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[2003:d8:2f20:7500:5f99:9633:990e:138]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3b79c4696c8sm4788092f8f.55.2025.08.01.00.21.30 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 01 Aug 2025 00:21:31 -0700 (PDT) Message-ID: Date: Fri, 1 Aug 2025 09:21:30 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/1] userfaultfd: fix a crash when UFFDIO_MOVE handles a THP hole To: Suren Baghdasaryan , akpm@linux-foundation.org Cc: 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: <20250731154442.319568-1-surenb@google.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: <20250731154442.319568-1-surenb@google.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: MzewNU7FeU7eLKs1jJtPvvrF6fpl-CaTwsHZq27_F7k_1754032893 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: hziabfcsfiokcu9cjoodsmywz4xysz3p X-Rspam-User: X-Rspamd-Queue-Id: 11DEC20004 X-Rspamd-Server: rspam02 X-HE-Tag: 1754032896-414423 X-HE-Meta: U2FsdGVkX1/80/go4+nO37WQbo2XA9j3NSXHA/YVBdHKPK6O4H/qqhPsUnoTgBsaekRYjQ/KhF4TIzxGlZxHQ3DL9EhHJwtAsF0c3ULBu4dgmKIeQeEaLcfZhstg/eZYoky7iYGrL3NDq7ehbmWhomdHiQemCzSHUavXQ4MCOWrwpZ4rcelctM7k2icEUCDnsP1AcffHoJ/qLnGTH3VBpz40mbOyIU77HJ0MHFQFRdCP9on6UBBlrClz+9+ix8EGUjXVWhyOZLCmjfHRWiAGGaxFHh/LSkWXEDQAWaYbAwwIOmIICBD0Lv7Pbo/LzTBQivrYKiq61d28noPXdtQkY8QU5zSteK0Fna3rrfJH4BNJnQV36amBTU+OCUfLoAK4+6DMjaqHE16N9zZNFEG4u0tpPOc5Jz17Fob0hMZ0zsYMewP8juuu183OK0Bj3r/tMi4M1vCdbOgO7VYjfGf5+sHVzE+/6zQ4SGPsg+G+OYbYGgO6JIQxM/p5J7EvtuKQn5V2o2r2Bz/DskdO7kKL0mt1NQaIR0clQ2ryaLYv7kpJkqT69bAooF0xFvVtgT8U23VnoGfTAusMAyR1jNCA4uDzkfmoPSh24U9Sbz/hIxHWy3UOjsNLlQ7J5MiGU+aC3Is4+AWtT74V91ZqESzdZIhcpFM6h2YlhSTNfLxU+xaxmdFcfMb35Eaz75ILQvF3KRs+zAHxrzE+Am06PfVlca1WhcfMV6BycEfggoj2GXAkc8RvgUHaBfZA057t5aXPSk/3B25lzYYVOzKcyAiuU+QV3EQ4nmFZyMUANOTg2Ny1r2/oRUdvR+10Pjx/MGjRcLA/KtR0UpDncQvho5srGSjHRzi9JClwVI29cx9awtlVau9XhxA4iJSqnuTPSB8IjvTmOwPA70SQf11Xg16SsPNm6xuY8Rdl9g4nEO6J46/Sm3JKqVj3sQK8QYIzTkI7Yis7CHiZLlfLHxQG6IP 3RV0XKPP 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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 31.07.25 17:44, Suren Baghdasaryan wrote: Hi! Did you mean in you patch description: "userfaultfd: fix a crash in UFFDIO_MOVE with some non-present PMDs" Talking about THP holes is very very confusing. > When UFFDIO_MOVE is used with UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES and it > encounters a non-present THP, it fails to properly recognize an unmapped You mean a "non-present PMD that is not a migration entry". > hole and tries to access a non-existent folio, resulting in > a crash. Add a check to skip non-present THPs. That makes sense. The code we have after this patch is rather complicated and hard to read. > > 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 > Cc: stable@vger.kernel.org > --- > Changes since v1 [1] > - Fixed step size calculation, per Lokesh Gidra > - Added missing check for UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES, per Lokesh Gidra > > [1] https://lore.kernel.org/all/20250730170733.3829267-1-surenb@google.com/ > > mm/userfaultfd.c | 45 +++++++++++++++++++++++++++++---------------- > 1 file changed, 29 insertions(+), 16 deletions(-) > > diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c > index cbed91b09640..b5af31c22731 100644 > --- a/mm/userfaultfd.c > +++ b/mm/userfaultfd.c > @@ -1818,28 +1818,41 @@ ssize_t move_pages(struct userfaultfd_ctx *ctx, unsigned long dst_start, > > ptl = pmd_trans_huge_lock(src_pmd, src_vma); > if (ptl) { > - /* 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 (pmd_present(*src_pmd) || is_pmd_migration_entry(*src_pmd)) { > + /* 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)) { > + if (pmd_present(*src_pmd)) { > + struct folio *folio = pmd_folio(*src_pmd); > + > + if (!folio || (!is_huge_zero_folio(folio) && > + !PageAnonExclusive(&folio->page))) { > + spin_unlock(ptl); > + err = -EBUSY; > + break; > + } > + } ... in particular that. Is there some way to make this code simpler / easier to read? Like moving that whole last folio-check thingy into a helper? -- Cheers, David / dhildenb