Messages in this thread | | | Subject | Re: [PATCH] usbip: vhci_sysfs: fix potential Spectre v1 | From | "Gustavo A. R. Silva" <> | Date | Thu, 17 May 2018 12:57:49 -0500 |
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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: stable@vger.kernel.org >> Signed-off-by: Gustavo A. R. Silva <gustavo@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?
Thanks -- Gustavo
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