[PATCH v2 04/12] cxl/cdat: Fix header sum value in CDAT checksum

[Jonathan Cameron <Jonathan.Cameron@huawei.com>]

From: Ira Weiny <ira.weiny@intel.com>

The addition of the DCD support for CXL type-3 devices extended the CDAT
table large enough that the checksum being returned was incorrect.[1]

This was because the checksum value was using the header length field
rather than each of the 4 bytes of the length field.  This was
previously not seen because the length of the CDAT data was less than
256 thus resulting in an equivalent checksum value.

Properly calculate the checksum for the CDAT header.

[1] https://lore.kernel.org/all/20231116-fix-cdat-devm-free-v1-1-b148b40707d7@intel.com/

Fixes: aba578bdace5 ("hw/cxl/cdat: CXL CDAT Data Object Exchange implementation")
Cc: Huai-Cheng Kuo <hchkuo@avery-design.com.tw>
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Fan Ni <fan.ni@samsung.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

---
Ammended buf naming to hdr_buf to avoid shadow issue with an existing buf variable
with more limited scope.
---
 hw/cxl/cxl-cdat.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/hw/cxl/cxl-cdat.c b/hw/cxl/cxl-cdat.c
index 24829cf242..2fea975671 100644
--- a/hw/cxl/cxl-cdat.c
+++ b/hw/cxl/cxl-cdat.c
@@ -49,6 +49,7 @@ static void ct3_build_cdat(CDATObject *cdat, Error **errp)
     g_autofree CDATTableHeader *cdat_header = NULL;
     g_autofree CDATEntry *cdat_st = NULL;
     uint8_t sum = 0;
+    uint8_t *hdr_buf;
     int ent, i;
 
     /* Use default table if fopen == NULL */
@@ -95,8 +96,12 @@ static void ct3_build_cdat(CDATObject *cdat, Error **errp)
     /* For now, no runtime updates */
     cdat_header->sequence = 0;
     cdat_header->length += sizeof(CDATTableHeader);
-    sum += cdat_header->revision + cdat_header->sequence +
-        cdat_header->length;
+
+    hdr_buf = (uint8_t *)cdat_header;
+    for (i = 0; i < sizeof(*cdat_header); i++) {
+        sum += hdr_buf[i];
+    }
+
     /* Sum of all bytes including checksum must be 0 */
     cdat_header->checksum = ~sum + 1;
 
-- 
2.39.2