linux-hardening - Re: [RFC PATCH v2 7/8] mseal:Check seal flag for mmap(2)

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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>
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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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