Re: [Xen-devel] [PATCH] xen/x86: Remap text/data/bss with appropriate permissions

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 17.03.16 at 13:43, <andrew.cooper3@xxxxxxxxxx> wrote:
> --- a/xen/arch/x86/setup.c
> +++ b/xen/arch/x86/setup.c
> @@ -529,9 +529,33 @@ static void noinline init_done(void)
>      }
>      else
>      {
> +        /* Mark .text as RX (avoiding the first 2M superpage). */
> +        map_pages_to_xen(XEN_VIRT_START + MB(2),
> +                         PFN_DOWN(__pa(XEN_VIRT_START + MB(2))),
> +                         PFN_DOWN(__2M_text_end -
> +                                  (const char *)(XEN_VIRT_START + MB(2))),
> +                         PAGE_HYPERVISOR_RX);
> +
> +        /* Mark .rodata as RO. */
> +        map_pages_to_xen((unsigned long)&__2M_rodata_start,
> +                         PFN_DOWN(__pa(__2M_rodata_start)),
> +                         PFN_DOWN(__2M_rodata_end - __2M_rodata_start),
> +                         PAGE_HYPERVISOR_RO);
> +
> +        /* Free and reuse .init. */
>          destroy_xen_mappings((unsigned long)&__init_begin,
>                               (unsigned long)&__init_end);
>          init_xenheap_pages(__pa(__init_begin), __pa(__init_end));
> +
> +        /* Mark .data and .bss as RW. */
> +        map_pages_to_xen((unsigned long)&__2M_rwdata_start,
> +                         PFN_DOWN(__pa(__2M_rwdata_start)),
> +                         PFN_DOWN(__2M_rwdata_end - __2M_rwdata_start),
> +                         PAGE_HYPERVISOR_RW);
> +
> +        /* Drop the remaining mappings in the shattered superpage. */
> +        destroy_xen_mappings((unsigned long)&__2M_rwdata_end,
> +                             ROUNDUP((unsigned long)&__2M_rwdata_end, 
> MB(2)));
>      }

I think this would be more appropriate to add to some __init
function (which the discarding of .init.* naturally can't live in).

Also - do we really want to make this code dependent on
map_pages_to_xen() not intermediately zapping the mappings
being changed?

Jan


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