On Thu, May 17, 2018 at 12:57:49PM -0500, Gustavo A. R. Silva wrote: > Hi Greg, > > On 05/17/2018 01:51 AM, Greg Kroah-Hartman wrote: > > On Wed, May 16, 2018 at 05:22:00PM -0500, 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' > > > > Nit, no need to line-wrap long error messages from tools :) > > > > Got it. > > > > 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: sta...@vger.kernel.org > > > Signed-off-by: Gustavo A. R. Silva <gust...@embeddedor.com> > > > --- > > > drivers/usb/usbip/vhci_sysfs.c | 6 ++++++ > > > 1 file changed, 6 insertions(+) > > > > > > diff --git a/drivers/usb/usbip/vhci_sysfs.c > > > b/drivers/usb/usbip/vhci_sysfs.c > > > index 4880838..9045888 100644 > > > --- a/drivers/usb/usbip/vhci_sysfs.c > > > +++ b/drivers/usb/usbip/vhci_sysfs.c > > > @@ -10,6 +10,8 @@ > > > #include <linux/platform_device.h> > > > #include <linux/slab.h> > > > +#include <linux/nospec.h> > > > + > > > #include "usbip_common.h" > > > #include "vhci.h" > > > @@ -235,6 +237,8 @@ static ssize_t detach_store(struct device *dev, > > > struct device_attribute *attr, > > > if (!valid_port(pdev_nr, rhport)) > > > return -EINVAL; > > > + pdev_nr = array_index_nospec(pdev_nr, vhci_num_controllers); > > > + rhport = array_index_nospec(rhport, VHCI_HC_PORTS); > > > > Shouldn't we just do this in one place, in the valid_port() function? > > > > That way it keeps the range checking logic in one place (now it is in 3 > > places in the function), which should make maintenance much simpler. > > > > Yep, I thought about that, the thing is: what happens if the hardware is > "trained" to predict that valid_port always evaluates to false, and then > malicious values are stored in pdev_nr and nhport? > > It seems to me that under this scenario we need to serialize instructions in > this place. > > What do you think?
I don't understand, it should not matter where you put the barrier. Be it a function call back or right after it, it does the same thing, it stops speculation from crossing that barrier. So it _should_ work either way, if I understand the issue correctly. If not, what am I missing? thanks, greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
