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Thu, 11 Jul 2024 14:51:42 -0700 (PDT) Message-ID: Date: Thu, 11 Jul 2024 23:51:41 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: Fix mmap_assert_locked() in follow_pte() From: David Hildenbrand To: Pei Li , Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, skhan@linuxfoundation.org, syzkaller-bugs@googlegroups.com, linux-kernel-mentees@lists.linuxfoundation.org, syzbot+35a4414f6e247f515443@syzkaller.appspotmail.com, Peter Xu References: <20240710-bug12-v1-1-0e5440f9b8d3@gmail.com> <92a2dc30-6e48-44ea-9cde-693b911f200d@redhat.com> <3879ee72-84de-4d2a-93a8-c0b3dc3f0a4c@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/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: <3879ee72-84de-4d2a-93a8-c0b3dc3f0a4c@redhat.com> 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-Rspamd-Queue-Id: 85A04C001D X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: m5fejasw59h5xw7fgd5ozg7m6ra14js4 X-HE-Tag: 1720734706-530410 X-HE-Meta: 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 t1W/eWzO 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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 11.07.24 23:45, David Hildenbrand wrote: > On 11.07.24 23:33, David Hildenbrand wrote: >> On 11.07.24 07:13, Pei Li wrote: >>> This patch fixes this warning by acquiring read lock before entering >>> untrack_pfn() while write lock is not held. >>> >>> syzbot has tested the proposed patch and the reproducer did not >>> trigger any issue. >>> >>> Reported-by: syzbot+35a4414f6e247f515443@syzkaller.appspotmail.com >>> Closes: https://syzkaller.appspot.com/bug?extid=35a4414f6e247f515443 >>> Tested-by: syzbot+35a4414f6e247f515443@syzkaller.appspotmail.com >>> Signed-off-by: Pei Li >>> --- >>> Syzbot reported the following warning in follow_pte(): >>> >>> WARNING: CPU: 3 PID: 5192 at include/linux/rwsem.h:195 rwsem_assert_held include/linux/rwsem.h:195 [inline] >>> WARNING: CPU: 3 PID: 5192 at include/linux/rwsem.h:195 mmap_assert_locked include/linux/mmap_lock.h:65 [inline] >>> WARNING: CPU: 3 PID: 5192 at include/linux/rwsem.h:195 follow_pte+0x414/0x4c0 mm/memory.c:5980 >>> >>> This is because we are assuming that mm->mmap_lock should be held when >>> entering follow_pte(). This is added in commit c5541ba378e3 (mm: >>> follow_pte() improvements). >>> >>> However, in the following call stack, we are not acquring the lock: >>> follow_phys arch/x86/mm/pat/memtype.c:957 [inline] >>> get_pat_info+0xf2/0x510 arch/x86/mm/pat/memtype.c:991 >>> untrack_pfn+0xf7/0x4d0 arch/x86/mm/pat/memtype.c:1104 >>> unmap_single_vma+0x1bd/0x2b0 mm/memory.c:1819 >>> zap_page_range_single+0x326/0x560 mm/memory.c:1920 >> >> That implies that unmap_vmas() is called without the mmap lock in read >> mode, correct? >> >> Do we know how this happens? >> >> * exit_mmap() holds the mmap lock in read mode >> * unmap_region is documented to hold the mmap lock in read mode > > I think this is it (missed the call from zap_page_range_single()): > > follow_phys arch/x86/mm/pat/memtype.c:957 [inline] > get_pat_info+0xf2/0x510 arch/x86/mm/pat/memtype.c:991 > untrack_pfn+0xf7/0x4d0 arch/x86/mm/pat/memtype.c:1104 > unmap_single_vma+0x1bd/0x2b0 mm/memory.c:1819 > zap_page_range_single+0x326/0x560 mm/memory.c:1920 > unmap_mapping_range_vma mm/memory.c:3684 [inline] > unmap_mapping_range_tree mm/memory.c:3701 [inline] > unmap_mapping_pages mm/memory.c:3767 [inline] > unmap_mapping_range+0x1ee/0x280 mm/memory.c:3804 > truncate_pagecache+0x53/0x90 mm/truncate.c:731 > simple_setattr+0xf2/0x120 fs/libfs.c:886 > notify_change+0xec6/0x11f0 fs/attr.c:499 > do_truncate+0x15c/0x220 fs/open.c:65 > handle_truncate fs/namei.c:3308 [inline] > > I think Peter recently questioned whether untrack_pfn() should be even > called from the place, but I might misremember things. > > Fix should work (I suspect we are not violating some locking rules?), > PFNMAP should not happen there too often that we really care. ... thinking again, likely we reach this point with "!mm_wr_locked" and the mmap lock already held in read mode. So I suspect the fix won't work as is. -- Cheers, David / dhildenb