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, 69 insertions, 0 deletions

diff --git a/rust/helpers/bitops.c b/rust/helpers/bitops.c
new file mode 100644
index 000000000..271b8a712
--- /dev/null
+++ b/rust/helpers/bitops.c
@@ -0,0 +1,69 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/bitops.h>
+#include <linux/find.h>
+
+__rust_helper
+void rust_helper___set_bit(unsigned long nr, unsigned long *addr)
+{
+	__set_bit(nr, addr);
+}
+
+__rust_helper
+void rust_helper___clear_bit(unsigned long nr, unsigned long *addr)
+{
+	__clear_bit(nr, addr);
+}
+
+__rust_helper
+void rust_helper_set_bit(unsigned long nr, volatile unsigned long *addr)
+{
+	set_bit(nr, addr);
+}
+
+__rust_helper
+void rust_helper_clear_bit(unsigned long nr, volatile unsigned long *addr)
+{
+	clear_bit(nr, addr);
+}
+
+/*
+ * The rust_helper_ prefix is intentionally omitted below so that the
+ * declarations in include/linux/find.h are compatible with these helpers.
+ *
+ * Note that the below #ifdefs mean that the helper is only created if C does
+ * not provide a definition.
+ */
+#ifdef find_first_zero_bit
+__rust_helper
+unsigned long _find_first_zero_bit(const unsigned long *p, unsigned long size)
+{
+	return find_first_zero_bit(p, size);
+}
+#endif /* find_first_zero_bit */
+
+#ifdef find_next_zero_bit
+__rust_helper
+unsigned long _find_next_zero_bit(const unsigned long *addr,
+				  unsigned long size, unsigned long offset)
+{
+	return find_next_zero_bit(addr, size, offset);
+}
+#endif /* find_next_zero_bit */
+
+#ifdef find_first_bit
+__rust_helper
+unsigned long _find_first_bit(const unsigned long *addr, unsigned long size)
+{
+	return find_first_bit(addr, size);
+}
+#endif /* find_first_bit */
+
+#ifdef find_next_bit
+__rust_helper
+unsigned long _find_next_bit(const unsigned long *addr, unsigned long size,
+			     unsigned long offset)
+{
+	return find_next_bit(addr, size, offset);
+}
+#endif /* find_next_bit */