Re: [Xen-devel] [PATCH 8 of 8] Tools: After a helper maps a ring, yank it from the guest physmap

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2012-03-06 at 18:50 -0500, Andres Lagar-Cavilla wrote:
> tools/tests/xen-access/xen-access.c |  5 +++++
>  tools/xenpaging/xenpaging.c         |  5 +++++
>  2 files changed, 10 insertions(+), 0 deletions(-)
> 
> 
> This limits the ability of the guest to play around with its own rings, and 
> DoS
> itself.
> 
> Signed-off-by: Andres Lagar-Cavilla <andres@xxxxxxxxxxxxxxxx>

Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>

> 
> diff -r b8c6f0af992a -r 13cddd7608bd tools/tests/xen-access/xen-access.c
> --- a/tools/tests/xen-access/xen-access.c
> +++ b/tools/tests/xen-access/xen-access.c
> @@ -269,6 +269,11 @@ xenaccess_t *xenaccess_init(xc_interface
>                     (mem_event_sring_t *)xenaccess->mem_event.ring_page,
>                     PAGE_SIZE);
>  
> +    /* Now that the ring is set, remove it from the guest's physmap */
> +    if ( xc_domain_decrease_reservation_exact(xch, 
> +                    xenaccess->mem_event.domain_id, 1, 0, &ring_pfn) )
> +        PERROR("Failed to remove ring from guest physmap");
> +
>      /* Get platform info */
>      xenaccess->platform_info = malloc(sizeof(xc_platform_info_t));
>      if ( xenaccess->platform_info == NULL )
> diff -r b8c6f0af992a -r 13cddd7608bd tools/xenpaging/xenpaging.c
> --- a/tools/xenpaging/xenpaging.c
> +++ b/tools/xenpaging/xenpaging.c
> @@ -420,6 +420,11 @@ static struct xenpaging *xenpaging_init(
>                     (mem_event_sring_t *)paging->mem_event.ring_page,
>                     PAGE_SIZE);
>  
> +    /* Now that the ring is set, remove it from the guest's physmap */
> +    if ( xc_domain_decrease_reservation_exact(xch, 
> +                    paging->mem_event.domain_id, 1, 0, &ring_pfn) )
> +        PERROR("Failed to remove ring from guest physmap");
> +
>      /* Get max_pages from guest if not provided via cmdline */
>      if ( !paging->max_pages )
>      {



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