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Message-ID: <400da248-a14e-46a4-420a-a3e075291085@redhat.com>
Date: Fri, 28 Apr 2023 17:23:29 +0200
From: David Hildenbrand <david@...hat.com>
To: Jason Gunthorpe <jgg@...dia.com>
Cc: Lorenzo Stoakes <lstoakes@...il.com>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>,
Jens Axboe <axboe@...nel.dk>,
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Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
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Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v5] mm/gup: disallow GUP writing to file-backed mappings
by default
>>
>> Security is the primary case where we have historically closed uAPI
>> items.
>
> As this patch
>
> 1) Does not tackle GUP-fast
> 2) Does not take care of !FOLL_LONGTERM
>
> I am not convinced by the security argument in regard to this patch.
>
>
> If we want to sells this as a security thing, we have to block it
> *completely* and then CC stable.
Regarding GUP-fast, to fix the issue there as well, I guess we could do
something similar as I did in gup_must_unshare():
If we're in GUP-fast (no VMA), and want to pin a !anon page writable,
fallback to ordinary GUP. IOW, if we don't know, better be safe.
Of course, this would prevent hugetlb/shmem from getting pinned writable
during gup-fast. Unless we're able to whitelist them somehow in there.
For FOLL_LONGTERM it might fairly uncontroversial. For everything else
I'm not sure if there could be undesired side-effects.
--
Thanks,
David / dhildenb
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