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, 67 insertions, 0 deletions

diff --git a/include/asm-generic/irqflags.h b/include/asm-generic/irqflags.h
new file mode 100644
index 000000000..19ccbf483
--- /dev/null
+++ b/include/asm-generic/irqflags.h
@@ -0,0 +1,67 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_GENERIC_IRQFLAGS_H
+#define __ASM_GENERIC_IRQFLAGS_H
+
+/*
+ * All architectures should implement at least the first two functions,
+ * usually inline assembly will be the best way.
+ */
+#ifndef ARCH_IRQ_DISABLED
+#define ARCH_IRQ_DISABLED 0
+#define ARCH_IRQ_ENABLED 1
+#endif
+
+/* read interrupt enabled status */
+#ifndef arch_local_save_flags
+unsigned long arch_local_save_flags(void);
+#endif
+
+/* set interrupt enabled status */
+#ifndef arch_local_irq_restore
+void arch_local_irq_restore(unsigned long flags);
+#endif
+
+/* get status and disable interrupts */
+#ifndef arch_local_irq_save
+static inline unsigned long arch_local_irq_save(void)
+{
+	unsigned long flags;
+	flags = arch_local_save_flags();
+	arch_local_irq_restore(ARCH_IRQ_DISABLED);
+	return flags;
+}
+#endif
+
+/* test flags */
+#ifndef arch_irqs_disabled_flags
+static inline int arch_irqs_disabled_flags(unsigned long flags)
+{
+	return flags == ARCH_IRQ_DISABLED;
+}
+#endif
+
+/* unconditionally enable interrupts */
+#ifndef arch_local_irq_enable
+static inline void arch_local_irq_enable(void)
+{
+	arch_local_irq_restore(ARCH_IRQ_ENABLED);
+}
+#endif
+
+/* unconditionally disable interrupts */
+#ifndef arch_local_irq_disable
+static inline void arch_local_irq_disable(void)
+{
+	arch_local_irq_restore(ARCH_IRQ_DISABLED);
+}
+#endif
+
+/* test hardware interrupt enable bit */
+#ifndef arch_irqs_disabled
+static inline int arch_irqs_disabled(void)
+{
+	return arch_irqs_disabled_flags(arch_local_save_flags());
+}
+#endif
+
+#endif /* __ASM_GENERIC_IRQFLAGS_H */