From: David Hildenbrand <david@redhat.com>
To: Linus Torvalds <torvalds@linux-foundation.org>,
Jason Gunthorpe <jgg@nvidia.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
stable@vger.kernel.org, Andrew Morton <akpm@linux-foundation.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Axel Rasmussen <axelrasmussen@google.com>,
Peter Xu <peterx@redhat.com>, Hugh Dickins <hughd@google.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Matthew Wilcox <willy@infradead.org>,
Vlastimil Babka <vbabka@suse.cz>,
John Hubbard <jhubbard@nvidia.com>
Subject: Re: [PATCH v1] mm/gup: fix FOLL_FORCE COW security issue and remove FOLL_COW
Date: Tue, 9 Aug 2022 21:20:42 +0200 [thread overview]
Message-ID: <5593cbb7-eb29-82f0-490e-dd72ceafff9b@redhat.com> (raw)
In-Reply-To: <CAHk-=wjh3wkhQWN8BHFUT6t52kfNMcRd+1JczD4Sgp_q11w8eA@mail.gmail.com>
On 09.08.22 21:07, Linus Torvalds wrote:
> On Tue, Aug 9, 2022 at 11:48 AM Jason Gunthorpe <jgg@nvidia.com> wrote:
>>
>> It is because of all this madness with COW.
>
> Yes, yes, but we have the proper long-term pinning now with
> PG_anon_exclusive, and it actually gets the pinning right not just
> over COW, but even over a fork - which that early write never did.
>
> David, I thought all of that got properly merged? Is there something
> still missing?
The only thing to get R/O longterm pins in MAP_PRIVATE correct that's
missing is that we have to break COW when taking a R/O longterm pin when
*not* finding an anon page inside a private mapping. Regarding anon
pages I am not aware of issues (due to PG_anon_exclusive).
If anybody here wants to stare at a webpage, the following commit
explains the rough idea for MAP_PRIVATE:
https://github.com/davidhildenbrand/linux/commit/cd7989fb76d2513c86f01e6f7a74415eee5d3150
Once we have that in place, we can mostly get rid of
FOLL_FORCE|FOLL_WRITE for R/O longterm pins. There are some corner cases
though that need some additional thought which i am still working on.
FS-handled COW in MAP_SHARED mappings is just nasty (hello DAX).
(the wrong use of FOLL_GET instead of FOLL_PIN for O_DIRECT and friends
still persists, but that's a different thing to handle and it's only
problematic with concurrent fork() IIRC)
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2022-08-09 19:22 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-08 7:32 [PATCH v1] mm/gup: fix FOLL_FORCE COW security issue and remove FOLL_COW David Hildenbrand
2022-08-08 16:02 ` David Hildenbrand
2022-08-09 18:27 ` Linus Torvalds
2022-08-09 18:45 ` David Hildenbrand
2022-08-09 18:59 ` Linus Torvalds
2022-08-09 19:07 ` Jason Gunthorpe
2022-08-09 19:21 ` Linus Torvalds
2022-08-09 21:16 ` David Laight
2022-08-11 7:13 ` [PATCH] sched/all: Change BUG_ON() instances to WARN_ON() Ingo Molnar
2022-08-11 20:43 ` Linus Torvalds
2022-08-11 21:28 ` Matthew Wilcox
2022-08-11 23:22 ` Jason Gunthorpe
2022-08-14 1:10 ` John Hubbard
2022-08-12 9:29 ` [PATCH v2] sched/all: Change all BUG_ON() instances in the scheduler to WARN_ON_ONCE() Ingo Molnar
2022-08-15 14:41 ` Mel Gorman
2022-08-15 22:12 ` John Hubbard
2022-08-16 9:40 ` Mel Gorman
2022-08-21 11:28 ` Ingo Molnar
2022-08-22 8:40 ` Mel Gorman
2022-08-12 9:57 ` [tip: sched/urgent] " tip-bot2 for Ingo Molnar
2022-08-09 18:40 ` [PATCH v1] mm/gup: fix FOLL_FORCE COW security issue and remove FOLL_COW Linus Torvalds
2022-08-09 18:48 ` Jason Gunthorpe
2022-08-09 18:53 ` David Hildenbrand
2022-08-09 19:07 ` Linus Torvalds
2022-08-09 19:20 ` David Hildenbrand [this message]
2022-08-09 18:48 ` Linus Torvalds
2022-08-09 19:09 ` David Hildenbrand
2022-08-09 20:00 ` Linus Torvalds
2022-08-09 20:06 ` David Hildenbrand
2022-08-09 20:07 ` David Hildenbrand
2022-08-09 20:14 ` Linus Torvalds
2022-08-09 20:20 ` David Hildenbrand
2022-08-09 20:30 ` Linus Torvalds
2022-08-09 20:38 ` Linus Torvalds
2022-08-09 20:42 ` David Hildenbrand
2022-08-09 20:20 ` Linus Torvalds
2022-08-09 20:23 ` David Hildenbrand
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