linux-kernel - Re: [PATCH 1/2] KVM: x86: Add emulation support for #GP triggered by VM instructions

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Date:   Tue, 12 Jan 2021 15:00:09 -0500
From:   Bandan Das <bsd@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Wei Huang <wei.huang2@....com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, pbonzini@...hat.com,
        vkuznets@...hat.com, joro@...tes.org, bp@...en8.de,
        tglx@...utronix.de, mingo@...hat.com, x86@...nel.org,
        jmattson@...gle.com, wanpengli@...cent.com, dgilbert@...hat.com,
        mlevitsk@...hat.com
Subject: Re: [PATCH 1/2] KVM: x86: Add emulation support for #GP triggered by VM instructions

Sean Christopherson <seanjc@...gle.com> writes:
...
>> -	if ((emulation_type & EMULTYPE_VMWARE_GP) &&
>> -	    !is_vmware_backdoor_opcode(ctxt)) {
>> -		kvm_queue_exception_e(vcpu, GP_VECTOR, 0);
>> -		return 1;
>> +	if (emulation_type & EMULTYPE_PARAVIRT_GP) {
>> +		vminstr = is_vm_instr_opcode(ctxt);
>> +		if (!vminstr && !is_vmware_backdoor_opcode(ctxt)) {
>> +			kvm_queue_exception_e(vcpu, GP_VECTOR, 0);
>> +			return 1;
>> +		}
>> +		if (vminstr)
>> +			return vminstr;
>
> I'm pretty sure this doesn't correctly handle a VM-instr in L2 that hits a bad
> L0 GPA and that L1 wants to intercept.  The intercept bitmap isn't checked until
> x86_emulate_insn(), and the vm*_interception() helpers expect nested VM-Exits to
> be handled further up the stack.
>
So, the condition is that L2 executes a vmload and #GPs on a reserved address, jumps to L0 - L0 doesn't
check if L1 has asked for the instruction to be intercepted and goes on with emulating
vmload and returning back to L2 ?

>>  	}
>>  
>>  	/*
>> -- 
>> 2.27.0
>>