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[91.12.97.173]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-435aab63baesm27114775e9.38.2024.12.10.11.35.31 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 10 Dec 2024 11:35:32 -0800 (PST) Message-ID: <3bd43f87-571a-4bc6-b068-69056ec18d85@redhat.com> Date: Tue, 10 Dec 2024 20:35:30 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] fork: avoid inappropriate uprobe access to invalid mm To: Lorenzo Stoakes , Peter Zijlstra Cc: Oleg Nesterov , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , Kan Liang , Masami Hiramatsu , linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, Andrew Morton , "Liam R . Howlett" , Vlastimil Babka , Jann Horn , linux-mm@kvack.org, Peng Zhang , syzbot+2d788f4f7cb660dac4b7@syzkaller.appspotmail.com References: <20241210172412.52995-1-lorenzo.stoakes@oracle.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: <20241210172412.52995-1-lorenzo.stoakes@oracle.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: CyddAmuh1vxpt5IXWWPq7cn82eCty4rgMr2YIjcPZ0c_1733859334 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 3C4BEC0007 X-Stat-Signature: bxy3r4368hy974kqctkds3jo8iqbc3ii X-HE-Tag: 1733859312-591846 X-HE-Meta: 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 U5vitUWx 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.262532, 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 10.12.24 18:24, Lorenzo Stoakes wrote: > If dup_mmap() encounters an issue, currently uprobe is able to access the > relevant mm via the reverse mapping (in build_map_info()), and if we are > very unlucky with a race window, observe invalid XA_ZERO_ENTRY state which > we establish as part of the fork error path. > > This occurs because uprobe_write_opcode() invokes anon_vma_prepare() which > in turn invokes find_mergeable_anon_vma() that uses a VMA iterator, > invoking vma_iter_load() which uses the advanced maple tree API and thus is > able to observe XA_ZERO_ENTRY entries added to dup_mmap() in commit > d24062914837 ("fork: use __mt_dup() to duplicate maple tree in > dup_mmap()"). > > This change was made on the assumption that only process tear-down code > would actually observe (and make use of) these values. However this very > unlikely but still possible edge case with uprobes exists and unfortunately > does make these observable. > > The uprobe operation prevents races against the dup_mmap() operation via > the dup_mmap_sem semaphore, which is acquired via uprobe_start_dup_mmap() > and dropped via uprobe_end_dup_mmap(), and held across > register_for_each_vma() prior to invoking build_map_info() which does the > reverse mapping lookup. > > Currently these are acquired and dropped within dup_mmap(), which exposes > the race window prior to error handling in the invoking dup_mm() which > tears down the mm. > > We can avoid all this by just moving the invocation of > uprobe_start_dup_mmap() and uprobe_end_dup_mmap() up a level to dup_mm() > and only release this lock once the dup_mmap() operation succeeds or clean > up is done. What I understand is: we need to perform the uprobe_end_dup_mmap() after the mmput(). I assume/hope that we cannot see another mmget() before we return here. In that case, this LGTM. -- Cheers, David / dhildenb