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[91.12.111.153]) by smtp.gmail.com with ESMTPSA id m16-20020a7bca50000000b0040841e79715sm8155647wml.27.2023.11.13.06.42.45 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 13 Nov 2023 06:42:45 -0800 (PST) Message-ID: Date: Mon, 13 Nov 2023 15:42:44 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [BUG?] mm/secretmem: memory address mapped to memfd_secret can be used in write syscall. To: Theodore Ts'o Cc: David Wang <00107082@163.com>, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Mike Rapoport References: <61159548.60cf.18baec1fd65.Coremail.00107082@163.com> <60081af2-d580-4f82-9233-3d3d7dd883bc@redhat.com> From: David Hildenbrand 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/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz 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+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: zd8h7dkcqqck98q1sqzb1xd716pk75sc X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: D83B74001B X-Rspam-User: X-HE-Tag: 1699886570-695603 X-HE-Meta: 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 zFr66u0e 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 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 13.11.23 14:26, Theodore Ts'o wrote: > On Mon, Nov 13, 2023 at 10:15:05AM +0100, David Hildenbrand wrote: >> >> According to the man page: >> >> "The memory areas backing the file created with memfd_secret(2) are visible >> only to the processes that have access to the file descriptor. The memory >> region is removed from the kernel page tables and only the page tables of >> the processes holding the file descriptor map the corresponding physical >> memory. (Thus, the pages in the region can't be accessed by the kernel >> itself, so that, for example, pointers to the region can't be passed to >> system calls.) >> >> I'm not sure if the last part is actually true, if the syscalls end up >> walking user page tables to copy data in/out. > > The idea behind removing it from the kernel page tables is so that > kernel code running in some other process context won't be able to > reference the memory via the kernel address space. (So if there is > some kind of kernel zero-day which allows arbitrary code execution, > the injected attack code would have to play games with page tables > before being able to reference the memory --- this is not > *impossible*, just more annoying.) > > But if you are doing a buffered write, the copy from the user-supplied > buffer to the page cache is happening in the process's context. So > "foreground kernel code" can dereference the user-supplied pointer > just fine. Right, so the statement in the man page is imprecise. -- Cheers, David / dhildenb