Yamada
2019-03-25T04:04:39Z

Hi Fredrik,

On Sun, Mar 24, 2019 at 3:37 PM Fredrik Noring <noring@nocrew.org> wrote:
>
> Masahiro, Michal --
>
> > Fix commit 56067812d5b0 ("kbuild: modversions: add infrastructure for
> > emitting relative CRCs") where CRCs are interpreted in host byte order
> > rather than proper kernel byte order.
> >
> > For example, when loading BE modules compiled with a LE system, the
> > error "disagrees about version of symbol module_layout" is produced.
> > A message such as "Found checksum D7FA6856 vs module 5668FAD7" will be
> > given with debug enabled, which indicates an obvious endian problem.
>
> I realise that the description above is perhaps a bit too brief; although
> the error is triggered by loading modules, the precise location of the
> error is within __kcrctab within the kernel image.
>
> > The general solution is to use the macro TO_NATIVE, as is done in
> > similar cases throughout modpost.c. With this correction it has been
> > verified that BE modules compiled with a LE system load properly into
> > a BE kernel.
>
> One could note that it has also been tested with a LE kernel compiled
> with a LE system, in which case TO_NATIVE returns its value unmodified
> since the byte orders match. This is by far the common case.
>
> Would you like me to send an updated description?

Either will do.

If you send v2, could you please check the possible
typo in the subject?

interpretion -> interpretation ?

Masahiro

> Fredrik
>
> > Signed-off-by: Fredrik Noring <noring@nocrew.org>
> > Fixes: 56067812d5b0 ("kbuild: modversions: add infrastructure for emitting relative CRCs")
> > Cc: stable@vger.kernel.org
> > ---
> > diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> > index 0b0d1080b1c5..f277e116e0eb 100644
> > --- a/scripts/mod/modpost.c
> > +++ b/scripts/mod/modpost.c
> > @@ -639,7 +639,7 @@ static void handle_modversions(struct module *mod, struct elf_info *info,
> > info->sechdrs[sym->st_shndx].sh_offset -
> > (info->hdr->e_type != ET_REL ?
> > info->sechdrs[sym->st_shndx].sh_addr : 0);
> > - crc = *crcp;
> > + crc = TO_NATIVE(*crcp);
> > }
> > sym_update_crc(symname + strlen("__crc_"), mod, crc,
> > export);

--
Best Regards
Masahiro Yamada