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, 35 insertions, 0 deletions

diff --git a/drivers/md/bcache/debug.h b/drivers/md/bcache/debug.h
new file mode 100644
index 000000000..fb3d4dff4
--- /dev/null
+++ b/drivers/md/bcache/debug.h
@@ -0,0 +1,35 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _BCACHE_DEBUG_H
+#define _BCACHE_DEBUG_H
+
+struct bio;
+struct cached_dev;
+struct cache_set;
+
+#ifdef CONFIG_BCACHE_DEBUG
+
+void bch_btree_verify(struct btree *b);
+void bch_data_verify(struct cached_dev *dc, struct bio *bio);
+
+#define expensive_debug_checks(c)	((c)->expensive_debug_checks)
+#define key_merging_disabled(c)		((c)->key_merging_disabled)
+#define bypass_torture_test(d)		((d)->bypass_torture_test)
+
+#else /* DEBUG */
+
+static inline void bch_btree_verify(struct btree *b) {}
+static inline void bch_data_verify(struct cached_dev *dc, struct bio *bio) {}
+
+#define expensive_debug_checks(c)	0
+#define key_merging_disabled(c)		0
+#define bypass_torture_test(d)		0
+
+#endif
+
+#ifdef CONFIG_DEBUG_FS
+void bch_debug_init_cache_set(struct cache_set *c);
+#else
+static inline void bch_debug_init_cache_set(struct cache_set *c) {}
+#endif
+
+#endif