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 --- samples/kdb/Makefile | 2 ++ samples/kdb/kdb_hello.c | 58 +++++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 60 insertions(+) create mode 100644 samples/kdb/Makefile create mode 100644 samples/kdb/kdb_hello.c (limited to 'samples/kdb') diff --git a/samples/kdb/Makefile b/samples/kdb/Makefile new file mode 100644 index 000000000..947cb8522 --- /dev/null +++ b/samples/kdb/Makefile @@ -0,0 +1,2 @@ +# SPDX-License-Identifier: GPL-2.0-only +obj-$(CONFIG_SAMPLE_KDB) += kdb_hello.o diff --git a/samples/kdb/kdb_hello.c b/samples/kdb/kdb_hello.c new file mode 100644 index 000000000..82736e5a5 --- /dev/null +++ b/samples/kdb/kdb_hello.c @@ -0,0 +1,58 @@ +/* + * Created by: Jason Wessel + * + * Copyright (c) 2010 Wind River Systems, Inc. All Rights Reserved. + * + * This file is licensed under the terms of the GNU General Public + * License version 2. This program is licensed "as is" without any + * warranty of any kind, whether express or implied. + */ + +#include +#include + +/* + * All kdb shell command call backs receive argc and argv, where + * argv[0] is the command the end user typed + */ +static int kdb_hello_cmd(int argc, const char **argv) +{ + if (argc > 1) + return KDB_ARGCOUNT; + + if (argc) + kdb_printf("Hello %s.\n", argv[1]); + else + kdb_printf("Hello world!\n"); + + return 0; +} + +static kdbtab_t hello_cmd = { + .name = "hello", + .func = kdb_hello_cmd, + .usage = "[string]", + .help = "Say Hello World or Hello [string]", +}; + +static int __init kdb_hello_cmd_init(void) +{ + /* + * Registration of a dynamically added kdb command is done with + * kdb_register(). + */ + kdb_register(&hello_cmd); + return 0; +} + +static void __exit kdb_hello_cmd_exit(void) +{ + kdb_unregister(&hello_cmd); +} + +module_init(kdb_hello_cmd_init); +module_exit(kdb_hello_cmd_exit); + +MODULE_AUTHOR("WindRiver"); +MODULE_DESCRIPTION("KDB example to add a hello command"); +MODULE_LICENSE("GPL"); -- cgit v1.3.1