Re: [PATCH v2 3/7] platform/x86/amd/hsmp: Unify response_sz validation to an upper-bound check

[Suma Hegde]

Reviewed-by: Suma Hegde <suma.hegde@xxxxxxx>


On 4/27/2026 9:21 PM, Muralidhara M K wrote:
> Caution: This message originated from an External Source. Use proper caution when opening attachments, clicking links, or responding.
>
>
> The original validate_message() enforced a strict equality check
> (response_sz != table.response_sz) for HSMP_SET and HSMP_GET messages,
> while only HSMP_SET_GET messages used a relaxed upper-bound check.
>
> As HSMP protocol versions increase, existing message IDs may gain
> additional response arguments on newer platforms.  The strict equality
> check rejects older userspace callers that were compiled against an
> earlier hsmp_msg_desc_table[] and request fewer response words than the
> current table defines, breaking backward compatibility unnecessarily.
>
> Replace the per-type branching with a single upper-bound check for all
> message types.  This allows older userspace to request fewer response
> words while still rejecting any request that exceeds the hardware
> capability defined in the descriptor table.
>
> Co-developed-by: Muthusamy Ramalingam <muthusamy.ramalingam@xxxxxxx>
> Signed-off-by: Muthusamy Ramalingam <muthusamy.ramalingam@xxxxxxx>
> Signed-off-by: Muralidhara M K <muralidhara.mk@xxxxxxx>
> ---
> Change v1->v2: New
>
>   drivers/platform/x86/amd/hsmp/hsmp.c | 21 ++++++++-------------
>   1 file changed, 8 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/platform/x86/amd/hsmp/hsmp.c b/drivers/platform/x86/amd/hsmp/hsmp.c
> index 631ffc0978d1..9bad58fef304 100644
> --- a/drivers/platform/x86/amd/hsmp/hsmp.c
> +++ b/drivers/platform/x86/amd/hsmp/hsmp.c
> @@ -182,20 +182,15 @@ static int validate_message(struct hsmp_message *msg)
>                  return -EINVAL;
>
>          /*
> -        * Some older HSMP SET messages are updated to add GET in the same message.
> -        * In these messages, GET returns the current value and SET also returns
> -        * the successfully set value. To support this GET and SET in same message
> -        * while maintaining backward compatibility for the HSMP users,
> -        * hsmp_msg_desc_table[] indicates only maximum allowed response_sz.
> +        * As the HSMP protocol evolves, newer platforms may define more
> +        * response arguments for existing messages.  Use an upper-bound
> +        * check so that older userspace callers requesting fewer response
> +        * words than what the current hsmp_msg_desc_table[] defines are
> +        * still accepted, while rejecting requests that exceed the
> +        * hardware capability.
>           */
> -       if (hsmp_msg_desc_table[msg->msg_id].type == HSMP_SET_GET) {
> -               if (msg->response_sz > hsmp_msg_desc_table[msg->msg_id].response_sz)
> -                       return -EINVAL;
> -       } else {
> -               /* only HSMP_SET or HSMP_GET messages go through this strict check */
> -               if (msg->response_sz != hsmp_msg_desc_table[msg->msg_id].response_sz)
> -                       return -EINVAL;
> -       }
> +       if (msg->response_sz > hsmp_msg_desc_table[msg->msg_id].response_sz)
> +               return -EINVAL;
>          return 0;
>   }
>
> --
> 2.34.1