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Thu, 11 Jul 2024 14:33:49 -0700 (PDT) Message-ID: <92a2dc30-6e48-44ea-9cde-693b911f200d@redhat.com> Date: Thu, 11 Jul 2024 23:33:48 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: Fix mmap_assert_locked() in follow_pte() 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 References: <20240710-bug12-v1-1-0e5440f9b8d3@gmail.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: <20240710-bug12-v1-1-0e5440f9b8d3@gmail.com> X-Mimecast-Spam-Score: 1 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: rspam06 X-Rspamd-Queue-Id: B58E9C000E X-Stat-Signature: wd58hq6p9kpnfqmor5hkc16741z9xzew X-Rspam-User: X-HE-Tag: 1720733633-420117 X-HE-Meta: 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 XCS9dqTP 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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 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 > > In zap_page_range_single(), we passed mm_wr_locked as false, as we do > not expect write lock to be held. > In the special case where vma->vm_flags is set as VM_PFNMAP, we are > hitting untrack_pfn() which eventually calls into follow_phys. > > 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: > > Tested on: > > commit: 9d9a2f29 Merge tag 'mm-hotfixes-stable-2024-07-10-13-1.. > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=13be8021980000 > kernel config: https://syzkaller.appspot.com/x/.config?x=3456bae478301dc8 > dashboard link: https://syzkaller.appspot.com/bug?extid=35a4414f6e247f515443 > compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40 > patch: https://syzkaller.appspot.com/x/patch.diff?x=145e3441980000 > > Note: testing is done by a robot and is best-effort only. > --- > mm/memory.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/mm/memory.c b/mm/memory.c > index d10e616d7389..75d7959b835b 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -1815,9 +1815,16 @@ static void unmap_single_vma(struct mmu_gather *tlb, > if (vma->vm_file) > uprobe_munmap(vma, start, end); > > - if (unlikely(vma->vm_flags & VM_PFNMAP)) > + if (unlikely(vma->vm_flags & VM_PFNMAP)) { > + if (!mm_wr_locked) > + mmap_read_lock(vma->vm_mm); > + > untrack_pfn(vma, 0, 0, mm_wr_locked); > > + if (!mm_wr_locked) > + mmap_read_unlock(vma->vm_mm); > + } > + > if (start != end) { > if (unlikely(is_vm_hugetlb_page(vma))) { I'm not sure if this is the right fix. I like to understand how we end up without the mmap lock at least in read mode in that path? -- Cheers, David / dhildenb