linux-kernel - Re: [PATCH v1 0/2] mremap refactor: check src address for vma boundaries first.

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Message-ID: <CABi2SkV2LcrkYOGzkGm80eYw-mhPNN=Q=P3aKGm0j8_gAwXjog@mail.gmail.com>
Date: Wed, 14 Aug 2024 09:57:09 -0700
From: Jeff Xu <jeffxu@...omium.org>
To: "Liam R. Howlett" <Liam.Howlett@...cle.com>, jeffxu@...omium.org, akpm@...ux-foundation.org, 
	willy@...radead.org, torvalds@...ux-foundation.org, pedro.falcato@...il.com, 
	linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org, 
	linux-mm@...ck.org, linux-hardening@...r.kernel.org, jeffxu@...gle.com, 
	lorenzo.stoakes@...cle.com, mpe@...erman.id.au, oliver.sang@...el.com, 
	vbabka@...e.cz, keescook@...omium.org
Subject: Re: [PATCH v1 0/2] mremap refactor: check src address for vma
 boundaries first.

On Wed, Aug 14, 2024 at 7:40 AM Liam R. Howlett <Liam.Howlett@...cle.com> wrote:
>
> * jeffxu@...omium.org <jeffxu@...omium.org> [240814 03:14]:
> > From: Jeff Xu <jeffxu@...omium.org>
> >
> > mremap doesn't allow relocate, expand, shrink across VMA boundaries,
> > refactor the code to check src address range before doing anything on
> > the destination, i.e. destination won't be unmapped, if src address
> > failed the boundaries check.
> >
> > This also allows us to remove can_modify_mm from mremap.c, since
> > the src address must be single VMA, can_modify_vma is used.
>
> I don't think sending out a separate patch to address the same thing as
> the patch you said you were testing [1] is the correct approach.  You
> had already sent suggestions on mremap changes - why send this patch set
> instead of making another suggestion?
>
As indicated in the cover letter, this patch aims to improve mremap
performance while preserving existing mseal's semantics. And this
patch can go in-dependantly regardless of in-loop out-loop discussion.

[1] link in your email is broken, but I assume you meant Pedro's V1/V2
of in-loop change. In-loop change has a semantic/regression risk to
mseal, and will take longer time to review/test/prove and bake.

We can leave in-loop discussion in Pedro's thread, I hope the V3 of
Pedro's patch adds more testing coverage and addresses existing
comments in V2.

Thanks
-Jeff

-Jeff