Re: [PATCH v25 29/30] mm: Update arch_validate_flags() to include vma anonymous

[Yu, Yu-cheng]

On 4/26/2021 4:11 AM, Catalin Marinas wrote:
> On Mon, Apr 26, 2021 at 09:40:56AM +0300, Kirill A. Shutemov wrote:
> > On Thu, Apr 15, 2021 at 03:14:18PM -0700, Yu-cheng Yu wrote:
> > > When newer VM flags are being created, such as VM_MTE, it becomes necessary
> > > for mmap/mprotect to verify if certain flags are being applied to an
> > > anonymous VMA.
> > >
> > > To solve this, one approach is adding a VM flag to track that MAP_ANONYMOUS
> > > is specified [1], and then using the flag in arch_validate_flags().
> > >
> > > Another approach is passing vma_is_anonymous() to arch_validate_flags().
> > > To prepare the introduction of PROT_SHSTK, which creates a shadow stack
> > > mapping and can only be applied to an anonymous VMA, update arch_validate_
> > > flags() to include anonymous VMA information.
> >
> > I would rather pass down whole vma. Who knows what else
> > arch_validate_flags() would need to know about the VMA tomorrow:
> >
> > 	arch_validate_flags(vma, newflags);
> >
> > should do the trick.
>
> A reason why we added a separate VM_MTE_ALLOWED flag was that we wanted
> MTE on other RAM-based based mappings, not just anonymous pages. See
> 51b0bff2f703 ("mm: Allow arm64 mmap(PROT_MTE) on RAM-based files").
>
> Anyway, the above change doesn't get in the way.

Thanks a lot for the clarification!

Yu-cheng