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

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Message-ID: <7053a505-be80-48d0-8b5d-7ce52ba56c3a@lucifer.local>
Date: Thu, 17 Oct 2024 10:48:35 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: jeffxu@...omium.org
Cc: 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,
        pedro.falcato@...il.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 10:46:10AM +0100, Lorenzo Stoakes wrote:
[snip]

> Anyway, let's try to decode (please take this as input as to how you should
> try to communicate these things):
>
>
> So we start with a VMA like this:
>
> 012345678901
> xxxxxxxxxxxx
>
> We then seal the middle, starting at offset 4:
>
> 012345678901
> xxxx****xxxx
>
> This sets the VM_SEALED flag in the middle and splits VMAs resulting in 3
> VMAs.
>
> We then attempt to unmap 4 pages from offset 2, but this fails, as
> expected.
>
> 012345678901
> xxxx****xxxx
>   |--| fail
>
> We then attempt to unmap 4 pages from offset 6, but this fails, as
> expected.
>
> 012345678901
> xxxx****xxxx
>       |--| fail
>
> At each stage we should observe 4 VMAs.

CORRECTION: 3 VMAs.

[snip]