Re: [PATCH 2/2] kvm: pr_guest: don't let guest invoke printk() on host

[Rusty Russell <rusty-8n+1lVoiYb80n/F98K4Iww@public.gmane.org>]

On Tue, 2007-07-24 at 13:19 +0300, Avi Kivity wrote:
> Rusty Russell wrote:
> > diff -r 3f158ee9df43 drivers/kvm/kvm_main.c
> > --- a/drivers/kvm/kvm_main.c	Tue Jul 24 16:22:39 2007 +1000
> > +++ b/drivers/kvm/kvm_main.c	Tue Jul 24 16:28:33 2007 +1000
> > @@ -425,8 +425,8 @@ inject_gp(struct kvm_vcpu *vcpu, const c
> >  	va_list args;
> >  
> >  	va_start(args, why_fmt);
> > -	printk(KERN_DEBUG "kvm: #GP ");
> > -	vprintk(why_fmt, args);
> > +	if (pr_guest(vcpu, "#GP "))
> > +		vprintk(why_fmt, args);
> >  	va_end(args);
> >  	kvm_arch_ops->inject_gp(vcpu, 0);
> >  }
> >   
> 
> Why go through this optimization?  If it happens frequently, we can just 
> remove the printk().  The printk()s are mostly on not-expected-to-happen 
> exceptions, and should just be removed if guests do exercise them.

It's not an optimization, just being thorough.  It raises it to
KERN_WARN and makes it a common format.  Importantly there should be no
unlimited printks which can be triggered by the guest.

KVM *will* be used to run malicious guests.  That's going to be hard to
lock down later, so I figure we should start now.

Thanks,
Rusty.


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