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

[Jorge Ramirez-Ortiz <jorge.ramirez@oss.qualcomm.com>]

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@oss.qualcomm.com>
---
 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@oss.qualcomm.com>
  */
 
+#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