[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-ppc] [PATCH 2/5] virtio-balloon: Corrections to address verifi
From: |
Greg Kurz |
Subject: |
Re: [Qemu-ppc] [PATCH 2/5] virtio-balloon: Corrections to address verification |
Date: |
Thu, 28 Feb 2019 10:09:17 +0100 |
On Wed, 27 Feb 2019 10:20:12 +1100
David Gibson <address@hidden> wrote:
> On Mon, Feb 25, 2019 at 10:26:51AM +0100, Greg Kurz wrote:
> > 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;
> > }
>
> Oh, I see what you mean. Hrm, I still kind of prefer visually
> separating the validity check from tests which depend on that validity.
>
Makes sense. It's alright then :)
> >
> > > >
> > > > 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);
> > > >
> > >
> >
>
>
>
pgp9yO1qkUOA4.pgp
Description: OpenPGP digital signature
[Qemu-ppc] [PATCH 4/5] virtio-balloon: Use ram_block_discard_range() instead of raw madvise(), David Gibson, 2019/02/13
[Qemu-ppc] [PATCH 5/5] virtio-balloon: Safely handle BALLOON_PAGE_SIZE < host page size, David Gibson, 2019/02/13
Re: [Qemu-ppc] [PATCH 0/5] Improve balloon handling of pagesizes other than 4kiB, Michael S. Tsirkin, 2019/02/28