Re: [PATCH v2 4/8] KVM: x86: Warn if userspace overrides existing injected exception/interrupt

["Radim Krčmář" <rkrcmar@redhat.com>]

2017-11-21 17:30+0200, Liran Alon:
> An alternative could have been done to return -EBUSY in this case.
> For now, we decided to just silently override exception and warn on
> such an attempt.
> 
> Signed-off-by: Liran Alon <liran.alon@oracle.com>
> Reviewed-by: Nikita Leshenko <nikita.leshchenko@oracle.com>
> Reviewed-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>
> Signed-off-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>
> ---
>  arch/x86/kvm/x86.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 1490da89de4b..c8cec7c39c1c 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -3153,12 +3153,25 @@ static int kvm_vcpu_ioctl_x86_set_vcpu_events(struct kvm_vcpu *vcpu,
>  		return -EINVAL;
>  
>  	process_nmi(vcpu);
> +
> +	/*
> +	 * Warn if userspace is overriding existing
> +	 * injected exception
> +	 */
> +	WARN_ON_ONCE(vcpu->arch.exception.injected &&
> +		     events->exception.injected);

I think that overwriting the injected exception/interrupt is a perfectly
valid operation -- userspace could have rolled back the state to a time
of the previous injection.

Syzkaller would complain sooner or later and I don't see it as a useful
printk, so dropping this patch would be preferred,

thanks.