Re: [Xen-devel] [PATCH 2/2] xen/physmap: Do not permit a guest to populate PoD pages for itself

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 19.08.16 at 16:12, <andrew.cooper3@xxxxxxxxxx> wrote:
> --- a/xen/common/memory.c
> +++ b/xen/common/memory.c
> @@ -903,7 +903,16 @@ long do_memory_op(unsigned long cmd, 
> XEN_GUEST_HANDLE_PARAM(void) arg)
>  
>          if ( op == XENMEM_populate_physmap
>               && (reservation.mem_flags & XENMEMF_populate_on_demand) )
> +        {
> +            /* Disallow populating PoD pages on oneself. */
> +            if ( d == curr_d )
> +            {
> +                rcu_unlock_domain(d);
> +                return start_extent;
> +            }
> +
>              args.memflags |= MEMF_populate_on_demand;
> +        }
>  
>          if ( xsm_memory_adjust_reservation(XSM_TARGET, curr_d, d) )
>          {

Considering the code continues

            rcu_unlock_domain(d);
            return start_extent;
        }

        switch ( op )
        {
        case XENMEM_increase_reservation:
            increase_reservation(&args);
            break;
        case XENMEM_decrease_reservation:
            decrease_reservation(&args);
            break;
        default: /* XENMEM_populate_physmap */
            populate_physmap(&args);
            break;
        }

I think it is time to move this XENMEM_populate_physmap specific
code chunk into populate_physmap(), at once eliminating the need
for another not entirely trivial error exit path here.

Jan


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