Re: [PATCH v5] mm/gup: disallow GUP writing to file-backed mappings by default

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, linux-kernel@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>,
	Jens Axboe <axboe@kernel.dk>,
	Matthew Wilcox <willy@infradead.org>,
	Dennis Dalessandro <dennis.dalessandro@cornelisnetworks.com>,
	Leon Romanovsky <leon@kernel.org>,
	Christian Benvenuti <benve@cisco.com>,
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	Ingo Molnar <mingo@redhat.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
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	Oleg Nesterov <oleg@redhat.com>,
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	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
Date: Fri, 28 Apr 2023 14:25:53 -0400	[thread overview]
Message-ID: <ZEwPscQu68kx32zF@mit.edu> (raw)
In-Reply-To: <ZEvZtIb2EDb/WudP@nvidia.com>

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