linux-kernel - Re: [PATCH] munmap sealed memory cause memory to split (bug)

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Message-ID: <CABi2SkWBFZkWxDPnc6g2odvvNuMQqL4wQcbQSN2cTow2JLMKJw@mail.gmail.com>
Date: Thu, 17 Oct 2024 13:12:36 -0700
From: Jeff Xu <jeffxu@...omium.org>
To: Pedro Falcato <pedro.falcato@...il.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, akpm@...ux-foundation.org, 
	keescook@...omium.org, torvalds@...ux-foundation.org, 
	usama.anjum@...labora.com, corbet@....net, Liam.Howlett@...cle.com, 
	jeffxu@...gle.com, jorgelo@...omium.org, groeck@...omium.org, 
	linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org, 
	linux-mm@...ck.org, jannh@...gle.com, sroettger@...gle.com, 
	linux-hardening@...r.kernel.org, willy@...radead.org, 
	gregkh@...uxfoundation.org, deraadt@...nbsd.org, surenb@...gle.com, 
	merimus@...gle.com, rdunlap@...radead.org
Subject: Re: [PATCH] munmap sealed memory cause memory to split (bug)

On Thu, Oct 17, 2024 at 12:14 PM Pedro Falcato <pedro.falcato@...il.com> wrote:
>
> On Thu, Oct 17, 2024 at 09:20:20AM -0700, Jeff Xu wrote:
> > On Thu, Oct 17, 2024 at 1:18 AM Lorenzo Stoakes
> > <lorenzo.stoakes@...cle.com> wrote:
> > >
> > > NACK. Greg's bot got to it but...
> > >
> > > As per Greg's bot, no signed-off-by line.
> > >
> > Sorry for confusion, I wasn't meant to send this as a PATCH, but
> > reporting the issue.
> > The diff was just sent as reference to repro the bug, and I forgot to
> > remove PATCH from the title. I apologize for the confusion.
> >
>
> Can you explain what the issue is? I don't get it.
>
The issue is there is one VMA that gets splitted after an unmap call fails.
Two splitted VMA share the same attributes. e.g.

- Allocate 12 pages (0-11).
- Seal middle 4 pages (4567)
- munmap (2345) - this will fail due to 4567 being sealed.

The VMA for page (0123) is split as 2 VMAs (01)-(23), those 2 VMA
have the same attribute, and should be merged as one.


> --
> Pedro