Re: [PATCH] cxl/acpi: Check ACPI companion before use

[Davidlohr Bueso]

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@xxxxxxxxxxxxxxx
> Signed-off-by: Jiale Yao <yaojiale02@xxxxxxx>

With Dave's comment,

Reviewed-by: Davidlohr Bueso <dave@xxxxxxxxxxxx>