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

Pawel Moll
2013-10-14T08:46:29Z

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>

Paweł