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Date: Tue, 30 Jun 2020 18:12:56 +0200
From: Adam Zabrocki <pi3@....com.pl>
To: lkrg-users@...ts.openwall.com
Subject: Re: p_install_arch_jump_label_transform_hook and
p_check_integrity lead to deadlock issue on unisoc SL8541E
Hi,
I've synced with Ethan offline about that problem. It looks like in a very slow
devices, some of the busy loop of locking/unlocking text_mutext is too tight
and optimize_kprobe() can't win the race of getting text_mutex. I've just
pushed a simple patch which helps to solve that problem:
https://bitbucket.org/Adam_pi3/lkrg-main/commits/ec595f555bcb9b81a1782d9e2c9651a8abf45aab
Thanks,
Adam
On Mon, Jun 29, 2020 at 10:12:50AM +0800, youyan wrote:
> Hi adam
>
> I have found the reason,why LKRG block on my device.
>
> 1: hardware and software: unisoc SL8541E, android Q, kernel version is 4.14
>
> 2: SL8541E is arm64 platform, but for some reason, we compile it as 32bit arm
>
> 3: On function p_create_database(),which in the file p_database.c,have the fellow execute flow:
>
> (1) if (p_register_arch_metadata() != P_LKRG_SUCCESS)
> [ 125.693391] c1 [<c01e379c>] (kick_kprobe_optimizer) from [<c01e4394>] (optimize_kprobe+0x108/0x118)
> [ 125.702389] c1 [<c01e4394>] (optimize_kprobe) from [<c01e5fe0>] (register_kprobe+0x548/0x5b0)
> [ 125.710871] c1 [<c01e5fe0>] (register_kprobe) from [<c01e63ac>] (register_kretprobe+0x114/0x178)
> [ 125.719671] c1 [<c01e63ac>] (register_kretprobe) from [<bf2d9f60>] (p_install_arch_jump_label_transform_hook+0x38/0xc0 [p_lkrg])
> [ 125.731224] c1 [<bf2d9f60>] (p_install_arch_jump_label_transform_hook [p_lkrg]) from [<bf2d9b98>] (p_register_arch_metadata+0x74/0xd0 [p_lkrg])
> (2) kick_kprobe_optimizer()->schedule_delayed_work(&optimizing_work, OPTIMIZE_DELAY)->kprobe_optimizer()->mutex_lock(&module_mutex)->do_optimize_kprobes()->mutex_lock(&text_mutex)
>
> (3) p_register_module_notifier();
>
> 4: some notifier or timer can trigger p_check_integrity()
>
> 5: p_module_event_notifier is execute after the p_register_module_notifier:
>
> p_module_event_notifier_live_retry:
>
> p_text_section_lock();
>
> /* We are heavily consuming module list here - take 'module_mutex' */
>
> //mutex_lock(&module_mutex);
>
> while (!mutex_trylock(&module_mutex)) {
>
> p_text_section_unlock();
>
> goto p_module_event_notifier_live_retry;
>
> }
>
> above will loop request exceute,and will consume a lot of cpu resource. It lead to do_optimize_kprobes can't get mutex_lock(&text_mutex);
>
> 7:when p_check_integrity execute,it first execute p_text_section_lock(),then mutex_lock(&module_mutex), and lead to deadlock.
>
>
>
> kprobe.c p_integrity_timer.c
>
> mutex_lock(&module_mutex)
>
> p_text_section_lock()->mutex_lock(P_SYM(p_text_mutex));
>
>
>
> mutex_lock(&text_mutex)
>
> mutex_lock(&text_mutex)
>
>
>
> 8:Maybe SL8541E run slowly cause this bug.
>
> 9:I try fellow three solutions to fix this issue:
>
> solution one:
>
> Before p_register_module_notifier(),add a some delay use msleep();
>
> solution two:
>
> (1) p_module_event_notifier request mutex_trylock(&module_mutex) loop,add msleep(10):
>
> p_module_event_notifier_going_retry:
>
> p_text_section_lock();
>
> while (!mutex_trylock(&module_mutex)) {
>
> msleep(10);
>
> p_text_section_unlock();
>
> goto p_module_event_notifier_going_retry;
>
> }
>
> (2)change request mutex order
>
> p_text_section_lock(); mutex_lock(&module_mutex);
>
> change to
>
> mutex_lock(&module_mutex); p_text_section_lock();
>
> solution third:
>
> p_text_section_lock(); p_check_integrity_mutex:
>
> change to
>
> mutex_lock(&module_mutex); p_text_section_lock();
>
> while (!mutex_trylock(&module_mutex)) {
>
> p_text_section_unlock();
>
> msleep(10);
>
> goto p_check_integrity_mutex;
>
> }
>
> 10:I maybe use use solution one, because I am not familiar with LKRG. Which solution do you suggest? If you have better idea,could you share me? Thanks!!!
>
>
>
>
>
>
--
pi3 (pi3ki31ny) - pi3 (at) itsec pl
http://pi3.com.pl
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