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Date: Fri, 25 Sep 2026 23:47:17 +0100
From: Jonathan Cameron <jic23@kernel.org>
To: Davidlohr Bueso <dave@stgolabs.net>
Cc: Jiale Yao <yaojiale02@163.com>, Dave Jiang <dave.jiang@intel.com>,
 Alison Schofield <alison.schofield@intel.com>, Vishal Verma
 <vishal.l.verma@intel.com>, Dan Williams <djbw@kernel.org>, Ira Weiny
 <iweiny@kernel.org>, Li Ming <ming.li@zohomail.com>,
 linux-cxl@vger.kernel.org, linux-kernel@vger.kernel.org,
 stable@vger.kernel.org, Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Subject: Re: [PATCH] cxl/acpi: Check ACPI companion before use
Message-ID: <20260925234718.37fdcc56@jic23-hlaptop>
In-Reply-To: <20260924164247.rsb4h7qjx5bvrthg@offworld>
References: <20260924125404.923551-1-yaojiale02@163.com>
	<20260924164247.rsb4h7qjx5bvrthg@offworld>
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On Thu, 24 Sep 2026 09:42:47 -0700
Davidlohr Bueso <dave@stgolabs.net> wrote:

> On Thu, 24 Sep 2026, Jiale Yao wrote:
> 
> >Platform drivers can be forced to match devices outside their ID tables
> >through driver_override.  cxl_acpi_probe() assumes that every bound device
> >has an ACPI companion and dereferences adev->dev.bus without checking the
> >result of ACPI_COMPANION().  Force-binding cxl_acpi to a platform device
> >without a companion therefore causes a NULL pointer dereference.
> >
> >This was reproduced by setting the driver override for the pcspkr platform
> >device to cxl_acpi and binding it through sysfs:
> >
> >  BUG: kernel NULL pointer dereference, address: 0000000000000280
> >  #PF: supervisor read access in kernel mode
> >  RIP: cxl_acpi_probe+0xf4/0x220
> >  Call Trace:
> >   platform_probe+0x4d/0x80
> >   really_probe+0x106/0x370
> >   device_driver_attach+0x4c/0xa0
> >   bind_store+0xd0/0x100
> >
> >Commit 2b3a5dabe89e ("platform/surface: acpi-notify: Check ACPI
> >companion before use") fixed the same force-binding issue in another
> >platform driver.  Check the companion before setting up the CXL root and
> >return -ENODEV when it is absent.
> >
> >Fixes: 7d4b5ca2e2cb ("cxl/acpi: Add downstream port data to cxl_port instances")
> >Cc: stable@vger.kernel.org
> >Signed-off-by: Jiale Yao <yaojiale02@163.com>  
> 
> With Dave's comment,
> 
> Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
Andy Shevchenko was looking at ways to have drivers set a flag to 
disable matches on driver_override. Not sure if that is still ongoing.

+CC Andy

Jonathan