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[2003:cb:c726:9300:1711:356:6550:7502]) by smtp.gmail.com with ESMTPSA id a18-20020a056000101200b002e61e002943sm21368158wrx.116.2023.04.28.08.23.30 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 28 Apr 2023 08:23:31 -0700 (PDT) Message-ID: <400da248-a14e-46a4-420a-a3e075291085@redhat.com> Date: Fri, 28 Apr 2023 17:23:29 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.10.0 Content-Language: en-US From: David Hildenbrand To: Jason Gunthorpe Cc: Lorenzo Stoakes , 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 References: <6b73e692c2929dc4613af711bdf92e2ec1956a66.1682638385.git.lstoakes@gmail.com> <094d2074-5b69-5d61-07f7-9f962014fa68@redhat.com> Organization: Red Hat Subject: Re: [PATCH v5] mm/gup: disallow GUP writing to file-backed mappings by default In-Reply-To: <094d2074-5b69-5d61-07f7-9f962014fa68@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org >> >> 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. Of course, this would prevent hugetlb/shmem from getting pinned writable during gup-fast. Unless we're able to whitelist them somehow in there. For FOLL_LONGTERM it might fairly uncontroversial. For everything else I'm not sure if there could be undesired side-effects. -- Thanks, David / dhildenb