Re: [Xen-devel] [PATCH v2 03/21] xen: allow console_io hypercalls from certain DomUs

[Julien Grall <julien.grall@xxxxxxx>]

Hi,

On 07/07/18 00:11, Stefano Stabellini wrote:
> Introduce an is_console option to allow certain classes of domUs to use
> the Xen console. Specifically, it will be used to give console access to
> all domUs started from Xen from information on device tree.
>
> Signed-off-by: Stefano Stabellini <stefanos@xxxxxxxxxx>
> CC: andrew.cooper3@xxxxxxxxxx
> CC: George.Dunlap@xxxxxxxxxxxxx
> CC: ian.jackson@xxxxxxxxxxxxx
> CC: jbeulich@xxxxxxxx
> CC: konrad.wilk@xxxxxxxxxx
> CC: tim@xxxxxxx
> CC: wei.liu2@xxxxxxxxxx
> CC: dgdegra@xxxxxxxxxxxxx
> ---
> Changes in v2:
> - introduce is_console
> - remove #ifdefs
> ---
>   xen/include/xen/sched.h | 2 ++
>   xen/include/xsm/dummy.h | 2 ++
>   xen/xsm/flask/hooks.c   | 5 ++++-
>   3 files changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
> index 99d2af2..d66cec0 100644
> --- a/xen/include/xen/sched.h
> +++ b/xen/include/xen/sched.h
> @@ -379,6 +379,8 @@ struct domain
>       bool             auto_node_affinity;
>       /* Is this guest fully privileged (aka dom0)? */
>       bool             is_privileged;
> +    /* Can this guest access the Xen console? */
> +    bool             is_console;
>       /* Is this a xenstore domain (not dom0)? */
>       bool             is_xenstore;
>       /* Domain's VCPUs are pinned 1:1 to physical CPUs? */
> diff --git a/xen/include/xsm/dummy.h b/xen/include/xsm/dummy.h
> index ff6b2db..3888817 100644
> --- a/xen/include/xsm/dummy.h
> +++ b/xen/include/xsm/dummy.h
> @@ -230,6 +230,8 @@ static XSM_INLINE int 
> xsm_memory_stat_reservation(XSM_DEFAULT_ARG struct domain
>   static XSM_INLINE int xsm_console_io(XSM_DEFAULT_ARG struct domain *d, int 
> cmd)
>   {
>       XSM_ASSERT_ACTION(XSM_OTHER);
> +    if ( d->is_console )
> +        return xsm_default_action(XSM_HOOK, d, NULL);
I will let Daniel commenting on this change. However ...

>   #ifdef CONFIG_VERBOSE_DEBUG
>       if ( cmd == CONSOLEIO_write )
>           return xsm_default_action(XSM_HOOK, d, NULL);
> diff --git a/xen/xsm/flask/hooks.c b/xen/xsm/flask/hooks.c
> index 78bc326..2551e4e 100644
> --- a/xen/xsm/flask/hooks.c
> +++ b/xen/xsm/flask/hooks.c
> @@ -443,7 +443,10 @@ static int flask_console_io(struct domain *d, int cmd)
>           return avc_unknown_permission("console_io", cmd);
>       }
>   
> -    return domain_has_xen(d, perm);
> +    if ( !d->is_console )
> +        return domain_has_xen(d, perm);
> +    else
> +        return 0;
... I don't think this change is correct. When a policy is used, the 
user is free to define what is the behavior. With your solution, you 
impose the console access even if the user didn't to not give the 
permission.
>   }
>   
>   static int flask_profile(struct domain *d, int op)
Cheers,

--
Julien Grall

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