Dave Jiang wrote:
> 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@xxxxxxxxx>
> Signed-off-by: Dave Jiang <dave.jiang@xxxxxxxxx>
>
> ---
> v3:
> - Just return the final sum. (Alison)
> v2:
> - Drop ACPI checksum export and just use local verification. (Dan)
> ---
> drivers/cxl/core/pci.c | 16 ++++++++++++++++
> 1 file changed, 16 insertions(+)
>
> diff --git a/drivers/cxl/core/pci.c b/drivers/cxl/core/pci.c
> index 25b7e8125d5d..9c7e2f69d9ca 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
> @@ -573,6 +583,12 @@ void read_cdat_data(struct cxl_port *port)
> }
>
> port->cdat.table = cdat_table + sizeof(__le32);
> + if (cdat_checksum(port->cdat.table, cdat_length)) {
> + /* Don't leave table data allocated on error */
> + devm_kfree(dev, cdat_table);
> + dev_err(dev, "CDAT data checksum error\n");
> + }
> +
> port->cdat.length = cdat_length;
I think read_cdat_data() is confused about error cases. I note that
/sys/firmware/acpi/tables does not emit the entry if the table has bad
length or bad checksum. If you want to have a debug mode then maybe make
it a compile time option, but I otherwise do not see the benefit of
publishing known bad tables to userspace.
