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[2003:d8:2f4e:fd00:8e13:e3b5:90c8:1159]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a6d0f104bbsm9437486f8f.4.2025.06.23.05.47.49 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 23 Jun 2025 05:47:49 -0700 (PDT) Message-ID: Date: Mon, 23 Jun 2025 14:47:48 +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: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 23.06.25 14:22, David Hildenbrand wrote: > 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 FWIW, a slight cow.c selftest modification can trigger the same: diff --git a/tools/testing/selftests/mm/cow.c b/tools/testing/selftests/mm/cow.c index 4214070d03ce..50c538b47bb4 100644 --- a/tools/testing/selftests/mm/cow.c +++ b/tools/testing/selftests/mm/cow.c @@ -991,6 +991,8 @@ static void do_run_with_thp(test_fn fn, enum thp_run thp_run, size_t thpsize) log_test_result(KSFT_FAIL); goto munmap; } + mem += pagesize; + size -= pagesize; break; default: assert(false); -- Cheers, David / dhildenb