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Mon, 24 Apr 2023 08:02:49 -0400 (EDT) Received: by box.shutemov.name (Postfix, from userid 1000) id 1FE9F10A0FA; Mon, 24 Apr 2023 15:02:47 +0300 (+03) Date: Mon, 24 Apr 2023 15:02:47 +0300 From: "Kirill A. Shutemov" To: Lorenzo Stoakes Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Jason Gunthorpe , 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 Subject: Re: [PATCH] mm/gup: disallow GUP writing to file-backed mappings by default Message-ID: <20230424120247.k7cjmncmov32yv5r@box.shutemov.name> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Queue-Id: 32180C0029 X-Rspamd-Server: rspam09 X-Stat-Signature: ro7764czza4c8jey6n6n6ukm7185hdpp X-HE-Tag: 1682337773-626991 X-HE-Meta: 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 AKCfZ0FO GURA+YFJl/J0uQGVTDrxHWWmg3H1ZBkI1fO17CkZwu2XdquHgMQX3LaZ/8oH2JV+egKsUgRf/5OqmWRh185S5/SxxwrdLmr4iKeJ0pzdYLtS9zMIZe6cLdmMI0W0mNGIVAiajPXlCLXnIZCEUlXTvmNJI3U7GJBnjAVEmNhCPvcAcJHjRAoQhclE4JCjjE+jqhWj07vljzDYkiPGJC302CQdwxlaYd957K+rbMS5EOO1RNWc+wrct13PGImayuxdXSkf1bbsBzC2NkMpAba7ZaTf+OtqEwGqXzTO1cP/dySbCPK//43qfiNvt7MG1UWD1KH9XIlTDopUDGVOEL08S4PytVFSFzUtRhH+8eX7N8mbQw54= 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 Sat, Apr 22, 2023 at 02:37:05PM +0100, Lorenzo Stoakes wrote: > @@ -959,16 +959,46 @@ static int faultin_page(struct vm_area_struct *vma, > return 0; > } > > +/* > + * Writing to file-backed mappings using GUP is a fundamentally broken operation > + * as kernel write access to GUP mappings may not adhere to the semantics > + * expected by a file system. > + * > + * In most instances we disallow this broken behaviour, however there are some > + * exceptions to this enforced here. > + */ > +static inline bool can_write_file_mapping(struct vm_area_struct *vma, > + unsigned long gup_flags) > +{ > + struct file *file = vma->vm_file; > + > + /* If we aren't pinning then no problematic write can occur. */ > + if (!(gup_flags & (FOLL_GET | FOLL_PIN))) > + return true; > + > + /* Special mappings should pose no problem. */ > + if (!file) > + return true; > + > + /* Has the caller explicitly indicated this case is acceptable? */ > + if (gup_flags & FOLL_ALLOW_BROKEN_FILE_MAPPING) > + return true; > + > + /* shmem and hugetlb mappings do not have problematic semantics. */ > + return vma_is_shmem(vma) || is_file_hugepages(file); Can this be generalized to any fs that doesn't have vm_ops->page_mkwrite()? -- Kiryl Shutsemau / Kirill A. Shutemov