Re: [PATCH 2/3] virtio: mmio: fix signature checking for BE guests

Pawel Moll
2013-11-05T10:46:02Z

On Tue, 2013-11-05 at 03:36 +0000, Rusty Russell wrote:
> Rusty Russell <rusty@rustcorp.com.au> writes:
> > Pawel Moll <pawel.moll@arm.com> writes:
> >> On Fri, 2013-10-11 at 15:36 +0100, Marc Zyngier wrote:
> >>> As virtio-mmio config registers are specified to be little-endian,
> >>> using readl() to read the magic value and then memcmp() to check it
> >>> fails on BE (as readl() has an implicit swab).
> >>>
> >>> Fix it by encoding the magic value as an integer instead of a string.
> >>>
> >>> Cc: Rusty Russell <rusty@rustcorp.com.au>
> >>> Cc: Michael S. Tsirkin <mst@redhat.com>
> >>> Cc: Pawel Moll <pawel.moll@arm.com>
> >>> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> >>> ---
> >>> drivers/virtio/virtio_mmio.c | 2 +-
> >>> 1 file changed, 1 insertion(+), 1 deletion(-)
> >>>
> >>> diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
> >>> index 1ba0d68..57f24fd 100644
> >>> --- a/drivers/virtio/virtio_mmio.c
> >>> +++ b/drivers/virtio/virtio_mmio.c
> >>> @@ -470,7 +470,7 @@ static int virtio_mmio_probe(struct platform_device *pdev)
> >>>
> >>> /* Check magic value */
> >>> magic = readl(vm_dev->base + VIRTIO_MMIO_MAGIC_VALUE);
> >>> - if (memcmp(&magic, "virt", 4) != 0) {
> >>> + if (magic != ('v' | 'i' << 8 | 'r' << 16 | 't' << 24)) {
> >>> dev_warn(&pdev->dev, "Wrong magic value 0x%08lx!\n", magic);
> >>> return -ENODEV;
> >>> }
> >>
> >> The new spec will clarify this:
> >>
> >> * 0x000 | R | MagicValue
> >> Magic value. Must be 0x74726976 (a Little Endian equivalent
> >> of a "virt" string).
> >>
> >> ... but I like the 'v'i'r't' characters still being there :-)
> >>
> >> Acked-by: Pawel Moll <pawel.moll@arm.com>
> >
> > Applied, thanks.
>
> OK, I *said* applied, but left it in my pending queue.
>
> Pawel, do you want to open this can of worms? If so, I'l merge this
> now.

This particular can is empty - all worms already escaped :-)

It's a bugfix, not changing anything for the existing hosts. So - yes
please, do merge this one.

Thanks

Paweł