ARM: 9485/1: mm: acquire mmap write lock around show_pte() for user faultsgrafted

When CONFIG_DEBUG_USER=y, and cmdline "user_debug=31" is set,
a user fault may trigger show_pte() without any lock.
If another thread in the same process concurrently calls munmap(),
the page table pages may be freed while show_pte() is still traversing
them, causing a use-after-free in show_pte().

If CONFIG_ARM_LPAE=y, this may cause a kernel panic if the pages table
of PMD are freed when show_pte() is running.

Acquire mmap_write_lock() around show_pte() for user faults to fix the
contention.

For user faults, additionally restrict that show_pte() is called only
when the addr is a user-space address (addr < TASK_SIZE). This is because
the lock of tsk->mm only protects the virtual memory of user address space,
furthermore, dumping the page tables of a kernel-space address for user
faults is unnecessary and may have security implications.

Keep everything unchanged for kernel faults, because the kernel is
already in the "oops" state, acquiring a lock may risk a deadlock.

Co-developed-by: Qi Xi <xiqi2@huawei.com>

Fixes: 6d021b724481 ("ARM: dump pgd, pmd and pte states on unhandled data abort faults")
Link: https://lore.kernel.org/20260716014022.2823-1-xieyuanbin1@huawei.com
Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Reviewed-by: Linus Walleij <linusw@kernel.org>
Signed-off-by: Qi Xi <xiqi2@huawei.com>
Signed-off-by: Xie Yuanbin <xieyuanbin1@huawei.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

1 files changed, 66 insertions, 0 deletions

diff --git a/include/trace/events/siox.h b/include/trace/events/siox.h
new file mode 100644
index 000000000..68a43fc2c
--- /dev/null
+++ b/include/trace/events/siox.h
@@ -0,0 +1,66 @@
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM siox
+
+#if !defined(_TRACE_SIOX_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_SIOX_H
+
+#include <linux/tracepoint.h>
+
+TRACE_EVENT(siox_set_data,
+	    TP_PROTO(const struct siox_master *smaster,
+		     const struct siox_device *sdevice,
+		     unsigned int devno, size_t bufoffset),
+	    TP_ARGS(smaster, sdevice, devno, bufoffset),
+	    TP_STRUCT__entry(
+			     __field(int, busno)
+			     __field(unsigned int, devno)
+			     __field(size_t, inbytes)
+			     __dynamic_array(u8, buf, sdevice->inbytes)
+			    ),
+	    TP_fast_assign(
+			   __entry->busno = smaster->busno;
+			   __entry->devno = devno;
+			   __entry->inbytes = sdevice->inbytes;
+			   memcpy(__get_dynamic_array(buf),
+				  smaster->buf + bufoffset, sdevice->inbytes);
+			  ),
+	    TP_printk("siox-%d-%u [%*phD]",
+		      __entry->busno,
+		      __entry->devno,
+		      (int)__entry->inbytes, __get_dynamic_array(buf)
+		     )
+);
+
+TRACE_EVENT(siox_get_data,
+	    TP_PROTO(const struct siox_master *smaster,
+		     const struct siox_device *sdevice,
+		     unsigned int devno, u8 status_clean,
+		     size_t bufoffset),
+	    TP_ARGS(smaster, sdevice, devno, status_clean, bufoffset),
+	    TP_STRUCT__entry(
+			     __field(int, busno)
+			     __field(unsigned int, devno)
+			     __field(u8, status_clean)
+			     __field(size_t, outbytes)
+			     __dynamic_array(u8, buf, sdevice->outbytes)
+			    ),
+	    TP_fast_assign(
+			   __entry->busno = smaster->busno;
+			   __entry->devno = devno;
+			   __entry->status_clean = status_clean;
+			   __entry->outbytes = sdevice->outbytes;
+			   memcpy(__get_dynamic_array(buf),
+				  smaster->buf + bufoffset, sdevice->outbytes);
+			  ),
+	    TP_printk("siox-%d-%u (%02hhx) [%*phD]",
+		      __entry->busno,
+		      __entry->devno,
+		      __entry->status_clean,
+		      (int)__entry->outbytes, __get_dynamic_array(buf)
+		     )
+);
+
+#endif /* if !defined(_TRACE_SIOX_H) || defined(TRACE_HEADER_MULTI_READ) */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>