linux-kernel - Re: [PATCH v2] kunit: run test suites only after module initialization completes

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Message-ID: <23e3e9b6-c6e2-4b89-b30e-0319f8789590@opensource.cirrus.com>
Date:   Wed, 6 Dec 2023 13:09:08 +0000
From:   Richard Fitzgerald <rf@...nsource.cirrus.com>
To:     Marco Pagani <marpagan@...hat.com>,
        Brendan Higgins <brendan.higgins@...ux.dev>,
        David Gow <davidgow@...gle.com>, Rae Moar <rmoar@...gle.com>,
        Jinjie Ruan <ruanjinjie@...wei.com>,
        Shuah Khan <skhan@...uxfoundation.org>
CC:     Javier Martinez Canillas <javierm@...hat.com>,
        <linux-kselftest@...r.kernel.org>, <kunit-dev@...glegroups.com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] kunit: run test suites only after module
 initialization completes

On 28/11/2023 10:16, Marco Pagani wrote:
> Commit 2810c1e99867 ("kunit: Fix wild-memory-access bug in
> kunit_free_suite_set()") fixed a wild-memory-access bug that could have
> happened during the loading phase of test suites built and executed as
> loadable modules. However, it also introduced a problematic side effect
> that causes test suites modules to crash when they attempt to register
> fake devices.
> 
> When a module is loaded, it traverses the MODULE_STATE_UNFORMED and
> MODULE_STATE_COMING states before reaching the normal operating state
> MODULE_STATE_LIVE. Finally, when the module is removed, it moves to
> MODULE_STATE_GOING before being released. However, if the loading
> function load_module() fails between complete_formation() and
> do_init_module(), the module goes directly from MODULE_STATE_COMING to
> MODULE_STATE_GOING without passing through MODULE_STATE_LIVE.
> 
> This behavior was causing kunit_module_exit() to be called without
> having first executed kunit_module_init(). Since kunit_module_exit() is
> responsible for freeing the memory allocated by kunit_module_init()
> through kunit_filter_suites(), this behavior was resulting in a
> wild-memory-access bug.
> 
> Commit 2810c1e99867 ("kunit: Fix wild-memory-access bug in
> kunit_free_suite_set()") fixed this issue by running the tests when the
> module is still in MODULE_STATE_COMING. However, modules in that state
> are not fully initialized, lacking sysfs kobjects. Therefore, if a test
> module attempts to register a fake device, it will inevitably crash.
> 
> This patch proposes a different approach to fix the original
> wild-memory-access bug while restoring the normal module execution flow
> by making kunit_module_exit() able to detect if kunit_module_init() has
> previously initialized the tests suite set. In this way, test modules
> can once again register fake devices without crashing.
> 
> This behavior is achieved by checking whether mod->kunit_suites is a
> virtual or direct mapping address. If it is a virtual address, then
> kunit_module_init() has allocated the suite_set in kunit_filter_suites()
> using kmalloc_array(). On the contrary, if mod->kunit_suites is still
> pointing to the original address that was set when looking up the
> .kunit_test_suites section of the module, then the loading phase has
> failed and there's no memory to be freed.
> 
> v2:
> - add include <linux/mm.h>
> 
> Fixes: 2810c1e99867 ("kunit: Fix wild-memory-access bug in kunit_free_suite_set()")
> Signed-off-by: Marco Pagani <marpagan@...hat.com>

Tested-by: Richard Fitzgerald <rf@...nsource.cirrus.com>

Fixed this crash:
https://lore.kernel.org/all/e239b94b-462a-41e5-9a4c-cd1ffd530d75@opensource.cirrus.com/

Also tested with sound/pci/hda/cirrus_scodec_test.c