Re: [Qemu-ppc] [PATCH 2/5] virtio-balloon: Corrections to address verification

[Greg Kurz]

On Mon, 25 Feb 2019 10:37:11 +1100
David Gibson <address@hidden> wrote:

> On Fri, Feb 22, 2019 at 10:08:22AM +0100, Greg Kurz wrote:
> > On Thu, 14 Feb 2019 15:39:13 +1100
> > David Gibson <address@hidden> wrote:
> >   
> > > The virtio-balloon device's verification of the address given to it by the
> > > guest has a number of faults:
> > >     * The addresses here are guest physical addresses, which should be
> > >       'hwaddr' rather than 'ram_addr_t' (the distinction is admittedly
> > >       pretty subtle and confusing)
> > >     * We don't check for section.mr being NULL, which is the main way that
> > >       memory_region_find() reports basic failures.  We really need to 
> > > check
> > >       that before looking at any other section fields, because
> > >       memory_region_find() doesn't initialize them on the failure path
> > >     * We're passing a length of '1' to memory_region_find(), but really 
> > > the
> > >       guest is requesting that we put the entire page into the balloon,
> > >       so it makes more sense to call it with BALLOON_PAGE_SIZE
> > > 
> > > Signed-off-by: David Gibson <address@hidden>
> > > Reviewed-by: David Hildenbrand <address@hidden>
> > > Reviewed-by: Michael S. Tsirkin <address@hidden>
> > > ---
> > >  hw/virtio/virtio-balloon.c | 17 ++++++++++-------
> > >  1 file changed, 10 insertions(+), 7 deletions(-)
> > > 
> > > diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
> > > index 43af521884..eb357824d8 100644
> > > --- a/hw/virtio/virtio-balloon.c
> > > +++ b/hw/virtio/virtio-balloon.c
> > > @@ -221,17 +221,20 @@ static void 
> > > virtio_balloon_handle_output(VirtIODevice *vdev, VirtQueue *vq)
> > >          }
> > >  
> > >          while (iov_to_buf(elem->out_sg, elem->out_num, offset, &pfn, 4) 
> > > == 4) {
> > > -            ram_addr_t pa;
> > > -            ram_addr_t addr;
> > > +            hwaddr pa;
> > > +            hwaddr addr;
> > >              int p = virtio_ldl_p(vdev, &pfn);
> > >  
> > > -            pa = (ram_addr_t) p << VIRTIO_BALLOON_PFN_SHIFT;
> > > +            pa = (hwaddr) p << VIRTIO_BALLOON_PFN_SHIFT;
> > >              offset += 4;
> > >  
> > > -            /* FIXME: remove get_system_memory(), but how? */
> > > -            section = memory_region_find(get_system_memory(), pa, 1);
> > > -            if (!int128_nz(section.size) ||
> > > -                !memory_region_is_ram(section.mr) ||
> > > +            section = memory_region_find(get_system_memory(), pa,
> > > +                                         BALLOON_PAGE_SIZE);
> > > +            if (!section.mr) {
> > > +                trace_virtio_balloon_bad_addr(pa);
> > > +                continue;
> > > +            }  
> > 
> > memory_region_unref(section.mr) with section.mr == NULL is safe and
> > resolves to a nop. Not sure you need a separate if to handle this
> > case.  
> 
> memory_region_is_ram() and friends are not, however - they will
> dereference their argument unconditionally.
> 

Indeed but the two ifs can be merged anyway:

            if (!section.mr ||
                !memory_region_is_ram(section.mr) ||
                memory_region_is_rom(section.mr) ||
                memory_region_is_romd(section.mr)) {
                trace_virtio_balloon_bad_addr(pa);
                memory_region_unref(section.mr);
                continue;
            }

> > 
> > Apart from that,
> > 
> > Reviewed-by: Greg Kurz <address@hidden>
> >   
> > > +            if (!memory_region_is_ram(section.mr) ||
> > >                  memory_region_is_rom(section.mr) ||
> > >                  memory_region_is_romd(section.mr)) {
> > >                  trace_virtio_balloon_bad_addr(pa);  
> >   
>

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