netdev - Re: [PATCH V4 1/2] pci: Add dev_flags bit to access VPD through function 0

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <5E6FC98D-C2B9-4F69-ABB9-84A39AE6D271@intel.com>
Date:	Tue, 15 Sep 2015 20:47:04 +0000
From:	"Rustad, Mark D" <mark.d.rustad@...el.com>
To:	Alex Williamson <alex.williamson@...hat.com>
CC:	"bhelgaas@...gle.com" <bhelgaas@...gle.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Myron Stowe <myron.stowe@...hat.com>
Subject: Re: [PATCH V4 1/2] pci: Add dev_flags bit to access VPD through
 function 0

> On Sep 15, 2015, at 12:04 PM, Alex Williamson <alex.williamson@...hat.com> wrote:
> 
> 
> FRU-type information is only one of the use cases of VPD, the spec also
> defines (PCI rev 3.0, 6.4):
> 
>        ... a mechanism for storing information such as performance and
>        failure data on the device being monitored.
> 
> That information could very much be function specific.

It is open to interpretation. I guess still I see it as the physical device as a whole.

> When I was looking at whether we should provide VPD access of an
> assigned device at all, I ran across this interesting statement in the
> PCI spec (rev 3.0, I.3.1.1):
> 
>        CP Extended Capability
> 
>        This field allows a new capability to be identified in the VPD
>        area. Since dynamic control/status cannot be placed in VPD, the
>        data for this field identifies where, in the device’s memory or
>        I/O address space, the control/status registers for the
>        capability can be found. Location of the control/status
>        registers is identified by providing the index (a value between
>        0 and 5) of the Base Address register that defines the address
>        range that contains the registers, and the offset within that
>        Base Address register range where the control/status registers
>        reside. The data area for this field is four bytes long. The
>        first byte contains the ID of the extended capability. The
>        second byte contains the index (zero based) of the Base Address
>        register used. The next two bytes contain the offset (in
>        little-endian order) within that address range where the
>        control/status registers defined for that capability reside.
> 
> Again, this sounds like function specific data, and both here and above,
> blocking access to VPD could affect the functionality of drivers.  It
> may be the case that Intel would find this use to be madness, but
> there's no PCI spec requirement that separate functions are in any way
> similar and we're looking at an interface that may be used by non-Intel
> devices as well.  Thanks,

It isn't an interface as such, it is a quirk to address some widespread design problems with multi function devices with VPD. And you are right that functions can be different. In fact this quirk is needed only because now they often (usually in fact) are not different! I do hope to see some non-Intel devices use the quirk, because I'm pretty sure there are other devices that have the same issue.

I realize that I covered a pretty wide swath by making the quirk apply to all Intel Ethernet devices, but that still seems correct. The Skylake is not an issue because it does not have VPD so the pci_find_capability will fail before any handling of the quirk is possible. The code that applies the quirk could check specific devices, but it would make the code a lot bigger, and I see this kind of code as dead weight for so many systems that I tried to make it as small as possible. Since all Intel Ethernet seems to be correct now and as far as I can see into the future, that is what I did.

Going back to something you mentioned before, I think you are right that the failure case for the pci_vpd_f0_dev_check could be made to simply clear the quirk and continue, since pci_vpd_f0_dev_check really should not fail in cases where the quirk is applicable. That does seem like a reasonable change to me the more I think about it.

I think a whitelist would be unnecessary dead weight.

--
Mark Rustad, Networking Division, Intel Corporation

Download attachment "signature.asc" of type "application/pgp-signature" (842 bytes)