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Thu, 9 Apr 2026 12:30:09 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id kWMCGdGb12myBwAAD6G6ig (envelope-from ); Thu, 09 Apr 2026 12:30:09 +0000 Date: Thu, 9 Apr 2026 13:30:07 +0100 From: Pedro Falcato To: "Denis M. Karpov" Cc: harry@kernel.org, rppt@kernel.org, akpm@linux-foundation.org, Liam.Howlett@oracle.com, ljs@kernel.org, vbabka@kernel.org, jannh@google.com, peterx@redhat.com, brauner@kernel.org, viro@zeniv.linux.org.uk, jack@suse.cz, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, usama.arif@linux.dev Subject: Re: [PATCH v2] userfaultfd: allow registration of ranges below mmap_min_addr Message-ID: References: <20260409103345.15044-1-komlomal@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260409103345.15044-1-komlomal@gmail.com> X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 38E04180012 X-Stat-Signature: 5q7fmmspzcjicjgs8zuzjkhucj9j34si X-HE-Tag: 1775737811-296646 X-HE-Meta: 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 nd2iGt1I OBeCKk48MuVT9JvI8wufTaB1/CjCy3YI0jcYUfltbiBR+z+I4Rva1zi0dTQ22lJ6GR8TsiY1GzhgPAIP4gUlUgYsikpfhJxCw15lvJlhOg1A2TNYzkPcGq9UJvipZjpfaq8ROjoaLaDSZvv2TouAHAAT6tZU0hG8f1ZtcHDCbwoaQacmdO7mT/1B5HfHJ+jpic74Dukc2hjkxaAXV+2L80SkDOUua5pzs/dbIjhCUZYgwiq747GBAQHd2ZFgy/m87ZffWC0o/SJFwB4V0nwmuyQSAhksbEmzVt50BJYfaVdMf0tpiVBsgQvew8HjUgETyuZjxNTszqeXxN5uZ6sv1MpCT4D3fG0jPMcW0VdfMBEmrvi/NtBbvkaLp9g== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Apr 09, 2026 at 01:33:45PM +0300, Denis M. Karpov wrote: > The current implementation of validate_range() in fs/userfaultfd.c > performs a hard check against mmap_min_addr. This is redundant because > UFFDIO_REGISTER operates on memory ranges that must already be backed > by a VMA. > > Enforcing mmap_min_addr or capability checks again in userfaultfd is > unnecessary and prevents applications like binary compilers from > using UFFD for valid memory regions mapped by application. > > Remove the redundant check for mmap_min_addr. > > Fixes: 86039bd3b4e6 ("userfaultfd: add new syscall to provide memory externalization") > Signed-off-by: Denis M. Karpov Reviewed-by: Pedro Falcato This looks relatively safe. However, I'm not sure if we want this in stable. This has been broken for 11 years now, with no complaints. -- Pedro