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

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Date:   Thu, 17 May 2018 14:29:17 -0500
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Valentina Manea <valentina.manea.m@...il.com>,
        Shuah Khan <shuah@...nel.org>, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usbip: vhci_sysfs: fix potential Spectre v1



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