Re: [PATCH v2 4/6] virtio: Initialize authorized attribute for confidential guest
From: "Michael S. Tsirkin" <mst@redhat.com>
Date: 2021-09-30 11:03:48
Also in:
linux-pci, linux-usb, lkml
On Wed, Sep 29, 2021 at 06:05:09PM -0700, Kuppuswamy Sathyanarayanan wrote:
Confidential guest platforms like TDX have a requirement to allow only trusted devices. By default the confidential-guest core will arrange for all devices to default to unauthorized (via dev_default_authorization) in device_initialize(). Since virtio driver is already hardened against the attack from the un-trusted host, override the confidential computing default unauthorized state Reviewed-by: Dan Williams <redacted> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Architecturally this all looks backwards. IIUC nothing about virtio makes it authorized or trusted. The driver is hardened, true, but this should be set at the driver not the device level. And in particular, not all virtio drivers are hardened - I think at this point blk and scsi drivers have been hardened - so treating them all the same looks wrong.
quoted hunk
--- drivers/virtio/virtio.c | 9 +++++++++ 1 file changed, 9 insertions(+)diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c index 588e02fb91d3..377b0ccdc503 100644 --- a/drivers/virtio/virtio.c +++ b/drivers/virtio/virtio.c@@ -5,6 +5,8 @@ #include <linux/module.h> #include <linux/idr.h> #include <linux/of.h> +#include <linux/cc_platform.h> +#include <linux/device.h> #include <uapi/linux/virtio_ids.h> /* Unique numbering for virtio devices. */@@ -390,6 +392,13 @@ int register_virtio_device(struct virtio_device *dev) dev->config_enabled = false; dev->config_change_pending = false; + /* + * For Confidential guest (like TDX), virtio devices are + * trusted. So set authorized status as true. + */ + if (cc_platform_has(CC_ATTR_GUEST_DEVICE_FILTER)) + dev->dev.authorized = true; + /* We always start by resetting the device, in case a previous * driver messed it up. This also tests that code path a little. */ dev->config->reset(dev);-- 2.25.1
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