Re: [PATCH v1 2/2] ufs: rpmb: use a fixed-length RPMB dev_id

Hi Jorge,

On Thu, Jul 16, 2026 at 10:37 AM Jorge Ramirez-Ortiz jorge.ramirez@oss.qualcomm.com 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.

Yes, if it's possible, It's nice to avoid that.

Hash the UFS id into a fixed 16-byte dev_id with blake2s 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.

Signed-off-by: Jorge Ramirez-Ortiz jorge.ramirez@oss.qualcomm.com

drivers/ufs/core/ufs-rpmb.c | 19 +++++++++++++++++-- 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/drivers/ufs/core/ufs-rpmb.c b/drivers/ufs/core/ufs-rpmb.c index d0c7ea7a36f4..b800871269bb 100644 --- a/drivers/ufs/core/ufs-rpmb.c +++ b/drivers/ufs/core/ufs-rpmb.c @@ -10,6 +10,7 @@

• Can Guo <can.guo@oss.qualcomm.com>
  

*/

+#include <crypto/blake2s.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 */

@@ -154,6 +156,7 @@ int ufs_rpmb_probe(struct ufs_hba *hba) { struct ufs_rpmb_dev *ufs_rpmb, *it, *tmp; struct rpmb_dev *rdev;

•   char *dev_id = NULL;
    char *cid = NULL;
    int region;
    u32 cap;
  

@@ -213,8 +216,17 @@ int ufs_rpmb_probe(struct ufs_hba *hba) goto err_out; }

•           descr.dev_id = cid;
  

•           descr.dev_id_len = strlen(cid);
  

•           dev_id = kzalloc(UFS_RPMB_ID_LEN, GFP_KERNEL);
  

•           if (!dev_id) {
  

•                   device_unregister(&ufs_rpmb->dev);
  

•                   ret = -ENOMEM;
  

•                   goto err_out;
  

•           }
  

•           blake2s(NULL, 0, cid, strlen(cid), dev_id, UFS_RPMB_ID_LEN);
  

•           descr.dev_id = dev_id;
  

•           descr.dev_id_len = UFS_RPMB_ID_LEN;
  

This change will break current users of this interface, if there are any. There are currently no upstream users in OP-TEE since you're adding that with https://github.com/OP-TEE/optee_os/pull/7881, but I suppose that's not the only use case.

Cheers, Jens

            descr.capacity = cap;

            /* Register RPMB device */

@@ -228,6 +240,8 @@ int ufs_rpmb_probe(struct ufs_hba *hba)

            kfree(cid);
            cid = NULL;

•           kfree(dev_id);
  

•           dev_id = NULL;
  
            ufs_rpmb->rdev = rdev;
            ufs_rpmb->region_id = region;
  

@@ -240,6 +254,7 @@ int ufs_rpmb_probe(struct ufs_hba *hba) return 0; err_out: kfree(cid);

•   kfree(dev_id);
    list_for_each_entry_safe(it, tmp, &hba->rpmbs, node) {
            list_del(&it->node);
            device_unregister(&it->dev);
  

-- 2.54.0