kvm: WARNING in vmx_handle_exit

Dmitry Vyukov
2017-01-02T10:23:59Z

Hello,

I've got the following warning while running syzkaller fuzzer:

WARNING: CPU: 2 PID: 13257 at arch/x86/kvm/vmx.c:8633
vmx_handle_exit+0x262b/0x38b0 arch/x86/kvm/vmx.c:8633
vmx: unexpected exit reason 0xb
CPU: 2 PID: 13257 Comm: syz-executor7 Not tainted 4.10.0-rc1+ #118
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:15 [inline]
dump_stack+0x292/0x3a2 lib/dump_stack.c:51
panic+0x1cb/0x3a9 kernel/panic.c:179
__warn+0x1c4/0x1e0 kernel/panic.c:539
warn_slowpath_fmt+0xc5/0x100 kernel/panic.c:562
vmx_handle_exit+0x262b/0x38b0 arch/x86/kvm/vmx.c:8633
vcpu_enter_guest arch/x86/kvm/x86.c:6884 [inline]
vcpu_run arch/x86/kvm/x86.c:6943 [inline]
kvm_arch_vcpu_ioctl_run+0xf3d/0x45f0 arch/x86/kvm/x86.c:7101
kvm_vcpu_ioctl+0x673/0x1120 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2569
vfs_ioctl fs/ioctl.c:43 [inline]
do_vfs_ioctl+0x1bf/0x1780 fs/ioctl.c:683
SYSC_ioctl fs/ioctl.c:698 [inline]
SyS_ioctl+0x8f/0xc0 fs/ioctl.c:689
entry_SYSCALL_64_fastpath+0x1f/0xc2
RIP: 0033:0x4438a9
RSP: 002b:00007f935aa2fb58 EFLAGS: 00000286 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000015 RCX: 00000000004438a9
RDX: 0000000000000000 RSI: 000000000000ae80 RDI: 0000000000000015
RBP: 00000000006ddb30 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000286 R12: 0000000000700000
R13: 0000000000000006 R14: 0000000000000015 R15: 0000000020014000
Dumping ftrace buffer:
(ftrace buffer empty)
Kernel Offset: disabled

Exit reason 0xb is GETSEC instruction. This does not look harmful as
it is handled as #UD. But I think we should print a single line
message regarding non-emulated instruction as in other cases, just to
not scare cloud admins and to make syzkaller ignore it.

FTR, a raw reproducer is here: