From mboxrd@z Thu Jan  1 00:00:00 1970
From: Pawel Moll <pawel.moll@arm.com>
Subject: Re: [PATCH 2/3] virtio: mmio: fix signature checking for BE guests
Date: Mon, 14 Oct 2013 09:46:25 +0100
Message-ID: <1381740385.3247.6.camel@hornet>
References: <1381502171-8187-1-git-send-email-marc.zyngier@arm.com>
	 <1381502171-8187-3-git-send-email-marc.zyngier@arm.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: QUOTED-PRINTABLE
Cc: "linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	"kvmarm@lists.cs.columbia.edu" <kvmarm@lists.cs.columbia.edu>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	Rusty Russell <rusty@rustcorp.com.au>,
	"Michael S. Tsirkin" <mst@redhat.com>
To: Marc Zyngier <Marc.Zyngier@arm.com>
Return-path: <kvm-owner@vger.kernel.org>
Received: from service87.mimecast.com ([91.220.42.44]:33212 "EHLO
	service87.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1754184Ab3JNIq3 convert rfc822-to-8bit (ORCPT
	<rfc822;kvm@vger.kernel.org>); Mon, 14 Oct 2013 04:46:29 -0400
In-Reply-To: <1381502171-8187-3-git-send-email-marc.zyngier@arm.com>
Sender: kvm-owner@vger.kernel.org
List-ID: <kvm.vger.kernel.org>

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).
>=20
> Fix it by encoding the magic value as an integer instead of a string.
>=20
> 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(-)
>=20
> diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmi=
o.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_devi=
ce *pdev)
> =20
>  	/* Check magic value */
>  	magic =3D readl(vm_dev->base + VIRTIO_MMIO_MAGIC_VALUE);
> -	if (memcmp(&magic, "virt", 4) !=3D 0) {
> +	if (magic !=3D ('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).

=2E.. but I like the 'v'i'r't' characters still being there :-)

Acked-by: Pawel Moll <pawel.moll@arm.com>

Pawe=C5=82