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Howlett" , Vlastimil Babka , Harry Yoo Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20250724-anonvma-uaf-debug-v1-1-29989ddc4e2a@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: <20250724-anonvma-uaf-debug-v1-1-29989ddc4e2a@google.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: TpzPy6OzL0BSRwRk-QqQf3QRhpjdKH4OBaB46J8cQMo_1753394166 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: C540540007 X-Rspam-User: X-Rspamd-Server: rspam09 X-Stat-Signature: 37mujfdkyghzb7hm1uhqkghirngzg98c X-HE-Tag: 1753394169-525034 X-HE-Meta: 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 vDA6PfJY 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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 24.07.25 21:13, Jann Horn wrote: > If an anon page is mapped into userspace, its anon_vma must be alive, > otherwise rmap walks can hit UAF. > > There have been syzkaller reports a few months ago[1][2] of UAF in rmap > walks that seems to indicate that there can be pages with elevated mapcount > whose anon_vma has already been freed, but I think we never figured out > what the cause is; and syzkaller only hit these UAFs when memory pressure > randomly caused reclaim to rmap-walk the affected pages, so it of course > didn't manage to create a reproducer. > > Add a VM_WARN_ON_FOLIO() when we add/remove mappings of anonymous pages to > hopefully catch such issues more reliably. > > Implementation note: I'm checking IS_ENABLED(CONFIG_DEBUG_VM) because, > unlike the checks above, this one would otherwise be hard to write such > that it completely compiles away in non-debug builds by itself, without > looking extremely ugly. > > [1] https://lore.kernel.org/r/67abaeaf.050a0220.110943.0041.GAE@google.com > [2] https://lore.kernel.org/r/67a76f33.050a0220.3d72c.0028.GAE@google.com > > Signed-off-by: Jann Horn > --- > include/linux/rmap.h | 13 +++++++++++++ > 1 file changed, 13 insertions(+) > > diff --git a/include/linux/rmap.h b/include/linux/rmap.h > index c4f4903b1088..ba694c436f59 100644 > --- a/include/linux/rmap.h > +++ b/include/linux/rmap.h > @@ -449,6 +449,19 @@ static inline void __folio_rmap_sanity_checks(const struct folio *folio, > default: > VM_WARN_ON_ONCE(true); > } > + > + /* > + * Anon folios must have an associated live anon_vma as long as they're > + * mapped into userspace. > + * Part of the purpose of the atomic_read() is to make KASAN check that > + * the anon_vma is still alive. > + */ > + if (IS_ENABLED(CONFIG_DEBUG_VM) && PageAnonNotKsm(page)) { 1) You probably don't need the CONFIG_DEBUG_VM check: the VM_WARN_ON_FOLIO should make everything get optimized out ... right? 2) We have a folio here, so ... better if (folio_test_anon(folio) && !folio_test_ksm(folio)) { ... } > + unsigned long mapping = (unsigned long)folio->mapping; > + struct anon_vma *anon_vma = (void *)(mapping - PAGE_MAPPING_ANON); > + > + VM_WARN_ON_FOLIO(atomic_read(&anon_vma->refcount) == 0, folio); > + } In general, Acked-by: David Hildenbrand -- Cheers, David / dhildenb