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SubjectRe: [PATCH 2/2] cxl/cdat: Fix header sum value in CDAT checksum
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On 11/17/23 18:14, Ira Weiny wrote:
> 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/
>
> Signed-off-by: Ira Weiny <ira.weiny@intel.com>
> ---
> hw/cxl/cxl-cdat.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/hw/cxl/cxl-cdat.c b/hw/cxl/cxl-cdat.c
> index 24829cf2428d..d93e2e4e64f2 100644
> --- a/hw/cxl/cxl-cdat.c
> +++ b/hw/cxl/cxl-cdat.c
> @@ -95,8 +95,15 @@ 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;
> +
> + do {
> + uint8_t *buf = (uint8_t *)cdat_header;
> +
> + for (i = 0; i < sizeof(*cdat_header); i++) {
> + sum += buf[i];
> + }
> + } while (0);

Why the empty do/while loop?

> +
> /* Sum of all bytes including checksum must be 0 */
> cdat_header->checksum = ~sum + 1;
>
>

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