Re: [PATCH 1/6] KVM: x86: Inject #GP if WRMSR sets reserved bits in APIC Self-IPI

[Maxim Levitsky]

On Sat, 2023-01-07 at 01:10 +0000, Sean Christopherson wrote:
> Inject a #GP if the guest attempts to set reserved bits in the x2APIC-only
> Self-IPI register.  Bits 7:0 hold the vector, all other bits are reserved.
> 
> Reported-by: Marc Orr <marcorr@xxxxxxxxxx>
> Cc: Ben Gardon <bgardon@xxxxxxxxxx>
> Cc: Venkatesh Srinivas <venkateshs@xxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> ---
>  arch/x86/kvm/lapic.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 80f92cbc4029..f77da92c6ea6 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -2315,10 +2315,14 @@ static int kvm_lapic_reg_write(struct kvm_lapic *apic, u32 reg, u32 val)
>  		break;
>  
>  	case APIC_SELF_IPI:
> -		if (apic_x2apic_mode(apic))
> -			kvm_apic_send_ipi(apic, APIC_DEST_SELF | (val & APIC_VECTOR_MASK), 0);
> -		else
> +		/*
> +		 * Self-IPI exists only when x2APIC is enabled.  Bits 7:0 hold
> +		 * the vector, everything else is reserved.
> +		 */
> +		if (!apic_x2apic_mode(apic) || (val & ~APIC_VECTOR_MASK))
>  			ret = 1;
> +		else
> +			kvm_apic_send_ipi(apic, APIC_DEST_SELF | val, 0);
>  		break;
>  	default:
>  		ret = 1;

Reviewed-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>

Best regards,
	Maxim Levitsky