Subject: [syzbot] [kernel?] general protection fault in vhost_task_start

From: syzbot <[email-masked]>
Date: Tue, 21 Mar 2023 10:03:55 -0700

Hello,

syzbot found the following issue on:

HEAD commit:    6f08c1de13a9 Add linux-next specific files for 20230317
git tree:       linux-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=13d954f6c80000
kernel config:  https://syzkaller.appspot.com/x/.config?x=b8cdb12af294ab55
dashboard link: https://syzkaller.appspot.com/bug?extid=6b27b2d2aba1c80cc13b
compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=137b6b11c80000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16358a16c80000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/300a30f8157b/disk-6f08c1de.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/7cad5b8b07a2/vmlinux-6f08c1de.xz
kernel image: https://storage.googleapis.com/syzbot-assets/eded56f08b63/bzImage-6f08c1de.xz

The issue was bisected to:

commit 5ab18f4b061ef24a71eea9ffafebd1a82ae2f514
Author: Mike Christie <[email-masked]>
Date:   Fri Mar 10 22:03:32 2023 +0000

    vhost: use vhost_tasks for worker threads

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=11d88e9ac80000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=13d88e9ac80000
console output: https://syzkaller.appspot.com/x/log.txt?x=15d88e9ac80000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email-masked]
Fixes: 5ab18f4b061e ("vhost: use vhost_tasks for worker threads")

RBP: 00007ffe3d8e6050 R08: 0000000000000001 R09: 0000000000000001
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000004
R13: 431bde82d7b634db R14: 0000000000000000 R15: 0000000000000000
 </TASK>
general protection fault, probably for non-canonical address 0xdffffc000000000c: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000060-0x0000000000000067]
CPU: 0 PID: 5103 Comm: syz-executor280 Not tainted 6.3.0-rc2-next-20230317-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/02/2023
RIP: 0010:vhost_task_start+0x22/0x40 kernel/vhost_task.c:115
Code: 00 00 00 00 00 0f 1f 00 f3 0f 1e fa 53 48 89 fb e8 c3 67 2c 00 48 8d 7b 70 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 75 0a 48 8b 7b 70 5b e9 fe bd 02 00 e8 79 ec 7e 00 eb
RSP: 0018:ffffc90003a9fc38 EFLAGS: 00010207
RAX: dffffc0000000000 RBX: fffffffffffffff4 RCX: 0000000000000000
RDX: 000000000000000c RSI: ffffffff81564c8d RDI: 0000000000000064
RBP: ffff88802b21dd40 R08: 0000000000000100 R09: ffffffff8c917cf3
R10: 00000000fffffff4 R11: 0000000000000000 R12: fffffffffffffff4
R13: ffff888075d000b0 R14: ffff888075d00000 R15: ffff888075d00008
FS:  0000555556247300(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffe3d8e5ff8 CR3: 00000000215d4000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 vhost_worker_create drivers/vhost/vhost.c:580 [inline]
 vhost_dev_set_owner+0x338/0xa90 drivers/vhost/vhost.c:603
 vhost_dev_ioctl+0xb4b/0xe70 drivers/vhost/vhost.c:1764
 vhost_vsock_dev_ioctl+0x389/0xb30 drivers/vhost/vsock.c:862
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl fs/ioctl.c:856 [inline]
 __x64_sys_ioctl+0x197/0x210 fs/ioctl.c:856
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f82c4252049
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 b1 14 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 c0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffe3d8e6038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 00007f82c4252049
RDX: 0000000000000000 RSI: 000000000000af01 RDI: 0000000000000003
RBP: 00007ffe3d8e6050 R08: 0000000000000001 R09: 0000000000000001
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000004
R13: 431bde82d7b634db R14: 0000000000000000 R15: 0000000000000000
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:vhost_task_start+0x22/0x40 kernel/vhost_task.c:115
Code: 00 00 00 00 00 0f 1f 00 f3 0f 1e fa 53 48 89 fb e8 c3 67 2c 00 48 8d 7b 70 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 75 0a 48 8b 7b 70 5b e9 fe bd 02 00 e8 79 ec 7e 00 eb
RSP: 0018:ffffc90003a9fc38 EFLAGS: 00010207
RAX: dffffc0000000000 RBX: fffffffffffffff4 RCX: 0000000000000000
RDX: 000000000000000c RSI: ffffffff81564c8d RDI: 0000000000000064
RBP: ffff88802b21dd40 R08: 0000000000000100 R09: ffffffff8c917cf3
R10: 00000000fffffff4 R11: 0000000000000000 R12: fffffffffffffff4
R13: ffff888075d000b0 R14: ffff888075d00000 R15: ffff888075d00008
FS:  0000555556247300(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffe3d8e5ff8 CR3: 00000000215d4000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess), 1 bytes skipped:
   0:	00 00                	add    %al,(%rax)
   2:	00 00                	add    %al,(%rax)
   4:	0f 1f 00             	nopl   (%rax)
   7:	f3 0f 1e fa          	endbr64
   b:	53                   	push   %rbx
   c:	48 89 fb             	mov    %rdi,%rbx
   f:	e8 c3 67 2c 00       	callq  0x2c67d7
  14:	48 8d 7b 70          	lea    0x70(%rbx),%rdi
  18:	48 b8 00 00 00 00 00 	movabs $0xdffffc0000000000,%rax
  1f:	fc ff df
  22:	48 89 fa             	mov    %rdi,%rdx
  25:	48 c1 ea 03          	shr    $0x3,%rdx
* 29:	80 3c 02 00          	cmpb   $0x0,(%rdx,%rax,1) <-- trapping instruction
  2d:	75 0a                	jne    0x39
  2f:	48 8b 7b 70          	mov    0x70(%rbx),%rdi
  33:	5b                   	pop    %rbx
  34:	e9 fe bd 02 00       	jmpq   0x2be37
  39:	e8 79 ec 7e 00       	callq  0x7eecb7
  3e:	eb                   	.byte 0xeb

---
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For information about bisection process see: https://goo.gl/tpsmEJ#bisection
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https://goo.gl/tpsmEJ#testing-patches