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

Rusty Russell
2013-10-14T21:43:00Z

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.

Cheers,
Rusty.