linux-kernel - Re: [PATCH] PCI/sysfs: Fix read permissions for VPD attributes

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Message-ID: <20241107145941.GA1613712@bhelgaas>
Date: Thu, 7 Nov 2024 08:59:41 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Leon Romanovsky <leon@...nel.org>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>,
	Krzysztof Wilczyński <kw@...ux.com>,
	linux-pci@...r.kernel.org, Ariel Almog <ariela@...dia.com>,
	Aditya Prabhune <aprabhune@...dia.com>,
	Hannes Reinecke <hare@...e.de>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Arun Easi <aeasi@...vell.com>, Jonathan Chocron <jonnyc@...zon.com>,
	Bert Kenward <bkenward@...arflare.com>,
	Matt Carlson <mcarlson@...adcom.com>,
	Kai-Heng Feng <kai.heng.feng@...onical.com>,
	Jean Delvare <jdelvare@...e.de>,
	Alex Williamson <alex.williamson@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI/sysfs: Fix read permissions for VPD attributes

On Thu, Nov 07, 2024 at 01:31:44PM +0200, Leon Romanovsky wrote:
> On Tue, Nov 5, 2024, at 18:26, Leon Romanovsky wrote:
> > On Tue, Nov 05, 2024 at 09:24:55AM -0600, Bjorn Helgaas wrote:
> >> On Tue, Nov 05, 2024 at 09:51:30AM +0200, Leon Romanovsky wrote:
> >> > On Mon, Nov 04, 2024 at 06:10:27PM -0600, Bjorn Helgaas wrote:
> >> > > On Sun, Nov 03, 2024 at 02:33:44PM +0200, Leon Romanovsky wrote:
> >> > > > On Fri, Nov 01, 2024 at 11:47:37AM -0500, Bjorn Helgaas wrote:
> >> > > > > On Fri, Nov 01, 2024 at 04:33:00PM +0200, Leon Romanovsky wrote:
> >> > > > > > On Thu, Oct 31, 2024 at 06:22:52PM -0500, Bjorn Helgaas wrote:
> >> > > > > > > On Tue, Oct 29, 2024 at 07:04:50PM -0500, Bjorn Helgaas wrote:
> >> > > > > > > > On Mon, Oct 28, 2024 at 10:05:33AM +0200, Leon Romanovsky wrote:
> >> > > > > > > > > From: Leon Romanovsky <leonro@...dia.com>
> >> > > > > > > > > 
> >> > > > > > > > > The Virtual Product Data (VPD) attribute is not
> >> > > > > > > > > readable by regular user without root permissions.
> >> > > > > > > > > Such restriction is not really needed, as data
> >> > > > > > > > > presented in that VPD is not sensitive at all.
> >> > > > > > > > > 
> >> > > > > > > > > This change aligns the permissions of the VPD
> >> > > > > > > > > attribute to be accessible for read by all users,
> >> > > > > > > > > while write being restricted to root only.
> >> > ...
> >> 
> >> > > What's the use case?  How does an unprivileged user use the VPD
> >> > > information?
> >> > 
> >> > We have to add new field keyword=value in VA section of VPD, which
> >> > will indicate very specific sub-model for devices used as a bridge.
> >> > 
> >> > > I can certainly imagine using VPD for bug reporting, but that
> >> > > would typically involve dmesg, dmidecode, lspci -vv, etc, all of
> >> > > which already require privilege, so it's not clear to me how
> >> > > public VPD info would help in that scenario.
> >> > 
> >> > I'm targeting other scenario - monitoring tool, which doesn't need
> >> > root permissions for reading data. It needs to distinguish between
> >> > NIC sub-models.
> >> 
> >> Maybe the driver could expose something in sysfs?  Maybe the driver
> >> needs to know the sub-model as well, and reading VPD once in the
> >> driver would make subsequent userspace sysfs reads trivial and fast.
> >
> > Our PCI driver lays in netdev subsystem and they have long-standing
> > position do not allow any custom sysfs files. To be fair, we (RDMA)
> > don't allow custom sysfs files too.
> >
> > Driver doesn't need to know this information as it is extra key=value in
> > existing [VA] field, while driver relies on multiple FW capabilities
> > to enable/disable functionality.
> >
> > Current [VA] line:
> > "[VA] Vendor specific: 
> > MLX:MN=MLNX:CSKU=V2:UUID=V3:PCI=V0:MODL=CX713106A"
> > Future [VA] line:
> > "[VA] Vendor specific: 
> > MLX:MN=MLNX:CSKU=V2:UUID=V3:PCI=V0:MODL=CX713106A,SMDL=SOMETHING"
> >
> > Also the idea that we will duplicate existing functionality doesn't
> > sound like a good approach to me, and there is no way that it is
> > possible to expose as subsystem specific file.
> >
> > What about to allow existing VPD sysfs file to be readable for everyone 
> > for our devices?
> > And if this allow list grows to much, we will open it for all devices 
> > in the world?
> 
> Bjorn,
> 
> I don't see this patch in
> https://git.kernel.org/pub/scm/linux/kernel/git/pci/pci.git/log/?h=next
> So what did you decide? How can we enable existing VPD access to
> regular users?

I think it's too risky to enable VPD to be readable by all users.

Bjorn