[PATCH v3 9/9] firmware: arm_scmi: Validate PCC shared memory signature

Validate the PCC shared memory signature when setting up an SCMI PCC
channel.

Reject channels whose shared memory signature does not encode
PCC_SIGNATURE combined with the PCC subspace ID, so misconfigured
firmware is caught before the transport starts using the shared memory
region.

Signed-off-by: Sudeep Holla <[email protected]>
---
 drivers/firmware/arm_scmi/transports/pcc.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/firmware/arm_scmi/transports/pcc.c b/drivers/firmware/arm_scmi/transports/pcc.c
index 337d551e3ad8..0ead0ec77162 100644
--- a/drivers/firmware/arm_scmi/transports/pcc.c
+++ b/drivers/firmware/arm_scmi/transports/pcc.c
@@ -623,8 +623,11 @@ static void rx_callback(struct mbox_client *cl, void *m)
 }
 
 static int pcc_chan_validate_shmem(struct scmi_chan_info *cinfo,
-				   struct scmi_pcc *smbox)
+				   struct scmi_pcc *smbox, int ss_id)
 {
+	struct pcc_shared_mem __iomem *shmem = smbox->pchan->shmem;
+	u32 valid_signature = ss_id + PCC_SIGNATURE;
+
 	if (smbox->pchan->shmem_size < SCMI_PCC_SHMEM_OVERHEAD ||
 	    smbox->pchan->shmem_size - SCMI_PCC_SHMEM_OVERHEAD <
 	    cinfo->max_msg_size) {
@@ -632,6 +635,11 @@ static int pcc_chan_validate_shmem(struct scmi_chan_info *cinfo,
 		return -ENOSPC;
 	}
 
+	if (ioread32(&shmem->header.signature) != valid_signature) {
+		dev_err(cinfo->dev, "invalid PCC shared memory signature\n");
+		return -EINVAL;
+	}
+
 	return 0;
 }
 
@@ -667,7 +675,7 @@ static int pcc_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
 		return ret;
 	}
 
-	ret = pcc_chan_validate_shmem(cinfo, smbox);
+	ret = pcc_chan_validate_shmem(cinfo, smbox, ss_id);
 	if (ret) {
 		pcc_mbox_free_channel(smbox->pchan);
 		return ret;

-- 
2.43.0