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[70.52.229.124]) by smtp.gmail.com with ESMTPSA id o16-20020ac872d0000000b003ef5ba0702fsm6392726qtp.7.2023.04.28.08.56.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 28 Apr 2023 08:56:58 -0700 (PDT) Date: Fri, 28 Apr 2023 11:56:55 -0400 From: Peter Xu To: David Hildenbrand Cc: Lorenzo Stoakes , 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: References: <6b73e692c2929dc4613af711bdf92e2ec1956a66.1682638385.git.lstoakes@gmail.com> <094d2074-5b69-5d61-07f7-9f962014fa68@redhat.com> <400da248-a14e-46a4-420a-a3e075291085@redhat.com> <077c4b21-8806-455f-be98-d7052a584259@lucifer.local> <62ec50da-5f73-559c-c4b3-bde4eb215e08@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <62ec50da-5f73-559c-c4b3-bde4eb215e08@redhat.com> Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Fri, Apr 28, 2023 at 05:34:35PM +0200, David Hildenbrand wrote: > On 28.04.23 17:33, Lorenzo Stoakes wrote: > > 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? > > PageAnon(page) can be called from GUP-fast after grabbing a reference. See > gup_must_unshare(). Hmm.. Is it a good idea at all to sacrifise all "!anon" fast-gups for this? People will silently got degrade even on legal pins on shmem/hugetlb, I think, which seems to be still a very major use case. -- Peter Xu