linux-kernel - [PATCH] iommu: Fix NULL pointer deref when io_page

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Message-Id: <20260116-iommu-io_page_fault_null_fix-v1-1-6c20c2e62987@riscstar.com>
Date: Fri, 16 Jan 2026 12:09:37 +0000
From: Daniel Thompson <daniel@...cstar.com>
To: Steven Rostedt <rostedt@...dmis.org>, 
 Masami Hiramatsu <mhiramat@...nel.org>, 
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org, 
 Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>, 
 linux-arm-kernel@...ts.infradead.org, Daniel Thompson <daniel@...cstar.com>
Subject: [PATCH] iommu: Fix NULL pointer deref when io_page_fault
 tracepoint fires

The arm-smmu driver is unable to allocate the blame for a page fault to
a specific device so it calls report_iommu_fault() with the dev argument
set to NULL. Normally this doesn't cause anything catastrophic but on a
system with the io_page_fault tracepoint enabled this results in a NULL
pointer deref (resulting in a fairly spectacular crash on the hardware
I'm currently working on).

Fix this by adding logic to the tracepoint to safely propagate NULL.

Signed-off-by: Daniel Thompson <daniel@...cstar.com>
---
 include/trace/events/iommu.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/trace/events/iommu.h b/include/trace/events/iommu.h
index 373007e567cb827458a729b8200bbcc1b7d76912..1315193f13b8812ad4e29e6b0c0c66ca806ce08d 100644
--- a/include/trace/events/iommu.h
+++ b/include/trace/events/iommu.h
@@ -131,8 +131,8 @@ DECLARE_EVENT_CLASS(iommu_error,
 	TP_ARGS(dev, iova, flags),
 
 	TP_STRUCT__entry(
-		__string(device, dev_name(dev))
-		__string(driver, dev_driver_string(dev))
+		__string(device, dev ? dev_name(dev) : NULL)
+		__string(driver, dev ? dev_driver_string(dev) : NULL)
 		__field(u64, iova)
 		__field(int, flags)
 	),

---
base-commit: 0f61b1860cc3f52aef9036d7235ed1f017632193
change-id: 20260116-iommu-io_page_fault_null_fix-f81b4e8b5423

Best regards,
-- 
Daniel Thompson <daniel@...cstar.com>