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, 81 insertions, 0 deletions

diff --git a/drivers/input/input-compat.h b/drivers/input/input-compat.h
new file mode 100644
index 000000000..99c87ceb9
--- /dev/null
+++ b/drivers/input/input-compat.h
@@ -0,0 +1,81 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef _INPUT_COMPAT_H
+#define _INPUT_COMPAT_H
+
+/*
+ * 32bit compatibility wrappers for the input subsystem.
+ *
+ * Very heavily based on evdev.c - Copyright (c) 1999-2002 Vojtech Pavlik
+ */
+
+#include <linux/compiler.h>
+#include <linux/compat.h>
+#include <linux/input.h>
+
+#ifdef CONFIG_COMPAT
+
+struct input_event_compat {
+	compat_ulong_t sec;
+	compat_ulong_t usec;
+	__u16 type;
+	__u16 code;
+	__s32 value;
+};
+
+struct ff_periodic_effect_compat {
+	__u16 waveform;
+	__u16 period;
+	__s16 magnitude;
+	__s16 offset;
+	__u16 phase;
+
+	struct ff_envelope envelope;
+
+	__u32 custom_len;
+	compat_uptr_t custom_data;
+};
+
+struct ff_effect_compat {
+	__u16 type;
+	__s16 id;
+	__u16 direction;
+	struct ff_trigger trigger;
+	struct ff_replay replay;
+
+	union {
+		struct ff_constant_effect constant;
+		struct ff_ramp_effect ramp;
+		struct ff_periodic_effect_compat periodic;
+		struct ff_condition_effect condition[2]; /* One for each axis */
+		struct ff_rumble_effect rumble;
+	} u;
+};
+
+static inline size_t input_event_size(void)
+{
+	return (in_compat_syscall() && !COMPAT_USE_64BIT_TIME) ?
+		sizeof(struct input_event_compat) : sizeof(struct input_event);
+}
+
+#else
+
+static inline size_t input_event_size(void)
+{
+	return sizeof(struct input_event);
+}
+
+#endif /* CONFIG_COMPAT */
+
+int input_event_from_user(const char __user *buffer,
+			 struct input_event *event);
+
+int input_event_to_user(char __user *buffer,
+			const struct input_event *event);
+
+int input_ff_effect_from_user(const char __user *buffer, size_t size,
+			      struct ff_effect *effect);
+
+int input_bits_to_string(char *buf, int buf_size, unsigned long bits,
+                         bool skip_empty);
+
+#endif /* _INPUT_COMPAT_H */