linux-kernel - Re: [PATCH v4] PCI: Relabel JHL6540 on Lenovo X1 Carbon 7,8

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Message-ID: <ZiyOpZlHVH2yaC1B@wunner.de>
Date: Sat, 27 Apr 2024 07:35:33 +0200
From: Lukas Wunner <lukas@...ner.de>
To: Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc: Esther Shimanovich <eshimanovich@...omium.org>,
	Mario Limonciello <mario.limonciello@....com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, Rajat Jain <rajatja@...gle.com>,
	Gil Fine <gil.fine@...ux.intel.com>
Subject: Re: [PATCH v4] PCI: Relabel JHL6540 on Lenovo X1 Carbon 7,8

On Fri, Apr 26, 2024 at 07:52:07AM +0300, Mika Westerberg wrote:
> On Thu, Apr 25, 2024 at 05:16:24PM -0400, Esther Shimanovich wrote:
> > I did find one example of a docking station that uses the DSL6540
> > chip, which has PCI IDs defined in include/linux/pci_ids.h:
> > #define PCI_DEVICE_ID_INTEL_ALPINE_RIDGE_4C_NHI     0x1577
> > #define PCI_DEVICE_ID_INTEL_ALPINE_RIDGE_4C_BRIDGE  0x1578
> > It seems like it has an NHI, despite being in an external, removable
> > docking station. This appears to contradict what you say about only
> > having "NHI" on a host router. I am assuming that by host router, you
> > mean the fixed discrete, fixed thunderbolt chip, or the thunderbolt
> > controller upstream to the root port. Please correct me if I got
> > anything wrong!
> 
> So it goes same way with other discrete chips from Intel at least. It is
> the same silicon but the NHI is disabled on device routers.
> 
> That said, it is entirely possible for a "malicious" device to pretend
> to have one so we need to be careful.

If a device (accidentally or maliciously) exposes an NHI, the thunderbolt
driver will try to bind to it.

Do we take any precautions to prevent that?

AFAICS we'd be allocating a duplicate root_switch with route 0.
Seems dangerous if two driver instances talk to the same Root Switch.

This looks like something that needs to be checked by Intel Validation
Engineering folks.  Have they been testing this?  (+cc Gil)

Thanks,

Lukas