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[86.156.84.164]) by smtp.gmail.com with ESMTPSA id ay37-20020a05600c1e2500b003f18b52c73asm24474839wmb.24.2023.04.28.08.33.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 28 Apr 2023 08:33:07 -0700 (PDT) Date: Fri, 28 Apr 2023 16:33:06 +0100 From: Lorenzo Stoakes To: David Hildenbrand Cc: Jason Gunthorpe , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Jens Axboe , Matthew Wilcox , Dennis Dalessandro , Leon Romanovsky , Christian Benvenuti , Nelson Escobar , Bernard Metzler , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Ian Rogers , Adrian Hunter , Bjorn Topel , Magnus Karlsson , Maciej Fijalkowski , Jonathan Lemon , "David S . Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Christian Brauner , Richard Cochran , Alexei Starovoitov , Daniel Borkmann , Jesper Dangaard Brouer , John Fastabend , linux-fsdevel@vger.kernel.org, linux-perf-users@vger.kernel.org, netdev@vger.kernel.org, bpf@vger.kernel.org, Oleg Nesterov , John Hubbard , Jan Kara , "Kirill A . Shutemov" , Pavel Begunkov , Mika Penttila , David Howells , Christoph Hellwig Subject: Re: [PATCH v5] mm/gup: disallow GUP writing to file-backed mappings by default Message-ID: <077c4b21-8806-455f-be98-d7052a584259@lucifer.local> References: <6b73e692c2929dc4613af711bdf92e2ec1956a66.1682638385.git.lstoakes@gmail.com> <094d2074-5b69-5d61-07f7-9f962014fa68@redhat.com> <400da248-a14e-46a4-420a-a3e075291085@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <400da248-a14e-46a4-420a-a3e075291085@redhat.com> X-Rspamd-Queue-Id: 6C2AB16001F X-Stat-Signature: xu8m4cxic3tp8ziifksz6pgckpd8ykwd X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1682695989-613380 X-HE-Meta: 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 HQBthOt8 KjaX7exXh8mKasPPk57TfFv6CXdph7nzo/PscCKjZV0FKIt3EpLC1KuRU+2KwclNaHgXPQftv8nPUVQG09vjCBSqhFQHfLv0B6Dl40pRs2TRy8Ut+muUSVGe9qPrPW29xkMAjnN97qoG82+Mw1l5YbnBSLD3gB2CftnnHOfMKxtoUyJO+qtLndXtjo6QVOcz1vqoq7UzVv9qF4m716zSRlGfxaCs5wnDkl4rFUPNSLgkXwwIlu7GQXi6uaOsvOc6sIEFUiovme57ouC+N+GDxVYFNsX8+FqL7XnrVtOomykFdTw2zD/0VXfTbFuIz8EF2W/rdkjrLc8nT+SaH9JWhNpXWWXAFw143IiyJK+S0KNQ2nUQeoIZDIC88T8D2fnOnA+o2ZU8rkUSuvIoEviLaFLd06KWBITD9JDYK5GJHhaS62jwMZ4mMaZaji/PcYd5F8feGd7T61q9ITY0= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Apr 28, 2023 at 05:23:29PM +0200, David Hildenbrand wrote: > > > > > > 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. How do we determine it's non-anon in the first place? The check is on the VMA. We could do it by following page tables down to folio and checking folio->mapping for PAGE_MAPPING_ANON I suppose? > > Of course, this would prevent hugetlb/shmem from getting pinned writable > during gup-fast. Unless we're able to whitelist them somehow in there. We could degrade those to non-fast assuming not FOLL_FAST_ONLY. But it'd be a pity. > > > For FOLL_LONGTERM it might fairly uncontroversial. For everything else I'm > not sure if there could be undesired side-effects. Yeah this is why I pared the patch down to this alone :) there are definitely concerns and issues with other cases, notably ptrace + friends but obviously not only. FOLL_LONGTERM is just the most egregious case. > > -- > Thanks, > > David / dhildenb >