Re: [PATCH] mm/nommu: Reject wrapping ranges in access_remote_vm()

[Hajime Tazaki]

Hello,

On Wed, 09 Sep 2026 16:13:41 +0900,
Andrew Morton wrote:
> 
> On Wed,  9 Sep 2026 09:42:31 +0300 Anastasios Papagiannis <tasos.papagiannnis@xxxxxxxxx> wrote:
> 
> > The NOMMU implementation of access_process_vm() rejects address ranges
> > whose end wraps around, but access_remote_vm() bypasses this check even
> > though both functions delegate to __access_remote_vm().
> > 
> > Move the wraparound check into __access_remote_vm() so it applies to
> > both entry points.
> 
> lgtm, thanks.
> 
> > This is originally reported in [1].
> > 
> > [1] https://lore.kernel.org/bpf/4ef240a5bea36ff84df9589671367832860795159386a4c8fba546a0fa8b786f@xxxxxxxxxxxxxxx/
> 
> Ah, bpfbot scored one.
> 
> Sashiko might have found more issues in there:
> 	https://sashiko.dev/#/patchset/20260909064231.18693-1-tasos.papagiannnis@xxxxxxxxx
> 
> I'll optimistically cc Hajime Tazaki, who has been doing some NOMMU
> work recently.

I got a similar review (from Sashiko) that current use of
!vma->vm_file isn't appropriate and should use vma_set_anonymous().  IIUC
that case happens only (I may miss something) with /dev/zero (via
mmap_zero_prepare()).

I also had a patch but am currently waiting for Lorenzo's input for
his work on /dev/zero, which mentioned in his reply.

https://lore.kernel.org/linux-mm/an8BlTgk7sc5vFJ1@lucifer/

Thus 3 comments of Sashiko (all about vma->vm_file) can be addressed
in future, and are not needed an immediate fix.

I wish to ask this to Lorenzo too.

-- Hajime