Re: [PATCH 4/8][KVM nVMX]: Check "load IA32_PERF_GLOBAL_CTRL" VM-exit control on vmentry of nested guests

From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Krish Sadhukhan <krish.sadhukhan@oracle.com>
Cc: kvm@vger.kernel.org, pbonzini@redhat.com, rkrcmar@redhat.com,
	jmattson@google.com
Subject: Re: [PATCH 4/8][KVM nVMX]: Check "load IA32_PERF_GLOBAL_CTRL" VM-exit control on vmentry of nested guests
Date: Mon, 13 May 2019 12:00:16 -0700	[thread overview]
Message-ID: <20190513190016.GI28561@linux.intel.com> (raw)
In-Reply-To: <20190424231724.2014-5-krish.sadhukhan@oracle.com>

On Wed, Apr 24, 2019 at 07:17:20PM -0400, Krish Sadhukhan wrote:
> According to section "Checks on Host Control Registers and MSRs" in Intel
> SDM vol 3C, the following check is performed on vmentry of nested guests:
> 
>     "If the "load IA32_PERF_GLOBAL_CTRL" VM-exit control is 1, bits reserved
>     in the IA32_PERF_GLOBAL_CTRL MSR must be 0 in the field for that
>     register."
> 
> Signed-off-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>
> Reviewed-by: Karl Heubaum <karl.heubaum@oracle.com>
> ---
>  arch/x86/kvm/vmx/nested.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 83cd887638cb..d2067370e288 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -2595,6 +2595,11 @@ static int nested_check_host_control_regs(struct kvm_vcpu *vcpu,
>  	    !nested_host_cr4_valid(vcpu, vmcs12->host_cr4) ||
>  	    !nested_cr3_valid(vcpu, vmcs12->host_cr3))
>  		return -EINVAL;
> +
> +	if (vmcs12->vm_exit_controls & VM_EXIT_LOAD_IA32_PERF_GLOBAL_CTRL &&
> +	   !kvm_valid_perf_global_ctrl(vmcs12->host_ia32_perf_global_ctrl))

If vmcs12->host_ia32_perf_global_ctrl were ever actually consumed, this
needs to ensure L1 isn't able to take control of counters that are owned
by the host.

> +		return -EINVAL;
> +
>  	/*
>  	 * If the load IA32_EFER VM-exit control is 1, bits reserved in the
>  	 * IA32_EFER MSR must be 0 in the field for that register. In addition,
> -- 
> 2.17.2
> 