Re: [PATCH v2 06/32] KVM: SVM: Kill the VM instead of the host if MSR interception is buggy

[Mi, Dapeng]

On 6/11/2025 6:57 AM, Sean Christopherson wrote:
> WARN and kill the VM instead of panicking the host if KVM attempts to set
> or query MSR interception for an unsupported MSR.  Accessing the MSR
> interception bitmaps only meaningfully affects post-VMRUN behavior, and
> KVM_BUG_ON() is guaranteed to prevent the current vCPU from doing VMRUN,
> i.e. there is no need to panic the entire host.
>
> Opportunistically move the sanity checks about their use to index into the
> MSRPM, e.g. so that bugs only WARN and terminate the VM, as opposed to
> doing that _and_ generating an out-of-bounds load.
>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> ---
>  arch/x86/kvm/svm/svm.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index c75977ca600b..7e39b9df61f1 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -824,11 +824,12 @@ static bool msr_write_intercepted(struct kvm_vcpu *vcpu, u32 msr)
>  				      to_svm(vcpu)->msrpm;
>  
>  	offset    = svm_msrpm_offset(msr);
> +	if (KVM_BUG_ON(offset == MSR_INVALID, vcpu->kvm))
> +		return false;
> +
>  	bit_write = 2 * (msr & 0x0f) + 1;
>  	tmp       = msrpm[offset];
>  
> -	BUG_ON(offset == MSR_INVALID);
> -
>  	return test_bit(bit_write, &tmp);
>  }
>  
> @@ -854,12 +855,13 @@ static void set_msr_interception_bitmap(struct kvm_vcpu *vcpu, u32 *msrpm,
>  		write = 0;
>  
>  	offset    = svm_msrpm_offset(msr);
> +	if (KVM_BUG_ON(offset == MSR_INVALID, vcpu->kvm))
> +		return;
> +
>  	bit_read  = 2 * (msr & 0x0f);
>  	bit_write = 2 * (msr & 0x0f) + 1;
>  	tmp       = msrpm[offset];
>  
> -	BUG_ON(offset == MSR_INVALID);
> -
>  	read  ? clear_bit(bit_read,  &tmp) : set_bit(bit_read,  &tmp);
>  	write ? clear_bit(bit_write, &tmp) : set_bit(bit_write, &tmp);
>  

Reviewed-by: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>