linux-kernel - kvm: WARNING in vmx_handle

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Date:   Mon, 2 Jan 2017 11:23:37 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        KVM list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Steve Rutherford <srutherford@...gle.com>
Cc:     syzkaller <syzkaller@...glegroups.com>
Subject: kvm: WARNING in vmx_handle_exit

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:
https://gist.githubusercontent.com/dvyukov/c762f6ea04ebbba49cdee0a6caca31b4/raw/f21deb04cdc70ae74100c12447d71bb0cd2025c7/gistfile1.txt