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 --- drivers/clocksource/dummy_timer.c | 37 +++++++++++++++++++++++++++++++++++++ 1 file changed, 37 insertions(+) create mode 100644 drivers/clocksource/dummy_timer.c (limited to 'drivers/clocksource/dummy_timer.c') diff --git a/drivers/clocksource/dummy_timer.c b/drivers/clocksource/dummy_timer.c new file mode 100644 index 000000000..6cee6dce5 --- /dev/null +++ b/drivers/clocksource/dummy_timer.c @@ -0,0 +1,37 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * linux/drivers/clocksource/dummy_timer.c + * + * Copyright (C) 2013 ARM Ltd. + * All Rights Reserved + */ +#include +#include +#include +#include +#include + +static DEFINE_PER_CPU(struct clock_event_device, dummy_timer_evt); + +static int dummy_timer_starting_cpu(unsigned int cpu) +{ + struct clock_event_device *evt = per_cpu_ptr(&dummy_timer_evt, cpu); + + evt->name = "dummy_timer"; + evt->features = CLOCK_EVT_FEAT_PERIODIC | + CLOCK_EVT_FEAT_ONESHOT | + CLOCK_EVT_FEAT_DUMMY; + evt->rating = 100; + evt->cpumask = cpumask_of(cpu); + + clockevents_register_device(evt); + return 0; +} + +static int __init dummy_timer_register(void) +{ + return cpuhp_setup_state(CPUHP_AP_DUMMY_TIMER_STARTING, + "clockevents/dummy_timer:starting", + dummy_timer_starting_cpu, NULL); +} +early_initcall(dummy_timer_register); -- cgit v1.3.1