[PATCH 5.15.y] cxl/acpi: Check ACPI companion before use

[Sasha Levin <sashal@kernel.org>]

From: Jiale Yao <yaojiale02@163.com>

[ Upstream commit 371c2ad1624283b6c7a62a28199f5161d388a738 ]

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>
Reviewed-by: Jonathan Cameron <jonathan.cameron@oss.qualcomm.com>
Link: https://patch.msgid.link/20260926071605.3013893-1-yaojiale02@163.com
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
[ sashal: Adjusted cxl_acpi_probe() declaration context to preserve the required acpi_status status variable. ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/cxl/acpi.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c
index 54e9d4d2cf5f5..f2203f14af2cd 100644
--- a/drivers/cxl/acpi.c
+++ b/drivers/cxl/acpi.c
@@ -377,11 +377,15 @@ static int add_root_nvdimm_bridge(struct device *match, void *data)
 
 static int cxl_acpi_probe(struct platform_device *pdev)
 {
-	int rc;
 	acpi_status status;
+	struct acpi_device *adev;
 	struct cxl_port *root_port;
 	struct device *host = &pdev->dev;
-	struct acpi_device *adev = ACPI_COMPANION(host);
+	int rc;
+
+	adev = ACPI_COMPANION(host);
+	if (!adev)
+		return -ENODEV;
 
 	root_port = devm_cxl_add_port(host, host, CXL_RESOURCE_NONE, NULL);
 	if (IS_ERR(root_port))
-- 
2.53.0