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 --- Documentation/dev-tools/testing-devices.rst | 47 +++++++++++++++++++++++++++++ 1 file changed, 47 insertions(+) create mode 100644 Documentation/dev-tools/testing-devices.rst (limited to 'Documentation/dev-tools/testing-devices.rst') diff --git a/Documentation/dev-tools/testing-devices.rst b/Documentation/dev-tools/testing-devices.rst new file mode 100644 index 000000000..ab26adb99 --- /dev/null +++ b/Documentation/dev-tools/testing-devices.rst @@ -0,0 +1,47 @@ +.. SPDX-License-Identifier: GPL-2.0 +.. Copyright (c) 2024 Collabora Ltd + +============================= +Device testing with kselftest +============================= + + +There are a few different kselftests available for testing devices generically, +with some overlap in coverage and different requirements. This document aims to +give an overview of each one. + +Note: Paths in this document are relative to the kselftest folder +(``tools/testing/selftests``). + +Device oriented kselftests: + +* Devicetree (``dt``) + + * **Coverage**: Probe status for devices described in Devicetree + * **Requirements**: None + +* Error logs (``devices/error_logs``) + + * **Coverage**: Error (or more critical) log messages presence coming from any + device + * **Requirements**: None + +* Discoverable bus (``devices/probe``) + + * **Coverage**: Presence and probe status of USB or PCI devices that have been + described in the reference file + * **Requirements**: Manually describe the devices that should be tested in a + YAML reference file (see ``devices/probe/boards/google,spherion.yaml`` for + an example) + +* Exist (``devices/exist``) + + * **Coverage**: Presence of all devices + * **Requirements**: Generate the reference (see ``devices/exist/README.rst`` + for details) on a known-good kernel + +Therefore, the suggestion is to enable the error log and devicetree tests on all +(DT-based) platforms, since they don't have any requirements. Then to greatly +improve coverage, generate the reference for each platform and enable the exist +test. The discoverable bus test can be used to verify the probe status of +specific USB or PCI devices, but is probably not worth it for most cases. -- cgit v1.3.1