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 --- tools/testing/shared/maple-shim.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) create mode 100644 tools/testing/shared/maple-shim.c (limited to 'tools/testing/shared/maple-shim.c') diff --git a/tools/testing/shared/maple-shim.c b/tools/testing/shared/maple-shim.c new file mode 100644 index 000000000..16252ee61 --- /dev/null +++ b/tools/testing/shared/maple-shim.c @@ -0,0 +1,14 @@ +// SPDX-License-Identifier: GPL-2.0-or-later + +/* Very simple shim around the maple tree. */ + +#include "maple-shared.h" +#include + +#include "../../../lib/maple_tree.c" + +void maple_rcu_cb(struct rcu_head *head) { + struct maple_node *node = container_of(head, struct maple_node, rcu); + + kmem_cache_free(maple_node_cache, node); +} -- cgit v1.3.1