Re: [PATCH v10 9/9] KVM: Enable and expose KVM_MEM_PRIVATE

Chao Peng
2023-01-06T04:18:18Z

On Thu, Jan 05, 2023 at 12:38:30PM -0800, Vishal Annapurve wrote:
> On Thu, Dec 1, 2022 at 10:20 PM Chao Peng <chao.p.peng@linux.intel.com> wrote:
> >
> > +#ifdef CONFIG_HAVE_KVM_RESTRICTED_MEM
> > +static bool restrictedmem_range_is_valid(struct kvm_memory_slot *slot,
> > + pgoff_t start, pgoff_t end,
> > + gfn_t *gfn_start, gfn_t *gfn_end)
> > +{
> > + unsigned long base_pgoff = slot->restricted_offset >> PAGE_SHIFT;
> > +
> > + if (start > base_pgoff)
> > + *gfn_start = slot->base_gfn + start - base_pgoff;
>
> There should be a check for overflow here in case start is a very big
> value. Additional check can look like:
> if (start >= base_pgoff + slot->npages)
> return false;
>
> > + else
> > + *gfn_start = slot->base_gfn;
> > +
> > + if (end < base_pgoff + slot->npages)
> > + *gfn_end = slot->base_gfn + end - base_pgoff;
>
> If "end" is smaller than base_pgoff, this can cause overflow and
> return the range as valid. There should be additional check:
> if (end < base_pgoff)
> return false;

Thanks! Both are good catches. The improved code:

static bool restrictedmem_range_is_valid(struct kvm_memory_slot *slot,
pgoff_t start, pgoff_t end,
gfn_t *gfn_start, gfn_t *gfn_end)
{
unsigned long base_pgoff = slot->restricted_offset >> PAGE_SHIFT;

if (start >= base_pgoff + slot->npages)
return false;
else if (start <= base_pgoff)
*gfn_start = slot->base_gfn;
else
*gfn_start = start - base_pgoff + slot->base_gfn;

if (end <= base_pgoff)
return false;
else if (end >= base_pgoff + slot->npages)
*gfn_end = slot->base_gfn + slot->npages;
else
*gfn_end = end - base_pgoff + slot->base_gfn;

if (*gfn_start >= *gfn_end)
return false;

return true;
}

Thanks,
Chao
>
>
> > + else
> > + *gfn_end = slot->base_gfn + slot->npages;
> > +
> > + if (*gfn_start >= *gfn_end)
> > + return false;
> > +
> > + return true;
> > +}
> > +