linux-kernel - Re: [PATCH v3 08/16] mm/mmap: Inline munmap operation in mmap

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Message-ID: <6vwpreukkricmwcuefxrp3w6sl55pzpxiau2ejaua3wdqjrk62@4ryovwh6pr5y>
Date: Wed, 10 Jul 2024 12:35:18 -0400
From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
To: Suren Baghdasaryan <surenb@...gle.com>
Cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>, Lorenzo Stoakes <lstoakes@...il.com>,
        Matthew Wilcox <willy@...radead.org>, sidhartha.kumar@...cle.com,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Bert Karwatzki <spasswolf@....de>, Jiri Olsa <olsajiri@...il.com>,
        linux-kernel@...r.kernel.org, Kees Cook <kees@...nel.org>
Subject: Re: [PATCH v3 08/16] mm/mmap: Inline munmap operation in
 mmap_region()

* Suren Baghdasaryan <surenb@...gle.com> [240710 12:16]:
> On Thu, Jul 4, 2024 at 11:27 AM Liam R. Howlett <Liam.Howlett@...cle.com> wrote:
> >
> > From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
> >
> > mmap_region is already passed sanitized addr and len, so change the
> > call to do_vmi_munmap() to do_vmi_align_munmap() and inline the other
> > checks.
> 
> Hmm. I think such refactoring when you want to skip some checks would
> be done a bit differently... You would introduce a __do_vmi_munmap()
> function which is called at the end of do_vmi_munmap() after the
> checks and then call __do_vmi_munmap() directly wherever you want to
> skip the checks. That would avoid code duplication. Any reason that
> can't be done here?

Because I'm going to completely change and remove the checks in future
patches.  I should have added this to the log that this is an internal
step for reviewing.

> 
> >
> > Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
> > ---
> >  mm/mmap.c | 20 ++++++++++++++------
> >  1 file changed, 14 insertions(+), 6 deletions(-)
> >
> > diff --git a/mm/mmap.c b/mm/mmap.c
> > index 8d9be791997a..e9858ca8bbd4 100644
> > --- a/mm/mmap.c
> > +++ b/mm/mmap.c
> > @@ -2937,12 +2937,20 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
> >                         return -ENOMEM;
> >         }
> >
> > -       /* Unmap any existing mapping in the area */
> > -       error = do_vmi_munmap(&vmi, mm, addr, len, uf, false);
> > -       if (error == -EPERM)
> > -               return error;
> > -       else if (error)
> > -               return -ENOMEM;
> > +
> > +       if (unlikely(!can_modify_mm(mm, addr, end)))
> > +               return -EPERM;
> > +
> > +        /* arch_unmap() might do unmaps itself.  */
> > +       arch_unmap(mm, addr, end);
> > +
> > +       /* Find the first overlapping VMA */
> > +       vma = vma_find(&vmi, end);
> > +       if (vma) {
> > +               if (do_vmi_align_munmap(&vmi, vma, mm, addr, end, uf, false))
> > +                       return -ENOMEM;
> > +               vma = NULL;
> > +       }
> >
> >         /*
> >          * Private writable mapping: check memory availability
> > --
> > 2.43.0
> >
>