linux-kernel - Re: [PATCH] mm: Enforce a minimal stack gap even against inaccessible VMAs

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Message-ID: <de4577ed-8794-43f0-8d8d-980abeccbf57@lucifer.local>
Date: Thu, 10 Oct 2024 18:31:06 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: kernel test robot <lkp@...el.com>, Jann Horn <jannh@...gle.com>,
        oe-kbuild-all@...ts.linux.dev,
        Linux Memory Management List <linux-mm@...ck.org>,
        Hugh Dickins <hughd@...gle.com>, Oleg Nesterov <oleg@...hat.com>,
        Michal Hocko <mhocko@...e.com>, Helge Deller <deller@....de>,
        Vlastimil Babka <vbabka@...e.cz>, Ben Hutchings <bwh@...nel.org>,
        Willy Tarreau <w@....eu>, Rik van Riel <riel@...hat.com>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] mm: Enforce a minimal stack gap even against
 inaccessible VMAs

On Wed, Oct 09, 2024 at 02:08:22PM -0700, Andrew Morton wrote:
> On Wed, 9 Oct 2024 15:53:50 +0100 Lorenzo Stoakes <lorenzo.stoakes@...cle.com> wrote:
>
> > > All errors (new ones prefixed by >>):
> > >
> > >    mm/mmap.c: In function 'expand_upwards':
> > > >> mm/mmap.c:1069:39: error: 'prev' undeclared (first use in this function)
> > >     1069 |                 if (vma_is_accessible(prev))
> >
> > Suspect this is just a simple typo and should be next rather than prev :>)
>
> Agree, I'll make that change.
>
> CONFIG_STACK_GROWSUP is only a parisc thing.  That makes runtime
> testing difficult.

Hi Andrew,

Would it be possible to drop this for now as it is not clear we want to
take this approach and there is some concern this could break some things?

I believe Jann was going to provide an alternative that attacked this from
the mmap()/mprotect() side also?

Thanks!