[U-Boot] [PATCH] drivers: optee: rpmb: fix returning CID to TEE

[Jens Wiklander]

Hi Jorge,

On Fri, Nov 15, 2019 at 10:37 PM Jorge Ramirez-Ortiz <jorge at foundries.io> wrote:
>
> The MMC CID value is one of the input parameters to unequivocally
> provision the the RPMB key.
>
> Before this patch, the value returned by the mmc driver in the Linux
> kernel differs from the one returned by uboot to optee.
>
> This means that if Linux provisions the RPMB key, uboot wont be able
> to access it (and the other way around).
>
> Fix it so both uboot and linux can access the RPMB partition
> independently of who provisions the key.
>
> Signed-off-by: Jorge Ramirez-Ortiz <jorge at foundries.io>
> ---
>  drivers/tee/optee/rpmb.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/tee/optee/rpmb.c b/drivers/tee/optee/rpmb.c
> index 955155b3f8..5dbb1eae4a 100644
> --- a/drivers/tee/optee/rpmb.c
> +++ b/drivers/tee/optee/rpmb.c
> @@ -98,6 +98,7 @@ static struct mmc *get_mmc(struct optee_private *priv, int dev_id)
>  static u32 rpmb_get_dev_info(u16 dev_id, struct rpmb_dev_info *info)
>  {
>         struct mmc *mmc = find_mmc_device(dev_id);
> +       int i;
>
>         if (!mmc)
>                 return TEE_ERROR_ITEM_NOT_FOUND;
> @@ -105,7 +106,9 @@ static u32 rpmb_get_dev_info(u16 dev_id, struct rpmb_dev_info *info)
>         if (!mmc->ext_csd)
>                 return TEE_ERROR_GENERIC;
>
> -       memcpy(info->cid, mmc->cid, sizeof(info->cid));
> +       for (i = 0; i < ARRAY_SIZE(mmc->cid); i++)
> +               ((u32 *) info->cid)[i] = be32_to_cpu(mmc->cid[i]);
> +

So it seems to be a byte order issue. I can't find the place in the
Linux kernel (or in tee-supplicant) where the corresponding byte
swapping is done. Have you been able to find it or you just tried to
swap the bytes and it seemed to work?

I'm not yet convinced that be32_to_cpu() is the correct function here.
OP-TEE masks out a few fields from the CID when deriving the key:

CID is a uint8_t[16] here
        /*
         * PRV/CRC would be changed when doing eMMC FFU
         * The following fields should be masked off when deriving RPMB key
         *
         * CID [55: 48]: PRV (Product revision)
         * CID [07: 01]: CRC (CRC7 checksum)
         * CID [00]: not used
         */

Will this work as expected on a big endian machine?

Cheers,
Jens

>         info->rel_wr_sec_c = mmc->ext_csd[222];
>         info->rpmb_size_mult = mmc->ext_csd[168];
>         info->ret_code = RPMB_CMD_GET_DEV_INFO_RET_OK;
> --
> 2.23.0
>