Re: [PATCH] x86/hyper-v: Validate entire GVA range for non-canonical addresses during PV TLB flush

[Vitaly Kuznetsov <vkuznets@redhat.com>]

Manuel Andreas <manuel.andreas@tum.de> writes:

> In KVM guests with Hyper-V hypercalls enabled, the hypercalls
> HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST and HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST_EX
> allow a guest to request invalidation of portions of a virtual TLB.
> For this, the hypercall parameter includes a list of GVAs that are supposed
> to be invalidated.
>
> Currently, only the base GVA is checked to be canonical. In reality,
> this check needs to be performed for the entire range of GVAs.
> This still enables guests running on Intel hardware to trigger a
> WARN_ONCE in the host (see prior commit below).
>
> This patch simply moves the check for non-canonical addresses to be
> performed for every single GVA of the supplied range. This should also
> be more in line with the Hyper-V specification, since, although
> unlikely, a range starting with an invalid GVA may still contain
> GVAs that are valid.
>
> Fixes: fa787ac07b3c ("KVM: x86/hyper-v: Skip non-canonical addresses during PV TLB flush")
> Signed-off-by: Manuel Andreas <manuel.andreas@tum.de>
> ---
>  arch/x86/kvm/hyperv.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> index de92292eb1f5..f4f6accf1a33 100644
> --- a/arch/x86/kvm/hyperv.c
> +++ b/arch/x86/kvm/hyperv.c
> @@ -1981,16 +1981,17 @@ int kvm_hv_vcpu_flush_tlb(struct kvm_vcpu *vcpu)
>  		if (entries[i] == KVM_HV_TLB_FLUSHALL_ENTRY)
>  			goto out_flush_all;
>  
> -		if (is_noncanonical_invlpg_address(entries[i], vcpu))
> -			continue;
> -
>  		/*
>  		 * Lower 12 bits of 'address' encode the number of additional
>  		 * pages to flush.
>  		 */
>  		gva = entries[i] & PAGE_MASK;
> -		for (j = 0; j < (entries[i] & ~PAGE_MASK) + 1; j++)
> +		for (j = 0; j < (entries[i] & ~PAGE_MASK) + 1; j++) {
> +			if (is_noncanonical_invlpg_address(gva + j * PAGE_SIZE, vcpu))
> +				continue;
> +
>  			kvm_x86_call(flush_tlb_gva)(vcpu, gva + j * PAGE_SIZE);
> +		}
>  
>  		++vcpu->stat.tlb_flush;
>  	}

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>

-- 
Vitaly