Re: [PATCH v3 6/9] module: switch to execmem API for remapping as RW and restoring ROX

Mike Rapoport
2025-01-28T10:01:18Z

On Mon, Jan 27, 2025 at 01:50:31PM +0100, Petr Pavlu wrote:
> On 1/26/25 08:47, Mike Rapoport wrote:
> > From: "Mike Rapoport (Microsoft)" <rppt@kernel.org>
> >
> > Instead of using writable copy for module text sections, temporarily remap
> > the memory allocated from execmem's ROX cache as writable and restore its
> > ROX permissions after the module is formed.
> >
> > This will allow removing nasty games with writable copy in alternatives
> > patching on x86.
> >
> > Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
>
> [...]
>
> > +static void module_memory_restore_rox(struct module *mod)
> > +{
> > + for_class_mod_mem_type(type, text) {
> > + struct module_memory *mem = &mod->mem[type];
> > +
> > + if (mem->is_rox)
> > + execmem_restore_rox(mem->base, mem->size);
> > + }
> > +}
> > +
>
> Can the execmem_restore_rox() call here fail? I realize that there isn't
> much that the module loader can do if that happens, but should it be
> perhaps logged as a warning?

It won't fail at this point. set_memory APIs may fail if they need to split
a large page and could not allocate a new page table, but here all the
splits were already done at module_memory_alloc() time.

> --
> Thanks,
> Petr

--
Sincerely yours,
Mike.