cxl: Fix the incorrect assignment of SSLBIS entry pointer initial location

The 'entry' pointer in cdat_sslbis_handler() is set to header +
sizeof(common header). However, the math missed the addition of the SSLBIS
main header. It should be header + sizeof(common header) + sizeof(*sslbis).
Use a defined struct for all the SSLBIS parts in order to avoid pointer
math errors.

The bug causes incorrect parsing of the SSLBIS table and introduces incorrect
performance values to the access_coordinates during the CXL access_coordinate
calculation path if there are CXL switches present in the topology.

The issue was found during testing of new code being added to add additional
checks for invalid CDAT values during CXL access_coordinate calculation. The
testing was done on qemu with a CXL topology including a CXL switch.

Fixes: 80aa780d ("cxl: Add callback to parse the SSLBIS subtable from CDAT")
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Fan Ni <fan.ni@samsung.com>
Link: https://lore.kernel.org/r/20240301210948.1298075-1-dave.jiang@intel.comSigned-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/cxl/core/cdat.c

@@ -389,36 +389,38 @@ EXPORT_SYMBOL_NS_GPL(cxl_endpoint_parse_cdat, CXL);
 static int cdat_sslbis_handler(union acpi_subtable_headers *header, void *arg,
 			       const unsigned long end)
 {
+	struct acpi_cdat_sslbis_table {
+		struct acpi_cdat_header header;
+		struct acpi_cdat_sslbis sslbis_header;
+		struct acpi_cdat_sslbe entries[];
+	} *tbl = (struct acpi_cdat_sslbis_table *)header;
+	int size = sizeof(header->cdat) + sizeof(tbl->sslbis_header);
 	struct acpi_cdat_sslbis *sslbis;
-	int size = sizeof(header->cdat) + sizeof(*sslbis);
 	struct cxl_port *port = arg;
 	struct device *dev = &port->dev;
-	struct acpi_cdat_sslbe *entry;
 	int remain, entries, i;
 	u16 len;
 
 	len = le16_to_cpu((__force __le16)header->cdat.length);
 	remain = len - size;
-	if (!remain || remain % sizeof(*entry) ||
+	if (!remain || remain % sizeof(tbl->entries[0]) ||
 	    (unsigned long)header + len > end) {
 		dev_warn(dev, "Malformed SSLBIS table length: (%u)\n", len);
 		return -EINVAL;
 	}
 
-	/* Skip common header */
-	sslbis = (struct acpi_cdat_sslbis *)((unsigned long)header +
-					     sizeof(header->cdat));
-
+	sslbis = &tbl->sslbis_header;
 	/* Unrecognized data type, we can skip */
 	if (sslbis->data_type > ACPI_HMAT_WRITE_BANDWIDTH)
 		return 0;
 
-	entries = remain / sizeof(*entry);
-	entry = (struct acpi_cdat_sslbe *)((unsigned long)header + sizeof(*sslbis));
+	entries = remain / sizeof(tbl->entries[0]);
+	if (struct_size(tbl, entries, entries) != len)
+		return -EINVAL;
 
 	for (i = 0; i < entries; i++) {
-		u16 x = le16_to_cpu((__force __le16)entry->portx_id);
-		u16 y = le16_to_cpu((__force __le16)entry->porty_id);
+		u16 x = le16_to_cpu((__force __le16)tbl->entries[i].portx_id);
+		u16 y = le16_to_cpu((__force __le16)tbl->entries[i].porty_id);
 		__le64 le_base;
 		__le16 le_val;
 		struct cxl_dport *dport;
@@ -448,8 +450,8 @@ static int cdat_sslbis_handler(union acpi_subtable_headers *header, void *arg,
 			break;
 		}
 
-		le_base = (__force __le64)sslbis->entry_base_unit;
-		le_val = (__force __le16)entry->latency_or_bandwidth;
+		le_base = (__force __le64)tbl->sslbis_header.entry_base_unit;
+		le_val = (__force __le16)tbl->entries[i].latency_or_bandwidth;
 
 		if (check_mul_overflow(le64_to_cpu(le_base),
 				       le16_to_cpu(le_val), &val))
@@ -462,8 +464,6 @@ static int cdat_sslbis_handler(union acpi_subtable_headers *header, void *arg,
 							  sslbis->data_type,
 							  val);
 		}
-
-		entry++;
 	}
 
 	return 0;