Re: [syzbot] [mm?] general protection fault in do_migrate_pages

[David Hildenbrand <david@redhat.com>]

On 20.11.24 01:00, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    f868cd251776 Merge tag 'drm-fixes-2024-11-16' of https://g..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=15473cc0580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=ff8e8187a30080b5
> dashboard link: https://syzkaller.appspot.com/bug?extid=3511625422f7aa637f0d
> compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=17e8d130580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=159c71a7980000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/a0d46da55993/disk-f868cd25.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/da57ef4813fd/vmlinux-f868cd25.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/3cdde892ea08/bzImage-f868cd25.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+3511625422f7aa637f0d@syzkaller.appspotmail.com
> 
> Oops: general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] PREEMPT SMP KASAN PTI
> KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
> CPU: 1 UID: 0 PID: 6021 Comm: syz-executor284 Not tainted 6.12.0-rc7-syzkaller-00187-gf868cd251776 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/30/2024
> RIP: 0010:migrate_to_node mm/mempolicy.c:1090 [inline]
> RIP: 0010:do_migrate_pages+0x403/0x6f0 mm/mempolicy.c:1194
> Code: 8b 54 24 30 41 83 c8 10 80 3a 00 4d 63 c0 0f 85 d1 02 00 00 48 89 c1 48 8b 54 24 18 48 be 00 00 00 00 00 fc ff df 48 c1 e9 03 <80> 3c 31 00 48 8b 92 b0 00 00 00 0f 85 74 02 00 00 48 8b 30 49 89
> RSP: 0018:ffffc9000375fd08 EFLAGS: 00010246
> RAX: 0000000000000000 RBX: ffffc9000375fd78 RCX: 0000000000000000
> RDX: ffff88807e171300 RSI: dffffc0000000000 RDI: ffff88803390c044
> RBP: ffff88807e171428 R08: 0000000000000014 R09: fffffbfff2039ef1
> R10: ffffffff901cf78f R11: 0000000000000000 R12: 0000000000000003
> R13: ffffc9000375fe90 R14: ffffc9000375fe98 R15: ffffc9000375fdf8
> FS:  00005555919e1380(0000) GS:ffff8880b8700000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00005555919e1ca8 CR3: 000000007f12a000 CR4: 00000000003526f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>   <TASK>
>   kernel_migrate_pages+0x5b2/0x750 mm/mempolicy.c:1709
>   __do_sys_migrate_pages mm/mempolicy.c:1727 [inline]
>   __se_sys_migrate_pages mm/mempolicy.c:1723 [inline]
>   __x64_sys_migrate_pages+0x96/0x100 mm/mempolicy.c:1723
>   do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>   do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
>   entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7fedcca74af9
> Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 c1 17 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 b8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007ffe4d85c278 EFLAGS: 00000206 ORIG_RAX: 0000000000000100
> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fedcca74af9
> RDX: 0000000020000000 RSI: 000000000000005a RDI: 0000000000001786
> RBP: 0000000000010bf2 R08: 0000000000006080 R09: 0000000000000006
> R10: 0000000020000040 R11: 0000000000000206 R12: 00007ffe4d85c28c
> R13: 431bde82d7b634db R14: 0000000000000001 R15: 0000000000000001
>   </TASK>
> Modules linked in:
> ---[ end trace 0000000000000000 ]---
> RIP: 0010:migrate_to_node mm/mempolicy.c:1090 [inline]
> RIP: 0010:do_migrate_pages+0x403/0x6f0 mm/mempolicy.c:1194
> Code: 8b 54 24 30 41 83 c8 10 80 3a 00 4d 63 c0 0f 85 d1 02 00 00 48 89 c1 48 8b 54 24 18 48 be 00 00 00 00 00 fc ff df 48 c1 e9 03 <80> 3c 31 00 48 8b 92 b0 00 00 00 0f 85 74 02 00 00 48 8b 30 49 89
> RSP: 0018:ffffc9000375fd08 EFLAGS: 00010246
> RAX: 0000000000000000 RBX: ffffc9000375fd78 RCX: 0000000000000000
> RDX: ffff88807e171300 RSI: dffffc0000000000 RDI: ffff88803390c044
> RBP: ffff88807e171428 R08: 0000000000000014 R09: fffffbfff2039ef1
> R10: ffffffff901cf78f R11: 0000000000000000 R12: 0000000000000003
> R13: ffffc9000375fe90 R14: ffffc9000375fe98 R15: ffffc9000375fdf8
> FS:  00005555919e1380(0000) GS:ffff8880b8700000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00005555919e1ca8 CR3: 000000007f12a000 CR4: 00000000003526f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> ----------------
> Code disassembly (best guess):
>     0:	8b 54 24 30          	mov    0x30(%rsp),%edx
>     4:	41 83 c8 10          	or     $0x10,%r8d
>     8:	80 3a 00             	cmpb   $0x0,(%rdx)
>     b:	4d 63 c0             	movslq %r8d,%r8
>     e:	0f 85 d1 02 00 00    	jne    0x2e5
>    14:	48 89 c1             	mov    %rax,%rcx
>    17:	48 8b 54 24 18       	mov    0x18(%rsp),%rdx
>    1c:	48 be 00 00 00 00 00 	movabs $0xdffffc0000000000,%rsi
>    23:	fc ff df
>    26:	48 c1 e9 03          	shr    $0x3,%rcx
> * 2a:	80 3c 31 00          	cmpb   $0x0,(%rcx,%rsi,1) <-- trapping instruction
>    2e:	48 8b 92 b0 00 00 00 	mov    0xb0(%rdx),%rdx
>    35:	0f 85 74 02 00 00    	jne    0x2af
>    3b:	48 8b 30             	mov    (%rax),%rsi
>    3e:	49                   	rex.WB
>    3f:	89                   	.byte 0x89
> 

Hmmm, there is not much meat in this report :)

The reproducer seems to execute migrate_pages() in a fork'ed child 
process, and kills that process after a while. Not 100% sure if the 
concurrent killing of the process is relevant.

Before the child process calls migrate_pages(), it executes 
MADV_DONTFORK on the complete address space (funny, I wonder what that 
does ...) and then calls clone3() without CLONE_VM.

-- 
Cheers,

David / dhildenb