2023-11-18 01:14:43

by Ira Weiny

Subject: [PATCH 2/2] cxl/cdat: Fix header sum value in CDAT checksum

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/[email protected]/

Signed-off-by: Ira Weiny <[email protected]>
---
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);
+
/* Sum of all bytes including checksum must be 0 */
cdat_header->checksum = ~sum + 1;


--
2.41.0

2023-11-20 15:44:28

by Dave Jiang

Subject: Re: [PATCH 2/2] cxl/cdat: Fix header sum value in CDAT checksum

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/[email protected]/
>
> Signed-off-by: Ira Weiny <[email protected]>
> ---
> 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;
>
>

2023-11-27 20:48:27

by Ira Weiny

Subject: Re: [PATCH 2/2] cxl/cdat: Fix header sum value in CDAT checksum

Dave Jiang wrote:
>

[snip]

> > 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?

Because I used the loop for debugging and forgot to clean up after it was
tested.

I'll send a v2,
Ira