[syzbot] [kvm?] WARNING in kvm_arch_vcpu_ioctl_run (5)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 64569520920a Merge tag 'block-6.4-2023-06-09' of git://git..
git tree: upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=12386cd9280000
kernel config: https://syzkaller.appspot.com/x/.config?x=3c980bfe8b399968
dashboard link: https://syzkaller.appspot.com/bug?extid=5feef0b9ee9c8e9e5689
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=13adcb43280000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13af3853280000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/4421ae3b4ee0/disk-64569520.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/9312cbb35f54/vmlinux-64569520.xz
kernel image: https://storage.googleapis.com/syzbot-assets/3476854febf3/bzImage-64569520.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+5feef0...@syzkaller.appspotmail.com

kvm_intel: L1TF CPU bug present and SMT on, data leak possible. See CVE-2018-3646 and https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/l1tf.html for details.
kvm: vcpu 1: requested 128 ns lapic timer period limited to 200000 ns
kvm: vcpu 1: requested lapic timer restore with starting count register 0x390=1812281087 (231971979136 ns) > initial count (200000 ns). Using initial count to start timer.
------------[ cut here ]------------
WARNING: CPU: 1 PID: 5004 at arch/x86/kvm/x86.c:11099 kvm_arch_vcpu_ioctl_run+0x2379/0x2820 arch/x86/kvm/x86.c:11099
Modules linked in:
CPU: 1 PID: 5004 Comm: syz-executor120 Not tainted 6.4.0-rc5-syzkaller-00245-g64569520920a #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/25/2023
RIP: 0010:kvm_arch_vcpu_ioctl_run+0x2379/0x2820 arch/x86/kvm/x86.c:11099
Code: fc ff ff e8 19 64 71 00 44 89 e6 48 c7 c7 40 8a 42 8a c6 05 cd e9 51 0d 01 e8 53 1f 39 00 0f 0b e9 2a fc ff ff e8 f7 63 71 00 <0f> 0b e9 26 fb ff ff e8 eb 63 71 00 0f b6 1d aa e9 51 0d 31 ff 89
RSP: 0018:ffffc90003a8fcb8 EFLAGS: 00010293
RAX: 0000000000000000 RBX: 0000000000000001 RCX: 0000000000000000
RDX: ffff888015b9d940 RSI: ffffffff8112e2e9 RDI: 0000000000000001
RBP: ffff88807dae8000 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000001 R12: ffffc900015a7918
R13: ffffc900015a7908 R14: 0000000000000000 R15: ffff88807dae82ec
FS: 00005555572d6300(0000) GS:ffff8880b9900000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020fe9008 CR3: 000000007be99000 CR4: 00000000003526e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
kvm_vcpu_ioctl+0x574/0xea0 arch/x86/kvm/../../../virt/kvm/kvm_main.c:4106
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: 0033:0x7f0464e7ec99
Code: 28 c3 e8 2a 14 00 00 66 2e 0f 1f 84 00 00 00 00 00 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:00007ffded877408 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f0464e7ec99
RDX: 0000000000000000 RSI: 000000000000ae80 RDI: 0000000000000005
RBP: 00007f0464e426f0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f0464e42780
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
</TASK>


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[Sean Christopherson]

KVM doesn't reject KVM_SET_SREGS with a bad CR0, which combined with an L2 that's
configured with unrestricted guest *disabled*, coerces KVM into stuffing VM86 state
to virtualize Real Mode, and eventually leads to all kinds of weirdness. Will post
a patch "shortly" (probably tomorrow at this point).