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Message-ID: <CAEAAPHYakbZxf7CYbhGVJ-sGM3KFP3vCMJ9kErbMpi75Ekg20A@mail.gmail.com>
Date:   Thu, 19 Oct 2023 09:27:03 +0200
From:   Stephen Röttger <sroettger@...gle.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     jeffxu@...omium.org, akpm@...ux-foundation.org,
        keescook@...omium.org, jannh@...gle.com, willy@...radead.org,
        gregkh@...uxfoundation.org, jeffxu@...gle.com,
        jorgelo@...omium.org, groeck@...omium.org,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-mm@...ck.org, surenb@...gle.com, alex.sierra@....com,
        apopple@...dia.com, aneesh.kumar@...ux.ibm.com,
        axelrasmussen@...gle.com, ben@...adent.org.uk,
        catalin.marinas@....com, david@...hat.com, dwmw@...zon.co.uk,
        ying.huang@...el.com, hughd@...gle.com, joey.gouly@....com,
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        vbabka@...e.cz, xiujianfeng@...wei.com, yu.ma@...el.com,
        zhangpeng362@...wei.com, dave.hansen@...el.com, luto@...nel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [RFC PATCH v2 7/8] mseal:Check seal flag for mmap(2)

> Without that practical reason, I think the only two sane sealing operations are:
>
>  - SEAL_MUNMAP: "don't allow this mapping address to go away"
>
>    IOW no unmap, no shrinking, no moving mremap
>
>  - SEAL_MPROTECT: "don't allow any mapping permission changes"
>
> Again, that permission case might end up being "don't allow
> _additional_ permissions" and "don't allow taking permissions away".
> Or it could be split by operation (ie "don't allow permission changes
> to writability / readability / executability respectively").
>
> I suspect there isn't a real-life example of splitting the
> SEAL_MPROTECT (the same way I doubt there's a real-life example for
> splitting the UNMAP into "unmap vs move"), so unless there is some
> real reason, I'd keep the sealing minimal and to just those two flags.

These two flags are exactly what we would use in Chrome. I can't think of a
use case for a more fine grained split either.

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