RE: [PATCH v2 3/4] Drivers: hv: vmbus: Enforce 'VMBus version >= 5.2' on isolated guests

[Michael Kelley <mikelley@microsoft.com>]

From: Andrea Parri (Microsoft) <parri.andrea@gmail.com> Sent: Tuesday, January 26, 2021 3:57 AM
> 
> Restrict the protocol version(s) that will be negotiated with the host
> to be 5.2 or greater if the guest is running isolated.  This reduces the
> footprint of the code that will be exercised by Confidential VMs and
> hence the exposure to bugs and vulnerabilities.
> 
> Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
> ---
>  drivers/hv/connection.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
> index 11170d9a2e1a5..bcf4d7def6838 100644
> --- a/drivers/hv/connection.c
> +++ b/drivers/hv/connection.c
> @@ -66,6 +66,13 @@ module_param(max_version, uint, S_IRUGO);
>  MODULE_PARM_DESC(max_version,
>  		 "Maximal VMBus protocol version which can be negotiated");
> 
> +static bool vmbus_is_valid_version(u32 version)
> +{
> +	if (hv_is_isolation_supported())
> +		return version >= VERSION_WIN10_V5_2;
> +	return true;
> +}
> +
>  int vmbus_negotiate_version(struct vmbus_channel_msginfo *msginfo, u32 version)
>  {
>  	int ret = 0;
> @@ -233,6 +240,12 @@ int vmbus_connect(void)
>  			goto cleanup;
> 
>  		version = vmbus_versions[i];
> +
> +		if (!vmbus_is_valid_version(version)) {

Outputting a message in this case could be useful.  The message should show
what version was negotiated and then deemed invalid. 

> +			ret = -EINVAL;
> +			goto cleanup;
> +		}
> +
>  		if (version > max_version)
>  			continue;
> 
> --
> 2.25.1