Re: [PATCH v2] kbuild: modversions: Fix relative CRC byte order interpretation

Masahiro Yamada
2019-03-28T09:06:53Z

On Thu, Mar 28, 2019 at 3:13 AM Fredrik Noring <noring@nocrew.org> wrote:
>
> 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. The bug is conditional on
> CONFIG_MODULE_REL_CRCS.
>
> For example, when loading a BE module into a BE kernel 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 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 a BE kernel compiled with a LE system accepts BE modules.
>
> This change has also been verified 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.
>
> Fixes: 56067812d5b0 ("kbuild: modversions: add infrastructure for emitting relative CRCs")
> Signed-off-by: Fredrik Noring <noring@nocrew.org>
> Cc: stable@vger.kernel.org

Applied to linux-kbuild/fixes. Thanks.

> ---
> Thank you for your review, Masahiro,
>
> Changes in v2:
> - Fix subject spelling mistake.
> - Note that the bug is conditional on CONFIG_MODULE_REL_CRCS.
> - Clarify kernel image and __kcrctab compilation details.
> - Mention verification of matching LE byte order common case.
>
> Fredrik
> ---
> 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