Re: [PATCH 1/2] KVM: arm64: vgic: check redist region is not above the VM IPA size

[Ricardo Koller <ricarkol@google.com>]

On Wed, Sep 08, 2021 at 09:32:05PM +0000, Oliver Upton wrote:
> Hi Ricardo,
> 
> On Wed, Sep 08, 2021 at 02:03:19PM -0700, Ricardo Koller wrote:
> > Extend vgic_v3_check_base() to verify that the redistributor regions
> > don't go above the VM-specified IPA size (phys_size). This can happen
> > when using the legacy KVM_VGIC_V3_ADDR_TYPE_REDIST attribute with:
> > 
> >   base + size > phys_size AND base < phys_size
> > 
> > vgic_v3_check_base() is used to check the redist regions bases when
> > setting them (with the vcpus added so far) and when attempting the first
> > vcpu-run.
> > 
> > Signed-off-by: Ricardo Koller <ricarkol@google.com>
> > ---
> >  arch/arm64/kvm/vgic/vgic-v3.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/arch/arm64/kvm/vgic/vgic-v3.c b/arch/arm64/kvm/vgic/vgic-v3.c
> > index 66004f61cd83..5afd9f6f68f6 100644
> > --- a/arch/arm64/kvm/vgic/vgic-v3.c
> > +++ b/arch/arm64/kvm/vgic/vgic-v3.c
> > @@ -512,6 +512,10 @@ bool vgic_v3_check_base(struct kvm *kvm)
> >  		if (rdreg->base + vgic_v3_rd_region_size(kvm, rdreg) <
> >  			rdreg->base)
> >  			return false;
> 
> Can we drop this check in favor of explicitly comparing rdreg->base with
> kvm_phys_size()? I believe that would be more readable.
>

You mean the integer overflow check above? in that case, I would prefer
to leave it, if you don't mind. It seems that this type of check is used
in some other places in KVM (like kvm_assign_ioeventfd and
vgic_v3_alloc_redist_region).

> > +
> > +		if (rdreg->base + vgic_v3_rd_region_size(kvm, rdreg) >
> > +			kvm_phys_size(kvm))
> > +			return false;
> >  	}
> >  
> >  	if (IS_VGIC_ADDR_UNDEF(d->vgic_dist_base))
> > -- 
> > 2.33.0.153.gba50c8fa24-goog
> > 
> 
> --
> Thanks,
> Oliver