[PATCH] KVM: nVMX: Reset nested_run_pending if the CPU is going to be reset

[Wanpeng Li]

Reported by syzkaller:

        WARNING: CPU: 1 PID: 27742 at arch/x86/kvm/vmx.c:11029
        nested_vmx_vmexit+0x5c35/0x74d0 arch/x86/kvm/vmx.c:11029
        CPU: 1 PID: 27742 Comm: a.out Not tainted 4.10.0+ #229
        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+0x2ee/0x3ef lib/dump_stack.c:51
         panic+0x1fb/0x412 kernel/panic.c:179
         __warn+0x1c4/0x1e0 kernel/panic.c:540
         warn_slowpath_null+0x2c/0x40 kernel/panic.c:583
         nested_vmx_vmexit+0x5c35/0x74d0 arch/x86/kvm/vmx.c:11029
         vmx_leave_nested arch/x86/kvm/vmx.c:11136 [inline]
         vmx_set_msr+0x1565/0x1910 arch/x86/kvm/vmx.c:3324
         kvm_set_msr+0xd4/0x170 arch/x86/kvm/x86.c:1099
         do_set_msr+0x11e/0x190 arch/x86/kvm/x86.c:1128
         __msr_io arch/x86/kvm/x86.c:2577 [inline]
         msr_io+0x24b/0x450 arch/x86/kvm/x86.c:2614
         kvm_arch_vcpu_ioctl+0x35b/0x46a0 arch/x86/kvm/x86.c:3497
         kvm_vcpu_ioctl+0x232/0x1120 
arch/x86/kvm/../../../virt/kvm/kvm_main.c:2721
         vfs_ioctl fs/ioctl.c:43 [inline]
         do_vfs_ioctl+0x1bf/0x1790 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
        
The syzkaller folks reported a nested_run_pending warning during userspace 
clear VMX 
capability which is exposed to L1 before. 

The warning gets thrown while doing

(*(uint32_t*)0x20aecfe8 = (uint32_t)0x1);
(*(uint32_t*)0x20aecfec = (uint32_t)0x0);
(*(uint32_t*)0x20aecff0 = (uint32_t)0x3a);
(*(uint32_t*)0x20aecff4 = (uint32_t)0x0);
(*(uint64_t*)0x20aecff8 = (uint64_t)0x0);
r[29] = syscall(__NR_ioctl, r[4], 0x4008ae89ul,
                0x20aecfe8ul, 0, 0, 0, 0, 0, 0);

i.e. KVM_SET_MSR ioctl with

struct kvm_msrs {
        .nmsrs = 1,
                .pad = 0,
                .entries = {
                        {.index = MSR_IA32_FEATURE_CONTROL,
                                .reserved = 0,
                                .data = 0}
                }
}

The VMLANCH/VMRESUME emulation should be stopped since the CPU is going to 
reset here. 
This patch resets the nested_run_pending since the CPU is going to be reset 
hence there 
should be nothing pending.

Reported-by: Dmitry Vyukov <dvyu...@google.com>
Suggested-by: Radim Krčmář <rkrc...@redhat.com>
Cc: Paolo Bonzini <pbonz...@redhat.com>
Cc: Radim Krčmář <rkrc...@redhat.com>
Cc: Dmitry Vyukov <dvyu...@google.com>
Signed-off-by: Wanpeng Li <wanpeng...@hotmail.com>
---
 arch/x86/kvm/vmx.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 283aa86..b4a757369 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -3310,8 +3310,10 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct 
msr_data *msr_info)
                     FEATURE_CONTROL_LOCKED && !msr_info->host_initiated))
                        return 1;
                vmx->msr_ia32_feature_control = data;
-               if (msr_info->host_initiated && data == 0)
+               if (msr_info->host_initiated && data == 0) {
+                       vmx->nested.nested_run_pending = 0;
                        vmx_leave_nested(vcpu);
+               }
                break;
        case MSR_IA32_VMX_BASIC ... MSR_IA32_VMX_VMFUNC:
                if (!msr_info->host_initiated)
-- 
2.7.4