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[2003:d8:2f4e:fd00:8e13:e3b5:90c8:1159]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-453646cb57fsm110754005e9.1.2025.06.23.05.22.03 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 23 Jun 2025 05:22:03 -0700 (PDT) Message-ID: Date: Mon, 23 Jun 2025 14:22:02 +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: [syzbot] [mm?] kernel BUG in sanity_check_pinned_pages From: David Hildenbrand To: Alexander Potapenko , axboe@kernel.dk Cc: syzbot , akpm@linux-foundation.org, catalin.marinas@arm.com, jgg@ziepe.ca, jhubbard@nvidia.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, peterx@redhat.com, syzkaller-bugs@googlegroups.com References: <6857299a.a00a0220.137b3.0085.GAE@google.com> <56862a1d-71c0-4f07-9c1a-9d70069b4d9e@redhat.com> 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 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: <56862a1d-71c0-4f07-9c1a-9d70069b4d9e@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 23.06.25 12:10, David Hildenbrand wrote: > On 23.06.25 11:53, Alexander Potapenko wrote: >> On Mon, Jun 23, 2025 at 11:29 AM 'David Hildenbrand' via >> syzkaller-bugs wrote: >>> >>> On 21.06.25 23:52, syzbot wrote: >>>> syzbot has found a reproducer for the following issue on: >>>> >>>> HEAD commit: 9aa9b43d689e Merge branch 'for-next/core' into for-kernelci >>>> git tree: git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci >>>> console output: https://syzkaller.appspot.com/x/log.txt?x=1525330c580000 >>>> kernel config: https://syzkaller.appspot.com/x/.config?x=27f179c74d5c35cd >>>> dashboard link: https://syzkaller.appspot.com/bug?extid=1d335893772467199ab6 >>>> compiler: Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6 >>>> userspace arch: arm64 >>>> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16d73370580000 >>>> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=160ef30c580000 >>> >>> There is not that much magic in there, I'm afraid. >>> >>> fork() is only used to spin up guests, but before the memory region of >>> interest is actually allocated, IIUC. No threading code that races. >>> >>> IIUC, it triggers fairly fast on aarch64. I've left it running for a >>> while on x86_64 without any luck. >>> >>> So maybe this is really some aarch64-special stuff (pointer tagging?). >>> >>> In particular, there is something very weird in the reproducer: >>> >>> syscall(__NR_madvise, /*addr=*/0x20a93000ul, /*len=*/0x4000ul, >>> /*advice=MADV_HUGEPAGE|0x800000000*/ 0x80000000eul); >>> >>> advise is supposed to be a 32bit int. What does the magical >>> "0x800000000" do? >> >> I am pretty sure this is a red herring. >> Syzkaller sometimes mutates integer flags, even if the result makes no >> sense - because sometimes it can trigger interesting bugs. >> This `advice` argument will be discarded by is_valid_madvise(), >> resulting in -EINVAL. > > I thought the same, but likely the upper bits are discarded, and we end > up with __NR_madvise succeeding. > > The kernel config has > > CONFIG_TRANSPARENT_HUGEPAGE_MADVISE=y > > So without MADV_HUGEPAGE, we wouldn't get a THP in the first place. > > So likely this is really just like dropping the "0x800000000" > > Anyhow, I managed to reproduce in the VM using the provided rootfs on > aarch64. It triggers immediately, so no races involved. > > Running the reproducer on a Fedora 42 debug-kernel in the hypervisor > does not trigger. Simplified reproducer that does not depend on a race with the child process. As expected previously, we have PAE cleared on the head page, because it is/was COW-shared with a child process. We are registering more than one consecutive tail pages of that THP through iouring, GUP-pinning them. These pages are not COW-shared and, therefore, do not have PAE set. #define _GNU_SOURCE #include #include #include #include #include #include #include #include int main(void) { struct io_uring_params params = { .wq_fd = -1, }; struct iovec iovec; const size_t pagesize = getpagesize(); size_t size = 2048 * pagesize; char *addr; int fd; /* We need a THP-aligned area. */ addr = mmap((char *)0x20000000u, size, PROT_WRITE|PROT_READ, MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE, -1, 0); if (addr == MAP_FAILED) { perror("MAP_FIXED failed\n"); return 1; } if (madvise(addr, size, MADV_HUGEPAGE)) { perror("MADV_HUGEPAGE failed\n"); return 1; } /* Populate a THP. */ memset(addr, 0, size); /* COW-share only the first page ... */ if (madvise(addr + pagesize, size - pagesize, MADV_DONTFORK)) { perror("MADV_DONTFORK failed\n"); return 1; } /* ... using fork(). This will clear PAE on the head page. */ if (fork() == 0) exit(0); /* Setup iouring */ fd = syscall(__NR_io_uring_setup, 1024, ¶ms); if (fd < 0) { perror("__NR_io_uring_setup failed\n"); return 1; } /* Register (GUP-pin) two consecutive tail pages. */ iovec.iov_base = addr + pagesize; iovec.iov_len = 2 * pagesize; syscall(__NR_io_uring_register, fd, IORING_REGISTER_BUFFERS, &iovec, 1); return 0; } [ 108.070381][ T14] kernel BUG at mm/gup.c:71! [ 108.070502][ T14] Internal error: Oops - BUG: 00000000f2000800 [#1] SMP [ 108.117202][ T14] Modules linked in: [ 108.119105][ T14] CPU: 1 UID: 0 PID: 14 Comm: kworker/u32:1 Not tainted 6.16.0-rc2-syzkaller-g9aa9b43d689e #0 PREEMPT [ 108.123672][ T14] Hardware name: QEMU KVM Virtual Machine, BIOS edk2-20250221-8.fc42 02/21/2025 [ 108.127458][ T14] Workqueue: iou_exit io_ring_exit_work [ 108.129812][ T14] pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--) [ 108.133091][ T14] pc : sanity_check_pinned_pages+0x7cc/0x7d0 [ 108.135566][ T14] lr : sanity_check_pinned_pages+0x7cc/0x7d0 [ 108.138025][ T14] sp : ffff800097ac7640 [ 108.139859][ T14] x29: ffff800097ac7660 x28: dfff800000000000 x27: 1fffffbff80d3000 [ 108.143185][ T14] x26: 01ffc0000002007c x25: 01ffc0000002007c x24: fffffdffc0698000 [ 108.146599][ T14] x23: fffffdffc0698000 x22: ffff800097ac76e0 x21: 01ffc0000002007c [ 108.150025][ T14] x20: 0000000000000000 x19: ffff800097ac76e0 x18: 00000000ffffffff [ 108.153449][ T14] x17: 703e2d6f696c6f66 x16: ffff80008ae33808 x15: ffff700011ed61d4 [ 108.156892][ T14] x14: 1ffff00011ed61d4 x13: 0000000000000004 x12: ffffffffffffffff [ 108.160267][ T14] x11: ffff700011ed61d4 x10: 0000000000ff0100 x9 : f6672ecf4f89d700 [ 108.163782][ T14] x8 : f6672ecf4f89d700 x7 : 0000000000000001 x6 : 0000000000000001 [ 108.167180][ T14] x5 : ffff800097ac6d58 x4 : ffff80008f727060 x3 : ffff80008054c348 [ 108.170807][ T14] x2 : 0000000000000000 x1 : 0000000100000000 x0 : 0000000000000061 [ 108.174205][ T14] Call trace: [ 108.175649][ T14] sanity_check_pinned_pages+0x7cc/0x7d0 (P) [ 108.178138][ T14] unpin_user_page+0x80/0x10c [ 108.180189][ T14] io_release_ubuf+0x84/0xf8 [ 108.182196][ T14] io_free_rsrc_node+0x250/0x57c [ 108.184345][ T14] io_rsrc_data_free+0x148/0x298 [ 108.186493][ T14] io_sqe_buffers_unregister+0x84/0xa0 [ 108.188991][ T14] io_ring_ctx_free+0x48/0x480 [ 108.191057][ T14] io_ring_exit_work+0x764/0x7d8 [ 108.193207][ T14] process_one_work+0x7e8/0x155c [ 108.195431][ T14] worker_thread+0x958/0xed8 [ 108.197561][ T14] kthread+0x5fc/0x75c [ 108.199362][ T14] ret_from_fork+0x10/0x20 When only pinning a single tail page (iovec.iov_len = pagesize), it works as expected. So, if we pinned two tail pages but end up calling io_release_ubuf()->unpin_user_page() on the head page, meaning that "imu->bvec[i].bv_page" points at the wrong folio page (IOW, one we never pinned). So it's related to the io_coalesce_buffer() machinery. And in fact, in there, we have this weird logic: /* Store head pages only*/ new_array = kvmalloc_array(nr_folios, sizeof(struct page *), GFP_KERNEL); ... Essentially discarding the subpage information when coalescing tail pages. I am afraid the whole io_check_coalesce_buffer + io_coalesce_buffer() logic might be flawed (we can -- in theory -- coalesc different folio page ranges in a GUP result?). @Jens, not sure if this only triggers a warning when unpinning or if we actually mess up imu->bvec[i].bv_page, to end up pointing at (reading/writing) pages we didn't even pin in the first place. Can you look into that, as you are more familiar with the logic? -- Cheers, David / dhildenb