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[87.161.165.196]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3ee0fbc7460sm29256281f8f.31.2025.09.24.11.15.50 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 24 Sep 2025 11:15:51 -0700 (PDT) Message-ID: Date: Wed, 24 Sep 2025 20:15:49 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V2] mm: swap: check for stable address space before operating on the VMA To: Charan Teja Kalla , Liam.Howlett@oracle.com, lorenzo.stoakes@oracle.com, akpm@linux-foundation.org, shikemeng@huaweicloud.com, kasong@tencent.com, nphamcs@gmail.com, bhe@redhat.com, baohua@kernel.org, chrisl@kernel.org, zhangpeng.00@bytedance.com Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20250924181138.1762750-1-charan.kalla@oss.qualcomm.com> From: David Hildenbrand Content-Language: en-US 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 ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20250924181138.1762750-1-charan.kalla@oss.qualcomm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 24.09.25 20:11, Charan Teja Kalla wrote: > It is possible to hit a zero entry while traversing the vmas in > unuse_mm() called from swapoff path and accessing it causes the > OOPS: > > Unable to handle kernel NULL pointer dereference at virtual address > 0000000000000446--> Loading the memory from offset 0x40 on the > XA_ZERO_ENTRY as address. > Mem abort info: > ESR = 0x0000000096000005 > EC = 0x25: DABT (current EL), IL = 32 bits > SET = 0, FnV = 0 > EA = 0, S1PTW = 0 > FSC = 0x05: level 1 translation fault > > The issue is manifested from the below race between the fork() on a > process and swapoff: > fork(dup_mmap()) swapoff(unuse_mm) > --------------- ----------------- > 1) Identical mtree is built using > __mt_dup(). > > 2) copy_pte_range()--> > copy_nonpresent_pte(): > The dst mm is added into the > mmlist to be visible to the > swapoff operation. > > 3) Fatal signal is sent to the parent > process(which is the current during the > fork) thus skip the duplication of the > vmas and mark the vma range with > XA_ZERO_ENTRY as a marker for this process > that helps during exit_mmap(). > > 4) swapoff is tried on the > 'mm' added to the 'mmlist' as > part of the 2. > > 5) unuse_mm(), that iterates > through the vma's of this 'mm' > will hit the non-NULL zero entry > and operating on this zero entry > as a vma is resulting into the > oops. > > The proper fix would be around not exposing this partially-valid tree to > others when droping the mmap lock, which is being solved with [1]. A > simpler solution would be checking for MMF_UNSTABLE, as it is set if > mm_struct is not fully initialized in dup_mmap(). > > Thanks to Liam/Lorenzo/David for all the suggestions in fixing this > issue. > > [1] https://lore.kernel.org/all/20250815191031.3769540-1-Liam.Howlett@oracle.com/ > > Fixes: d24062914837 ("fork: use __mt_dup() to duplicate maple tree in dup_mmap()") > Suggested-by: David Hildenbrand > Signed-off-by: Charan Teja Kalla I assume we want to CC stable? > --- > > V1: > -- Checking for xa_zero_entry() instead of most cleaner way of > checking for MMF_UNSTABLE > -- https://lore.kernel.org/linux-mm/20250808092156.1918973-1-quic_charante@quicinc.com/ > > mm/swapfile.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/mm/swapfile.c b/mm/swapfile.c > index 890b410d77b6..10760240a3a2 100644 > --- a/mm/swapfile.c > +++ b/mm/swapfile.c > @@ -2389,6 +2389,8 @@ static int unuse_mm(struct mm_struct *mm, unsigned int type) > VMA_ITERATOR(vmi, mm, 0); > > mmap_read_lock(mm); > + if (check_stable_address_space(mm)) > + goto unlock; > for_each_vma(vmi, vma) { > if (vma->anon_vma && !is_vm_hugetlb_page(vma)) { > ret = unuse_vma(vma, type); > @@ -2398,6 +2400,7 @@ static int unuse_mm(struct mm_struct *mm, unsigned int type) > > cond_resched(); > } > +unlock: > mmap_read_unlock(mm); > return ret; > } Yeah, this should do until Liam's rework is in. Acked-by: David Hildenbrand -- Cheers David / dhildenb