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

["Gustavo A. R. Silva" <gustavo@embeddedor.com>]

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@vger.kernel.org
>> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
>> ---
>> 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@kernel.org>
> 

Thanks
--
Gustavo