Transports using shared memory have to consider the overhead due to the
layout area when determining the area effectively available for messages.

Till now, such definitions were ambiguos across the SCMI stack and the
overhead layout area was not considered at all.

Add proper checks in the shmem layer to validate the provided max_msg_size
against the effectively available memory area, less the layout.

Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
---
v2 --> v3
- using a single SCMI_SHMEM_PAYLOAD_SIZE common define
---
Note that as a consequence of this fix the default max_msg_size is reduced
to 104 bytes for shmem-based transports, in order to fit into the most
common implementations where the whole shmem area is sized at 128,
including the 24 bytes of standard layout area.

This should have NO bad side effects, since the current maximum payload
size of any messages across any protocol (including all the known vendor
ones) is 76 bytes.
---
 drivers/firmware/arm_scmi/common.h             | 6 +++++-
 drivers/firmware/arm_scmi/driver.c             | 1 +
 drivers/firmware/arm_scmi/shmem.c              | 7 +++++++
 drivers/firmware/arm_scmi/transports/mailbox.c | 2 +-
 drivers/firmware/arm_scmi/transports/optee.c   | 8 +++-----
 drivers/firmware/arm_scmi/transports/smc.c     | 2 +-
 6 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/drivers/firmware/arm_scmi/common.h b/drivers/firmware/arm_scmi/common.h
index 6c2032d4f767..cb39b6bbcffd 100644
--- a/drivers/firmware/arm_scmi/common.h
+++ b/drivers/firmware/arm_scmi/common.h
@@ -31,6 +31,8 @@
 
 #define SCMI_MAX_RESPONSE_TIMEOUT	(2 * MSEC_PER_SEC)
 
+#define SCMI_SHMEM_MAX_PAYLOAD_SIZE	104
+
 enum scmi_error_codes {
 	SCMI_SUCCESS = 0,	/* Success */
 	SCMI_ERR_SUPPORT = -1,	/* Not supported */
@@ -165,6 +167,7 @@ void scmi_protocol_release(const struct scmi_handle *handle, u8 protocol_id);
  *	 channel
  * @is_p2a: A flag to identify a channel as P2A (RX)
  * @rx_timeout_ms: The configured RX timeout in milliseconds.
+ * @max_msg_size: Maximum size of message payload.
  * @handle: Pointer to SCMI entity handle
  * @no_completion_irq: Flag to indicate that this channel has no completion
  *		       interrupt mechanism for synchronous commands.
@@ -177,6 +180,7 @@ struct scmi_chan_info {
 	struct device *dev;
 	bool is_p2a;
 	unsigned int rx_timeout_ms;
+	unsigned int max_msg_size;
 	struct scmi_handle *handle;
 	bool no_completion_irq;
 	void *transport_info;
@@ -224,7 +228,7 @@ struct scmi_transport_ops {
  * @max_msg: Maximum number of messages for a channel type (tx or rx) that can
  *	be pending simultaneously in the system. May be overridden by the
  *	get_max_msg op.
- * @max_msg_size: Maximum size of data per message that can be handled.
+ * @max_msg_size: Maximum size of data payload per message that can be handled.
  * @force_polling: Flag to force this whole transport to use SCMI core polling
  *		   mechanism instead of completion interrupts even if available.
  * @sync_cmds_completed_on_ret: Flag to indicate that the transport assures
diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c
index dccd066e3ba8..015a4d52ae37 100644
--- a/drivers/firmware/arm_scmi/driver.c
+++ b/drivers/firmware/arm_scmi/driver.c
@@ -2645,6 +2645,7 @@ static int scmi_chan_setup(struct scmi_info *info, struct device_node *of_node,
 
 	cinfo->is_p2a = !tx;
 	cinfo->rx_timeout_ms = info->desc->max_rx_timeout_ms;
+	cinfo->max_msg_size = info->desc->max_msg_size;
 
 	/* Create a unique name for this transport device */
 	snprintf(name, 32, "__scmi_transport_device_%s_%02X",
diff --git a/drivers/firmware/arm_scmi/shmem.c b/drivers/firmware/arm_scmi/shmem.c
index e9f30ab671a8..11c347bff766 100644
--- a/drivers/firmware/arm_scmi/shmem.c
+++ b/drivers/firmware/arm_scmi/shmem.c
@@ -16,6 +16,8 @@
 
 #include "common.h"
 
