linux-kernel - Re: [RFC PATCH 0/2] vfio/pci: Block and audit accesses to unassigned config regions

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Message-ID: <20250428132455.GC1213339@ziepe.ca>
Date: Mon, 28 Apr 2025 10:24:55 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Chathura Rajapaksha <chathura.abeyrathne.lk@...il.com>
Cc: kvm@...r.kernel.org, Chathura Rajapaksha <chath@...edu>,
	Alex Williamson <alex.williamson@...hat.com>,
	Paul Moore <paul@...l-moore.com>, Eric Paris <eparis@...hat.com>,
	Giovanni Cabiddu <giovanni.cabiddu@...el.com>,
	Xin Zeng <xin.zeng@...el.com>, Yahui Cao <yahui.cao@...el.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Kevin Tian <kevin.tian@...el.com>,
	Niklas Schnelle <schnelle@...ux.ibm.com>,
	Yunxiang Li <Yunxiang.Li@....com>,
	Dongdong Zhang <zhangdongdong@...incomputing.com>,
	Avihai Horon <avihaih@...dia.com>, linux-kernel@...r.kernel.org,
	audit@...r.kernel.org
Subject: Re: [RFC PATCH 0/2] vfio/pci: Block and audit accesses to unassigned
 config regions

On Sat, Apr 26, 2025 at 09:22:47PM +0000, Chathura Rajapaksha wrote:
> Some PCIe devices trigger PCI bus errors when accesses are made to
> unassigned regions within their PCI configuration space. On certain
> platforms, this can lead to host system hangs or reboots.

Do you have an example of this? What do you mean by bus error?

I would expect the device to return some constant like 0, or to return
an error TLP. The host bridge should convert the error TLP to
0XFFFFFFF like all other read error conversions.

Is it a device problem or host bridge problem you are facing?

> 1. Support for blocking guest accesses to unassigned
>    PCI configuration space, and the ability to bypass this access control
>    for specific devices. The patch introduces three module parameters:
> 
>    block_pci_unassigned_write:
>    Blocks write accesses to unassigned config space regions.
> 
>    block_pci_unassigned_read:
>    Blocks read accesses to unassigned config space regions.
> 
>    uaccess_allow_ids:
>    Specifies the devices for which the above access control is bypassed.
>    The value is a comma-separated list of device IDs in
>    <vendor_id>:<device_id> format.
> 
>    Example usage:
>    To block guest write accesses to unassigned config regions for all
>    passed through devices except for the device with vendor ID 0x1234 and
>    device ID 0x5678:
> 
>    block_pci_unassigned_write=1 uaccess_allow_ids=1234:5678

No module parameters please.

At worst the kernel should maintain a quirks list to control this,
maybe with a sysfs to update it.

Jason