Re: [PATCH v5 4/5] common/domain: add a domain context record for shared_info...

[Jan Beulich <jbeulich@suse.com>]

On 21.05.2020 18:19, Paul Durrant wrote:
> @@ -1649,6 +1650,70 @@ int continue_hypercall_on_cpu(
>      return 0;
>  }
>  
> +static int save_shared_info(const struct domain *d, struct domain_context *c,
> +                            bool dry_run)
> +{
> +    struct domain_shared_info_context ctxt = {
> +#ifdef CONFIG_COMPAT
> +        .flags = has_32bit_shinfo(d) ? DOMAIN_SAVE_32BIT_SHINFO : 0,
> +#endif
> +        .buffer_size = sizeof(shared_info_t),

But this size varies between native and compat.

> +static int load_shared_info(struct domain *d, struct domain_context *c)
> +{
> +    struct domain_shared_info_context ctxt;
> +    size_t hdr_size = offsetof(typeof(ctxt), buffer);
> +    unsigned int i;
> +    int rc;
> +
> +    rc = DOMAIN_LOAD_BEGIN(SHARED_INFO, c, &i);
> +    if ( rc )
> +        return rc;
> +
> +    if ( i ) /* expect only a single instance */
> +        return -ENXIO;
> +
> +    rc = domain_load_data(c, &ctxt, hdr_size);
> +    if ( rc )
> +        return rc;
> +
> +    if ( ctxt.buffer_size != sizeof(shared_info_t) )
> +        return -EINVAL;

While on the save side things could be left as they are (yet
I'd prefer a change), this should be flexible enough to allow
at least the smaller compat size as well in the compat case.
I wonder whether any smaller sizes might be acceptable, once
again with the rest getting zero-padded.

> +    if ( ctxt.flags & DOMAIN_SAVE_32BIT_SHINFO )
> +#ifdef CONFIG_COMPAT
> +        has_32bit_shinfo(d) = true;
> +#else
> +        return -EINVAL;
> +#endif

Am I mis-remembering or was a check lost of the remaining
flags being zero? If I am, one needs adding in any case, imo.

Jan