Re: [PATCH v3] usbip: vhci_sysfs: fix potential Spectre v1

[Gustavo A. R. Silva]

On 05/22/2018 10:56 AM, Shuah Khan wrote:
> On 05/18/2018 07:13 PM, Gustavo A. R. Silva wrote:
> > pdev_nr and rhport can be controlled by user-space, hence leading to
> > a potential exploitation of the Spectre variant 1 vulnerability.
> >
> > This issue was detected with the help of Smatch:
> > drivers/usb/usbip/vhci_sysfs.c:238 detach_store() warn: potential spectre issue 'vhcis'
> > drivers/usb/usbip/vhci_sysfs.c:328 attach_store() warn: potential spectre issue 'vhcis'
> > drivers/usb/usbip/vhci_sysfs.c:338 attach_store() warn: potential spectre issue 'vhci->vhci_hcd_ss->vdev'
> > drivers/usb/usbip/vhci_sysfs.c:340 attach_store() warn: potential spectre issue 'vhci->vhci_hcd_hs->vdev'
> >
> > Fix this by sanitizing pdev_nr and rhport before using them to index
> > vhcis and vhci->vhci_hcd_ss->vdev respectively.
> >
> > Notice that given that speculation windows are large, the policy is
> > to kill the speculation on the first load and not worry if it can be
> > completed with a dependent load/store [1].
> >
> > [1] https://marc.info/?l=linux-kernel&m=152449131114778&w=2
> >
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx>
> > ---
> > Changes in v3:
> >   - Pass the addresses of pdev_nr and rhport into valid_port and
> >     valid_args.
> >
> > Changes in v2:
> >   - Place the barriers into valid_port.
> >
> >   drivers/usb/usbip/vhci_sysfs.c | 24 ++++++++++++++++--------
> >   1 file changed, 16 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/usb/usbip/vhci_sysfs.c b/drivers/usb/usbip/vhci_sysfs.c
> > index 4880838..be37aec 100644
> > --- a/drivers/usb/usbip/vhci_sysfs.c
> > +++ b/drivers/usb/usbip/vhci_sysfs.c
> > @@ -10,6 +10,9 @@
> >   #include <linux/platform_device.h>
> >   #include <linux/slab.h>
> >   
> > +/* Hardening for Spectre-v1 */
> > +#include <linux/nospec.h>
> > +
> >   #include "usbip_common.h"
> >   #include "vhci.h"
> >   
> > @@ -205,16 +208,20 @@ static int vhci_port_disconnect(struct vhci_hcd *vhci_hcd, __u32 rhport)
> >   	return 0;
> >   }
> >   
> > -static int valid_port(__u32 pdev_nr, __u32 rhport)
> > +static int valid_port(__u32 *pdev_nr, __u32 *rhport)
> >   {
> > -	if (pdev_nr >= vhci_num_controllers) {
> > -		pr_err("pdev %u\n", pdev_nr);
> > +	if (*pdev_nr >= vhci_num_controllers) {
> > +		pr_err("pdev %u\n", *pdev_nr);
> >   		return 0;
> >   	}
> > -	if (rhport >= VHCI_HC_PORTS) {
> > -		pr_err("rhport %u\n", rhport);
> > +	*pdev_nr = array_index_nospec(*pdev_nr, vhci_num_controllers);
> > +
> > +	if (*rhport >= VHCI_HC_PORTS) {
> > +		pr_err("rhport %u\n", *rhport);
> >   		return 0;
> >   	}
> > +	*rhport = array_index_nospec(*rhport, VHCI_HC_PORTS);
> > +
> >   	return 1;
> >   }
> >   
> > @@ -232,7 +239,7 @@ static ssize_t detach_store(struct device *dev, struct device_attribute *attr,
> >   	pdev_nr = port_to_pdev_nr(port);
> >   	rhport = port_to_rhport(port);
> >   
> > -	if (!valid_port(pdev_nr, rhport))
> > +	if (!valid_port(&pdev_nr, &rhport))
> >   		return -EINVAL;
> >   
> >   	hcd = platform_get_drvdata(vhcis[pdev_nr].pdev);
> > @@ -258,7 +265,8 @@ static ssize_t detach_store(struct device *dev, struct device_attribute *attr,
> >   }
> >   static DEVICE_ATTR_WO(detach);
> >   
> > -static int valid_args(__u32 pdev_nr, __u32 rhport, enum usb_device_speed speed)
> > +static int valid_args(__u32 *pdev_nr, __u32 *rhport,
> > +		      enum usb_device_speed speed)
> >   {
> >   	if (!valid_port(pdev_nr, rhport)) {
> >   		return 0;
> > @@ -322,7 +330,7 @@ static ssize_t attach_store(struct device *dev, struct device_attribute *attr,
> >   			     sockfd, devid, speed);
> >   
> >   	/* check received parameters */
> > -	if (!valid_args(pdev_nr, rhport, speed))
> > +	if (!valid_args(&pdev_nr, &rhport, speed))
> >   		return -EINVAL;
> >   
> >   	hcd = platform_get_drvdata(vhcis[pdev_nr].pdev);
>
> Looks good to me. Thanks for taking care of this.

Glad to help. :)

> Acked-by: Shuah Khan (Samsung OSG) <shuah@xxxxxxxxxx>

Thanks
--
Gustavo