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

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Message-ID: <CAJuCfpFNJ1j7Kcf3Z6efBB0xmvpRCWnfZhnNOuD_hBZmKc-bqA@mail.gmail.com>
Date: Wed, 10 Jul 2024 09:15:42 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: "Liam R. Howlett" <Liam.Howlett@...cle.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()

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?

>
> 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
>