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

2018-05-17 Thread 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!
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Re: [PATCH] usbip: vhci_sysfs: fix potential Spectre v1

2018-05-17 Thread 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=152449131114778=2
> > > 
> > > Cc: sta...@vger.kernel.org
> > > Signed-off-by: Gustavo A. R. Silva 
> > > ---
> > >   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 
> > >   #include 
> > > +#include 
> > > +
> > >   #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
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Re: [PATCH] usbip: vhci_sysfs: fix potential Spectre v1

2018-05-17 Thread 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=152449131114778=2

Cc: sta...@vger.kernel.org
Signed-off-by: Gustavo A. R. Silva 
---
  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 
  #include 
  
+#include 

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

2018-05-17 Thread 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=152449131114778=2
> 
> Cc: sta...@vger.kernel.org
> Signed-off-by: Gustavo A. R. Silva 
> ---
>  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 
>  #include 
>  
> +#include 
> +
>  #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
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[PATCH] usbip: vhci_sysfs: fix potential Spectre v1

2018-05-16 Thread 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=152449131114778=2

Cc: sta...@vger.kernel.org
Signed-off-by: Gustavo A. R. Silva 
---
 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 
 #include 
 
+#include 
+
 #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

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