linux-kernel - Re: [PATCH 1/5] modpost: fix tee MODULE_DEVICE

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Date:   Mon, 9 Oct 2023 11:57:00 +0530
From:   Sumit Garg <sumit.garg@...aro.org>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        Bhupesh Sharma <bhsharma@...hat.com>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Jens Wiklander <jens.wiklander@...aro.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Schier <nicolas@...sle.eu>
Subject: Re: [PATCH 1/5] modpost: fix tee MODULE_DEVICE_TABLE built on big
 endian host

Hi Masahiro,

On Sat, 7 Oct 2023 at 22:34, Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> When MODULE_DEVICE_TABLE(tee, ) is built on a host with a different
> endianness from the target architecture, it results in an incorrect
> MODULE_ALIAS().
>
> For example, see a case where drivers/char/hw_random/optee-rng.c
> is built as a module.
>
> If you build it on a little endian host, you will get the correct
> MODULE_ALIAS:
>
>     $ grep MODULE_ALIAS drivers/char/hw_random/optee-rng.mod.c
>     MODULE_ALIAS("tee:ab7a617c-b8e7-4d8f-8301-d09b61036b64*");
>
> However, if you build it on a big endian host, you will get a wrong
> MODULE_ALIAS:
>
>     $ grep MODULE_ALIAS drivers/char/hw_random/optee-rng.mod.c
>     MODULE_ALIAS("tee:646b0361-9bd0-0183-8f4d-e7b87c617aab*");
>
> This issue has been unnoticed because the ARM kernel is most likely built
> on a little endian host (cross-build on x86 or native-build on ARM).
>
> The uuid field must not be reversed because uuid_t is an array of __u8.
>

To me it wasn't obvious that DEF_FIELD() has certain endianness limitations.

> Fixes: 0fc1db9d1059 ("tee: add bus driver framework for TEE based devices")
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> ---
>
>  scripts/mod/file2alias.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/scripts/mod/file2alias.c b/scripts/mod/file2alias.c
> index 7056751c29b1..70bf6a2f585c 100644
> --- a/scripts/mod/file2alias.c
> +++ b/scripts/mod/file2alias.c
> @@ -1348,13 +1348,13 @@ static int do_typec_entry(const char *filename, void *symval, char *alias)
>  /* Looks like: tee:uuid */
>  static int do_tee_entry(const char *filename, void *symval, char *alias)
>  {
> -       DEF_FIELD(symval, tee_client_device_id, uuid);

As you have mentioned in patch #3: the limitations of TO_NATIVE(), if
you can update comments for DEF_FIELD() as well to make it clear that
it doesn't support byte arrays/strings would be helpful. I think the
following check that you have introduced in patch #3 can still be
bypassed for byte arrays/strings.

+ _Static_assert(sizeof(x) == 1 || sizeof(x) == 2 || \
+       sizeof(x) == 4 || sizeof(x) == 8, "bug");

BTW, for this fix feel free to add:

Reviewed-by: Sumit Garg <sumit.garg@...aro.org>

-Sumit

> +       DEF_FIELD_ADDR(symval, tee_client_device_id, uuid);
>
>         sprintf(alias, "tee:%02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x-%02x%02x%02x%02x%02x%02x",
> -               uuid.b[0], uuid.b[1], uuid.b[2], uuid.b[3], uuid.b[4],
> -               uuid.b[5], uuid.b[6], uuid.b[7], uuid.b[8], uuid.b[9],
> -               uuid.b[10], uuid.b[11], uuid.b[12], uuid.b[13], uuid.b[14],
> -               uuid.b[15]);
> +               uuid->b[0], uuid->b[1], uuid->b[2], uuid->b[3], uuid->b[4],
> +               uuid->b[5], uuid->b[6], uuid->b[7], uuid->b[8], uuid->b[9],
> +               uuid->b[10], uuid->b[11], uuid->b[12], uuid->b[13], uuid->b[14],
> +               uuid->b[15]);
>
>         add_wildcard(alias);
>         return 1;
> --
> 2.39.2
>