Messages in this thread | | | Date | Thu, 25 Nov 2021 15:39:29 +0100 | From | Petr Mladek <> | Subject | Re: [PATCH 3/3] selftests/livepatch: Test of the API for specifying functions to search for on a stack |
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On Fri 2021-11-19 10:03:27, Miroslav Benes wrote: > Add a test for the API which allows the user to specify functions which > are then searched for on any tasks's stack during a transition process. > > --- /dev/null > +++ b/lib/livepatch/test_klp_funcstack_mod.c > @@ -0,0 +1,72 @@ > +// SPDX-License-Identifier: GPL-2.0 > +// Copyright (C) 2021 Miroslav Benes <mbenes@suse.cz> > + > +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt > + > +#include <linux/module.h> > +#include <linux/kernel.h> > +#include <linux/debugfs.h> > +#include <linux/delay.h> > + > +static int sleep_length = 10000; > +module_param(sleep_length, int, 0644); > +MODULE_PARM_DESC(sleep_length, "length of sleep in seconds (default=10)"); > + > +static noinline void child_function(void) > +{ > + pr_info("%s enter\n", __func__); > + msleep(sleep_length);
The hardcoded sleep is not ideal. It might be too low or non-necessary high.
If I get it correctly, we are trying to achieve here the same as busymod_work_func() in test_klp_callbacks_busy.c.
The approach with debugfs is an interesting trick. Though, I slightly prefer using the scheduled work. The workqueue API looks less tricky to me than sysfs/debugfs API. Also it does not block the module in the init() callback[*]. But I might be biased.
Anyway, it might make sense to use the same trick in both situations. It would make it easier to maintain the test modules.
[*] There is actually a race in the workqueue approach. The module init() callback should wait until the work is really scheduled and sleeping. It might be achieved by similar hand-shake like with @block_transition variable. Or completion API might be even more elegant.
> + pr_info("%s exit\n", __func__); > +} > + > +static noinline void child2_function(void) > +{ > + pr_info("%s\n", __func__); > +} > + > +static noinline void parent_function(void) > +{ > + pr_info("%s enter\n", __func__); > + child_function(); > + child2_function();
This would deserve some explanation what we try to simulate here and how it is achieved. It is not easy for me even with the background that I have freshly in my mind.
Also I think about more descriptive names ;-)
What about something like this (using workqueue work and completion):
/* * Simulate part of the caller code that is in another .elf section * and is reached via jump. It this was really the case then the stack * unwinder might not be able to detect that the process is sleeping * in the caller. */ static void simulate_jump_part(void) { pr_info("%s enter\n", __func__);
/* Stay in the jump part unless told to leave. */ wait_for_completion(finish_jump);
pr_info("%s exit\n", __func__); }
/* * Simulate modified part of the caller code. It should never get * livepatched when the caller is sleeping in the just_part(). */ static void simulate_modified_part(void) { pr_info("%s\n", __func__); }
static void test_not_on_stack_func_work(struct work_struct *work) { pr_info("%s enter\n", __func__);
/* Simulation ready */ complete(work_started);
simulate_jump_part(); simulate_modified_part();
pr_info("%s exit\n", __func__); }
static int test_klp_no_on_stack_init(void) { pr_info("%s\n", __func__);
schedule_work(&work); wait_for_completion(&work_started);
return 0; }
static void test_not_on_stack_exit(void) { complete(&finish_jump); flush_work(&work); pr_info("%s\n", __func__); }
module_init(test_klp_not_on_stack_init); module_exit(test_klp_not_on_stack_exit);
> + pr_info("%s exit\n", __func__); > +} > +
Best Regards, Petr
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