cxl: Add checksum verification to CDAT from CXL

A CDAT table is available from a CXL device. The table is read by the
driver and cached in software. With the CXL subsystem needing to parse the
CDAT table, the checksum should be verified. Add checksum verification
after the CDAT table is read from device.

Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/169713682277.2205276.2687265961314933628.stgit@djiang5-mobl3
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/cxl/core/pci.c

@@ -595,6 +595,16 @@ static int cxl_cdat_read_table(struct device *dev,
 	return 0;
 }
 
+static unsigned char cdat_checksum(void *buf, size_t size)
+{
+	unsigned char sum, *data = buf;
+	size_t i;
+
+	for (sum = 0, i = 0; i < size; i++)
+		sum += data[i];
+	return sum;
+}
+
 /**
  * read_cdat_data - Read the CDAT data on this port
  * @port: Port to read data from
@@ -634,15 +644,21 @@ void read_cdat_data(struct cxl_port *port)
 		return;
 
 	rc = cxl_cdat_read_table(dev, cdat_doe, cdat_table, &cdat_length);
-	if (rc) {
-		/* Don't leave table data allocated on error */
-		devm_kfree(dev, cdat_table);
-		dev_err(dev, "CDAT data read error\n");
-		return;
-	}
+	if (rc)
+		goto err;
 
-	port->cdat.table = cdat_table + sizeof(__le32);
+	cdat_table = cdat_table + sizeof(__le32);
+	if (cdat_checksum(cdat_table, cdat_length))
+		goto err;
+
+	port->cdat.table = cdat_table;
 	port->cdat.length = cdat_length;
+	return;
+
+err:
+	/* Don't leave table data allocated on error */
+	devm_kfree(dev, cdat_table);
+	dev_err(dev, "Failed to read/validate CDAT.\n");
 }
 EXPORT_SYMBOL_NS_GPL(read_cdat_data, CXL);