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

["Jan Beulich" <jbeulich@xxxxxxxx>]

>>> David Woodhouse <dwmw2@xxxxxxxxxxxxx> 07/31/17 1:19 AM >>>
>On Sun, 2017-07-30 at 13:50 +0100, Andrew Cooper wrote:
>> 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.
>
>Hm, efi/mkreloc.c was already emitting relocations in the .rodata
>section before this change. Are you saying that was already broken?

Are there any such relocations? The compiler shouldn't emit data needing
relocation to .rodata, so if at all such might live in assembly code. But yes,
if there are any, things would have been latently broken even before.

Jan


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