Re: [Xen-devel] [PATCH 26/27] xen/arm: mm: Handling permission flags when adding a new mapping

[Andre Przywara <andre.przywara@xxxxxxx>]

Hi,

On 14/08/17 15:24, Julien Grall wrote:
> Currently, all the new mappings will be read-write non-executable. Allow the
> caller to use other permissions.
> 
> Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
> ---
>  xen/arch/arm/mm.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
> index cd7bcf7aca..fe0646002e 100644
> --- a/xen/arch/arm/mm.c
> +++ b/xen/arch/arm/mm.c
> @@ -1022,6 +1022,14 @@ static int create_xen_entries(enum xenmap_operation op,
>                  if ( op == RESERVE )
>                      break;
>                  pte = mfn_to_xen_entry(mfn, PAGE_AI_MASK(flags));
> +                pte.pt.ro = PAGE_RO_MASK(flags);
> +                pte.pt.xn = PAGE_XN_MASK(flags);
> +                if (  !pte.pt.ro && !pte.pt.xn )
> +                {
> +                    printk("%s: Incorrect combination for addr=%lx\n",
> +                           __func__, addr);
> +                    return -EINVAL;

I don't think this should be a handled runtime error, but rather a
BUG_ON() or an ASSERT().
I chased down the call chain for all create_xen_entries() invocations,
and they all stem from some constant (combination of) hard coded flags.
So ending up with an invalid combination here is clearly a bug in the
code and should be treated as such.

Cheers,
Andre.

> +                }
>                  pte.pt.table = 1;
>                  write_pte(entry, pte);
>                  break;
> 

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel