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

[Dmitry Vyukov]

On Sat, Mar 4, 2017 at 5:03 AM, Wanpeng Li <kernellwp@xxxxxxxxx> wrote:
> 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.

Applied on bots. Thanks!

> Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Suggested-by: Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx>
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx>
> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
> ---
>  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
>