driver: tee: Handle NULL pointer indication from client

TEE Client introduce a new capability "TEE_GEN_CAP_MEMREF_NULL"
to handle the support of the shared memory buffer with a NULL pointer.

This capability depends on TEE Capabilities and driver support.
Driver and TEE exchange capabilities at driver initialization.

Signed-off-by: Michael Whitfield <michael.whitfield@nxp.com>
Signed-off-by: Cedric Neveux <cedric.neveux@nxp.com>
Reviewed-by: Joakim Bech <joakim.bech@linaro.org>
Tested-by: Joakim Bech <joakim.bech@linaro.org> (QEMU)
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>

3 files changed, 41 insertions, 18 deletions

diff --git a/drivers/tee/optee/core.c b/drivers/tee/optee/core.c
index b373b1b08b6d..cf4718c6d35d 100644
--- a/drivers/tee/optee/core.c
+++ b/drivers/tee/optee/core.c
@@ -216,6 +216,8 @@ static void optee_get_version(struct tee_device *teedev,
 
 	if (optee->sec_caps & OPTEE_SMC_SEC_CAP_DYNAMIC_SHM)
 		v.gen_caps |= TEE_GEN_CAP_REG_MEM;
+	if (optee->sec_caps & OPTEE_SMC_SEC_CAP_MEMREF_NULL)
+		v.gen_caps |= TEE_GEN_CAP_MEMREF_NULL;
 	*vers = v;
 }
 
@@ -262,6 +264,11 @@ static int optee_open(struct tee_context *ctx)
 	mutex_init(&ctxdata->mutex);
 	INIT_LIST_HEAD(&ctxdata->sess_list);
 
+	if (optee->sec_caps & OPTEE_SMC_SEC_CAP_MEMREF_NULL)
+		ctx->cap_memref_null  = true;
+	else
+		ctx->cap_memref_null = false;
+
 	ctx->data = ctxdata;
 	return 0;
 }
diff --git a/drivers/tee/optee/optee_smc.h b/drivers/tee/optee/optee_smc.h
index c72122d9c997..777ad54d4c2c 100644
--- a/drivers/tee/optee/optee_smc.h
+++ b/drivers/tee/optee/optee_smc.h
@@ -215,6 +215,9 @@ struct optee_smc_get_shm_config_result {
  */
 #define OPTEE_SMC_SEC_CAP_DYNAMIC_SHM		BIT(2)
 
+/* Secure world supports Shared Memory with a NULL buffer reference */
+#define OPTEE_SMC_SEC_CAP_MEMREF_NULL		BIT(4)
+
 #define OPTEE_SMC_FUNCID_EXCHANGE_CAPABILITIES	9
 #define OPTEE_SMC_EXCHANGE_CAPABILITIES \
 	OPTEE_SMC_FAST_CALL_VAL(OPTEE_SMC_FUNCID_EXCHANGE_CAPABILITIES)
diff --git a/drivers/tee/tee_core.c b/drivers/tee/tee_core.c
index 64637e09a095..ce0f0309b6ac 100644
--- a/drivers/tee/tee_core.c
+++ b/drivers/tee/tee_core.c
@@ -383,25 +383,38 @@ static int params_from_user(struct tee_context *ctx, struct tee_param *params,
 		case TEE_IOCTL_PARAM_ATTR_TYPE_MEMREF_OUTPUT:
 		case TEE_IOCTL_PARAM_ATTR_TYPE_MEMREF_INOUT:
 			/*
-			 * If we fail to get a pointer to a shared memory
-			 * object (and increase the ref count) from an
-			 * identifier we return an error. All pointers that
-			 * has been added in params have an increased ref
-			 * count. It's the callers responibility to do
-			 * tee_shm_put() on all resolved pointers.
+			 * If a NULL pointer is passed to a TA in the TEE,
+			 * the ip.c IOCTL parameters is set to TEE_MEMREF_NULL
+			 * indicating a NULL memory reference.
 			 */
-			shm = tee_shm_get_from_id(ctx, ip.c);
-			if (IS_ERR(shm))
-				return PTR_ERR(shm);
-
-			/*
-			 * Ensure offset + size does not overflow offset
-			 * and does not overflow the size of the referred
-			 * shared memory object.
-			 */
-			if ((ip.a + ip.b) < ip.a ||
-			    (ip.a + ip.b) > shm->size) {
-				tee_shm_put(shm);
+			if (ip.c != TEE_MEMREF_NULL) {
+				/*
+				 * If we fail to get a pointer to a shared
+				 * memory object (and increase the ref count)
+				 * from an identifier we return an error. All
+				 * pointers that has been added in params have
+				 * an increased ref count. It's the callers
+				 * responibility to do tee_shm_put() on all
+				 * resolved pointers.
+				 */
+				shm = tee_shm_get_from_id(ctx, ip.c);
+				if (IS_ERR(shm))
+					return PTR_ERR(shm);
+
+				/*
+				 * Ensure offset + size does not overflow
+				 * offset and does not overflow the size of
+				 * the referred shared memory object.
+				 */
+				if ((ip.a + ip.b) < ip.a ||
+				    (ip.a + ip.b) > shm->size) {
+					tee_shm_put(shm);
+					return -EINVAL;
+				}
+			} else if (ctx->cap_memref_null) {
+				/* Pass NULL pointer to OP-TEE */
+				shm = NULL;
+			} else {
 				return -EINVAL;
 			}