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[2003:d8:2f49:bc00:12fa:1681:c754:1630]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-459e587e154sm116116445e9.27.2025.08.07.12.42.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 07 Aug 2025 12:42:48 -0700 (PDT) Message-ID: <43f91e3e-84c5-4fd1-9b63-4e2cb28dab36@redhat.com> Date: Thu, 7 Aug 2025 21:42:47 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 1/1] userfaultfd: fix a crash in UFFDIO_MOVE when PMD is a migration entry To: Suren Baghdasaryan Cc: akpm@linux-foundation.org, peterx@redhat.com, aarcange@redhat.com, lokeshgidra@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, syzbot+b446dbe27035ef6bd6c2@syzkaller.appspotmail.com, stable@vger.kernel.org References: <20250806220022.926763-1-surenb@google.com> <3eba855a-740c-4423-b2ed-24d622af29a5@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/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: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: _ADe1rJwQ9xqpR727LjzsO4LdVP5StXbtB-tVYw7ocU_1754595770 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Stat-Signature: iqy7xeuf95q91tb77zuy74wiu4ta7cga X-Rspamd-Queue-Id: F2EA61C000E X-Rspamd-Server: rspam10 X-Rspam-User: X-HE-Tag: 1754595772-409639 X-HE-Meta: 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 TzEw/JH6 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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 07.08.25 17:27, Suren Baghdasaryan wrote: > On Thu, Aug 7, 2025 at 3:31 AM David Hildenbrand wrote: >> >> On 07.08.25 00:00, Suren Baghdasaryan wrote: >>> When UFFDIO_MOVE encounters a migration PMD entry, it proceeds with >>> obtaining a folio and accessing it even though the entry is swp_entry_t. >>> Add the missing check and let split_huge_pmd() handle migration entries. >>> >>> Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI") >>> Reported-by: syzbot+b446dbe27035ef6bd6c2@syzkaller.appspotmail.com >>> Closes: https://lore.kernel.org/all/68794b5c.a70a0220.693ce.0050.GAE@google.com/ >>> Signed-off-by: Suren Baghdasaryan >>> Reviewed-by: Peter Xu >>> Cc: stable@vger.kernel.org >>> --- >>> Changes since v3 [1] >>> - Updated the title and changelog, per Peter Xu >>> - Added Reviewed-by: per Peter Xu >>> >>> [1] https://lore.kernel.org/all/20250806154015.769024-1-surenb@google.com/ >>> >>> mm/userfaultfd.c | 17 ++++++++++------- >>> 1 file changed, 10 insertions(+), 7 deletions(-) >>> >>> diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c >>> index 5431c9dd7fd7..116481606be8 100644 >>> --- a/mm/userfaultfd.c >>> +++ b/mm/userfaultfd.c >>> @@ -1826,13 +1826,16 @@ ssize_t move_pages(struct userfaultfd_ctx *ctx, unsigned long dst_start, >>> /* Check if we can move the pmd without splitting it. */ >>> if (move_splits_huge_pmd(dst_addr, src_addr, src_start + len) || >>> !pmd_none(dst_pmdval)) { >>> - struct folio *folio = pmd_folio(*src_pmd); >>> - >>> - if (!folio || (!is_huge_zero_folio(folio) && >>> - !PageAnonExclusive(&folio->page))) { >>> - spin_unlock(ptl); >>> - err = -EBUSY; >>> - break; >>> + /* Can be a migration entry */ >>> + if (pmd_present(*src_pmd)) { >>> + struct folio *folio = pmd_folio(*src_pmd); >>> + >>> + if (!folio >> >> >> How could you get !folio here? That only makes sense when calling >> vm_normal_folio_pmd(), no? > > Yes, I think you are right, this check is not needed. I can fold it > into this fix or post a separate cleanup patch. I'm guessing a > separate patch would be better? I think you can just post a fixup inline here and ask Andrew to squash it. He will shout if he wants a completely new version :) -- Cheers, David / dhildenb