linux-kernel - Re: [PATCH] KVM: VMX: Fix vmx->nested freeing when no SMI handler

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Date:   Thu, 23 Nov 2017 17:13:32 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Liran Alon <LIRAN.ALON@...cle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        kvm <kvm@...r.kernel.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH] KVM: VMX: Fix vmx->nested freeing when no SMI handler

d2017-11-23 0:56 GMT+08:00 Paolo Bonzini <pbonzini@...hat.com>:
> On 22/11/2017 10:43, Liran Alon wrote:
>>>>
>>>> I think we should also set "vmx->nested.smm.vmxon = false;"
>>>> after "vmx->nested.vmxon = false;" to correctlyhandle the case
>>>> VMXOFF is executed from SMI handler. Otherwise, when SMI handler
>>>> executes RSM, we will reach vmx_pre_leave_smm() which will set
>>>> again "vmx->nested.vmxon = true;" which I think shouldn't
>>>> happen.
>>>
>>> I didn't see a real scenario for this.
>>
>> Actually I later saw that handle_vmoff() calls
>> nested_vmx_check_permission() which indeed won't allow to continue
>> executing if running from SMI because vmx->nested.vmxon=false; and
>> therefore this will raise a #UD. So you are right. :)
>
> Still, not clearing the flag is wrong.  free_nested is also called by
> vmx_leave_nested when the host writes 0 to MSR_IA32_FEATURE_CONTROL with
> KVM_SET_MSRS.

Do it in v2. :)

Regards,
Wanpeng Li