Re: [PATCH v2 7/8] KVM: MMU: Validate all gptes during fetch, not just those used for new pages

[Avi Kivity <avi@redhat.com>]

On 07/12/2010 02:30 PM, Avi Kivity wrote:
> Currently, when we fetch an spte, we only verify that gptes match those that
> the walker saw if we build new shadow pages for them.
>
> However, this misses the following race:
>
>    vcpu1            vcpu2
>
>    walk
>                    change gpte
>                    walk
>                    instantiate sp
>
>    fetch existing sp
>
> Fix by validating every gpte, regardless of whether it is used for building
> a new sp or not.
>
>
> +	/*
> +	 * Verify that the top-level gpte is still there.  Since the page
> +	 * is a root page, it is either write protected (and cannot be
> +	 * changed from now on) or it is invalid (in which case, we don't
> +	 * really care if it changes underneath us after this point).
> +	 */
> +	if (!FNAME(validate_indirect_spte)(vcpu, sptep, sp,
> +					   gw, top_level))
> +		goto out_error;
> +
>    

This bit is a little broken.  Will post v3 soon.

-- 
error compiling committee.c: too many arguments to function