Re: [PATCH v2 32/33] s390: Implement the architecture-specific kmsan functions

[Ilya Leoshkevich]

On Mon, 2023-12-11 at 11:26 +0100, Alexander Potapenko wrote:
> > +static inline void *arch_kmsan_get_meta_or_null(void *addr, bool
> > is_origin)
> > +{
> > +       if (addr >= (void *)&S390_lowcore &&
> > +           addr < (void *)(&S390_lowcore + 1)) {
> > +               /*
> > +                * Different lowcores accessed via S390_lowcore are
> > described
> > +                * by the same struct page. Resolve the prefix
> > manually in
> > +                * order to get a distinct struct page.
> > +                */
> > +               addr += (void *)lowcore_ptr[raw_smp_processor_id()]
> > -
> > +                       (void *)&S390_lowcore;
> > +               return kmsan_get_metadata(addr, is_origin);
> > +       }
> > +       return NULL;
> > +}
> 
> Is there a possibility for infinite recursion here? E.g. can
> `lowcore_ptr[raw_smp_processor_id()]` point somewhere in between
> `(void *)&S390_lowcore` and `(void *)(&S390_lowcore + 1))`?

No, it's allocated with __get_free_pages() or memblock_alloc_low().
But since this question came up, I should probably add a check and
a WARN_ON_ONCE() here.