[PATCH] usbip: vhci_sysfs: fix potential Spectre v1

[PATCH] usbip: vhci_sysfs: fix potential Spectre v1

[Gustavo A. R. Silva]

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@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);
 	hcd = platform_get_drvdata(vhcis[pdev_nr].pdev);
 	if (hcd == NULL) {
 		dev_err(dev, "port is not ready %u\n", port);
@@ -325,6 +329,8 @@ static ssize_t attach_store(struct device *dev, struct device_attribute *attr,
 	if (!valid_args(pdev_nr, rhport, speed))
 		return -EINVAL;
 
+	pdev_nr = array_index_nospec(pdev_nr, vhci_num_controllers);
+	rhport = array_index_nospec(rhport, VHCI_HC_PORTS);
 	hcd = platform_get_drvdata(vhcis[pdev_nr].pdev);
 	if (hcd == NULL) {
 		dev_err(dev, "port %d is not ready\n", port);
-- 
2.7.4

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

[Greg Kroah-Hartman]

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 :)

> 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.

thanks,

greg k-h

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

[Gustavo A. R. Silva]

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

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

[Greg Kroah-Hartman]

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: 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?

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

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

[Gustavo A. R. Silva]

On 05/17/2018 02:15 PM, Greg Kroah-Hartman wrote:
>>> 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.
> 

Yeah. It makes sense.

> So it _should_ work either way, if I understand the issue correctly.
> 
> If not, what am I missing?
> 

No. It seems I'm the one who was missing something.

I'll place the barrier into valid_port and send v2 shortly.

Thanks!
--
Gustavo