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

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Message-ID: <44d6b910-8778-44cf-b432-4d0f112397f8@lucifer.local>
Date: Fri, 5 Jul 2024 20:39:55 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: "Liam R. Howlett" <Liam.Howlett@...cle.com>
Cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        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 04, 2024 at 02:27:10PM GMT, Liam R. Howlett 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.
>
> 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 */

This feels like an important comment, I know 'find the first overlapping
VMA' below alludes to it but whenever I've read through this function this
comment has actually been quite useful to know what the intent is.

Could we reinstate it?

> -	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
>
>

Other than trivial point above, LGTM.

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>