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Date:   Fri, 28 Apr 2023 14:25:53 -0400
From:   "Theodore Ts'o" <tytso@mit.edu>
To:     Jason Gunthorpe <jgg@nvidia.com>
Cc:     David Hildenbrand <david@redhat.com>,
        Lorenzo Stoakes <lstoakes@gmail.com>, linux-mm@kvack.org,
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        Leon Romanovsky <leon@kernel.org>,
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        Bernard Metzler <bmt@zurich.ibm.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
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        Mark Rutland <mark.rutland@arm.com>,
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        Namhyung Kim <namhyung@kernel.org>,
        Ian Rogers <irogers@google.com>,
        Adrian Hunter <adrian.hunter@intel.com>,
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        Magnus Karlsson <magnus.karlsson@intel.com>,
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        "David S . Miller" <davem@davemloft.net>,
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        Daniel Borkmann <daniel@iogearbox.net>,
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        John Fastabend <john.fastabend@gmail.com>,
        linux-fsdevel@vger.kernel.org, linux-perf-users@vger.kernel.org,
        netdev@vger.kernel.org, bpf@vger.kernel.org,
        Oleg Nesterov <oleg@redhat.com>,
        John Hubbard <jhubbard@nvidia.com>, Jan Kara <jack@suse.cz>,
        "Kirill A . Shutemov" <kirill@shutemov.name>,
        Pavel Begunkov <asml.silence@gmail.com>,
        Mika Penttila <mpenttil@redhat.com>,
        David Howells <dhowells@redhat.com>,
        Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH v5] mm/gup: disallow GUP writing to file-backed mappings
 by default
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 <afcc124e-7a9b-879c-dfdf-200426b84e24@redhat.com>
 <ZEvZtIb2EDb/WudP@nvidia.com>
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On Fri, Apr 28, 2023 at 11:35:32AM -0300, Jason Gunthorpe wrote:
> 
> It has been years now, I think we need to admit a fix is still years
> away. Blocking the security problem may even motivate more people to
> work on a fix.

Do we think we can still trigger a kernel crash, or maybe even some
more exciting like an arbitrary buffer overrun, via the
process_vm_writev(2) system call into a file-backed mmap'ed region?

Maybe if someone can come up with an easy-to-expliot security proof of
aconcept, that doesn't require special RDMA hardware or some special
libvirt setup, we could finally get motivation to get it fixed, or at
least blocked?  :-)

We've only been talking about it for years, after all...

       	       	    	      		- Ted

> Security is the primary case where we have historically closed uAPI
> items.
> 
> Jason