[PATCH v3] cxl: Add checksum verification to CDAT from CXL

From: Dave Jiang <dave.jiang@intel.com>
To: dan.j.willimans@intel.com
Cc: Ira Weiny <ira.weiny@intel.com>,
	Jonathan Cameron <Jonathan.Cameron@huawei.com>,
	Davidlohr Bueso <dave@stgolabs.net>,
	linux-cxl@vger.kernel.org
Subject: [PATCH v3] cxl: Add checksum verification to CDAT from CXL
Date: Fri, 12 May 2023 15:01:24 -0700	[thread overview]
Message-ID: <168392888452.286187.18112582667622962209.stgit@djiang5-mobl3> (raw)
In-Reply-To: <645eb1bd61964_1e6f29419@dwillia2-xfh.jf.intel.com.notmuch>

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>

---
Post patch series split:
v3:
- Use single error out path. (Dan)
v2:
- Split out fix for cdat_read() error path return. (Davidlohr)
- Make port->cdat consistent. (Davidlohr)

___
v5:
- Return on CDAT errors. (Dan)
v3:
- Just return the final sum. (Alison)
v2:
- Drop ACPI checksum export and just use local verification. (Dan)
---
 drivers/cxl/core/pci.c |   30 +++++++++++++++++++++++-------
 1 file changed, 23 insertions(+), 7 deletions(-)

diff --git a/drivers/cxl/core/pci.c b/drivers/cxl/core/pci.c
index f332fe7af92b..103c27f5e2a9 100644
--- a/drivers/cxl/core/pci.c
+++ b/drivers/cxl/core/pci.c
@@ -528,6 +528,16 @@ 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
@@ -567,15 +577,21 @@ 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);
 


