linux-kernel - Re: [PATCH V3 1/2] PCI: Allow drivers to request exclusive config regions

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Date:   Tue, 27 Sep 2022 09:27:10 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     ira.weiny@...el.com
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Alison Schofield <alison.schofield@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Ben Widawsky <bwidawsk@...nel.org>, linux-cxl@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH V3 1/2] PCI: Allow drivers to request exclusive config
 regions

On Mon, Sep 26, 2022 at 02:57:10PM -0700, ira.weiny@...el.com wrote:
> From: Ira Weiny <ira.weiny@...el.com>
> 
> PCI config space access from user space has traditionally been
> unrestricted with writes being an understood risk for device operation.
> 
> Unfortunately, device breakage or odd behavior from config writes lacks
> indicators that can leave driver writers confused when evaluating
> failures.  This is especially true with the new PCIe Data Object
> Exchange (DOE) mailbox protocol where backdoor shenanigans from user
> space through things such as vendor defined protocols may affect device
> operation without complete breakage.
> 
> A prior proposal restricted read and writes completely.[1]  Greg and
> Bjorn pointed out that proposal is flawed for a couple of reasons.
> First, lspci should always be allowed and should not interfere with any
> device operation.  Second, setpci is a valuable tool that is sometimes
> necessary and it should not be completely restricted.[2]  Finally
> methods exist for full lock of device access if required.
> 
> Even though access should not be restricted it would be nice for driver
> writers to be able to flag critical parts of the config space such that
> interference from user space can be detected.
> 
> Introduce pci_request_config_region_exclusive() to mark exclusive config
> regions.  Such regions trigger a warning and kernel taint if accessed
> via user space.
> 
> Create pci_warn_once() to restrict the user from spamming the log.
> 
> [1] https://lore.kernel.org/all/161663543465.1867664.5674061943008380442.stgit@dwillia2-desk3.amr.corp.intel.com/
> [2] https://lore.kernel.org/all/YF8NGeGv9vYcMfTV@kroah.com/
> 
> Cc: Bjorn Helgaas <bhelgaas@...gle.com>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> Suggested-by: Dan Williams <dan.j.williams@...el.com>
> Signed-off-by: Ira Weiny <ira.weiny@...el.com>

Acked-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>