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SubjectRe: [PATCH v2 01/10] kvm: Restrict non-existing slot state transitions
On Tue, Dec 11, 2012 at 11:29:09PM -0200, Marcelo Tosatti wrote:
> On Mon, Dec 10, 2012 at 10:32:45AM -0700, Alex Williamson wrote:
> > The API documentation states:
> >
> > When changing an existing slot, it may be moved in the guest
> > physical memory space, or its flags may be modified.
> >
> > An "existing slot" requires a non-zero npages (memory_size). The only
> > transition we should therefore allow for a non-existing slot should be
> > to create the slot, which includes setting a non-zero memory_size. We
> > currently allow calls to modify non-existing slots, which is pointless,
> > confusing, and possibly wrong.
> >
> > With this we know that the invalidation path of __kvm_set_memory_region
> > is always for a delete or move and never for adding a zero size slot.
> >
> > Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
> > ---
> > virt/kvm/kvm_main.c | 9 +++++++--
> > 1 file changed, 7 insertions(+), 2 deletions(-)
> >
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index 6e8fa7e..e426704 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -753,10 +753,15 @@ int __kvm_set_memory_region(struct kvm *kvm,
> > new.npages = npages;
> > new.flags = mem->flags;
> >
> > - /* Disallow changing a memory slot's size. */
> > + /*
> > + * Disallow changing a memory slot's size or changing anything about
> > + * zero sized slots that doesn't involve making them non-zero.
> > + */
> > r = -EINVAL;
> > if (npages && old.npages && npages != old.npages)
> > goto out_free;
> > + if (!npages && !old.npages)
> > + goto out_free;
>
> /* General sanity checks */
> if (mem->memory_size & (PAGE_SIZE - 1))
> goto out;
> if (mem->guest_phys_addr & (PAGE_SIZE - 1))
> goto out;
>
> if (mem->guest_phys_addr + mem->memory_size < mem->guest_phys_addr)
> goto out;
>
> If mem->memory_size is zero, then check above fails.

Err, no read a "<=" while writing that.

> If mem->memory_size > 0, it must be at least PAGE_SIZE, in which case
> npages == 1.
>
> Which means the code does not allow changes to non-existing slots.
> Yes?
>


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