linux-kernel - Re: [PATCH v2] usbip: vhci_sysfs: fix potential Spectre v1

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Date:   Fri, 18 May 2018 10:06:27 -0600
From:   Shuah Khan <shuah@...nel.org>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Valentina Manea <valentina.manea.m@...il.com>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Shuah Khan <shuah@...nel.org>
Subject: Re: [PATCH v2] usbip: vhci_sysfs: fix potential Spectre v1

On 05/18/2018 07:47 AM, Greg Kroah-Hartman wrote:
> On Thu, May 17, 2018 at 03:16:28PM -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'
>>
>> 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@...r.kernel.org
>> Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
>> ---
>> Changes in v2:
>>  - Place the barriers into valid_port.

attach_store() doesn't call valid_port() - can you make the change to
have attach_store() call valid_port() to protect that code path.

> 
> Thanks for the change.  I'll wait for Shuah's ack/review before queueing
> this up just as she knows that codebase much better than anyone else.
> > 

thanks,
-- Shuah