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b=ciHXz99fGb5B0cEhiZ9bJENrAhhbjSas0N3a4t5aBuTm20qGPFUUmmVTnOZw2lxOG hpYLJ/MtYrEf8l4St60yfQLPEVNl+B6cq8LUMoY4Z/G/jXpJox02xpAM5+0BFfNo+p 78EljrTa3GIU4lqvzAhlWbq2hUaP829zr+AK/nLJuqksc+3C6xT4JYS2MHXbJir/f9 h7DzEjBGOasBSxDpv9fdhzNt9KBOqmkYE3YdHb28zou1stCoUOKQI7E3XS6ZWI+qJ8 vyA5ubKXEEaPXCUIFXM+y6q/ndigJsJzLpBFwaiDFdLC9RHNvjSPxGE6V1i1f4fprn A3qEZjVHUwXiQ== Date: Wed, 12 Mar 2025 09:45:09 -0700 From: Kees Cook To: Lorenzo Stoakes Cc: jeffxu@chromium.org, akpm@linux-foundation.org, vbabka@suse.cz, Liam.Howlett@oracle.com, broonie@kernel.org, skhan@linuxfoundation.org, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, jorgelo@chromium.org, pedro.falcato@gmail.com, rdunlap@infradead.org, jannh@google.com Subject: Re: [RFC PATCH v1 2/2] mseal: allow noop mprotect Message-ID: <202503120931.3BD7A36445@keescook> References: <20250312002117.2556240-1-jeffxu@google.com> <20250312002117.2556240-3-jeffxu@google.com> <64B6294F-B059-4744-8548-89D7B519BE72@kernel.org> <9b3a3ac6-a947-4be2-98b3-c35c195d87ab@lucifer.local> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <9b3a3ac6-a947-4be2-98b3-c35c195d87ab@lucifer.local> X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 5D0D4180009 X-Stat-Signature: zcsagfkeqrgi5ppdzsugwf9uqfoks3c8 X-HE-Tag: 1741797915-1717 X-HE-Meta: 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 j+hCK76w EzwaUGhJnUWdkNb7Ty80uGV+MgZAAgs7Gv+3S/MbRqXekzdvUDWUj38wJbEG5D3N3r7jK4N7rlp2svpL9oXyuR38Tfn3SOSqHZFXFcRlEJ7nfjwYncxNMajmq5boUvIrF0Mq+QLll3WWN5dDDDXSFS1kL4ZEF7kys7hoZIYkvvoVzvykRlsLqlDroVKMKYxyjqIm6QNuHadVyIsWyay9w/lgXYtVeYLhKbnrHSW00jqTwDBRkzfosbfsx7jgOJJxP/nA4eQVcljPnHQkpM0EWnWe61c7eQlYEUEzgqQQmWziLoLtStBNe4bHjnWb1ajKpWHbiTNXkusL/Myo= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000845, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Mar 12, 2025 at 03:50:40PM +0000, Lorenzo Stoakes wrote: > What about madvise() with MADV_DONTNEED on a r/o VMA that's not faulted in? > That's a no-op right? But it's not permitted. Hmm, yes, that's a good example. Thank you! > So now we have an inconsistency between the two calls. Yeah, I see your concern now. > I don't know what you mean by 'ergonomic'? I was thinking about idempotent-ness. Like, some library setting up a memory region, it can't call its setup routine twice if the second time through (where no changes are made) it gets rejected. But I think this is likely just a userspace problem: check for the VMAs before blindly trying to do it again. (This is strictly an imagined situation.) > My reply seemed to get truncated at the end here :) So let me ask again - > do you have a practical case in mind for this? Sorry, I didn't have any reply to that part, so I left it off. If Jeff has a specific case in mind, I'll let him answer that part. :) -Kees -- Kees Cook