Re: [PATCH 5/7] x86/mkreloc: remove warning about relocations to RO section

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Wed, Mar 19, 2025 at 11:46:22AM +0100, Jan Beulich wrote:
> On 19.03.2025 11:32, Jan Beulich wrote:
> > On 18.03.2025 18:35, Roger Pau Monne wrote:
> >> Relocations are now applied after having moved the trampoline,
> > 
> > That's two entirely different sets of relocations, isn't it? 

Right, this is the plain .reloc, while the trampoline one is
.trampoline_{rel,seg}

> > What we generate
> > here is what is to be encoded in the PE binary's .reloc section, for the PE
> > loader to process. And for us to then process again once we move Xen back to
> > its linked position (by virtue of leaving physical mode). Therefore what
> > matters here is whether these relocations are still carried out while on the
> > page tables to boot loader created, or when already on page tables we 
> > control.
> > In the former case any relocation to a non-writable section would be liable
> > to fault when applied.
> 
> And yes - both calls to efi_arch_relocate_image() are ahead of switching page
> tables. The first call is benign - no writes occur there. The second call
> would cause #PF though for any relocs applied to .text or .rodata or 
> .init.text
> or whatever else is non-writable.

I wonder how this worked then, as I've tested with the xen.efi smoke
test in gitlab CI.  Maybe ovmf doesn't acknowledge the RX sections and
unconditionally sets all mappings as writable?

Thanks, Roger.