+#define SCMI_SHMEM_LAYOUT_OVERHEAD	24
+
 /*
  * SCMI specification requires all parameters, message headers, return
  * arguments or any protocol data to be expressed in little endian
@@ -221,6 +223,11 @@ static void __iomem *shmem_setup_iomap(struct scmi_chan_info *cinfo,
 	}
 
 	size = resource_size(res);
+	if (cinfo->max_msg_size + SCMI_SHMEM_LAYOUT_OVERHEAD > size) {
+		dev_err(dev, "misconfigured SCMI shared memory\n");
+		return IOMEM_ERR_PTR(-ENOSPC);
+	}
+
 	addr = devm_ioremap(dev, res->start, size);
 	if (!addr) {
 		dev_err(dev, "failed to ioremap SCMI %s shared memory\n", desc);
diff --git a/drivers/firmware/arm_scmi/transports/mailbox.c b/drivers/firmware/arm_scmi/transports/mailbox.c
index e7efa3376aae..b66df2981456 100644
--- a/drivers/firmware/arm_scmi/transports/mailbox.c
+++ b/drivers/firmware/arm_scmi/transports/mailbox.c
@@ -371,7 +371,7 @@ static struct scmi_desc scmi_mailbox_desc = {
 	.ops = &scmi_mailbox_ops,
 	.max_rx_timeout_ms = 30, /* We may increase this if required */
 	.max_msg = 20, /* Limited by MBOX_TX_QUEUE_LEN */
-	.max_msg_size = 128,
+	.max_msg_size = SCMI_SHMEM_MAX_PAYLOAD_SIZE,
 };
 
 static const struct of_device_id scmi_of_match[] = {
diff --git a/drivers/firmware/arm_scmi/transports/optee.c b/drivers/firmware/arm_scmi/transports/optee.c
index 663272879edf..3949a877e17d 100644
--- a/drivers/firmware/arm_scmi/transports/optee.c
+++ b/drivers/firmware/arm_scmi/transports/optee.c
@@ -17,8 +17,6 @@
 
 #include "../common.h"
 
-#define SCMI_OPTEE_MAX_MSG_SIZE		128
-
 enum scmi_optee_pta_cmd {
 	/*
 	 * PTA_SCMI_CMD_CAPABILITIES - Get channel capabilities
@@ -299,7 +297,7 @@ static int invoke_process_msg_channel(struct scmi_optee_channel *channel, size_t
 
 	param[2].attr = TEE_IOCTL_PARAM_ATTR_TYPE_MEMREF_OUTPUT;
 	param[2].u.memref.shm = channel->tee_shm;
-	param[2].u.memref.size = SCMI_OPTEE_MAX_MSG_SIZE;
+	param[2].u.memref.size = SCMI_SHMEM_MAX_PAYLOAD_SIZE;
 
 	ret = tee_client_invoke_func(scmi_optee_private->tee_ctx, &arg, param);
 	if (ret < 0 || arg.ret) {
@@ -332,7 +330,7 @@ static void scmi_optee_clear_channel(struct scmi_chan_info *cinfo)
 
 static int setup_dynamic_shmem(struct device *dev, struct scmi_optee_channel *channel)
 {
-	const size_t msg_size = SCMI_OPTEE_MAX_MSG_SIZE;
+	const size_t msg_size = SCMI_SHMEM_MAX_PAYLOAD_SIZE;
 	void *shbuf;
 
 	channel->tee_shm = tee_shm_alloc_kernel_buf(scmi_optee_private->tee_ctx, msg_size);
@@ -519,7 +517,7 @@ static struct scmi_desc scmi_optee_desc = {
 	.ops = &scmi_optee_ops,
 	.max_rx_timeout_ms = 30,
 	.max_msg = 20,
-	.max_msg_size = SCMI_OPTEE_MAX_MSG_SIZE,
+	.max_msg_size = SCMI_SHMEM_MAX_PAYLOAD_SIZE,
 	.sync_cmds_completed_on_ret = true,
 };
 
diff --git a/drivers/firmware/arm_scmi/transports/smc.c b/drivers/firmware/arm_scmi/transports/smc.c
index 2f0e981e7599..f632a62cfb3e 100644
--- a/drivers/firmware/arm_scmi/transports/smc.c
+++ b/drivers/firmware/arm_scmi/transports/smc.c
@@ -282,7 +282,7 @@ static struct scmi_desc scmi_smc_desc = {
 	.ops = &scmi_smc_ops,
 	.max_rx_timeout_ms = 30,
 	.max_msg = 20,
-	.max_msg_size = 128,
+	.max_msg_size = SCMI_SHMEM_MAX_PAYLOAD_SIZE,
 	/*
 	 * Setting .sync_cmds_atomic_replies to true for SMC assumes that,
 	 * once the SMC instruction has completed successfully, the issued
-- 
2.47.0