linux-kernel - [PATCH v2] platform: Fix race condition during DMA configure at IOMMU probe time

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Message-ID: <20250424180420.3928523-1-willmcvicker@google.com>
Date: Thu, 24 Apr 2025 11:04:19 -0700
From: Will McVicker <willmcvicker@...gle.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "Rafael J. Wysocki" <rafael@...nel.org>, 
	Danilo Krummrich <dakr@...nel.org>, Lorenzo Pieralisi <lpieralisi@...nel.org>, 
	Robin Murphy <robin.murphy@....com>, Joerg Roedel <jroedel@...e.de>, 
	Bjorn Helgaas <bhelgaas@...gle.com>, "Rob Herring (Arm)" <robh@...nel.org>, Jason Gunthorpe <jgg@...pe.ca>
Cc: iommu@...ts.linux.dev, Saravana Kannan <saravanak@...gle.com>, 
	Will McVicker <willmcvicker@...gle.com>, kernel-team@...roid.com, 
	linux-kernel@...r.kernel.org
Subject: [PATCH v2] platform: Fix race condition during DMA configure at IOMMU
 probe time

To avoid a race between the IOMMU probing thread and the device driver
async probing thread during configuration of the platform DMA, update
`platform_dma_configure()` to read `dev->driver` once and test if it's
NULL before using it. This ensures that we don't de-reference an invalid
platform driver pointer if the device driver is asynchronously bound
while configuring the DMA.

Fixes: bcb81ac6ae3c ("iommu: Get DT/ACPI parsing into the proper probe path")
Signed-off-by: Will McVicker <willmcvicker@...gle.com>
---
 drivers/base/platform.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/base/platform.c b/drivers/base/platform.c
index 1813cfd0c4bd..cfccf3ff36e7 100644
--- a/drivers/base/platform.c
+++ b/drivers/base/platform.c
@@ -1440,7 +1440,7 @@ static void platform_shutdown(struct device *_dev)
 
 static int platform_dma_configure(struct device *dev)
 {
-	struct platform_driver *drv = to_platform_driver(dev->driver);
+	struct device_driver *drv = READ_ONCE(dev->driver);
 	struct fwnode_handle *fwnode = dev_fwnode(dev);
 	enum dev_dma_attr attr;
 	int ret = 0;
@@ -1451,8 +1451,8 @@ static int platform_dma_configure(struct device *dev)
 		attr = acpi_get_dma_attr(to_acpi_device_node(fwnode));
 		ret = acpi_dma_configure(dev, attr);
 	}
-	/* @drv may not be valid when we're called from the IOMMU layer */
-	if (ret || !dev->driver || drv->driver_managed_dma)
+	/* @dev->driver may not be valid when we're called from the IOMMU layer */
+	if (ret || !drv || to_platform_driver(drv)->driver_managed_dma)
 		return ret;
 
 	ret = iommu_device_use_default_domain(dev);
-- 
2.49.0.850.g28803427d3-goog