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Howlett" , Vlastimil Babka , Jann Horn , Pedro Falcato , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Jeff Xu References: <202507241352.22634450C9@keescook> <202507241528.A73E1178@keescook> <28bf0b31-8b51-4acd-ae09-890a952501f4@redhat.com> Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAmgsLPQFCRvGjuMACgkQTd4Q 9wD/g1o0bxAAqYC7gTyGj5rZwvy1VesF6YoQncH0yI79lvXUYOX+Nngko4v4dTlOQvrd/vhb 02e9FtpA1CxgwdgIPFKIuXvdSyXAp0xXuIuRPQYbgNriQFkaBlHe9mSf8O09J3SCVa/5ezKM OLW/OONSV/Fr2VI1wxAYj3/Rb+U6rpzqIQ3Uh/5Rjmla6pTl7Z9/o1zKlVOX1SxVGSrlXhqt kwdbjdj/csSzoAbUF/duDuhyEl11/xStm/lBMzVuf3ZhV5SSgLAflLBo4l6mR5RolpPv5wad GpYS/hm7HsmEA0PBAPNb5DvZQ7vNaX23FlgylSXyv72UVsObHsu6pT4sfoxvJ5nJxvzGi69U s1uryvlAfS6E+D5ULrV35taTwSpcBAh0/RqRbV0mTc57vvAoXofBDcs3Z30IReFS34QSpjvl Hxbe7itHGuuhEVM1qmq2U72ezOQ7MzADbwCtn+yGeISQqeFn9QMAZVAkXsc9Wp0SW/WQKb76 FkSRalBZcc2vXM0VqhFVzTb6iNqYXqVKyuPKwhBunhTt6XnIfhpRgqveCPNIasSX05VQR6/a OBHZX3seTikp7A1z9iZIsdtJxB88dGkpeMj6qJ5RLzUsPUVPodEcz1B5aTEbYK6428H8MeLq NFPwmknOlDzQNC6RND8Ez7YEhzqvw7263MojcmmPcLelYbfOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCaCwtJQUJG8aPFAAKCRBN3hD3AP+DWlDnD/4k2TW+HyOOOePVm23F5HOhNNd7nNv3 Vq2cLcW1DteHUdxMO0X+zqrKDHI5hgnE/E2QH9jyV8mB8l/ndElobciaJcbl1cM43vVzPIWn 01vW62oxUNtEvzLLxGLPTrnMxWdZgxr7ACCWKUnMGE2E8eca0cT2pnIJoQRz242xqe/nYxBB /BAK+dsxHIfcQzl88G83oaO7vb7s/cWMYRKOg+WIgp0MJ8DO2IU5JmUtyJB+V3YzzM4cMic3 bNn8nHjTWw/9+QQ5vg3TXHZ5XMu9mtfw2La3bHJ6AybL0DvEkdGxk6YHqJVEukciLMWDWqQQ RtbBhqcprgUxipNvdn9KwNpGciM+hNtM9kf9gt0fjv79l/FiSw6KbCPX9b636GzgNy0Ev2UV m00EtcpRXXMlEpbP4V947ufWVK2Mz7RFUfU4+ETDd1scMQDHzrXItryHLZWhopPI4Z+ps0rB CQHfSpl+wG4XbJJu1D8/Ww3FsO42TMFrNr2/cmqwuUZ0a0uxrpkNYrsGjkEu7a+9MheyTzcm vyU2knz5/stkTN2LKz5REqOe24oRnypjpAfaoxRYXs+F8wml519InWlwCra49IUSxD1hXPxO WBe5lqcozu9LpNDH/brVSzHCSb7vjNGvvSVESDuoiHK8gNlf0v+epy5WYd7CGAgODPvDShGN g3eXuA== Organization: Red Hat In-Reply-To: <28bf0b31-8b51-4acd-ae09-890a952501f4@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: OFElnpEpmdqw_k98XeWeOA0DjdYWl4Teq-Zpbpenhy0_1753429305 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: rspam12 X-Rspamd-Queue-Id: 047BCC0003 X-Stat-Signature: xry7jis771p4qd7u4ssk9p1ryhz6xiaf X-Rspam-User: X-HE-Tag: 1753429308-207375 X-HE-Meta: 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 VgiMmirS lM/4MFR9t/nEp1QmcdV9iRrW/OJVqpLsRgGFnlAJCdHt19TpTQ1EMFkhao9qP4w+FtKv56CoD5b55IEX2zeZhD/3ZiYgznk2dBvXDLdUlxzVJsi6OXtj7ziPHxrlV6fjh8F0rHgD/23Ur3JpZ2sXtqRt37FuAPehdnEWD4w4nH/tSDBA9zSjt/wawf1m1goIdQPsRtO+IhVLQxJHN7Dplc0fjDFIcUGVwS5MH3i0IfYhE6sHj1FR42tzr2VonYAsj8jtTcrXdonst/gEylMdCea3iyauBaTmy5YEir9MumXQT139aOm2l1j3WTk+N0WUUro6q10Ktm7m9Lr788ICr1h/haKvfcCTet2lw9qI1pBSI0M1zDuv8bqRKrprXuykhGjCOhg0MSa/EB+UQkJtAN4om/5BjvXX5RqdCr9pXlMHpx4tx4eIRC+dNF47WWdYH1+vUNxZgSFXX9xXEER0g8B3IdQ== 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: List-Subscribe: List-Unsubscribe: On 25.07.25 00:47, David Hildenbrand wrote: > On 25.07.25 00:29, Kees Cook wrote: >> On Thu, Jul 24, 2025 at 11:41:04PM +0200, David Hildenbrand wrote: >>> On 24.07.25 23:32, David Hildenbrand wrote: >>>>> As an aside, why should discard work in this case even without step 4? >>>>> Wouldn't setting "read-only" imply you don't want the memory to change >>>>> out from under you? I guess I'm not clear on the semantics: how do memory >>>>> protection bits map to madvise actions like this? >>>> >>>> They generally don't affect MADV_DONTNEED behavior. The only documented >>>> (man page) reason for EPERM in the man page is related to MADV_HWPOISON. >>>> >>> >>> (Exception: MADV_POPULATE_READ/MADV_POPULATE_WRITE requires corresponding >>> permissions) >> >> Shouldn't an MADV action that changes memory contents require the W bit >> though? > Pondering about this some more, at least MADV_DONTNEED is mostly a cheaper way of doing mmap(MAP_FIXED): in other word, zap everything but leave the original mapping unchanged. So if you allow for mmap(MAP_FIXED) -- ignore any permissions bits, of course -- nothing really wrong about allowing MADV_DONTNEED. With mseal(), it got all weird I am afraid, because we have this exception list, and apparently, it has holes. :( -- Cheers, David / dhildenb