Re: [syzbot] [mm?] BUG: unable to handle kernel paging request in move_pages

[Peter Xu <peterx@redhat.com>]

Copy Lokesh and Suren.

On Thu, Jul 17, 2025 at 12:13:32PM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    e8352908bdcd Add linux-next specific files for 20250716
> git tree:       linux-next
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=17f81382580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=b7b0e60e17dc5717
> dashboard link: https://syzkaller.appspot.com/bug?extid=b446dbe27035ef6bd6c2
> compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10041382580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10eb158c580000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/ae8cc81c1781/disk-e8352908.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/57aaea991896/vmlinux-e8352908.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/feb871619bd4/bzImage-e8352908.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+b446dbe27035ef6bd6c2@syzkaller.appspotmail.com
> 
> BUG: unable to handle page fault for address: ffffea6000391008
> #PF: supervisor read access in kernel mode
> #PF: error_code(0x0000) - not-present page
> PGD 13fff8067 P4D 13fff8067 PUD 0 
> Oops: Oops: 0000 [#1] SMP KASAN PTI
> CPU: 1 UID: 0 PID: 5860 Comm: syz-executor832 Not tainted 6.16.0-rc6-next-20250716-syzkaller #0 PREEMPT(full) 
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
> RIP: 0010:_compound_head include/linux/page-flags.h:284 [inline]
> RIP: 0010:move_pages+0xbe6/0x1430 mm/userfaultfd.c:1824
> Code: c1 ec 06 4b 8d 1c 2c 48 83 c3 08 48 89 d8 48 c1 e8 03 48 b9 00 00 00 00 00 fc ff df 80 3c 08 00 74 08 48 89 df e8 9a 30 f4 ff <48> 8b 1b 48 89 de 48 83 e6 01 31 ff e8 59 70 8f ff 48 89 d8 48 83
> RSP: 0018:ffffc90003f778a8 EFLAGS: 00010246
> RAX: 1ffffd4c00072201 RBX: ffffea6000391008 RCX: dffffc0000000000
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
> RBP: 0000000000000000 R08: 0000000000000003 R09: 0000000000000004
> R10: dffffc0000000000 R11: fffff520007eef00 R12: 0000006000391000
> R13: ffffea0000000000 R14: 200018000e4401fd R15: 00002000003ab000
> FS:  00007ff35708f6c0(0000) GS:ffff8881258aa000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: ffffea6000391008 CR3: 0000000074390000 CR4: 00000000003526f0
> Call Trace:
>  <TASK>
>  userfaultfd_move fs/userfaultfd.c:1923 [inline]
>  userfaultfd_ioctl+0x2e8b/0x4c80 fs/userfaultfd.c:2046
>  vfs_ioctl fs/ioctl.c:51 [inline]
>  __do_sys_ioctl fs/ioctl.c:598 [inline]
>  __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:584
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7ff3570d6519
> Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 51 18 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b0 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007ff35708f218 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 00007ff357160308 RCX: 00007ff3570d6519
> RDX: 0000200000000180 RSI: 00000000c028aa05 RDI: 0000000000000003
> RBP: 00007ff357160300 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00007ff35712d074
> R13: 0000200000000180 R14: 0000200000000188 R15: 00002000002b9000
>  </TASK>
> Modules linked in:
> CR2: ffffea6000391008
> ---[ end trace 0000000000000000 ]---
> RIP: 0010:_compound_head include/linux/page-flags.h:284 [inline]
> RIP: 0010:move_pages+0xbe6/0x1430 mm/userfaultfd.c:1824
> Code: c1 ec 06 4b 8d 1c 2c 48 83 c3 08 48 89 d8 48 c1 e8 03 48 b9 00 00 00 00 00 fc ff df 80 3c 08 00 74 08 48 89 df e8 9a 30 f4 ff <48> 8b 1b 48 89 de 48 83 e6 01 31 ff e8 59 70 8f ff 48 89 d8 48 83
> RSP: 0018:ffffc90003f778a8 EFLAGS: 00010246
> RAX: 1ffffd4c00072201 RBX: ffffea6000391008 RCX: dffffc0000000000
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
> RBP: 0000000000000000 R08: 0000000000000003 R09: 0000000000000004
> R10: dffffc0000000000 R11: fffff520007eef00 R12: 0000006000391000
> R13: ffffea0000000000 R14: 200018000e4401fd R15: 00002000003ab000
> FS:  00007ff35708f6c0(0000) GS:ffff8881258aa000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: ffffea6000391008 CR3: 0000000074390000 CR4: 00000000003526f0
> ----------------
> Code disassembly (best guess):
>    0:	c1 ec 06             	shr    $0x6,%esp
>    3:	4b 8d 1c 2c          	lea    (%r12,%r13,1),%rbx
>    7:	48 83 c3 08          	add    $0x8,%rbx
>    b:	48 89 d8             	mov    %rbx,%rax
>    e:	48 c1 e8 03          	shr    $0x3,%rax
>   12:	48 b9 00 00 00 00 00 	movabs $0xdffffc0000000000,%rcx
>   19:	fc ff df
>   1c:	80 3c 08 00          	cmpb   $0x0,(%rax,%rcx,1)
>   20:	74 08                	je     0x2a
>   22:	48 89 df             	mov    %rbx,%rdi
>   25:	e8 9a 30 f4 ff       	call   0xfff430c4
> * 2a:	48 8b 1b             	mov    (%rbx),%rbx <-- trapping instruction
>   2d:	48 89 de             	mov    %rbx,%rsi
>   30:	48 83 e6 01          	and    $0x1,%rsi
>   34:	31 ff                	xor    %edi,%edi
>   36:	e8 59 70 8f ff       	call   0xff8f7094
>   3b:	48 89 d8             	mov    %rbx,%rax
>   3e:	48                   	rex.W
>   3f:	83                   	.byte 0x83
> 
> 
> ---
> This report is generated by a bot. It may contain errors.
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> 
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> 
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> 
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> 

-- 
Peter Xu