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[159.2.239.150]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-91ca807047bsm17117606d6.39.2026.10.30.08.11.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 30 Oct 2026 08:11:17 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1xMoGB-00000000v1Y-0kVg; Fri, 30 Oct 2026 12:11:15 -0300 Date: Fri, 30 Oct 2026 12:11:15 -0300 From: Jason Gunthorpe To: "David Hildenbrand (Arm)" Cc: Samiullah Khawaja , Andrew Morton , Hugh Dickins , Baolin Wang , Muchun Song , Oscar Salvador , Jeff Layton , Chuck Lever , Alexander Aring , Shuah Khan , Gerd Hoffmann , Vivek Kasireddy , Jeff Xu , David Matlack , Pasha Tatashin , linux-mm@kvack.org, linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 0/2] mm/memfd: add F_SEAL_PUNCH_HOLE Message-ID: <20261030151115.GD3889730@ziepe.ca> References: <20261026220546.3114241-1-skhawaja@google.com> <20261030121113.GB3889730@ziepe.ca> <2c7aa5c1-3af3-4654-b244-1257d05c9d45@kernel.org> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2c7aa5c1-3af3-4654-b244-1257d05c9d45@kernel.org> X-Rspamd-Queue-Id: 64355C0005 X-Stat-Signature: q4rm8bpyrky6wwojwdhxns9mkxmf9qji X-Spam-Status: No, score=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=no autolearn_force=no version=4.0.1 X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1793373080-671669 X-HE-Meta: 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 TwlyrhqP 2fWa7ZiVawTeGUqqYQoYA22eQyCXkbrcBO0agOVh8Cpe1CxVIkeGmClrzuxlBUSVKCxKxYAAb4ZuCPqmOFAV6gg9+OwJZIVPpbFePyFQZy02ND2LGbzT7uHcwMUyDNpjXsda8QNHGiAJIDXDFGZQraPz0VVAmzZmfoah7SAdapx+aN0v5WooU6/qiZAUJSCRd8UwjbHshH4m7NdCFjEDrFF+Nf6hnFAAwYNWtuKtlRsH8of6PylqaDGIZCklOKotBr1FMbeU2AvJpr8wWPjGTr8RWTH2uaYwmP71RL7Ii40GN7LblmCDNN3ea9rA+Gbr5BtIZj4dF5GsIuDzGWG4u/Oaoj/ehTebEHiUs6at04a+zlUCW3Yw4mgNhgWKz9RpL4pycDsPlawZnAldMLBzbjPn3gGNxmJOlkkdL Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Fri, Oct 30, 2026 at 03:39:40PM +0100, David Hildenbrand (Arm) wrote: > >> I don't see a reason to make userspace (that should not shoot itself into the > >> foot) a kernel feature it must activate itself to not shoot itself into the foot. > > > > The issue is live update doesn't preserve those background punched > > folios and now we have created an UAF attack on the kernel across > > kexec if you don't do something about it. > > > > There was some notion here that with the right sealing flags we could > > tell if everything was 'live update compatible' and then know that > > these attacks are impossible. > Just remember that there was any hole punch and refuse to live update this instance. > > We could likely implement "we saw hole punch on a pinned folio" as well, but I > don't think that's required initially. > > No need for more shaky seals. Ah, yeah that might work out. It has to be checked really late though, after userspace cannot change the memfd any further. Jason