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[2003:cb:c726:9300:1711:356:6550:7502]) by smtp.gmail.com with ESMTPSA id r16-20020a5d4e50000000b002c7066a6f77sm21439153wrt.31.2023.04.28.08.43.53 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 28 Apr 2023 08:43:55 -0700 (PDT) Message-ID: <6ddc7ac4-4091-632a-7b2c-df2005438ec4@redhat.com> Date: Fri, 28 Apr 2023 17:43:52 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.10.0 Subject: Re: [PATCH v5] mm/gup: disallow GUP writing to file-backed mappings by default From: David Hildenbrand To: Lorenzo Stoakes 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 . 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Shutemov" , Pavel Begunkov , Mika Penttila , David Howells , Christoph Hellwig 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> Organization: Red Hat In-Reply-To: <62ec50da-5f73-559c-c4b3-bde4eb215e08@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: C75FF20011 X-Stat-Signature: ndibkimc9rdzqufq483u1hse9a53se96 X-Rspam-User: X-HE-Tag: 1682696643-104007 X-HE-Meta: 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 XTRUMCTb a1Lgg43NFsYQAdmR3PfNa6V4UVM0gjpEVPtSrRXYTWtSt7bnW8g5JlixDA4SOM840dWp/uDn9lwqzgZvgzzJ9H3/HavSFfK4/o84vOsb+QTOleiE5E9xAmjSVY81ro4XzCLuyC/aqBr9cQyJQeDwgN/sDDVf2NgfKzyFYCrmYhl32ZGWf+Kt3Vrh2tGLEDCR0+GPLM+X9MPp6RhO7TUOp4ELjwZqZgSi3Wo7SJxyXH66a50+J5Rykr+996gDd96vabVqzx0BSoiZ1TUySdRIeD7hUsc9SavqnJENHTbdAzRVLp6s6V8OZZoQKNxhbUeLq3TzqdYbWMHW/7Qb6LrkwZyK+h09T+MPTfyjammPUdxGRMZaPORYQQ7y+ywpQY0hInQETE3JUZhmJGsAttRkjhymTOBUT0G097OfVtugJ41ZCRUcLb9DU/0I/3K/8O5/lWEqOhgtLGvHyUAY= 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 28.04.23 17:34, 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(). IIRC, PageHuge() can also be called from GUP-fast and could special-case hugetlb eventually, as it's table while we hold a (temporary) reference. Shmem might be not so easy ... -- Thanks, David / dhildenb