6.15-stable review patch. If anyone has any objections, please let me know.
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From: Robin Murphy robin.murphy@arm.com
[ Upstream commit 152f33ee30ee6a7f4c15bedd7529dc5945315547 ]
Since it's not currently safe to take device_lock() in the IOMMU probe path, that can race against really_probe() setting dev->driver before attempting to bind. The race itself isn't so bad, since we're only concerned with dereferencing dev->driver itself anyway, but sadly my attempt to implement the check with minimal churn leads to a kind of TOCTOU issue, where dev->driver becomes valid after to_fsl_mc_driver(NULL) is already computed, and thus the check fails to work as intended.
Will and I both hit this with the platform bus, but the pattern here is the same, so fix it for correctness too.
Reported-by: Will McVicker willmcvicker@google.com Fixes: bcb81ac6ae3c ("iommu: Get DT/ACPI parsing into the proper probe path") Signed-off-by: Robin Murphy robin.murphy@arm.com Reviewed-by: Will McVicker willmcvicker@google.com Link: https://lore.kernel.org/r/20250425133929.646493-3-robin.murphy@arm.com Signed-off-by: Christophe Leroy christophe.leroy@csgroup.eu Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/bus/fsl-mc/fsl-mc-bus.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/drivers/bus/fsl-mc/fsl-mc-bus.c b/drivers/bus/fsl-mc/fsl-mc-bus.c index 0c3a38d7f3358..7671bd1585455 100644 --- a/drivers/bus/fsl-mc/fsl-mc-bus.c +++ b/drivers/bus/fsl-mc/fsl-mc-bus.c @@ -139,9 +139,9 @@ static int fsl_mc_bus_uevent(const struct device *dev, struct kobj_uevent_env *e
static int fsl_mc_dma_configure(struct device *dev) { + const struct device_driver *drv = READ_ONCE(dev->driver); struct device *dma_dev = dev; struct fsl_mc_device *mc_dev = to_fsl_mc_device(dev); - struct fsl_mc_driver *mc_drv = to_fsl_mc_driver(dev->driver); u32 input_id = mc_dev->icid; int ret;
@@ -153,8 +153,8 @@ static int fsl_mc_dma_configure(struct device *dev) else ret = acpi_dma_configure_id(dev, DEV_DMA_COHERENT, &input_id);
- /* @mc_drv may not be valid when we're called from the IOMMU layer */ - if (!ret && dev->driver && !mc_drv->driver_managed_dma) { + /* @drv may not be valid when we're called from the IOMMU layer */ + if (!ret && drv && !to_fsl_mc_driver(drv)->driver_managed_dma) { ret = iommu_device_use_default_domain(dev); if (ret) arch_teardown_dma_ops(dev);