Re: [PATCH v3 2/2] ufs: rpmb: use a fixed-length RPMB dev_id

[Jorge Ramirez]

On 21/08/26 17:06:08, Jorge Ramirez-Ortiz wrote:
> The RPMB authentication key is derived from the dev_id handed to the
> RPMB subsystem. OP-TEE implements the eMMC RPMB flow, where the dev_id
> is the eMMC CID, a fixed 16-byte value, and it derives the key on that
> assumption.
>
> The UFS RPMB id built here is "<device_id>-R<region>", which is variable
> length and longer than 16 bytes. Passing it verbatim would tie the
> derived key to a length OP-TEE does not expect and diverge from the
> fixed-CID eMMC ABI, requiring OP-TEE to be taught about variable-length
> UFS ids.
>
> Hash the UFS id into a fixed 16-byte dev_id with blake2b instead. This
> keeps the derived key stable and unique per region while matching the
> eMMC CID layout OP-TEE relies on, so the key-derivation ABI stays
> identical and no OP-TEE change is needed. blake2b is used because it is
> already available in bootloaders such as U-Boot that must derive the
> same dev_id, avoiding the need to add a blake2s implementation there.
>
> Signed-off-by: Jorge Ramirez-Ortiz <jorge.ramirez@xxxxxxxxxxxxxxxx>
> ---
>  drivers/ufs/Kconfig         | 1 +
>  drivers/ufs/core/ufs-rpmb.c | 9 +++++++--
>  2 files changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/ufs/Kconfig b/drivers/ufs/Kconfig
> index f662e7ce71f1..b62c00e7ff06 100644
> --- a/drivers/ufs/Kconfig
> +++ b/drivers/ufs/Kconfig
> @@ -7,6 +7,7 @@ menuconfig SCSI_UFSHCD
>  	tristate "Universal Flash Storage Controller"
>  	depends on SCSI && SCSI_DMA
>  	depends on RPMB || !RPMB
> +	select CRYPTO_LIB_BLAKE2B if RPMB
>  	select PM_DEVFREQ
>  	select DEVFREQ_GOV_SIMPLE_ONDEMAND
>  	select NLS
> diff --git a/drivers/ufs/core/ufs-rpmb.c b/drivers/ufs/core/ufs-rpmb.c
> index d0c7ea7a36f4..a1e169ad3096 100644
> --- a/drivers/ufs/core/ufs-rpmb.c
> +++ b/drivers/ufs/core/ufs-rpmb.c
> @@ -10,6 +10,7 @@
>   *	Can Guo <can.guo@xxxxxxxxxxxxxxxx>
>   */
>
> +#include <crypto/blake2b.h>
>  #include <linux/module.h>
>  #include <linux/device.h>
>  #include <linux/kernel.h>
> @@ -21,6 +22,7 @@
>  #include <linux/unaligned.h>
>  #include "ufshcd-priv.h"
>
> +#define UFS_RPMB_ID_LEN			16	/* Match eMMC CID Length */
>  #define UFS_RPMB_SEC_PROTOCOL		0xEC	/* JEDEC UFS application */
>  #define UFS_RPMB_SEC_PROTOCOL_ID	0x01	/* JEDEC UFS RPMB protocol ID, CDB byte3 */
>
> @@ -153,6 +155,7 @@ static void ufs_rpmb_device_release(struct device *dev)
>  int ufs_rpmb_probe(struct ufs_hba *hba)
>  {
>  	struct ufs_rpmb_dev *ufs_rpmb, *it, *tmp;
> +	u8 dev_id[UFS_RPMB_ID_LEN];
>  	struct rpmb_dev *rdev;
>  	char *cid = NULL;
>  	int region;
> @@ -213,8 +216,10 @@ int ufs_rpmb_probe(struct ufs_hba *hba)
>  			goto err_out;
>  		}
>
> -		descr.dev_id = cid;
> -		descr.dev_id_len = strlen(cid);
> +		blake2b(NULL, 0, cid, strlen(cid), dev_id, UFS_RPMB_ID_LEN);
> +
> +		descr.dev_id = dev_id;
> +		descr.dev_id_len = UFS_RPMB_ID_LEN;
>  		descr.capacity = cap;
>
>  		/* Register RPMB device */
> --
> 2.54.0
>

just a keep alive, any issues to merge these?

TIA