Re: [Xen-devel] xen/link: Move .data.rel.ro sections into .rodata for final link

["Jan Beulich" <jbeulich@xxxxxxxx>]

>>> Andrew Cooper <andrew.cooper3@xxxxxxxxxx> 07/30/17 2:50 PM >>>
>On 30/07/17 07:16, Jan Beulich wrote:
>>>>> David Woodhouse <dwmw2@xxxxxxxxxxxxx> 07/20/17 5:22 PM >>>
>>> This includes stuff lke the hypercall tables which we really want
>>> to be read-only. And they were going into .data.read-mostly.
>> Yes, we'd like them to be read-only, but what if EFI properly assigned r/o
>> permissions to the .rodata section when loading xen.efi? We'd then be
>> unable to apply relocations when switching from 1:1 to virtual mappings
>> (see efi_arch_relocate_image()).
>
>Ah yes.  I'd overlooked that point when considering the ramifications of
>this change.
>
>efi_arch_relocate_image() should probably do the same as what we do with
>livepatching, and temporarily clear CR0.WP for the duration of the patching.

Yes, we could do that, but with some care - we should no play with CR0.WP
prior to ExitBootServices(), so we would need to avoid actually writing out
relocated values for that first pass even in the 64-bit reloc case.

Jan



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