linux-kernel - Re: [PATCH 2/2] pci: Update VPD size with correct length

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Message-ID: <CAKgT0Uc9vZGHvtUuzv4EkE2d4-U5F=22-YeSAOWBH=vGa4yJ5Q@mail.gmail.com>
Date:	Fri, 18 Dec 2015 06:02:19 -0800
From:	Alexander Duyck <alexander.duyck@...il.com>
To:	Hannes Reinecke <hare@...e.de>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>,
	Michal Kubecek <mkubecek@...e.com>,
	"Shane M. Seymour" <shane.seymour@....com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Bjorn Helgaas <helgaas@...nel.org>
Subject: Re: [PATCH 2/2] pci: Update VPD size with correct length

On Fri, Dec 18, 2015 at 5:57 AM, Hannes Reinecke <hare@...e.de> wrote:
> On 12/18/2015 02:49 PM, Alexander Duyck wrote:
>>
>> On Fri, Dec 18, 2015 at 12:35 AM, Hannes Reinecke <hare@...e.de> wrote:
>>>
>>> PCI-2.2 VPD entries have a maximum size of 32k, but might actually
>>> be smaller than that. To figure out the actual size one has to read
>>> the VPD area until the 'end marker' is reached.
>>> Trying to read VPD data beyond that marker results in 'interesting'
>>> effects, from simple read errors to crashing the card. And to make
>>> matters worse not every PCI card implements this properly, leaving
>>> us with no 'end' marker or even completely invalid data.
>>> This path modifies the size of the VPD attribute to the available
>>> size, or set it to '0' if no valid data could be read.
>>
>>
>> This isn't what I had in mind.  There is no need to add an f0 version
>> of the size function.  The size for all functions other than function
>> 0 when the F0 flag is set is 0.  We aren't going to be reading their
>> VPD, we only read the VPD region of function 0.
>>
> Ah. (I'm a bit confused about the proposed action for VPD other than
> function 0).
> So the idea here is to _disallow_ access to VPDs from functions other than
> '0' unless these functions have different PCI IDs?

If you take a look at the F0 functions what they do is bypass the VPD
of the functions other than function 0.  As such setting the size to 0
should really have no effect since the VPD of the function isn't
actually read if the F0 flag is set.

- Alex
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