From 1039bffd6ae9c75b42b7d148d6c1106134107b66 Mon Sep 17 00:00:00 2001 From: Xie Yuanbin Date: Tue, 28 Jul 2026 03:16:42 +0100 Subject: ARM: 9485/1: mm: acquire mmap write lock around show_pte() for user faults 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 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) Reviewed-by: Linus Walleij Signed-off-by: Qi Xi Signed-off-by: Xie Yuanbin Signed-off-by: Russell King --- lib/kunit/debugfs.h | 30 ++++++++++++++++++++++++++++++ 1 file changed, 30 insertions(+) create mode 100644 lib/kunit/debugfs.h (limited to 'lib/kunit/debugfs.h') diff --git a/lib/kunit/debugfs.h b/lib/kunit/debugfs.h new file mode 100644 index 000000000..dcc7d7556 --- /dev/null +++ b/lib/kunit/debugfs.h @@ -0,0 +1,30 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * Copyright (C) 2020, Oracle and/or its affiliates. + */ + +#ifndef _KUNIT_DEBUGFS_H +#define _KUNIT_DEBUGFS_H + +#include + +#ifdef CONFIG_KUNIT_DEBUGFS + +void kunit_debugfs_create_suite(struct kunit_suite *suite); +void kunit_debugfs_destroy_suite(struct kunit_suite *suite); +void kunit_debugfs_init(void); +void kunit_debugfs_cleanup(void); + +#else + +static inline void kunit_debugfs_create_suite(struct kunit_suite *suite) { } + +static inline void kunit_debugfs_destroy_suite(struct kunit_suite *suite) { } + +static inline void kunit_debugfs_init(void) { } + +static inline void kunit_debugfs_cleanup(void) { } + +#endif /* CONFIG_KUNIT_DEBUGFS */ + +#endif /* _KUNIT_DEBUGFS_H */ -- cgit v1.3.1