[RFC PATCH v2 08/14] cxl/cdat: Introduce cdat_hdr_valid()

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

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

The CDAT data is protected by a checksum which should be checked when
the CDAT is read to ensure it is valid.  In addition the lengths
specified should be checked.

Introduce cdat_hdr_valid() to check the checksum.  While at it check and
store the sequence number.

Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
---
 drivers/cxl/cdat.h |  2 ++
 drivers/cxl/pci.c  | 32 ++++++++++++++++++++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/drivers/cxl/cdat.h b/drivers/cxl/cdat.h
index 4722b6bbbaf0..a7725d26f2d2 100644
--- a/drivers/cxl/cdat.h
+++ b/drivers/cxl/cdat.h
@@ -88,10 +88,12 @@
  *
  * @table: cache of CDAT table
  * @length: length of cached CDAT table
+ * @seq: Last read Sequence number of the CDAT table
  */
 struct cxl_cdat {
 	void *table;
 	size_t length;
+	u32 seq;
 };
 
 #endif /* !__CXL_CDAT_H__ */
diff --git a/drivers/cxl/pci.c b/drivers/cxl/pci.c
index ebd98a8a310f..ed94a6bef2de 100644
--- a/drivers/cxl/pci.c
+++ b/drivers/cxl/pci.c
@@ -522,6 +522,35 @@ static int cxl_setup_doe_devices(struct cxl_dev_state *cxlds)
 	return 0;
 }
 
+static bool cxl_cdat_hdr_valid(struct device *dev, struct cxl_cdat *cdat)
+{
+	u32 *table = cdat->table;
+	u8 *data8 = cdat->table;
+	u32 length, seq;
+	u8 check;
+	int i;
+
+	length = FIELD_GET(CDAT_HEADER_DW0_LENGTH, table[0]);
+	if (length < CDAT_HEADER_LENGTH_BYTES)
+		return false;
+
+	if (length > cdat->length)
+		return false;
+
+	seq = FIELD_GET(CDAT_HEADER_DW3_SEQUENCE, table[3]);
+
+	/* Store the sequence for now. */
+	if (cdat->seq != seq) {
+		dev_info(dev, "CDAT seq change %x -> %x\n", cdat->seq, seq);
+		cdat->seq = seq;
+	}
+
+	for (check = 0, i = 0; i < length; i++)
+		check += data8[i];
+
+	return check == 0;
+}
+
 #define CDAT_DOE_REQ(entry_handle)					\
 	(FIELD_PREP(CXL_DOE_TABLE_ACCESS_REQ_CODE,			\
 		    CXL_DOE_TABLE_ACCESS_REQ_CODE_READ) |		\
@@ -594,6 +623,9 @@ static int cxl_cdat_read_table(struct cxl_dev_state *cxlds,
 
 	} while (entry_handle != 0xFFFF);
 
+	if (!cxl_cdat_hdr_valid(cxlds->dev, cdat))
+		return -EIO;
+
 	return 0;
 }
 
-- 
2.32.0